Chinook & other tandem rotors discussions

[Vfrpilotpb]

I am asking any of your ex mil Pro's out there, in simple terms how do you fly a Chinook, I am always in awe of these "flying buildings " whenever I see one, but yet I can never detect any cyclic movement to the rear blade's, is it all done at the front set, can you help?
My regards

[Fr O'Blivien]

Nothin to do with the green ones mate, this is the story according to the late lamented BV234!

Flying controls operate as any other helo.

Rotor articulation is a bit different.

There is no fore and aft (cyclic) movement in either disk. (there cant be, theyd strike each other) Aircraft pitch is controlled by differential collective between the disks.

Roll is produced by lateral (cyclic) in both disks simultaneously, and yaw by differential lateral cyclic, if you follow my terminology.

Actually there is a slight fore and aft input by a systen called LCT (Longitudinal cyclic trim) that tilts the gearboxes fore and aft to reduce excessive deck angle at speed, but it is not part of the primary flight controls.Conventional flight controls produce these rather unusual inputs via a very complex mechanical mixing unit in the broom cupboard behing the P1.

Due to the dynamics the Chinook develops maximum translational lift in sideways flight to the left, hence the antics of the logging machines plugung sideways on the end of theit long cables - gives them greatly increased lift capacity.

Chinook is extremely docile in handling, yet extremely maneuverable when light. Autorotation is of the thistledown type, rotor inertia is massive and the beggar wont come down fast even if you want it too. Engine off landing is merely a continuous flare to a running landing on the rear wheels which requires quite a lot of runway. I dont know if the military use other techniques.

Take off requires progressive fwd movement on the cyclic as the nose rises to prevent it scuttling off backwards, and vv for landing. There are no torque effects. On icy surfaces it is semi-hover taxiied on the back wheels - groung handling is not helped by rather delicate landing gear, fronts fixed, aft portside castoring and aft stbd only steerable.

What a fabulous toy!

Flying an ILS backwards was fun too (in the sim). Lift off on the landing datum, translate backwards and climb up the slope on instruments. 60Kts sideways and backwards rings a bell??



[This message has been edited by Fr O'Blivien (edited 21 April 2001).]

[Vfrpilotpb]

FO'B, thank you for that explanation, I admire all fellow pilots be they pro's or ppls, but to stand and watch one of these double eggbeaters fly and land is something quite different, more than any other craft, I still find it fasinating to watch them fly! my regards

[The Nr Fairy]

I had the opportunity last year to spend an hour in a Chinook simulator, with a standards guy in the left hand seat, and another standards guy acting as crewman.

After some initial collective pumping, it felt pretty straightforward to fly - mind you that was probably the AFCS, rather than me !! I got to try some general wazzing, an auto, formation flight and some sling load pickups and drops - one to take the aircraft weight to just under max. All good fun - now, where can I get my hands on the money required to buy that simulator mouldering up in Scotland ?

[Shackman]

Cannot bettr Fr O'Blivien for the tech bit, but the mil version flew just the same - actually even more manoeuvrable 'cos it was lighter. Fighter affil in the wocker was awesome, even 2 A10's had difficulty, and power margins impressive. On leaving the fleet to go to Gazelles was told to expect sports car - ugh! Chinook was faster, more fun and could lift more than almost anything else we have in the mil (I don't know about Merlin). It could even fly for ages with the overload tanks on. Odiham - Nimes or 7 hours over the Atlantic (Air India SAR), and the seat was even comfortable.

Yes I miss it - great aircraft, shame about the reputation.


Pertama

[PurplePitot]

Otherwise known as the Boeing Body Bag.... I have only declined a cabbie in two helicopters to date, this one and an Mi8 (Hip)

[MightyGem]

Wimp!

[Chinook]

Went to Chinooks after a joyful few years flying UH-1H with the strap-on offensive bits ..... have to say I love the Huey, but adore the chook ..

She's a joy to fly (as long as one doesn't think too much about the tech), bags of power, can haul a sh**load of coffee home from PNG and is faster than a Blackhawk (much to my brethren's chagrin at times)

Just a pain to pre-flight is all .....

Anyone who wishes to fly the Chinook in Oz ... apply for a job, we need drivers!!!



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Park it, tie it down, lock it, lets go to the pub!!!!!

[VLift]

The A models were a hoot. The tail was pointed as apposed to blocked, called them pin tails, also had no stabilizing "strakes" so, if the SAS came off in a turn the aircraft would fight you tooth and nail to swap ends. If the Longitudinal Cyclic Trim (LCT) fails it means the automatic forward tilt of the rotor system, not transmissions, doesn't happen which carries with it an airspeed limit or malfunction procedure depending when they fail. This aircraft was ment to work hard. I too spent many years in UH-1D & H aircraft and the Hook. Two really great aircraft.

[pedroalpha]

CHINOOK? I love it to bits! I joined the team in 1982 and thoroughly loved my 5 years on the best pilots' machine in the world. I've lifted another CH47, carried 11700 Kg underslung and enjoyed two-wheel taxy games with the best. Its a beast in turbulence; a delight in straight & level (can you do 160 Kts without a dive?) and I hated my family being a passenger in it!!!!!!!!! This machine has attitude.

[Chinook]

Sure would enjoy another posting to Hueys after this !!!!

Life is good, even if we do bitch about Timor, Bougainville and Risk Managment !@

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Park it, tie it down, lock it, lets go to the pub!!!!!

[Thud_and_Blunder]

Chinook,

Heartily concur - had 2.5 years on single Hueys starting in '82, did Chinooks from '89 to '98 and have been enjoying twin Hueys since then. Best of all worlds, eh?

PS I think that while you're Long Looking, there should be a Stn Master at Odiham who thoroughly enjoyed his exchange tour in Oz. Good timing on your part, I reckon. If you go there with the same attitude as the 2 crewmen who came through around 1997 you'll have a whale of a time; they were good ambassadors for all things Antipodean.

[Arm out the window]

I've just started reading a book called "Chinook", and according to that it's actually the crewman who flies the aircraft.

Not only that, but apparently the best way to pass your aircrew training course is to do no study, drink Pi55 heavily and steal the exam papers!

I can hardly wait for the next in the series, "Orderly Room Clerk".

[Lu Zuckerman]

To: Fr. O’Blivien

You stated:

“There is no fore and aft (cyclic) movement in either disk. (There can’t be, they’d strike each other) Aircraft pitch is controlled by differential collective between the disks”.

You further stated,

“Actually there is a slight fore and aft input by a system called LCT (Longitudinal cyclic trim) that tilts the gearboxes fore and aft to reduce excessive deck angle at speed, but it is not part of the primary flight controls. Conventional flight controls produce these rather unusual inputs via a very complex mechanical mixing unit in the broom cupboard behind the P1”.


Actually, there is a forward cyclic component but it is not introduced by the forward tilting of the gearboxes. An electromechanical actuator that is attached to an arm extension of the swash plates introduces forward cyclic. It does not actuate until the helicopter reaches a forward speed in excess of 60 Knots (approx.). Since the blades intermesh, they can’t contact each other when cyclic is input is made by the automatic system. The pilot does not have direct control of this system and therefore the pilot can’t perform a cyclic flare while flying forward. He can introduce a cyclic flare while flying sideways and because of this, autorotatations must be entered into while flying sideways.


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The Cat

[This message has been edited by Lu Zuckerman (edited 30 April 2001).]

[VLift]

Hey Lu

This is humor, right?

"The pilot does not have direct control of this system and therefore the pilot can’t perform a cyclic flare while flying forward. He can introduce a cyclic flare while flying sideways and because of this, autorotatations must be entered into while flying sideways."

[Cyclic Hotline]

This is a link to the accident report for C-FHFH, a BV234, which crashed in Canada in 1997.

Just thought it might be of interest to any of you Chinookies.

http://www.tsb.gc.ca/ENG/reports/air/1997/a97p0303/ea97p0303.htm

[heedm]

Thanks for the info on the Chinook crash. I wasn't on the mission but our CH113 (Canadian Forces BV107) was the helicopter on scene for the rescue (wasn't possible).

We were all very interested in why this crashed. Similiar flight control systems in the two helicopters.

For Lu, I assume that the "autorotations must be entered sideways" was a joke. Although fore and aft cyclic works differently than in tail rotor helicopters, it works the same from a practical point of view. Including autorotation.

Matthew.

[Lu Zuckerman]

To: heedm

The pilot of a CH-47 has absolutely no fore and aft cyclic input. As I had indicated previously the cyclic is input automatically when the aircraft reaches approximately 60 Knots.** The pilot has no part in it. The cyclic that is input is forward cyclic and this forward cyclic will be removed when the aircraft reaches a speed below 60 Knots. In a conventional helicopter the pilot can pull the cyclic back to flare to arrest his speed and at the same time increase rotor speed. This can’t be done on a CH-47 if you enter an autorotation going forward. Cyclic input can only be made when the aircraft is flying sideways and the reason for that is the pilot introduced left or right cyclic.

**On the CH-47 the highest contributor to maintenance action and overhaul cost are the two rotorheads. Because the rotorheads are mainly in full collective in a hover and a reduced collective on the Fwd. Rotor and an increased collective on the rear rotor when flying forward the rotor heads are 90% scrapped during overhaul due to the high stress levels. Boeing is developing a new elastomeric rotorhead and I will guarantee you that it won’t last as long as the rotor system it replaces


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The Cat

[Chinook]

Lu,

Tell me again how I can't reduce speed or increase RRPM autorotating a CH-47D going forward?

[Arm out the window]

Sounds like just semantics to me.

I stand to be corrected, but I think Lu's saying that cyclic pitch changes can't be made on the rotors in the fore and aft sense, and therefore it would technically be wrong to say that pitch controlling is done 'cyclically'.

However, in any helicopter I'd call that stick between my legs (now, now) the cyclic, and I'd be extremely surprised if a Chinook pilot can't pull back on that and make the aircraft flare, in autorotation or not.

If you can pull the nose up, you can change the relative airflow into the disc and therefore get flare effect.

Right or wrong?

[heedm]

To: Lu
Either you're joking around or are much too compulsively pedantic. If it's the former...you got me. You're right that fore and aft movement of that control does not result in any cyclic changes.

If I assume the latter, then I must point out that the basis of your argument is the definition of the word cyclic. A valid argument, but when you referred to "the cyclic" you were using a noun form of the word cyclic. I could find no dictionary definition for cyclic the noun. In common usage it is the pitch and bank control in a helicopter.

Since that control moved aft causes pitching up and increases Nr during autorotation, it behaves the same as a cyclic control to the user. If it looks like a duck....

Until Oxford adds cyclic the noun this argument could keep going in circles. Cyclically.

Matthew.

[This message has been edited by heedm (edited 02 May 2001).]

[Lu Zuckerman]

Regarding the pilot’s ability to introduce a cyclic flare by pulling back on the cyclic that result in an increase in rotor RPM you may be correct. However in order to do so he must severely increase the collective pitch in the forward rotor system while at the same time decreasing pitch in the rear rotor. This will change the angle of attack in relation to the relative wind causing an increase in rotor RPM by changing the attitude of the airframe but at the same time the rotors are being subjected to a severe drag penalty because of the increased pitch in the rotor heads. The only power being supplied to the rotor system is that of the autorotative forces however there are anti autorotative forces in action coupled with the increase in drag. If all of this were true, it would seem to me that if the pilot went straight in on an autorotation he would have only one chance.

However, if he entered into an autorotation going sideways he would be in complete control and he could make several cyclic flares during his descent with out the drag penalties associated with increased collective.

That's my theory but I could be totally wrong.


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The Cat

[VLift]

Lu, you gotta quit doing this. Stop making wild statements that lean on your previously posted "I'm an engineer" credentials and then backing off (I could be wrong) when challenged.

The Chinook was designed to respond to flight control inputs as other helicopters respond. When the pilot applies aft cyclic differential collective pitch produces a reduction in aft rotor pitch and a corresponding increase in forward rotor pitch, the nose pitches up (flare) and, the speed of the aircraft decreases. When the speed decrease is sensed in the AFCS computer the Longitudinal Cyclic Trim (LCT) actuator is adjusted to apply the equivalent of aft cyclic for rotor system tilt as necessary to remain coordinated to the current airspeed.
The aircraft flares in auto just like any other helicopter. If you flare and don't reduce power in cruise, the aircraft will climb, just like any other helicopter.

[Lu Zuckerman]

To: VLift

Please tell me where I went wrong. In a conventional single rotor helicopter when entering an autorotation the pilot will lower collective and adjust his cyclic to establish a specified rate of descent and a specified forward speed in accordance with the weight of the helicopter. In the process of descending the pilot can arrest his forward and downward movement by making a cyclic flare. This change in attitude in relation to the incoming air stream will result in an increase in rotor speed and arrest the forward movement. The pilot can do this several times to increase the inertia of the rotor system and then make his final flare with the attendant increase in rotor speed and then move his cyclic forward and pull and drop collective to make his touchdown.

Now to the CH-47. It is my understanding that the LCT actuators can be operated manually and automatically. It is also my understanding that these actuators are in the normal state when the swash plate is in the neutral position relative to fore and aft travel. I don’t remember if they extend or retract when in operation in order to introduce forward cyclic upon reaching 60 Knots. When the aircraft drops below 60 knots the actuator will return to the normal condition. I do not believe that the actuators will extend or retract beyond the normal position and therefore can’t introduce aft cyclic. Incidentally, the cyclic stick is actually the pitch and roll stick.

If the autorotation speed is in excess of 60 Knots there will be a forward cyclic component in both rotorheads and when the pilot pulls back on the pitch roll stick he will increase the actuator induced cyclic setting by increasing the pitch on the forward rotor and decrease pitch on the rear rotor but any collective input will be modified by the cyclic input.

The CH-47 control system is the most complex of any helicopter and most probably any fixed wing system. It obviously works but based on some of the postings on this thread there are not too many people that have a full understanding of the mechanics of the system and that includes me.

The V-22 has a similar control system to that of the CH-47 but it is not as mechanically complex. The complexity lies in a couple of electronic boxes as the V-22 is totally fly-by-wire.


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The Cat

[pedroalpha]

Vlift is right on the button and the ignorance portrayed on these pages is incredible. The pitch attitude of the CH47 is controlled by DIFFERENTIAL COLLECTIVE PITCH - less on the front and more on the back puts the nose down & so on. Forget the LCTs - they are a distraction. Oh yes, you can autorotate (but only to a firm surface) for a medium speed run on landing without touching the collective. Listen to those who fly it & not the "experts"!

[matspart3]

Always pleased to see RAF Chinooks who regularly train and refuel at my airfield. Taxiing backwards on the rear wheels around a 130° bend when the marshallers had cocked up the parking arrangements was most impressive!

My five year old daughter calls them 'Wocca Wocca' helicopters!

[Arm out the window]

With reference to Lu's statement about the pilot being able to flare several times to boost Nr in auto, there seems to be a bit of confusion as well.

As most pilots would know, the first flare when entering auto helps (along with lowering the collective) to regain lost Nr.

Once you're established in steady autorotation there should be no need to flare unless you want to change your speed, or at the bottom when you want to bleed off speed and rate of descent, whilst maintaining Nr by flare effect.

Sometimes in auto you're carrying a bit of collective to stop the Nr overspeeding.

Your statement seemed to indicate that there might be a need to flare a few times on the way down to keep the Nr up, Lu, but as I said, in steady state autorotation there's no need to.

Sorry if I've misinterpreted your post.

Cheers

[heedm]

I had assumed most of you in this discussion had a general understanding of the tandem rotor controls. Not entirely the case, so I thought I'd lay out how things happen and where the LCT comes in. Just to keep things simple I'll refer to the pilot's right hand interface as the stick rather than the cyclic.

Two rotors means two lift vectors. By varying the magnitude of the vectors you can change total lift or you can initiate a moment about the pitch axis. The collective changes total lift and the stick moved fore and aft creates the moment by varying the collective pitch of each rotor differently, or "differential collective pitch".

To go into forward flight, you use forward stick to pitch the helicopter to an accelerating attitude and increase collective to make up for the loss of the vertical component of total lift (same as all helicopters). As the helicopter is pitched down, forward flight creates drag forces on the fuselage that make the helicopter want to pitch up again, so forward stick must be maintained, and in fact, increased through the speed range.

Once higher speeds are obtained, the drag combined with the higher collective setting on the aft head (from forward stick) stresses the aft pylon shaft (shaft between aft transmission and aft rotor). To reduce that stress, the difference in the magnitudes of the two lift vectors must be reduced. To accomplish this, one or both of the lift vectors are tilted forward, allowing the helicopter to have a less nose down pitch attitude. (should probably draw a picture at this point) This tilting of the lift vector(s) is done by the LCT. An LCT (longitudinal cyclic trim) is a system that controls an actuator that tilts the corresponding swashplate to create cyclic pitch changes that tilt the rotor disk forward.

If in forward flight the engines fail, lowering of the collective and aft stick will reduce blade drag, induce autorotative forces, and with enough aft stick will get the relative airflow moving up into the disk (ie flare). The LCT actuators move relatively slowly and tilt the rotor disk by only a few degrees. In a flare, the stick changes the pitch attitude of the helicopter
(and thus the angle of attack of the rotor disks) by about 20 degrees for a gentle flare rather than a few degrees from the LCT.

One person mentioned that we should listen to the people who fly rather than the "experts". One of the nice things about this system is that to fly them you don't have to learn anything special...they behave the same as tail rotor helicopters. (For the record I fly a tandem rotor helicopter).

I tried to make this clear rather than precise. Feel free to point out where I was less than precise.

Matthew.

[This message has been edited by heedm (edited 03 May 2001).]

[Vfrpilotpb]

The answers and information to my initial question has been A1, and a mighty thanks to all of you , I wonder if you would answer this, I once stood in the entrance to the cockpit of a Brit Army Helio , twin rotor I think it was called a Belvedere, but I plainly remember two huge sticks almost like ski poles, with what seemd to be guarded or shrouded twist grips at the very top of these stick's, is that like the Chinook or does it have a single Cyclic, like say a B206, and a single collective, or am I still way of beam, can a chinook do spot turns like a normal Heli, if so how, I must say all the input to this thread, has been brilliant to read, despite some bad press about the Chinnok, I would ride in one, ( suppose that makes me a bit of a kid)but what the hell,

[The Nr Fairy]

VfrPilotb :

To the best of my recollection, sopt turns are accomplished by a combination of differential torque and differential cyclic ( i.e. to spot turn right, front blades give a right moving component, rear ones a left moving component ).

Combinations of pedal and left/right cyclic vary the pivot point from the front head through the centre of the aircraft to the rear head.

Have I got it right ?

[matspart3]

Had one of a pair divert in today with one engine shut down. Commander elected to land with a 10kt tailwind (nearest runway). I'd appreciate any info on the handling charactersitics/special requirements in similar situations for future reference...strictly layman's terms...I can't understand the physics of your spirally-whirly things...I'm only an ATCO

[Arm out the window]

Matspart3,

For a Chinook it's probably not as much of a problem to land with a tailwind as for a tail rotor helicopter because of the lesser tendency for it weathercock into the wind, therefore easier directional control.

However as a rule I think it's preferable to approach into wind whenever you can:

-less ground speed for a given airspeed, easier to stop the beast and less chance of bending yourself if you contact some fixed object!

-will have translational lift longer, therefore less power required, (or later requirement for high power)

-less likely to put you in a situation where the rotor's ingesting its own vortices, so less chance of vortex ring problems

The only time I'd land with a significant downwind is if I had to due to terrain/landing area considerations, or if I had a time-critical emergency that demanded landing right now - maybe that was the situation in this case?

[Chinook]

OK ....

Lu .... here's the empirical data:

straight and level, 100 kias, 100% RRPM ...

Auto entered .....

aft cyclic introduced (pitch 10 deg NU)

shazzam ...

70 kias, RRPM 103% ...

speak about what you KNOW

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Park it, tie it down, lock it, lets go to the pub!!!!!

[sling load]

Heedm and Chinook, Thank you,

Lu Zuckerman, in your post 2 may 2001 you stated that after autorotation the pilot pulls and pushes collective down to effect touchdown. If you push the collective down to effect touchdown your going to chop your tailboom off, or end up in a spinal ward. You pull the collective till you cant pull any more, straight and level after the flare, and hold collective and freeze the cylic, please tell us thats a typo Lu,

[timmccall]

Good posts, but I think I know why all of the confusion. I have been teaching BV-234 and 47 aerodynamics for the last 14 years and one area of confusion is the LCT's. Remember in a single rotor helicopter, cyclic feathering is used to combat dissymetry of lift and to set the required rotor disc pitch. In a tandem rotor helicopter, dissymetry of lift is controlled by blade flapping up to around 60-70KIAS. After that a means of cyclic feathering is needed to combat this tendency and reduce blade stresses imposed by excessive blade flapping since this cannot be accomplished by the pilot. LCT's accomplish this by inducing cyclic feathering, i.e. the input is made throught the swashplate(fwd disc) on the blade out the right door and left door so that the disc will react 90 degrees later, "phase lag", to pitch down or up as required. This is cyclic feathering that a single rotor pilot moves his cyclic to tilt its disc in the direction the pilot wants to go. The 47 pilot cant induce fore and aft cyclic feathering as was stated above, differential collective pitch is what tilts the fuseloge forward or aft and then combined collective (thrust)will keep it in the air. Also remember that the (DASH) Differential Air Speed Hold) is what gives the chinook the same handling characteristics as a single rotor (i.e. pushing forward on the cyclic and increasing thrust to increase speed). Without the dash, the tandem rotor would require the pilot to increase speed in the same manner (cyclic forward) but when he got to the desired speed, the cyclic would actually come back a certain extent to a neutral position which is inconsistent with a single rotor. Just ask anyone who has flown the aircraft without the PSAS or AFCS. The DASH works by increasing or decreasing the length of the cyclic pitch control rod so that the cyclic does not have to go back to the neutral position as stated above.
LCT's are a function of speed and standard pressure so the higher the altitude the earlier the LCT's start to extend. In a 47 around 15,000 feet (or less), in a hover, the LCT's are almost or fully extended.

This is very basic and changed some of the names (i.e. cyclic control rod) just so you could understand the concept. This info is in the Aerodynamics for Navy Flyers, Fudementals of flight (FM 1-203, Army) and Sikorsky Helicopter Aerodynamics. All are great sleeping aids!!! See Ya!
P.S. This is by no means all inclusive, you could go on for hours on this specific subject.

[Vfrpilotpb]

Thankyou all for your replys to my original question, your answers have been extremly well explained, and very informative, now I need to try and get a ride in one! if anyone could suggest how I could achieve this in the UK , I would be grateful, My regards to you all.

[Flying Lawyer]

Vfrpilotpb
If you get an invitation, please see if they can take two - I'd jump at the chance! :)

http://www.vhfcn.org/pics/anihook.gif

[This message has been edited by Flying Lawyer (edited 15 May 2001).]

[Vfrpilotpb]

FL, will do, by the way I sent an E to you several weeks ago re your earlier comments on Gazelles, seems like it didn't reach you.I will call you thru the Prune site if I get a ride offer! My Regards

[Lemoncake]

Just a quickie. On wednesday evening circa 1800 hrs I heard a very pleasant sound, looked out my window and saw a Chinook possibly heading South East, circa 800ft. Have never seen one over London before. Any ideas what it was doing?

Thanks

[what checks?]

uuuuurrrrrggghhh?

Not too sure about that. Fly them daily and haven't encountered this technique yet!

Nobody has mentioned the DASH yet which is fixed into the cyclic pitch control run. It fools you into thinking that the controls move EXACTLY like a 'normal'chopper, whereas the fact that the two heads go translational at slightly different times would otherwise give an odd feel. It just does this by expanding and contracting within the control run, all controlled by the AFCS (Auto Flight Control System)

Awesome helicopter, and great when people are shooting at you!!!!!

[Flying Lawyer]

Not such an unusual sight.
They usually follow the river, which explains the Hammersmith sighting, and occasionally land at Chelsea Barracks.
Impressive sight - I agree.

http://www.vhfcn.org/pics/anihook.gif

[Thud_and_Blunder]

Whatchecks,

I think you'll find a brief summary of the DASH functions about 4 posts above yours, in the dit from timmccall.

Agree about it being the right heli to be in when going somewhere iffy, though.

[HeliEng]

I live just the other side of the Chelsea Barracks, and frequently have the big boys coming and going!

I too saw the Chinook, wonderful site!

[Per Ordure Ad Asti]

I'm surprised that this is the first time you've seen us. The London heli-lanes are an easy way to get to the Stamford Training Area from Odiham and return. It is good training for the new guys as well because you really have to get on top of the radio calls, the nav (on the legs away from the river) and the required height changes. Thames Radar can get seriously p****d off if you f**k up. Of course the fact that the view is spectacular is merely coincidental.

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Through S**t to the Bar

[Per Ordure Ad Asti]

Very interesting thread. I can see I'll need to do some serious revision before my next standards check.
One minor point, the Chinook doesn't handle quite like a normal helicopter in roll. In a normal helicopter, once you have banked, the pendulum force of the cab tries to pull you wings level again, forcing you to keep some into-turn cyclic to maintain your angle of bank. For some unknown reason Boeing decided that the Chinook should fly like a fixed wing aircraft in roll. When you push the stick sideways the AFCS interprets this as a demand for a rate of roll proportional to the displacement. It will keep rolling the aircraft until you are upside down if you let it. You have to put the stick back in the middle to stop the roll, at which point the AFCS will automatically hold the angle of bank.

Lu: Your sideways stick stuff is not a problem in autorotation. As has been said, we can fly just like any other helicopter. It does play a major part in Vortex Ring or "settling with power" as the Americans would say. Although I know people who say that you can power out of Vortex Ring in the mighty wocca, and they have, the best solution is to accelerate, as it's impossible to maintain Vortex Ring above 30kts. Trying to pitch forward in the Chinook would only lead to an increase in collective pitch on the aft head which would go deeper into Vortex Ring and fail to pitch up. The way out of Vortex Ring in the Chinook is to accelerate sideways because, as you pointed out, this cyclically pitches both heads which gets round the problem.

Arm: All very good points and I wouldn't argue with any of them. The Chinook has a wind limit of 45kts from any direction and is very tolerant of downwind approaches/hover with very little increase in power demand. Even single engine, at training weights, the pilot would have plenty of power in hand, especially if he did a running landing (max speed 60kts). Into wind is better, but downwind at 10kts is not a problem.

Vfrpilotpb: Ever since the Wessex crash a few years ago, in which three ATC cadets died, the MOD have become EXTREMELY resrictive about carriage of civilians. It has to be approved from on high, and then only for a good reason. We would love to take you flying but, normally, they won't let us. I suggest you try to think of a cunning reason and write to the Station Commander at Odiham to ask. What have you got to lose?

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Through S**t to the Bar

[pedroalpha]

POAA

Its called a negative stick gradient and it really is VERY nice to fly - move the stick until you have the right attitude and then centralise; even pilots can do it!!!!!!!!!!!!

[Vfrpilotpb]

Good morning POAA,
Thanks for the suggestion, will try, like you say , Nothing ventured!!!( if I had Flying Lawyers software I'd show a little Woca flying about , but alas )

[Balance!]

VFRpilot
You don't need any special software to insert these little pictures. You just need to make a reference to an image file held elsewhere on the web. Take a look at this message by editing it - you'll see what I mean (and how it works).
http://www.vhfcn.org/pics/anihook.gif

A good source of 'smilies' and other aviation related gifs like the one above can be found at
http://www.stopstart.fsnet.co.uk
It even shows you how you can insert them into your text
http://www.stopstart.fsnet.co.uk/smilie/awink.gif

Regards
Balance!

Oh, and make that 3 please.... I'll get in the queue with FL http://www.stopstart.fsnet.co.uk/smilie/cheesy.gif


[This message has been edited by Balance! (edited 21 May 2001).]

[Vfrpilotpb]

Hi Balance, it must be an age thing, but I'll keep on trying, thanks for the tip.
Regards :)

[VLift]

Down wind landings. The Chinook has a lot of flexibility in this area but every thing has a limit. I'll tell on myself a bit. This was back in my early Chinook days.
The aircraft was a "small C", L-7C engines, I believe, and metal blades. Landing at 8400'MSL and about 25deg C. Slight down wind. Not much down wind but when you’re too fast, which can happen very easy at that altitude, a little down wind is allot.
My last thought before touch down was that if I can keep the VSI at less than 492FPM at touch down then, according to the book, I shouldn't do any damage. The book is a bad bet when you are using it as a hedge against poor technique.

[t'aint natural]

And then....?

[Heliport]

PHILADELPHIA, June 29, 2001
http://www.boeing.com/news/releases/2001/photorelease/q2/010629o.jpg
Press Release
Boeing has launched another chapter in the history of its longest-running continuous aircraft production program. The new CH-47F Chinook prototype heavy-lift helicopter, the sixth Chinook type designed for the U.S. Army, recently completed its first flight at the Boeing Philadelphia manufacturing facility. The June 25 flight, which involved hover and basic maneuvers, capped a series of comprehensive system checks leading to takeoff precisely as scheduled in the CH-47F program agreement completed three years ago.
"The first flight was flawless," said Roger A. Krone, vice president and general manager, Boeing Army Programs/Rotorcraft. "Our Chinook Team demonstrated not only technical excellence, but also a total commitment to our U.S. Army customer. The entire first- flight crew-pilots, engineers, technicians and support personnel-accomplished our program-schedule goals with consistently good performance and solid teamwork. They set a high standard for all our production programs." A Boeing Philadelphia flight crew consisting of Erik Kocher, Chinook program chief test pilot; Randy Wells, test pilot; Joe Schluck, flight test engineer; and John Rose, crew chief, lifted off shortly before 7 p.m., EDT, and remained airborne for about five minutes to validate aircraft handling qualities. "It was wonderful," Kocher said. "The aircraft performed right up to expectations while we completed rotor blade track and balance and crosswind hover as scheduled. The aircraft controlled nicely, and all systems functioned as advertised." The CH-47F modernization program will sustain the U.S. Army's Chinook fleet to provide rotary-wing heavy-lift capabilities well into the 21st century. Modernization will include aircraft remanufacturing, vibration reduction, improved avionics with integrated digital mission management systems and a digital map, and installation of more powerful Honeywell T55-GA-14A-714 engines. These core elements of the program will reduce operational and support costs to below those of the original CH-47D and provide at least another 20 years of economical and effective service. That means Chinooks will wind up serving in the Army's inventory for more than 70 years, an unprecedented record of service for military aircraft. The Boeing Company develops and produces military rotorcraft and provides support services worldwide from its production facilities in Philadelphia and Mesa, Ariz. Among its products are the AH-64D Apache Longbow attack helicopter, CH-47 Chinook, the RAH-66 Comanche armed reconnaissance helicopter and the V-22 Osprey tiltrotor aircraft.

[Thud_and_Blunder]

<font face="Verdana, Arial, Helvetica" size="2">Chinooks will wind up </font>

...like it!! :)

[Lu Zuckerman]

“Modernization will include aircraft remanufacturing, vibration reduction, improved avionics with integrated digital mission management systems and a digital map, and installation of more powerful Honeywell T55-GA-14A-714 engines. These core elements of the program will reduce operational and support costs to below those of the original CH-47D and provide at least another 20 years of economical and effective service. That means Chinooks will wind up serving in the Army's inventory”.

The article did not indicate if the new elastomeric rotor system was installed on this aircraft. If and when this new rotorhead design is incorporated the operational costs at least for the rotorhead will be higher than the existing design and that design is the highest maintenance cost driver on the CH-47. The elastomeric concept on paper reduces operational costs and maintenance by reducing parts count and eliminating the need to lubricate the rotorhead elements. However, what they can’t eliminate are the stresses and strains that exist in the rotorhead because a great deal of the flight time is in a hover or at speeds less than 60 Knots which is at hover pitch.

The steel elements of the existing design are 70-80% scrapped when the rotorhead comes in for overhaul or refurbishment. With this high level of operational stresses the elastomeric elements will degrade at a much higher level than on similar designs using elastomeric bearings. Because of the nature of the elastomeric bearings they must be matched to within 5% of each other relative to durometer (stiffness). If these elements go outside of that range the offending bearing must be changed and the remaining two bearings removed and tested for stiffness which runs up the ground maintenance times on the aircraft. If the remaining two bearings can’t be matched to the new bearing two new bearings must be installed and the other two put into the supply room to be referenced against the next bearing failure. This runs up the maintenance costs.


------------------
The Cat

[This message has been edited by Lu Zuckerman (edited 02 July 2001).]

[Copter Cody]

Nice........
Wished I owned one, Bet the are 'bout 5mil. Oh well, maybe I'll win the lotto some day.
Is this going to be used in the navy as well as the US Army?

Cody

[hun]

G'Day Guys and Girls

Need some help i need to know the chinooks fuel flows by tomorrow

thanks

[morro]

hun

Sorry, reply is probably too late. However:

At a basic weight (std crew/fuel) of 30k-32k lb you can plan on about 2400 lb/hr. Remains fairly steady until about 42k lb, where it climbs to around 2750 lb/hr at a 135 TAS cruise. At 50k lb it can exceed 3000 lb/hr in hover, or with large external loads, and probably drops back to around 2800 lb/hr in cruise. Endurance/holding - about 2100 lb/hr. Start/taxi uses about 600 lb for first start of day plus IFR checks.

All info is off the top of my head, and for a '47D with the -712 engines (nil FADEC). If you need grater accuracy I can get you a fuel flow chart.

Cheers BFSC

[hun]

cheers man every little bit helps

[VLift]

Hover FF on a cool day at 1000'PA with a 23,400 LB. F-4 on the end of 125' of rigging will be about 3200 PPH and the engines will be nice and warm.

Two kinds of helicopter, Cargo and external load.

[rotorboy]

Here is my question.

Is possible to get vrs in on tandem (ch46/47)rotor system (front or rear) independantly of the other. I would guess it wouold be the rear rotor.

Can this happen?

Can anyone explin it to me..

Thanks

RB

[Per Ordure Ad Asti]

Rotorboy,
for the reasons behind VRS in any helicopter I would recommend that you read the excellent thread about the Blackhawk accident which covered it in detail. Nick Lappos has a link to a site that explains it fairly clearly.
To get into VRS you need to be in the parameters for your aircraft with power applied. In a tandem rotor helicopter you can't tilt the discs as you would normally in a single rotor because you will chop the cabin in half. I order to pitch the CH47 forward the pitch is increased on the rear head and decreased on the front head when the stick is pushed forward. This is known as Differential Collective Pitch (DCP) as the blades on each head are pitched collectively but differently between the heads. If you were in the speed and ROD limits for VRS and then pitched forward or backwards it would be possible to get one head into VRS by itself.
In addition to this, the normal recovery technique for single rotor helis is to pitch forward to gain some flying speed. In a tandem this will probably only settle the aft disc further into VRS and you probably won't pitch forward at all. The recommended tandem recovery technique is to pitch sideways which only puts a cyclic input to each head and not a collective one.

[Gunship]

Morning all,

Another question please....

We are in the process of upgrading / rebuilding our runway / helicopter area.

Please can anybody advise me what the PCN of a Mauw Chinook is ?

Much appreciated in advance.

Gunsss

[Winnie]

Alot!
I miss your pictures!

[Gunship]

Alot!
I miss your pictures!



Hey WINNIE answer me on this one and the pics will flow ... ;)

[AlanM]

Is this what you are after???

From the RAF Flight Information Handbook:

Chinook HC Mk2:
AUW/MTWA/OWE = 50044lbs - 22700kgs
Tyre Pressure in PSI = 87

Rigid pavement subgrades:
High = 11
Med = 11
Low = 12
Ultra Low = 12

Flexible Pavement subgrades:
High = 8
Med = 10
Low = 12
Ultra Low = 13

Given that they land in fields/car parks I guess you wouldn't need too much LCG.

Cheers

[Gunship]

Many many thanks AlanM !

Exactly what we needed !

Many thanks !

Gunsss :ok:

[AlanM]

You are welcome - the only note of caution comes from the fact that I have just realised that MY FIH expired on 22 JUN 99!!

Should be fairly accurate for planning though - can't imagine much as changed a great deal.

Can Winnie have his pics now!?

Alan

[Gunship]

Lo ALAN,

Yip - I pressume that is somethng that should remain "within limits". We just realized we might have ANOTHER real B I E G visitor ... Mi-26 ( 56 tons) ...

So back to the drawing board ... you will actually see on a photo I have posted a while ago - the Mi-26's used to operate from our strip (and Chinooks) but now we are extending and the original drawings and engineer - they are not with us any more !

Cheers and if Winnie is Winnie as in Pooh - that is ok but if he / she is anything to do with the Mosquito Mandela ... then NO :*

Just kiddin .. :p

Will publish soon .. ;)

[Winnie]

GUNSHIP!

Yaya

Nothing to do with the Mandela Family, I am a HE, and Winnie the Pooh is correct!

If you want to know the AUW of the Schweizer 300CB it is 1750 lbs!!:D

Just missing your impressive pictures of the "Aligator/Crocodil" and wish I was flying some russian heavy iron!:ok:

[EnnArr]

Gunsss, MAUM of a UK CH-47 is 24,500 Kgs. Some cabs can only go to 22.7 but some others can go all the way up to 24.5. Just thought I'd let you know, but I guess it doesn't matter if you're having a 56t visitor!!

Fly safe.

EnnArr.

[Gunship]

Lo Winnie - tx for the Schweitzer weight - you never know it might have a higher PCN ;)

EnnAr, many thanks. Although we are battling to find the Mi-26 tyre pressure, I am sure we will have to follow the Mi-26 specs.

Many thanks in any way ! :ok:

Cheers and best regards,

Gunnss

[WhiskeyNovember]

Hello,

I'm a fixed-wing pilot who knows almost nothing about rotary-wing ops, but I've always wondered if twin-tandem (I think that's the correct term) helis such as the Chinook are any easier to hover. It seems that the torque effects of the rotors would cancel each other out and make things much easier for the pilot.


-WN

[ShyTorque]

No-one is really sure if they are actually easier but designed to be more difficult, or if they are more difficult but designed to be easier.

They feel quite conventional, though, just bigger.

[SASless]

Being a former Chinook pilot....who is now forced by economic necessity to endure mere single rotor devices...I will wholeheartedly confirm real helicopters are easier to hover. We Chinook pilots of years past, certify that is due to the very careful selection process that manned the cockpits (with some small assistance from sheer mass and inertia), Chinooks do hover better.;)

[ShyTorque]

SASless,

Yep. Some Chinook pilots do have sheer mass and inertia! :p

[Shawn Coyle]

The Chinook, and it's smaller brother, the CH-46 are helped immensely by a very capable automatic flight control system that provides attitude hold. Basically, when you have the attitude you want and have trimmed up the cyclic and pedals, the system will hold that until you run out of gas.
But even with the AFCS off, it is still quite easy to hover - helped not only by the lack of torque reaction, but also by the lack of side force and roll changes with tail rotor changes required by power changes.

[Nipper]

Its even easier if you have the radalt hold engaged and taking in to account that it will hold heading unless you push the pedals.

Crew Chief bring me another coffee;) :E

[Jcooper]

One thing Ive wondered is the yaw weird in the chinook. Seems like a big thing to be whipping around with the pedals and I am guessing it yaws around the CG which would prolly be somewhere inbetween the two rotors. Any thing to relate it too or am I talking out of my not so sunny side.

[SASless]

Jcoop....Chinook pilots are used to swinging large things around thus tromping on the footrests is a snap. One interesting fact about the CH-47 is the length of the allowable CG travel....on the order of 144 inches range....just under four meters (metres) for Euro spenders in the crowd.

Shawn...your statements might mean something when describing the C model and later variants. The B model with the square tail fin was somewhat better than the A model with the sharp tail....but the A model without SAS was real sport in Yaw. Felt as though you were pedalling the thing to keep the rotors turning or something. With SAS on...the old A model was rather docile, the B even better, and the C with Pitch SAS and SAS was pretty tame. Add the modern goodies and sooth....what more could a guy ask for...."white with two sugars" maybe.:O

[Autorotate]

So what then is the difference between the Boeing 234 and a CH47, and what model CH47 would the 234 be closest it, if any.

Autorotate.

P.S. I watched them moving a drill rig in the PNG jungles and it was an amazing site to watch with a 260 ft longline. :eek:

[Red Wine]

Large Helicopters large thing!

Small Helicopters all thing!!

[The Nr Fairy]

I had a trip in a Chinook sim some years ago - thanks JJ and John - and had a bit of a play.

Spot turns with no cyclic input turned about the centre of the aircraft. Spot turns with right or left cyclic turned about the rear or front of the aircraft - but I can't for the life of me remember which cyclic went with which end.

But as a low time pilot (then 70 hours and a PPL on R22s) it didn't take too long to get comfortable enough to sling loads and fly formation . . . but the AFCS is really good !

[Lu Zuckerman]

This is slightly off track but.....

My very first ride in a helicopter was in a Piaseki HRP-1 the original flying banana. The engine was in the rear of the passenger compartment completely exposed (a mechanics’ dream) along with the fuel bladder. I was sitting near the combining gearbox when the pilot put the helicopter into autorotation and the helicopter did not have a freewheeling unit. Instead it had a spring-loaded jaw clutch which sounded like a machine gun going off. It scared the hell out of us that were not familiar with the HRP-1.

:E :E

[Shawn Coyle]

The CH-46 and CH-47 families have had a very interesting history of AFCS' (whatever Boeing wanted to call them, they eventually are all an Automatic system of some sort).
The latest version is probably one of the finest systems I've ever seen. Simple (relatively) to understand, does a nice job, and makes both the aircraft quite docile.
The CH-46 is the worse of the two with the AFCS off, and is probably due to the aerodynamic shape of the rear fin. I can't speak for earlier models of the CH-47, but the C and D are not bad with everything turned off.
The BV 234 is probably pretty close to the CH-47D, with differences in the electrics and flight instruments.
And the way to turn about the nose is simple to do, but difficult to describe - basically pedal against the cyclic. Turn about the tail is pedal with cyclic.
Empty? They are sports cars.

[idle stop]

I seem to rememebr that when lifting to the hover and the weight comes off ( the microswitches associated with) the rear wheels, the longitudinal cyclic control re-datums itself through subtle length changes, via screw jacks, of the control runs. And AFCS Off, the stick gradient is reversed translating to and from the hover. (Now that's inviting the purists to put me right!!)
But that said, an R22 pilot should still have little difficulty hovering a Chinook.

[the wizard of auz]

But that said, an R22 pilot should still have little difficulty hovering a Chinook.
Bloody Bonza!, where do I sign up to have a shot?.
:} ;)

[OFBSLF]

Bloody Bonza!, where do I sign up to have a shot?Any US Army recruiting office;)

[Shawn Coyle]

wizard of oz:
Doesn't the Australian Army operate Chinooks too?

[Bad medicine]

Shawn,

They sure do.

Cheers,

BM

[Thomas coupling]

http://homepage.mac.com/helipilot/PPRuNe/chinook2.JPG

Stealth Chinook:suspect:

[SASless]

Stealth Hook? Looks like a Semi-trailer that sat too long in a gang neighborhood and got "Tagged"!:ok:

[Aser]

To me looks like a chinook used in a secret british SAS operation...
Irak? Afganistan? :E
cool.

[matador]

Back in 1985 the Spanish Army bought some new models from Boeing, since all "D" production line was going to the US Army they sold the Boeing Vertol 414, which was the civil version half way between the Super C and D.
Those 414 had the L-712 engines on them, FRB's and RPM's indicators in %'s, although oil cooling system and AGB's were the same as in C models.
The other day I was invited to go to my former Chinook batallion brand new Delta simulator. The cockpit and instruments all looked quite alike a C model. Although I haven't seen the BV 234 I would think that they would be closer to the BV 414 than to a D model.
Just my 2 cents.
Buen Vuelo

[pulse1]

I was watching the programme "Combat Helicopters" on Channel 5 last night and was amazed to see a US Chinook landing on the sea to pick up a RIB. The initial splash was quite big and, when they showed a shot from inside, the crew were ankle deep in water as they pulled the boat inboard. In fact, they seemed to rely on the backwash to bring the boat inside.

Is this a procedure used and trained for regularly by any Chinook operators?

When you think how that amount of water can capsize a ferry, the control and stability problems for a helicopter must be quite interesting.

[Whipping Boy's SATCO]

I think you will find that the "amphibious" footage was of an RAF Chinook.

[BossEyed]

Indeed so.

At least some of the footage (that showing a Chinook with plimsoll lines on the outside) was of an aircraft from Boscombe. Venue was Lyn Brenig.

I think the interior footage of the surfing crewman was of the BD trial, too.

[Straight Up Again]

I have seen several pictures of Chinooks landing on lakes (but have nowhere to host them so can't post them), including one of a RIB coming into the back, looks quite impressive taking off with all the water gushing out.

I believe all the pictures I have seen have been on lakes, not the sea, ie fresh, not salt, water. I seem to remember that salt water can be very damaging to aircraft, but fresh water isn't so bad, am I wrong? (it has been known to happen)

[Hydraulic Palm Tree]

I have seen several pictures of Chinooks landing on lakes (but have nowhere to host them so can't post them), including one of a RIB coming into the back

That would be bloody impressive - a MIB maybe, perhaps 2 of them, but not a RIB!!

HPT

[ppf]

Any one got any pictures to post of Chinnooks landing on water??

Silly question time: I take it Chinooks can't float on water without a certain amount of collective input, would I be right in assuming this?? If so how do you keep a large helo on the water rather than upside down/under the water!?! :confused:

[Yeller_Gait]

HPT,

Not quite sure what the MIB you refer to is, but it is quite feasable that a RIB (rigid inflatable boat) could enter a the rear of a chinook

[Gainesy]

The boat on the Boscombe footage is indeed a RIB, it enters the Wokka at a fair rate, about 5kt. Better carried inside than underslung , as a surprised motorist found when one was dumped (Oscillating badly) from a Wokka near the A303 some years ago.

Then there was Smokey's (IIRC?) attempt to undersling the Ark Royal on Ex Purple Helmet in 1987...:)

[Hydraulic Palm Tree]

The MIB is a Medium Inflatable Boat, flat bottomedwith no hard bits. The RIB is rigid bottomed as you describe and either 21 or 28 ft long.

The RIB, due to hull shape, could not get into the Chinook fully and was not claered to do so in the UK. Of course they may have driven up to the ramp and transferred pax, but don't see the benefit of that.

Gainsy - I have never seen a RIB in the back of one, perhaps this precedes my experiences. The Boscombe pictures I have access to do not show a RIB, its a MIB.

PPF - The Chinook will float quite happily at collective gound detent position which is positive pitch giving about 20 torque. By the way, this exactly the collective position that is used during ground operations following landing.

The procedure itself is quite straight forward and the speed is controlled by collective and water depth by cyclic - its best to give the crewman a good six inches in my experience :O . The Chinook has a power down ramp facility, i.e, one that doesn't freefall under gravity, so you can for the buoyant ramp into the water.

HPT

[Gainesy]

HPT,
OK, 'twas the boffin at Boscombe said it was a RIB. To me it was just a speed boaty thing. V impressive technique though. They released the film to the Beeb but the d'head producer ditched it (and some v. low level parachute trials) in favour of some Bona mates doing press ups.:zzz:

[wub]

Chinook taking a bath:


http://www.boeing.com/companyoffices/gallery/images/military/rotorcraft/ch47sd/images/dvd-110-05.jpg

Water landings on the Delaware River next to the Boeing Philadelphia factory.
The Chinook is watertight and fully capable of landing on water for special operations and similar missions. The Chinook remains afloat even with the rotors not turning, and a special kit facilitates water operations.

http://www.boeing.com/companyoffices/gallery/images/military/rotorcraft/ch47sd/images/dvd-110-05.htm

(Look at gallery for more)

[Straight Up Again]

OK, I just looked at the pictures again, it was a MIB (never heard that term before), as it didn't look like any of the RIBS I've dived from, none of which would have fitted.

Apologies for the mistake, but my boat knowledge is a bit limited (that's why I work in aviation).

The pic I've got from the inside of the boat coming in quite good, the loadie is seeing how high up the inside he can climb.

If any wants a look or can host then, PM/Email me.

[Tiger_mate]

http://www.chinook-helicopter.com/history/CH47_On_The_Water.jpg

Pasted from www.chinook-helicopter.com where they reckon a CH47 can float for 30 mins without engine power.
http://www.army-technology.com/projects/chinook/images/chinook14.jpg

[MadsDad]

An argument came up in the pub yesterday between me and a mate which raised a question concerning helicopters which hopefully someone here can answer.

The basis of the argument was as follows (and this is very basic stuff, so please forgive me). On a normal helicopter there is a single rotor. When this revolves to provide lift it generates torque which will cause the fuselage to revolve in the opposite direction to the rotor. To counteract this a tail rotor is fitted to provide a counter-thrust to the fuselage so it doesn’t spin. However if a helicopter has two contra-rotating rotors the forces between the two balance out so there is no need for a tail rotor to stop the fuselage spinning.

But (and here the argument started) there is still a requirement to turn the fuselage (to face the direction of travel, saves getting a crick in the neck when flying backward). In the standard single-rotor machine this is, I believe, done by varying the thrust from the tail rotor so it provides either too much or too little (which will turn the fuselage). However how is it done on a multi-rotor machine?

I claimed it could be done, at least theoretically, by varying the properties between the rotors (different pitch or, less likely, different speed for the two would produce a torque imbalance which would turn the machine). He insisted that they must have some external thrust, either from a tail rotor or variable ducting for the exhaust (for the turbine powered machines) to turn them (I cited the Chinook as not having a rotor but he insisted it has ducted thrust).

Does anyone know if this is possible (or even has been done) or am I talking through my posterial orifice again? (And there is a pint riding on this).

[copterfamily]

I believe I am correct when I say that there is definately no "notar" type system on a chinook or a tail rotor. Essentially when pedals are pressed in the cockpit both rotor systems are tilted in opposite directions.

I got this from another website:
"This is accomplished by pedal only inputs. By depressing one pedal over the other, cyclic inputs are put in both systems in opposite directions to pivot about the center of the aircraft. Both rotor systems receive equal cyclic inputs, and the helicopter just spins nicely at its center without the pilot having to move his cyclic control at all. A pivot around the tail is accomplished by heavy cyclic inputs by the pilot, and little or no pedal inputs. This will make the tail stay in one place, and the nose of the aircraft move laterally until it spins about the aft mast."

Needless to say it is a complicated system that requires a lot of linkages, a lot of control tubes, and a pilot who trusts his maintenance crew to make sure it all was put together properly!

Hope you won that pint....

[MightyGem]

MadsDad, as copterfamily states, there is no sideways thrust in the Chinook other than from the main rotors.

You may like to look at this thread (http://www.pprune.org/forums/showthread.php?threadid=20312&highlight=chinook+AND+yaw) for a more indepth explanation.

PS, the BV234 was/is the civil version of the Chinook.

[Hilico]

When both rotors are on the same shaft, one above the other, applying different cyclic to both would serve only to bend the shaft (or if you're really out of luck, the tips would touch).

Being on the same shaft and generating equal amounts of lift and torque, they normally cancel each other out. When you want to turn on your axis, pressing, say, left pedal reduces the pitch on the anti-clockwise rotor and increases it on the clockwise rotor - result, fuselage turns anti-clockwise, or 'left'.

[Dave_Jackson]

You win the beer.

Your only mistake was the statement "On a normal helicopter, there is a single rotor."

The single rotor is an abnormality. Future rotorcraft will have lateral symmetry, just like every other vehicle; and animal for that mater.
http://www.unicopter.com/No_Tail_Rotor.gif

With apologies to those who ride around in motorcycle sidecars.
:D

[Lu Zuckerman]

Discount just about everything stated by Fr O'Blivien in the above referenced post.

As previously stated if you push the "rudder" pedals the helicopter will spin about the center of the fuselage. This is differential pitch input in the fact that one rotor has a cyclic input to the left and the other rotor system has a cyclic input to the right. Pressing the opposite pedal will result in the helicopter spinning in the opposite direction. Cyclic input will not cause the blades to hit each other as they are locked in a fixed position relative to each other this is called phasing.

If the pilot moves the cyclic to the left or the right the helicopter will move in the direction of cyclic movement and once again cyclic input will not cause the blades to strike each other due to the fixed phasing. A coordinated pilot can input cyclic movement and at the same time press the pedals and the helicopter can be made to pivot either about the forward mast or the rear mast depending on the coordinated pitch input. A really coordinated pilot can perform a maneuver called walking the dog in which he alternates the pivoting from the front mast to the rear mast and back again.

Fr O’Blivien made a statement about the tilting of the transmissions when the pilot inputs forward cyclic. This is not the case. Movement of the cyclic either forward or rearward will cause one rotor system to increase collective pitch and the other to decrease collective pitch which causes the helicopter to move in the direction of the decreased collective pitch.

The pilot does not have any input relative to forward or aft cyclic stick movement other than to effect the collective pitch levels of the respective rotor system. When the helicopter reaches a forward speed of around sixty knots forward cyclic pitch is automatically applied to both rotor systems and at this time the pilot can lower his collective stick. When the speed drops below sixty knots the forward cyclic input is removed and most likely the pilot will have to increase collective pitch to a level it takes to fly with decreased weight.

:E :E

[Woolf]

Good evening all!

Correct me if I'm wrong but I always thought that the big russian coaxial twin rotors use their downwash wich acts on the tailboom rudder to turn?

[SASless]

Lu,

Why is it the Chinook has only Pivoting and Swiveling Actuators on the rotor heads....One of each per head...driven by two independent hydraulic systems?

[Hilico]

Woolf, you suddenly made me wonder if my information was correct. Then I thought about autorotation.

With the airflow up through the rotor (and of course the tail), what happens? If it's the sheets of metal on the tail that are used for yaw control, then the effect of the pedals will be reversed. If it's differential collective, they won't.

I'm imagining that yaw control by the tail fins would be achieved by pivoting them at the top and swinging them in the opposite direction to which you want to spot-turn.

[Lu Zuckerman]

To: SASless

To the best of my knowledge the swash plates on the CH-47 have two each hydraulic actuators that impart both lateral (cyclic) input as well as collective input. Each swashplate has an extension arm that is about a foot or more in length. Attached to this extension arm is an electrical actuator that retracts to provide forward cyclic when the helicopter reaches approximately sixty knots. When dropping below sixty knots the actuator is commanded to extend returning the respective swashplates to the commanded collective setting.

The control geometry is such the when applying lateral cyclic the swashplate pivots on the extension attach bearing for the electrical actuator. When forward cyclic is imparted by the electrical actuator the swashplate pivots on the bearings on the hydraulic control actuators.

An added side note: The CH-47 is a cargo and troop carrier and at that time (below sixty knots) the rotor systems are operating at high collective settings and at high power settings. When the rotorheads are returned for overhaul many of the high value components are scrapped due to cracking from high stress levels.
This is especially true for the rear rotor.


:E :E

[Flingwing207]

Oookay, well someone might beat me to this, but…

Tandem rotor system, like the Chinook:

To yaw, one rotor “banks” left while the other banks right, fuselage pivots in middle. I hear (but have no firsthand experience) that a good Chinook pilot can, through finesse with cyclic, collective and pedals induce the big tandem to pivot around the nose or tail.

Coaxial rotor system (contra-rotating rotors stacked on top of each other), like the Kamov:

To yaw, one rotor increases collective pitch while the other decreases collective pitch. The resulting difference in torque about the rotor driveshaft(s) causes the aircraft to pivot about the rotor mast. The vertical tail surface provides stability in forward flight

Synchromesh counter-rotating rotors (side-by side), like the Kaman:

One rotor pitches forward while the other pitches back, dragging the fuselage around a point between the rotor masts (a lateral version of the tandem, I suppose). Again, the vertical stab provides stability in forward flight.

That's as far as I know, anyway.

[Dave_Jackson]

What Flingwing207 says is essentially correct, with one small exception. The "Synchromesh" description is totally correct for the Side-by-side configuration, and part of the answer for the Intermeshing configuration.

The Intermeshing configuration is sort of a hybrid between the Side-by-side and the Coaxial. Most Intermeshing helicopters use both opposed longitudinal cyclic and differential collective.

http://www.unicopter.com/B318.jpg

[Scud-U-Like]

Times Article (http://www.timesonline.co.uk/article/0,,2-1065688,00.html)

[Arkroyal]

Crew of two to four and can carry 54 troop members eh?

[Ian Corrigible]

Also reported by the Beeb, for those without a subscription to The Times: Blunders lead to helo shortage (http://news.bbc.co.uk/2/hi/uk_news/3606325.stm). No sign of the report on the NAO website yet.

I/C

[HectorusRex]

£260m SAS helicopters can't fly with a cloud in the sky
By Michael Smith, Defence Correspondent
(Filed: 07/04/2004)


Eight special forces helicopters delivered to the Ministry of Defence in 2001 at a cost of nearly £260 million have not been used in Afghanistan or Iraq because they cannot fly if it is cloudy.

The first SAS team to enter Afghanistan was delayed by six days because of the problems with the Chinooks, which are allowed to fly above 500ft only in clear skies.


£127 million must be spent so the Chinook can carry out the missions they were bought for

The problems, disclosed today in a National Audit Office report, were the result of "one of the most incompetent procurements of all time", Edward Leigh, the chairman of the Commons public accounts committee said yesterday.

"Eight brand new Chinook HC3s costing £259 million were delivered in 2001 but will be sitting on the ground until 2007," he said. "Because of a massively botched job, they cannot be flown when there is a cloud in the sky. The MoD might as well have bought eight turkeys."

In what Mr Leigh described as "an atrocious oversight", the ministry had decided to cut costs by refusing to pay for a fully digital cockpit. The result was a compromise that did not match British defence safety standards.

The 500ft restriction means that the helicopters "cannot be used other than for limited flight trials", the report says.

It will take £127 million more to bring them up to British standards and enable them to carry out the tasks for which they are needed.

The helicopters were ordered from Boeing in 1995. They were tailored to the needs of the SAS and Special Boat Service, with satellite communications technology, extra fuel tanks and in-flight refuelling probes for long flights.

At the start of the war in Afghanistan, when there was no moon - in theory the best conditions for a special forces insertion - the SAS could not move because its Chinook pilots relied on light-enhancing night vision goggles.

As a result, the troops were unable to fly into Afghanistan until six days after their American counterparts.

The report is also critical of the ministry for the failure to provide enough helicopters to carry troops into action. It says: "There is an overall deficit of 38 per cent in helicopter lift. There is also an 87 per cent shortfall in ship-optimised helicopter lift."

The criticism coincides with proposals from MoD working groups to axe all RAF Puma and all Royal Navy Sea King helicopters as part of a drive to save £1.2 billion from this year's defence budget. But the Merlin helicopters that would take over responsibility for airlifting troops into operations are "restricted to essential flying" because of a suspected tail rotor fault.

The report recommends that the Royal Navy and the RAF follow the Army Air Corps in using senior NCOs to fly aircraft rather than confining the role to commissioned officers.
"one of the most incompetent procurements of all time" (http://www.telegraph.co.uk/news/main.jhtml?xml=/news/2004/04/07/nchopa07.xml)

[Mr C Hinecap]

The report recommends that the Royal Navy and the RAF follow the Army Air Corps in using senior NCOs to fly aircraft rather than confining the role to commissioned officers.

Interesting. Hmm....... Nice little line to slip in there.:E

[BEagle]

Perhaps,

But totally irrelevant to the topic. Yet again a cash strapped MoD has made a total bolleaux of a new aircraft project - but the government will seek to blame anyone other than themselves.

THe root cause is having people like Blar, Hoon and Gordon-the-greedy in power.

How much does the nation waste on paying econmic migrants with their ever outstretched hands? And how much do Trust-me-Tone's bring-a-bottle wars cost the nation?

And we can't even afford 8 helicopters! E I G H T !!

But I supose if the RAF can't even afford to buy its own basic trainers or ME training aeroplanes anymore, the fact that we can't afford a few helicopters shouldn't come as a huge surprise....

How did it ever get into such a state?

[ORAC]

Full Report (http://www.nao.org.uk/publications/nao_reports/03-04/0304486.pdf) (989K). Executive Summary (http://www.nao.org.uk/publications/nao_reports/03-04/0304486es.pdf) (140K).

[Low Ball]

Beags,

On Radio 4 interview with Minister for Def Procurement this morning as I drove to work he said that the contract was let in 1995. Therefore it was the Tory Band that were playing and not the Socialists.

What gets no mention at all, and maybe I'm jumping to conclusions here, is that the contract was changed/amended after it was let.

That would be another story and something which the uniformed members of the MOD are often guilty of.

Low Ball

[BEagle]

From the report:

Flawed procurement of eight Chinook HC3 helicopters means that, although they were delivered to specification by the contractor in December 2001, they cannot yet be used operationally, principally because there is insufficient evidence to demonstrate that the avionics software meets United Kingdom Defence standards. This is primarily because the programme was not de-risked prior to investment decisions being taken; nor did the contract specify that the software should be analysed in accordance with United Kingdom Defence standards. Other user requirements categorised as essential have not been delivered because, for a variety of reasons, they too were not included in the contract. To bring the helicopters broadly up to the standard of the existing Chinook fleet would require approximately £127 million, over and above the £259 million originally estimated, and would mean the helicopter would enter service in mid-2007 - some nine years later than the original In-Service Date, although this latter was re-defined in March 1998 to June 2002.

The shortfall in battlefield helicopter capability will continue

Even if improvements to efficiency and effectiveness are made, there will still be a shortfall in helicopter capability. A recent Departmental study concluded that there is currently a 38 per cent shortfall in overall battlefield support helicopter lift, which includes an 87 per cent shortfall in ship-optimised support helicopter lift. Primarily, the latter deficit is a manifestation of a changed strategic environment over the past decade, which has generated a greater requirement to undertake littoral operations. According to the Department, the shortfall in ship-optimised lift will remain until 2018, while overall battlefield lift will remain inadequate until 2017.

In addition, the nature of the legacy fleet means that many platforms are not fully equipped to undertake missions in certain operational and environmental conditions, including those recently experienced in Afghanistan and Iraq. The helicopter force has a number of critical capability shortfalls, some of which can only be addressed by expensive modifications. Owing principally to a lack of resources, these capability shortfalls are often met by Urgent Operational Requirements. For example, part of the current Chinook fleet has acquired the necessary capabilities to meet operational demands. However, this process has often not only been costly but it is essentially short-term in nature.

[HOGE]

Chinook blunder 'left RAF short'

The Chinooks were meant to be in service in 1998
Eight new helicopters worth £259m are grounded due to a "botched" procurement, a study by the National Audit Office has said.

more at

http://news.bbc.co.uk/1/hi/uk/3606325.stm

[Flatus Veteranus]

Were these the aircraft that were bought as "stocking fillers" - ie, late purchases to soak up an unexpected budget surplus? Did some blokes from OR and PE literally fly into Seattle waving cheque books? Did Boeing's sell any more aircraft to this standard to any other customers? If so, are they accepting the same operating restrictions, or are Boscombe and PE over-egging their standards? It would not be the first time THAT has happened. It was amazing during the "Malvinas Arse-kicking" who many radical mods and capabilities were cleared by Boscombe in short order because it was also a "PE Arse-kicking" exercise. :confused:

[Flytest]

MOD place a contract, then change it right left and centre, procured items don't work, over budget, late, etc etc..

Same old same old.

:mad:

[MightyGem]

Perhaps I'm missing something here? So the HC3 is limited to day/night VMC only. Isn't that what most of you do anyway? The 500' restriction seems strange, as you're looking out below that height anyway, so the lack of IF capability hardly seems relevant.

Surely the aircraft should be able to carry out most of the missions that the rest can do at present.

[simfly]

mightygem, think about it, when £260 million is spent so the aircraft can do more/fly in less...............

[Tandemrotor]

Flatus Veteranus

Think you will find they are made in Philly PA,. Only planks are made in Seattle!

[sycamore]

Since there is no suitable tanker available for SF ops as well, why has`nt that problem been addressed?

[Spaced]

Ive been doing some reading lately, mainly from Proutys and Johnstones books.
In reading about tandem helicopters I was struck by a few of things.
1, Longitudinal control of the helo is acheived by differential collective, does this mean that there is no longitudinal cyclic control? Or is there some and its used for trimming the helo?

2, Why are the tandems so quick? Considering they are of an older design yet can cruise at 150knts. Is it due to the large amount of horse power installed? Or because retreating blade stall isnt as important with two advancing blades.

3, has anyone, or do you know anyone who has had the rear rotor go through ETL while doing a turn about the nose? Is this very severe when it happens, or relatively controlable?

One more, when picking up to the hover, in nil wind, do you have to make any corrections, I understand the torque will be canelled out, Im just wondering if there is any other cross coupling due to the seperation of the rotors.
Thanx in advance

[Head Turner]

Dave Jackson's your man on this topic. However if you look back in the Forum you will probably find all the answers. Just look for DJ and somewhere is the info. Sorry I am so vague but I don't have time to look back for the precise locations.

[Lu Zuckerman]

To: Spaced

1, Longitudinal control of the helo is acheived by differential collective, does this mean that there is no longitudinal cyclic control? Or is there some and its used for trimming the helo?

When you go into a hover the pitch on both rotors is the same. When you push forward cyclic the front rotor decreases in pitch and the rear rotor increases pitch. Upon reaching a forward speed of around 60 knots there is an automatic system that inputs forward cyclic and at this time the pilot can decrease his collective input.

I think.

:E :E

[Shawn Coyle]

Longitudinal control is through a combination of differential collective and tilting of the main rotor heads by the Automatic Flight Control System.
One of the features (and probably a reason why the Chinook is so speedy) is that the fuselage is pretty well level throughout the flight envelope - there isn't the nose-down tilt that single rotor helicopters have. As airspeed increases, the AFCS tilts the two swashplates by electric motors - this system is called Longitudinal Cyclic Trim (LCT). The mechanical control system only has two actuators (for collective and roll control).
When you move the cyclic fore-aft, it does introduce differential collective pitch, but as the airspeed changes the LCTs program to take out some of the differential collective effect.
The AFCS is incredibly complicated, and incorporates Differential Airspeed Hold (DASH) actuators to require the cyclic to move forward with increasing airspeed (basically to keep the pilot happy - more forward stick is needed with airspeed is the natural thing).
They are quick because of incredible amounts of power, and reasonably streamlined fuselages.
You'd have to do a really fast turn to generate translational lift on the outside rotor - and the AFCS does a remarkable job of maintaining the attitude constant without the pilot, so the effect would be masked as far as the pilot was concerned anyway (turn the AFCS off and you'd see it).
Hope that helps.

[Dave_Jackson]

:confused: :confused: What's a tandem helicopter? :confused: :confused:


_________________________

Shawn and Lu are the men.

My specialty is 'theoretical flights of fancy'. :O

[heedm]

Shawn is correct regarding systems on the Chinook, and perhaps other tandems. They can be flown without LCT, DASH, AFCS, and DCPT (Differential Collective Pitch Trim). All those devices are made to reduce pilot workload, make flight more comfortable, and expand the flight envelope.

1. Longitudinal cyclic only controls differential collective pitch. Any fore and aft tilting of the disc is controlled with speed sensors and cockpit switches.

2. Retreating blade stall is important in tandems. I think part of the reason for the increased speed is a lower tip speed is possible due to having a larger rotor area for the same rotor diameter (because there are two circles).

The speed limit is normally imposed by loads on the necessarily large aft mast. These are reduced by tilting the disk forward with the LCT.

3. As Shawn mentioned, the turn rate required would be rather uncomfortable. Also, in a turn the blades wouldn't experience ETL at the same time, so I'd expect unusual flight characteristics to appear before fully realizing ETL. The sidewards flight limit we had would have kept you below ETL.

I haven't flown a tandem with an AFCS, just a rate damping SAS. The SAS would not have hidden these effects. SAS (or AFCS) off flight is very possible but does require a much higher workload. To realize what is happening in tandem rotor flight I think SAS off flight is required. The higher lift on the aft rotor makes it want to go faster than the forward rotor, resulting in yaw instability (divergent). Typical roll control but very rapid pitch rates will occur for small inputs.

4. When picking up into the hover, the only change from tail rotor flight is that you don't have to change pedal based on power. There is still the requirement to finely adjust all four axes together, resulting in a similiar workload. The SAS or AFCS lowers the workload vice the tandem rotor configuration. I'd expect most experienced pilots will have fully adapted to a new configuration before 200 hours on type or less (going t/r to tandem or tandem to t/r).

[Shawn Coyle]

Sorry - forgot to comment on the 'picking up to the hover' question.
There is no need for the pilot to move the pedals when lifting to the hover, for two reasons -
a) the AFCS keeps the heading constant
b) the two rotors have no overall torque effect to be cancelled.
Having said that, the two rotors do not carry the load equally, even with a mid-CG. I've been told the aft rotor carries about 55% of the load, and the forward one, 45% (obviously). The rotor configuration means that you can lift the nose of the machine into the air quite precisely, and then control pitch attitude with power, not cyclic (within a fairly small range).
In fact, two wheel taxiing a tandem (either CH-46 or CH-47) is quite an art and a bag of fun. Three wheel taxiing the CH-46 is very challenging and needs a whole new set of skills.

[Lu Zuckerman]

The CH-47 spends a great deal of time in a hover for cargo hookup and drop off and much of its’ time below 60-knots at which point forward cyclic would be added by the black boxes. That being said when the rotorheads are returned to the factory many if not all life cycle components are scrapped. They are excessively worn and many of the parts have stress cracks beyond the point of repair.

On a Sikorsky rotorhead most of the parts can be refurbished or overhauled when the heads are returned to the factory or an overhaul facility.

Although the question was not asked I provided an answer.


:E :E

[heedm]

Shawn, I have to admit that I'm a little confused with your responses. The question was about tandem rotor configuration, and you exclusively talked about augmented modes of flight. The right AFCS in any machine can reduce the workload down to what you're mentioning.

In the flight test community, is it the norm to ignore the limitations of a configuration if a computer can compensate?

I hear you on the two vs three wheel taxiing of the H46. Last trip down memory lane this summer in Trenton when we say good bye to the last of the labs.

Matthew.

[Spaced]

Thanx for the relpy guys and sorry for my delay in posting, work keeps getting in the way of my leisure.
I did a search and found some good stuff which cleared up a couple of other questions I had, but one more if you would be so kind.
Assuming the all the electronic gismos are turned off to give a true representation of the flight characteristics;
Say you pick up to the hover in nil wind, I understand that the torque from the collective pull is blalnced, but say you add fore or aft cyclic, does this then mean you would have to add pedal to correct for the difference in torque? And with the gismos turned on is this effect masked completely or partially?

[Shawn Coyle]

Both the CH-47 and CH-46 have duplex AFCS which means that it is an emergency situation to have both fail. Hence, you probably wouldn't spend much time taking off with them both off.
The AFCSs are sufficiently complex and layered so that parts of it, like the LCTs, are working even if you shut off the attitude hold part.
In fact, lifting off to the hover can be accomplished in both machines by merely lifting up the collective - no need to come to the rear wheel position (except perhaps caution and good airmanship). I've seen an awesome demonstration of a 'jump' takeoff in a Chinook that literally didn't blow any snow around - a quick and large pull on the collective and we were rocketing up.

[Pub User]

Spaced

The RAF demonstrate the phenomenon of the rear rotor experiencing ETL when turining about the nose, to students on the Chinook conversion course. It requires quite a high turn rate, well beyond what you would normally input for positioning, and is not difficult to control. It happens with the AFCS in too.

[heedm]

Current models of the H46 and H47 do have AFCS.

All the other tandem rotor helicopters also demonstrate tandem rotor flight characteristics. Some without any significant SAS/AFCS.

I've flown tandem configuration without augmentation many times in a non-emergency situation. Once in the hover, a change in one axis requires retrimming all other axes. There is no anticipation of a change in pedal due to incresed torque or due to pitch changes. However, the inherent instability in the configuration requires so much control that it may mask any anticipated control inputs.

Lifting to the hover requires significant longitudinal cyclic changes, even more so if you're doing a no hover or jump takeoff. This is to avoid putting excess pressure on oleos and because droop stops can be contacted with low power settings and undue cyclic movement.

The H46 sits level while taxiing, nose up in the hover, and level to nose down in forward flight. To take off without hover requires you increase collective while moving cyclic aft, to avoid pressure on the nose wheel oleo, then continue to increase collective while adding forward cyclic to set up for forward flight. The point that you change cyclic movement is approximately when it feels like the nose wheel is unloaded. During this evolution, you initially set your pedals as power is increased to eliminate yaw, then add a small amount of right pedal as you get into forward flight. I think this is more due to aerodynamic characteristics rather than any difference in torque between the heads.

[Dave_Jackson]

http://www.lafhelicopters.com/pictures/company/historique32.jpg


Hi Spaced,

You are probably aware of the Leflamme, so the link below is for others who might not be.
Laflamme Tandem Helicopter (http://www.lafhelicopters.com/english/index_en.htm)

Are you wondering how this tandem might perform after they add the rear rotor and remove the test stand?

[Spaced]

Thanx for all the info guys, cleared alot up.

Dave, yeh Ive seen that one, seems as though the Canuks like 2 rotors, eh?
That was what actually got me curious as to the performance of the tandem layout, as far as I know its the only small one thats been tried since about '52. I thought it was interesting to seen how they were trying to overcome the yaw instability by sweeping back the Hstab, putting the Vstab further aft. I would guess that they have moved the CG forward as well to try and keep the back behind the front, it will be interesting to see how well it flys. I didnt realise how dependant the tandem layout was on artificial stabilisation, sounds like the first few flights will be interesting.:ok:

[Shawn Coyle]

I would predict that M. Laflamme is going to have severe directional control problems with his machine.
Way too much side area head of the front rotor, not much behind the rear one.
There is a very good reason why the Boeing machines have such high rear rotors, with such large fins. In fact, both of them have a number of very subtle but powerful aerodynamic fixes, such as strakes on the front pylon to break up airflow and stop the front pylon acting as a wing with any sideslip, blunt back fin on the CH-47 and cambered fin on the H-46, and so on.
And that's without the AFCS and sideslip ports sensing sideslip and yaw rate gyros to sense yaw rate and keep the whole thing pointing frontwards.
Good luck to him, but this is a pretty complex business.

[Tandemrotor]

Wow, when I saw this, I though somebody wanted to get to know ME better!!

The AFCS in the CH47 (the only tandem I have flown) is, for a helicopter, excellent. It enables any pilot to pole a Chinook much the same as any other helicopter. Nothing is really any different (with the exception of ETL on the aft rotor during rapid spot turns)

HOWEVER, with the AFCS out they are PIGS to fly. Especially on instruments!

With the aft rotor producing the majority of the power, and very little inherent stability, the aft rotor constantly tries to overtake the forward rotor ANY WAY IT CAN!

I haven't got time to talk about 'Positive Stick Gradient', but any orthodox helicopter pilot would find the idea of bringing the cyclic back into their stomach, as the speed increases, not to mention, pushing it fully forward as the speed decreases, absolutely bizarre. (This is only AFCS out!)

All in all though, when it's working, it's the dog's bo**ocks.

As a footnote, anybody interested in Chinooks, may care to look at the thread in the 'Military Pilots' section, regarding a Royal Air Force accident on the Mull of Kintyre, Scotland. The 2 (tragically deceased) pilots need all the support they can get.

[46Driver]

Actually, when taxiing the "46", its easier to beep the NR down to about 90% and steer. Why, I have no idea.

I was also told that tandem rotors are less efficient than single rotors due to the weight of the two transmissions as well as disturbed airflow over the fuselage and the overlapping rotors - I would like to see a comparison from someone in the know.

As for blade stall, our NATOPS says that you don't know which way the helicopter will roll because you don't know which rotor system will stall first - ahhhh, the joys of the "46" (and probably the "47" although I have never flown a Chinook.

[heedm]

46driver, you're right about the efficiency concerns. While there isn't a tail rotor robbing power, the final word should be performance. The Canadian H46's and Sea Kings use identical engines, have similiar AUW, yet the Sea Kings have far superior single engine performance. The useful loads are comparable, but I think it's slightly better with the Sea King (hard to tell because of the amount of mission kit in each).

I don't have the details but I'm guessing that the H46 outperforms the Seaking in the hover only at extreme weights where the tail rotor losses are highest and when the wind is not favourable for the tail rotor. Also, the H46 cruises faster except at highest weights.

In the end both configurations are practical, the mission will dictate which is best.

[Heliport]

Click here (http://www.catalyst-band.pwp.blueyonder.co.uk/Ground_Resonance_Rear_View.mpg)

It's quite a big file. Best to save first if you're on dial-up.

[Collective Bias]

It was worth waiting on:uhoh:

Any Chinook driver want to make a comment?

[SASless]

I cannot get it to open...but I ask the question...was it for sure ground resonance or was it a blade phasing problem? Having several thousand hours in the Chinook...I would love to see the video...although viewing it might add to my bar bill!

[BlenderPilot]

Sasless . . . .

Click HERE, (http://www.apple.com/quicktime/download/) and download the Quicktime player required to view this movie, its the best and most common player around and its worth having on your computer.

I saw something just like that in person a few years back as some soldiers were playing soccer and they kicked the ball vertically and it landed on the turning rotor of an idling allouette, and after that pretty much the same happened, the XMSN was ripped off the fuselage.

[NickLappos]

That was clearly a test operation, looks unmanned and without full landing gear. I think it is controlled from a remote site I think the aircraft is heavily loaded (shortened oleos) and tied down to simulate shipboard operations. The crew usually starts the cycle with cyclic stick circular motions at the ground resonance frequency (a beep tone in the headset helps the test pilots get the right frequency), I can't see them in this clip, but they could be small, or it could be that they are not needed, as the resonance was self exciting.

Note the engines cut back about 1/3 of the way in, this is the testers probably trying to get control of things, the second big white puffs are the engines actually being destroyed by the excessive vibrations, possibly as the shafts were cut due to excessive motions. It is the cut shafts that mistime the rotors and cause the blade meshing.

Looks like things got out of hand. Anyone recognize the footage/location/warstory? Probably a Boeing Philadelphia film, as they would do this kind of work for the Army (paint job), could be quite old. My guess - a ship tie-down program for the Special Ops folks.

If you have trouble downloading, try right-clicking on the link given, and pull down the "Save Target as" selection, then put the file onto a known file , amybe the desktop. It can be played from there easily. It is 12 Megs, though, so dial-up is daunting.

(edited after seeing the side view film)

[The Nr Fairy]

There is also a video of this shot from the side.

Because the video part of the site is currently unavailable, in part perhaps due to Draper posting a link in his JB thread, it's exceeded its bandwidth limit for the month !

I seem to recall reading that the airframe involved was one which had barrel rolled in the US somewhere after a hydraulics contamination, and was being used as a test airframe at Aberdeen Privong Grounds, Maryland.

[FunkyMunky]

I've uploaded side view here (http://www.catalyst-band.pwp.blueyonder.co.uk/Ground_Resonance_Side_View.mpg) if anyone's interested.

[Vfrpilotpb]

I have finally watched the Vid via my desktop which was the most succesful download, the sound on my comp was accidently up at the max ( courtesy of my son) and because of this I heard the engines spooling down just about at the point where the R/H engine seems to go under strain( darker smoke) then you can hear the turbs whining down then the puffs of white smoke as Nick suggests they are giving up, the noise of the destruction is quite sureal, and seems less that what I would have expected.

Unbelievable to watch how quickly this giant piece of engineering "spits its dummy out" how quick for the little R22?

Peter R-B
Vfr

[Delta Julliet Golf]

amazing.....at least it didn't roll over ;)

[Shawn Coyle]

I asked some folks at Boeing Philadelphia about this.
Evidently it was a scrap fuselage and rotor blades that were being prepared for being shot at anyway.
The normal flight departments (production and experimental flight test) declined to be involved as it was not going to be inspected or subject to normal scrutiny.
It appears that the chains may have been tied down too tightly to prevent the oleos from working properly.
Impressive footage. Glad I wasn't in the machine.

[Rotorbee]

quote from: Vfrpilotpb

-----------------------------------------------------------------------------------

Unbelievable to watch how quickly this giant piece of engineering "spits its dummy out" how quick for the little R22?
-----------------------------------------------------------------------------------


And how exactly do you want to wreck an R22? I heard they are very diffucult to destroy by ground resonance. Use a hammer instead.

Try a H300. Much easier.


:}

[waivar]

Bad day in the office dear?

Excellent instructional video.

[D. Insider]

I believe a commercial operator is due to take over the Queensland Rescue operation Mid next year, for a 12 month trial. This, I believe, followed a confidential report outlining the extraordinary financial liability of Queensland Rescue on the Government. Not surprising considering the amount of staff they have at those bases.
No doubt a commercial or non-profit organisation could do it cheaper.
:ok:

[ground effect]

Here is a dead simple one...
Who out there can tell me how tandem rotor helicopters (eg chinook ch-47 etc) are yawed around the normal axis?? I realise there is some type of control input going on but what is it and what effect does that have on the aircraft in order for it to yaw left and right??

All I can dream up is that moving the pedals(they do have pedals right??) results in some type of opposing lateral rotor disc tilt/bias between the front and rear rotors:confused: :confused:

ie - to yaw left around normal axis,left pedal in causes left `tilt` of front rotor disc and associated total rotor thrust ...and right `tilt` of rear rotor disc and associated total rotor thrust.

...opposite of above for right pedal

While on the subject of counter-rotating helicopter designs how the hell do you yaw/control kamovs and k-maxs around the normal axis??? (ie- turn around the mast)

Please enlighten me on what really happens in these beasties!!

:):confused:

[SASless]

My recall of the Chinook....

Each head has a pivoting actuator and a swiveling actuator to control the rotor inputs. Each head also has a trim actuator that tilts the heads to reduce form drag by leveling the fuselage in forward flight.

Pedals, known as Yaw control pedals vice anti-torque pedals, do just as you suggest. Pitch attitude control is done by varying the amount of pitch in the two rotor heads....forward stick decreases pitch in the forward head and increases pitch in the aft head.

Lateral control is very similar to regular helicopters....

Tandem helicopters do not like to take off in trim....in the Chinook one can depart with more weight by taking off with the nose offset so as to allow the aft head to operate in clean air vice disturbed air from the forward head.

Being able to get up....and take a short walk around helps on long flying days....try that in your Bell.

To Chinook pilots....there are Chinooks and slingloads....when it comes to helicopters anyway.

[Dave_Jackson]

http://www.synchrolite.com/B318.jpg

[Thud_and_Blunder]

Anyone else here remember Lu's version of tandem rotor control from a couple of years ago? I laughed 'til I stopped....

[Lu Zuckerman]

To: Thud_and_Blunder

A couple of years ago? I can't remember what I had for breakfast yesterday. However, If I described the workings of the flight control system on the CH-47 I got the information from the factory-training manual. I didn’t see anything funny in that but then again I lost my sense of humor a long time ago.

I think SASless got it wrong. Each rotorhead has two servos, both of which can work in the same direction and effect collective pitch, or they can work in opposition and effect lateral control. The pilot cannot input forward cyclic. As SASless indicated there is an electric servo attached to an extension of the swashplate and when the helicopter reaches about 60-knots the servo actuates lowering the forward end of the swashplate introducing forward cyclic allowing the pilot to lower collective reducing the stress on the two rotors.

Because of the nature of operations the CH-47 spends a great deal of flight time at less than 60-knots causing the rotors to operate at very high stress levels. When the rotors are returned for overhaul more than 70% of the parts in the rotorhead are scrapped where most of the steel parts in a Sikorsky head can be reprocessed and returned to service.


:E :E

[SASless]

Lu,

Before Nick beats yer butt on this....what do you mean by your statement..."A Pilot cannot input forward cyclic."?

One must remember Lu....the hydraulic system drives the flight controls including cyclic pitch control.....the speed trim system is electrical and operates off air speed generated signals sensed by the pitot static system.

The trim system acutators work together on each head.

The point of major stress on the Chinook is the aft vertical shaft....that is why the speed trims exist actually more than as a trim for fuselage leveling. There is a lot of bending moment applied to the aft vertical shaft much the same as in Bell 206/204/205/212 aircraft.

The Chinook is quite speed limited without a functioning speed trim system.

Lu...you reckon Frank Robinson had anything to do with the design of the Boeing-Vertol rotor head?

[NickLappos]

At the risk of piling on, let me pile on....

The Chinook has normal cyclic control on each rotor, both lateral and longitudinal. The Chinook data that I have specifies that each rotor has almost 50 degrees of longitudinal cyclic capability (as measured in blade pitch angle). Lu is wrong, Chinooks have longitudinal cyclic.

Furthermore, with the drivel about spending more time at low speed somehow adding to stresses, Lu is also dead wrong. Not only is low speed the LOW stress regime, but even the ill-founded rumor mill that Lu owns can't invent bad component lives for helicopters that have good lives.

Give it a rest, Lu.

[Lu Zuckerman]

To: SASless and Nick

To: Nick in response to your post above:

Fore and aft cyclic movement introduces differential collective not cyclic.



QUOTE: Before Nick beats yer butt on this....what do you mean by your statement..."A Pilot cannot input forward cyclic."?

RESPONSE: If the pilot moves the cyclic stick laterally he will introduce left or right cyclic causing both rotors to move in the same direction. However if the cyclic is moved along the longitudinal axis the pilot introduces differential collective. With forward cyclic movement the forward rotor will decrease in collective and the rear rotor will increase in collective causing forward movement.

QUOTE: One must remember Lu....the hydraulic system drives the flight controls including cyclic pitch control.....the speed trim system is electrical and operates off air speed generated signals sensed by the pitot static system.

RESPONSE: This is true. When the helicopter reaches around 60-knots a signal is sent to the speed trim servo and it retracts or, gets shorter. This causes the swashplate(s) to dip down and pivots around the two hydraulic servos. This introduces forward cyclic in both rotors and the pilot can lower the collective thus reducing the stresses on the rotor system and the masts.

QUOTE: The trim system actuators work together on each head.

RESPONSE: Again this is true. If you are addressing the electrical trim servo both will retract when commanded or, extend when the helicopter drops below 60-knots.

QUOTE: The point of major stress on the Chinook is the aft vertical shaft....that is why the speed trims exist actually more than as a trim for fuselage leveling. There is a lot of bending moment applied to the aft vertical shaft much the same as in Bell 206/204/205/212 aircraft.

RESPONSE: This is very true however I could only address the rotorheads as I did not see the gear boxes being overhauled so I can’t talk about parts rejection on the gear boxes during overhaul.

QUOTE: Lu...you reckon Frank Robinson had anything to do with the design of the Boeing-Vertol rotor head?

RESPONSE: Frank was a young man when the rotorheads on the CH-47 and its’ predecessors were designed. Actually another Frank developed the concept for this rotorhead. Frank Piaseki. I believe it has the same design concept as the Sikorsky S-51.

For what it’s worth, my first ride in a helicopter was in a Piaseki HRP-1 back in 1949. Hey Nick where were you in 1949?

Why would Nick beat my butt? Now I know.

[SASless]

Lu,

The correct term for the effect of fore and aft cyclic stick movement is DCP...differential collective pitch. I assure you...the pilot can input forward cyclic whilst commanding Sheba to dance. ...along with rear cyclic and left cyclic and right cyclic and all sorts of combinations of cyclic.

The aft vertical shaft is in actuality not a part of the aft tranny...but rather acts as a "mast" to raise the aft rotor head to a height well above the plane of rotation of the forward head.

My first tandem rotor experience was an Air Force H-21....at Langley AFB in the early 60's....and resulted in a forced landing....it should have told me something...but then I had already shed a set of blades off a Bensen gyrocopter that was loosely afixed to the back of a pickup truck. After that...the H-21 ride was kinda tame. The bladeshed was not tame!

You left out a few words Lu....your concept was good...but your implementation fell short of the mark.

[NickLappos]

Lu, in 1949 I was doing what I still do, and what you forgot to do, LEARN.

The Chinook has BOTH DCP and cyclic to control longitudinal, and it uses both. It has cyclic Lu. Cyclic, Lu. Read that and say it slowly, you might then learn it. I doubt it, actually. Your next post should prove it, I think.

[ground effect]

Thanks folks for the feedback...was also wondering who of you out there have flown tilt rotors v-22, ba609 (test pilots/military) how different are they from conventional helicopters and how complex will the training transition process be for pilots when they are eventually used in the civilian world?

[Mr Toad]

ground effect
-----------------

I warn you that the more you think about the Chinook's levers and pulleys, the less confidence you will have to execute a given manoeuvre.

The Boeing TP who did my conversion lifted to the hover for me, then put his snake-skin boots up onto the dash and commanded: "spot turn around the aft head". Seeing my face, he said "don't even think about it, just do it". He appeared to go to sleep after that while I explored the incredible abilities of this machine. Gently does it at first though, and still wind until you know what to expect!

I don't doubt they're even more complicated now than they were then; but no, they're not much like a conventional helicopter to fly. But the training process was very pleasant (ground school excepted); as for civilian use, they aren't very passenger-friendly and accidents are nearly always BIG accidents. They are however brilliant load-lifters, nothing can touch them. Columbia are the absolute masters of this.

On the North Sea (1980's) they certainly scared the accountants and sometimes they scared the passengers; I loved them but usually tried not to think about the mechanical complexities too much, especially when airborne. Hope that's some help to you...

[Vfrpilotpb]

Hi GE,

some time during 2001/02 I posed a similar question, the replies from the current flyers then, really did explain how these giants worked, and how to do most of the tasks in the book with them.

I stand in awe of such Helicopters and would dearly like to snitch a ride one day, even by clandestine means if needed, and then rewarding the crew afterwards !


Vfr:ok:

[Heliport]

Thanks Vfr.

That thread (and others) found and now merged.

Heliport

[Lu Zuckerman]

To: NickLappos

The following is taken from the CH-47D Airframe Drive/Rotor Systems H7-U-10-1
Volume 2 (Customer Training Manual published by Boeing Helicopters) (page 6-24).

FLIGHT CONTROLS

PITCH INPUT FORWARD

When the pilot moves the cyclic stick forward the 1st stage mixing unit will extend the output control of the aft head, and retract the output control to the forward head. This extension and retraction is called differential thrust between heads or differential collective pitch. The second stage mixing unit will extend the two outputs to the aft rotor system, and retract the outputs to the forward rotor system.

There is no aft cyclic input. Forward cyclic input is made by the retraction of the electric actuators attached to the forward and aft swashplates when the helicopter reaches around 60 knots. When the helicopter slows down below 60 knots the actuators extend removing forward cyclic input. Lateral cyclic is available at all times.


TO: SASless: Thanks for the correction however the movement of the cyclic stick fore and aft does not effect the fore and aft rotors cyclically it effects them collectively. This input either raises or lowers the swashplates it does not tilt them. Due to the design of the swashplates and their connection to the electric actuator there may be a very slight cyclic input but this is not intentionally input by the pilot.

:E :E

[GTNav]

After some great years flying the CH47 I have my annual company check tomorrow and I must say I am dreading (as ever) the scarry tail rotor failures I will have to do just for fun!! When will the rest of the world realise that tail rotors are just not cool!! I long to be flying with foot rests again, not moving foot pedals!!

Also miss not taking my car with me where ever I go.

[heights good]

To clear up any confusion, the chinook transitions by applying more or less lift to the rear rotor. This can only be done 1 way collectively. When it gets to a point the pilot would then have to pull back slightly to maintain the transition at higher speeds without hitting the ground. To stop this the aircraft is fitted with DASH (Digital Airspeed Hold) This keep the floor level and stops the pilot having to make unconventional corrections.

[SASless]

Lu,

Lets clear up some of your misunderstanding of what you read.

Early on in this thread....I corrected one of your posts by clearly stating the concept was "differential collective pitch....DCP". You come late with that excerpt from the manual or what ever you are reading from.

You mix two systems up here...the normal hydraulic controlled and operated flight controls and the electrically operated Speed Trim System.

Lu, if you switch the Speed Trims off.....they do not operate....the speed trim system is inoperative...the aircraft is Vne limited...greatly limited. But Lu, the hydraulic flight controls continue working normally.

Two independent systems Lu....nothing to do with each other at all.

Lu...where do you come up with the idea that anyone said the two rotor heads moved cyclically in movements of the cyclic stick in a fore and aft direction. Are you not the one that stated "the pilot cannot input forward cyclic"?

Also Lu, when the speed trims function...there is no coorelation to Thrust Lever position....any reduction, if any of Thrust Lever position,is not noticeable and since the speed trim actuators are moving as the aircraft is accelerating...the only Thrust Lever reduction would be as a triming effort by the pilot to achieve a desired airspeed/altitude combination. Thrust Lever Lu is the correct nomenclature for the "collective lever" .

I know the Chinook is a bit more complicated than a Robinson...and according to several posters you had some problems with that rotorhead....but Lu....read and quote from all of the pertinent sections of the manual if you are going to do so. Be thorough in your submissions.

[excrewingbod]

Mr Toad,

I take it you used to fly with BAH?

My father, a/c engineer, worked on BA's BV234s, and was never overly enthusiastic about the machine.

He once took me out to Longside airfield, to see one of them, which had diverted following engine problems. I got to spend a couple of hours looking over this fascinating machine - a pretty magical experience for a 10 year old. Can't quite believe it was 20 odd years ago though.

I remember the time a BV234 did a small flight display at the yearly fete at RAF Buchan. During a climbing spot turn (I don't know the correct term for the manoeuvre), they managed to quite literally blow away the cricket team in the adjoining playing field. I met the pilot in question a number of years later, when he was re-telling the story in the crewroom at Longside.

There is a BV234 related story that I've been told a number of times, when Max Bailey (sp?) and crew did a medivac from the East Shetland Basin with two critically injured person's, one of whom sadly passed away. I've never known if it was a semi-urban legend, but it was claimed that the machine they used was never quite the same afterwards, whether it was due to the effort of the crew to get to ABZ asap or what.

Does anyone know if Max Bailey is still around?

[Skaz]

There was a link to a video clip of a Chinook beating itself to death due ground resonance posted in a thread in the past.
Ive done a search but couldnt find it, anybody knows where it is?
thanks

[tolipZO]

http://www.chinook-helicopter.com/history/aircraft/D_Models/84-24156/84-24156.html

One quick google search for Chinook Ground Resonance.

This link gives you the rear and side video which the other link only gave you the rear view.

Awsome enjoy, humbling video.

[BossEyed]

Worth noting that aircraft is tied down, and in a very non-standard way.

Yes, it's GR, but don't think your Chinook is going to do that to ya. You'll need to abuse her heavily first!

[rjsquirrel]

Reports were that it was a tie-down flight test to try and find ground resonance. I think they did......

[Tony Chambers]

imagine trying to eat your inflight meal :rolleyes:

[SASless]

I read somewhere they were preparing for shooting the old girl to determine its resistance to hits by various weapons but never quite got to the scheduled tests due to the minor problem encountered as evidenced by the video.

Was there not a thread on this before?

[Lu Zuckerman]

I went on the web site and was only able to download the rear view. The video lasted about 5 seconds and I saw no evidence of ground resonance. Did I do something wrong?

:confused: :E :E :confused:

[Tony Chambers]

yep u missed the 30 scallys going into the chinook and shaking it from the inside. Talk about inflight disruption.

[Heliport]

Threads merged.

[M609]

I saw a video on Discovery Ch. once, a Chinook landing on water, and a SOF team in a Zodiac or simmilar embarked via the rear ramp. Looked kinda cool!

But landing the thing in slat water must raise a lot of questions about corrosion?

[DSpice]

As an old chinook pilot during training way back in 1969, we received training in landing in the water and taxing around on a fresh water lake. The aircraft handled very well.

[Thud_and_Blunder]

For a short while the RAF tried using a professional Educator, instead of aircrew, to carry out some of the Groundschool classroom teaching on the Chinook course. It didn't last - poor bloke tried to convince us that the water-dam was there to hold water inside the fuselage so's it could be used for water bombing...

[ConwayB]

Hi all,

I am organising the reunion of all persons involved in the re-introduction and operation of D Model Chinooks in the Australian Army. A piss up will be held in Townsville at 5 Avn Regt on 20 May and a more genteel cocktail party to include partners the following day at Kissing Point in Townsville. (It's just a name... not a requirement).

If you have any questions, please contact me, Conway Bown, at [email protected].

Also, if you're interested in aviation and military art, visit my website at www.ipas.com.au

Safe flying.
CB

[Ascend Charlie]

As a proud owner of some of Boner's artwork, I can say that he is a very talented artist with a unique point of view. The gallery is well worth a look.

he can't fly for nuts, though.....:8

[Tiger_mate]

woops - Tricycle Chinook


What happened at Abingdon Chinook chappies?

Looked like a benign landing (1502L) followed by a departure to Odiham with three wheels, having lost back right somewhere!

Was Odiham the nearest suitable landing site from Abingdon?

Seriously though, good display until then and it did not appear to be a "heavy" landing.

[Green Bottle 2]

Yes TM Odiham would have been the most suitable aerodrome. The ac cannot land and shutdown without the wheel. There is an SOP at Odiham to deal with such eventualities and all the kit is readily available, so it is the best diversion.

[Conan the Librarian]

Yup, thought I was seeing things for a second or two. Am just downloading over 300 pics to the PC and may have something there. Far more important to know that crew and aircraft are safe. If the guys pick up this thread, thank you for a truly superb display.

[Onan the Clumsy]

all the kit is readily available you mean a big block of wood?

[Conan the Librarian]

I have one picture available - if anybody can either host it, or wants to have the original, please PM me and tell me who you are. Time now 1949L and will be here until 2015L

Otherwise a lovely show. Well done to the organisers.

regards,

J

[rotorcraig]

We took some photos too. The earlier ones with 4 wheels...

http://img.photobucket.com/albums/v225/rotorcraig/post/DSCN1851.jpg

http://img.photobucket.com/albums/v225/rotorcraig/post/DSCN1855.jpg

... and the later ones with 3!

http://img.photobucket.com/albums/v225/rotorcraig/post/DSCN1856.jpg

http://img.photobucket.com/albums/v225/rotorcraig/post/DSCN1858.jpg

Good to hear all safe and well!

RC

[diginagain]

Which jobsworth decreed that a hi-vis jacket was required in the back?:cool:

Seriously though, good to hear that it all turned out OK.

[ShyTorque]

3 wheels on my Wokka, an' I'm still rollin' along.......
OC JHC is after me,
Flamin' spears burn my ears,
But I'm singing a happy song....

Well someone had to say it..... :O

Saw this happen to a Helikopter Service 432, at Forus Heliport, Stavanger, about twenty years ago.

[PileUp Officer]

http://img.photobucket.com/albums/v225/rotorcraig/post/DSCN1855.jpg

Typical crewman! ;)

[Chinook]

Not wishing to spread a rumour or disparage anyone, but I sincerely hope the swivel locks were 'locked' ......

[diginagain]

I'm sure we'll find out, one way or t'other, in the fullness of time!

[rivetjoint]

Hi-viz jacket was a new touch for the display season, not H&S gone made, unlike the Merlin display you could actually see the loadie on the ramp!

[Agaricus bisporus]

The only "steerable" wheel on a Chinook is the RH rear and this puts it under quite a lot of strain when turning - and to taxy with due consideration, I remember being well aware of this during ground ops. I also seem to remember that we were told that the rear u/c legs were a weak point in an otherwise incredibly tough aircraft. I was told in my conversion (to a BV234 which is identical in most respects) that this wheel had a history of falling off occasionally and I think (I cant find my old checklist right now) that we had a procedure in there to deal with it - like Don't land until there's a cushion of tyres or similar.

Hardly a big dealthough, is it?

[PICKS135]

the moment of truth

Ooops (http://www.ukar.co.uk/board/ikonboard.cgi?;act=ST;f=10;t=2437)

[Skeleton]

Didn't realise crime happened in places such as Abingdon.

2 seconds on the ground and some bugger is off with a wheel......:p

[ConwayB]

Well, well, well!

Same thing happened to me... same wheel, too! And I was on the ground!

Was doing a torque differential check as part of a maintenance test flight. 60% torque on one engine and it will usually lift the forward gear off the ground... and that's the configuration and attitude we were in. Wind was a direct headwind of about 15 knots which was pushing against the belly of the aircraft which was bearing the force of that 15 knots.

Suddenly, there was an odd sound and the aircraft lurched. The aft right gear collapsed and we had to hover taxi back to the apron where our maintenance personnel had a jack ready and a stack of tyres (tires for our American friends).

After some ginger hovering/resting on the tyres, the jack was put in place on the jacking point and the weight taken.

Then a normal shutdown... and then the abnormal paperwork.

The cause? Not quite sure. Could have been a failure of the swivel locks (or a failure to put them on by the other pilot) or fatigue of the strut. It's interesting to see other Chinook drivers experience the same problem or witness it.

The aircraft was flying again the next day.

Overall, no big deal. The 'Chook' is a great aircraft to fly!

If you're interested in aviation art (including Chinook pictures), check out my website at www.ipas.com.au

Cheers and safe flying.

[airborne_artist]

Here are Conan's pictures of the rotary Reliant Robin, sorry Chinook

http://www.flynavy.flyer.co.uk/three_wheels_large.jpg

http://www.flynavy.flyer.co.uk/three_wheels.jpg

[NineLima]

Glad to hear everbody got home safe and well!

http://www.pbase.com/stevieb/image/42862422.jpg

http://www.pbase.com/stevieb/image/42862431.jpg

http://www.pbase.com/stevieb/image/42862628.jpg

http://www.pbase.com/stevieb/image/42846133.jpg

[Always_broken_in_wilts]

RJ,
Why would the crowd wish to see someone SAT, legs dangling in the wind and looking like a "lime green dosser":rolleyes: .....not very proffesional looking and no doubt his display season is about to finish:yuk:

all spelling misatkes are "df" alcohol induced

[rivetjoint]

I was stood next to an 18 Sqn pilot who was talking a 28 Sqn pilot through their display (until the wheel fell off) and it seems the hi-viz has gone down well...

[Door Slider]

I was working in the Guard room at a certain SH base not far from Abingdon. Lots of flying and noise complaints recieved :-(
One bloke complained saying he thought world war three had started. If it had would he mind us low flying then????

[airborne_artist]

Door Slider

Hope the complainers were all from Abingdon - I'm about 2m SW of you, and we had no air show traffic here at all, with the possible of two inbound Moths in the am.

Your turn will come when you host Families Day - then the wallys of Wallyford will be bending your ear!

[tmmorris]

Oh for C4ri5t's sake, it's one airshow a year, not low flying every day of the month!

Sadly I was stuck in the garden about 3 miles NE putting up a new climbing frame for the boy - I really wanted to go. Grrr. Still, a few things did fly over on their way to/fro (and I saw some of the practice on Sat!)

Tim

[Door Slider]

airborne_artist


Dont know if you saw or heard the F3 we had in last week, that generated a few complaints and it only landed and took off once!

[BEagle]

Have just seen the video of the aircraft losing the rear starboard undercarriage at Abingdon on Central TV South news. Presented by the delightful Hannah who even knows how to pronounce 'Chinook' correctly!

The aircraft was in a nose high attitude on the RW and came to a halt before slowly reversing. As it did so, the rear starboard undercarriage leg appeared to rotate rapidly around the vertical axis before failing. The aircraft was very rapidly lifted off the RW before departing the display.

The only thing I've learned about those 'orrid clatterin' things (apart from what fun they can be - thanks, JJ!) is that they're at their most dangerous when on the ground with rotors running. Lifting off smartish seemed a very sound and instinctive move by the mate at the helm!

[FlyAny]

Flew Chinooks 18 years. Never heard of a wheel falling off before.

I too would consider that it had been stolen!

[smithoag]

airborne artist/doorslider,
noted your comments re aircraft noise complaints in S.Oxon with interest.
I am an aviation enthusiast living in Diddycot,not too far from you guys,where I run an aviation enthusiasts club(Oxfordshire Aviation Group).Obviously we are biased toward there being more aircraft noise in these 'ere parts,but seriously,if there is anything we can do to help you keep the natives friendly let me know...after all we're all on the same side!!!!!
rgds
Colin
(smithoag)

[airborne_artist]

I'm all for plenty of LL noise - it's the sound of freedom, but the old dears of Wallyford need a change of underwear if a FJ goes overhead at less than 30,000'. They got very moany about the last families day at Benson - much of which could have been solved if they had been told about it in advance.

The problem was that some muppet decided that it would be a security risk for the station to pre-warn (rolls eyes with total amusement) - despite the fact that the Falcons freefall team website had their schedule for the year (dated April 2004) fully detailed, inc. the Benson day ...

The day itself was fine, but the departing Tonka driver (the next day) clearly needed to show off to all the girls he'd tried chatting up in the bar, and so he cranked a tight turn at about 2,000' above Artist Towers, in preparation for a run-in across the airfield, to the slight consternation of my pikey-style collection of nags.

Back to the topic - the 28 Sqn Merlin ALM displaying at Abi says he's got the missing wheel, destined for 28's bar!

[animo et fide]

AA - You need to tell your magical merlin alm that he talks poop, the wheel was taken back to Odi for the Boeing rep to look at


AeF

[TheWizard]

AA - You need to tell your magical merlin alm that he talks poop, the wheel was taken back to Odi for the Boeing rep to look at

Only after it had been indeed taken back to 28 crewroom and then collected for its journey to Odious, so not entirely poop really.:D


http://img.photobucket.com/albums/v289/Brighton_Tiger/wfo.jpg

[raid]

Well i was at Odiham when the chinook returned. They used sandbags to make up for the wheel lost.


Please repost the picture in a smaller size ... it's way too big for PPRuNe !! Thanks. PPRuNe Admin team

[The Helpful Stacker]

I remember being at Ex-RAF Finningly a few years back on an exercise with a Herc, a Chinook and some Lynx helicopters and the A/C hadn't been there more than half an hour before someone was at the gate complaining. BTW, this was at the time many of the locals were campaigning to turn the airfield into Doncaster International!!

A 747 cargo conversion is ever so slightly more noisy than a Herc I believe.

[Safety_Helmut]

THS

"I remember when...."
So what's your point then ?

SH

[TheWizard]

THS
wrong thread methinks???:confused:

[The Helpful Stacker]

So what's your point then ?

Errr, folk moaning about low flying A/C noise.

Try reading the whole thread rather than taking titbits at random eh?

:rolleyes:

[The Helpful Stacker]

Been following thread for a while. I thought it was all about a lost wheel, and, I suspect that the 30 odd other posts on the same subject support that view.

What apart from,

I was working in the Guard room at a certain SH base not far from Abingdon. Lots of flying and noise complaints recieved :-(
One bloke complained saying he thought world war three had started. If it had would he mind us low flying then????

by 'Door Slider' followed by,

Hope the complainers were all from Abingdon - I'm about 2m SW of you, and we had no air show traffic here at all, with the possible of two inbound Moths in the am.

Your turn will come when you host Families Day - then the wallys of Wallyford will be bending your ear!

from 'Airborne Artist', then a comment from 'tmmorris', another by 'Door Slider', one by 'smithoag', another from 'Airborne Artist' then followed up with my comment.

As for,

Reminds me a bit of a stacker who once asked if he could put a large STC containing some very delicate and expensive avionics on its side on a pallet. The large letters SHOUTING "this way up" complete with arrows didn't convince him of the need to keep it upright. Wasn't you was it ?

Pathetic, very pathetic, although if its true it makes a change from some Cosford by-product taking STC's home to turn into a shed or bird table. And no it wasn't me BTW. I've never had the misfortune to work in an ESG luckily.

Come back when you've learnt to be more witty eh?



:rolleyes:

[Conan the Librarian]

Have found a most wonderful picture of the moment where the Wokka went from free wheeling to three wheeling. Not one of mine though and in consequence, I am trying to contact the photographer for permission to post his work here. It really is a beaut - so watch this space!

Hope to be back soonest with good news and a picture or two


nitey nite!

[Conan the Librarian]

Yesterday, I found the picture that I think everyone has been looking for. Sadly, despite strenuous and more than reasonable efforts, I haven't as yet been able to source the photographer. However, the shot was in the public domain and so I foresee no obvious problems.

Andy Evans, wherever you are - this is your work and I am sure that everyone here will join me in saying well done on a superb picture.

Conan the Librarian

http://i5.photobucket.com/albums/y192/zorbathegeek/heli08emJPEG.jpg

[camaro]

Another shot just prior to wheel collapse. (http://www.airliners.net/open.file/834534/L/)



....and after. (http://www.airliners.net/open.file/833528/L/ )

[WokkaCrewman]

I was in Norway very recently and exactly the same thing happened. The aircraft was landed onto the taxiway very gently and on touch down the rear right wheel became detached from the aircraft. On recovering the wheel a relatively clean shear was observed just below the pivot point of the wheel.

As far as I am aware the incident is still under investigation.

My own thoughts for these occurences however are these :

The aircraft operates normally at around 15 to 16 tonnes and short field running landings are practised from time to time. Obviously the aim is to land on with a very slight (4 - 5 kt ) fwd gnd speed. However depending on Pilot experience, visual references, condition of terrain and slope this is not always achieved causing a faster or heavier landing than preffered. I wonder if there is a form of accumulative fatigue creeping in here? Bearing in mind the power steering module is located on the rh rw and most of the instances seem to be with the rh wheel perhaps there is overloading of the wheel structure occuring?

Just my thoughts however
I might be talking bo**ocks:O

[rhmaddever]

How does a chinook yaw? With no tail rotor do they slow one rotor and use the torque reaction from the other to turn the helicopter, and could a chinook do a full spot turn in the hover?

Just made me think after seening the police arrive by chinook at the G8 summit in Scotland,

RHM

[Droopy]

It was some heck of a flare on the clip I saw; I bet those new boys fresh from the box at Hendon had eyes like the South Park kids :ooh:

[puntosaurus]

I'm sure there's a Chinook driver out there can give you chapter and verse, but the HCGB organised a tour of the simulators at Benson, which included the Chinook, and this subject came up.

With two rotors independently controlled you can simply point them in different directions and get a yaw effect. Must be very cunning electronics to get the pedals to do that though.

[teeteringhead]

Yawing is indeed accomplished by "differential cyclic pitch", ie, to yaw left the front rotor banks left and the rear rotor banks right. It's all done by a "suitable system of push-pull rods and bellcranks", rather than electronics - remember the age of the basic design. The pilot input is just the same, through the yaw pedals, and the result is the same, it just does it diffrently.

And like a convential helo, judicious coordination between feet and hands can engender a spot turn around any point, inside or outside the aircraft.

Slowing one down would not be a good idea rhmaddever, as the blades intermesh!!

[rhmaddever]

hey I was only asking the question - not making a suggestion...

[ConwayB]

Teetering Head is right, although one of his terms is not quite correct.

Differential Collective Pitch refers to when you push the cyclic forward, the front rotor blades do not change pitch, but the aft ones do.

Confused? Well, consider this... if you push the cyclic forward in a conventional single rotor helo, the disc tilts, the fuselage moves forward and tilts, the pilot applies collective so the aircraft maintains altitude.

If a chinook did the same, and both rotors tilted forward, then there would be a significant fuselage profile would be presented to the relative airflow. To counter this, by moving the cyclic forward, the aft rotor's blades increase pitch and the whole aircraft pitches forward at which time the pilot applies thrust (our name for the collective) which does the same thing as in a single rotor aircraft. (There's also two nifty little DC powered motors called longtitudinal cyclic trim actuators which will tilt the rotor head forward with increasing airspeed which reduces the profile of the fuselage presented to the relative airflow).

Also, just to elaborate, when the left pedal is pushed in, then the forward rotor tilts left and the aft tilts right... and vice versa.

If the cyclic is pushed left, then both rotors tilt left and vice versa.

Like Teetering head said, it's all done with push rods and bell cranks but the pilot inputs are just the same. I recently did a MD500 endorsement and a Schweizer 300 endorsement... and the control inputs are exactly the same. The little aircraft are more squirrelly and manoueverable... but the chinook has tons of grunt and is very quick (140knots).

Hope this helps.

CB

[g-mady]

presumably with hydraulics ... ???

Blades are too big for direct connection by push/pull rods?

R

[SASless]

3000 PSI hydraulics.....lots of boost there. 1500 PSI for the SAS actuators....and the engine starters, ramp, cargo winch....

[helimann]

Does anyone out there know of a civilian chinook in service in the UK?

[SASless]

It would have to be from Columbia Helicopters....they own all the civvie Chinooks built.

[helimann]

Thanks SASless

I got their details off the net and have sent an enquiry - any other info would be much appreciated