Chinook & other tandem rotors discussions

[NorthSeaTiger]

I believe there was a guy who had an ex-military machine and was looking for companies to do his maintenace, this was a couple of years back.

[Helitemp]

Yep,
Columbia is they only civil owner operator of the Chinook these days they have all the ex British Airways and Helikopter service machines. Columbia have them spread between the western us and asia on heavy lift work, fire fighting.

The MOD has wanted a civil sourced machine to go into the Falklands for some time now to release the RAF machine. Its required to lift 12ton generator sets around the various sites on the Falklands.

Hope the info is of some assistance.

Helitemp

[Cyclic Hotline]

Columbia owns almost all the commercial 234's. There are still 3 in Taiwan.

[Thud_and_Blunder]

required to lift 12ton generator sets around the various sites on the Falklands
That's inflation for you. The generators down there only used to be 8.5 tonnes each. No wonder they need the REAL heavylift experts, eh? :cool:

[hemac]

Helimann

Why does it have to be a civilian Chinook?
Depending on what you want it for and if the money is right I'm sure the military would be prepared to get involved, we all know they love to show off their skills and hardware.

H.

[helimann]

Hemac

any contact details or leads in this respect?

Helimann

[Tony Chambers]

Depending what your lifting the offshore guys can lease you a heli and i believe that there is a 212 at middle wallop being used for training AAC but if its quiet they may be able to lease it out.
Why a chinook though? Very noisy beast.

[helimann]

Chinook required to deliver to a product launch, open the doors and reveal!

H

[Tony Chambers]

contact RAF Odiham or even 606 Chiltern sqn they might be able to lease you a chinook or a merlin both have tail gates. let me know how you get on.

[amanoffewwords]

These things keep buzing over my house every other day - sometimes as a pair in close formation (never when I have my camera handy of course). A question that's been nagging me (not that I wish to sound fatalistic) but what happens if it should have to shut down an engine - can it auto-rotate on one rotor ?

http://www.ecusb.net/att/chinook.jpg

Just curious,

amofw

[wg13_dummy]

can it auto-rotate on one rotor

No.

I think you may have a misunderstanding as to how the Chinook works. It is twin engined and tandem rotor'd.

But the engines go into a gearbox providing power to both rotors. So, either engine and both engines power the blades (via the gearbox). If one engine fails, the remaining engine automatically takes up the power, feeds power through to the gearbox thus still turning both sets of blades. Even if both engines failed, both sets of blades will still go round under autorotation (so long as you dump the lever quick enough!). I take it you arent a helicopter type of chap?

[amanoffewwords]

I take it you arent a helicopter type of chap?

Nope, I'm in IT but I like the concept of helicopters - if I could start again...

So in essence it's the same principle as a Sea King perhaps? Saw one on TV the other with an engine failure during a rescue but managed to carry on for a while while looking for a suitable landing spot. Take it the other engine was taking some of the load?

Thanks for your prompt and interesting response.

While I'm here, here's another that was buzzing over me:

http://www.ecusb.net/att/police.jpg

Cheers,

amofw

[wg13_dummy]

Take it the other engine was taking some of the load?

If one had failed, the remaining would be taking all the load.

Think about it as a car having two engines going into one gearbox. Using a clever free wheel arrangement, both engines provide power to the gearbox in roughly equal amounts. Power from the gearbox then goes to the wheels (Rotor and tail rotor). If one engine failed, the other needs to provide double the power to keep the wheels turning at the same speed. (A constant rotor speed is what is required).

For example, a Lynx helicopter (twin engined) in the cruise would be showing approx 70% torque (power indication). Thats both needles (one for each engine) showing 70% each. If one engine failed, the failed engine torque needle would fall to zero and the remaining engine torque would effectively rise and read 140%. Because it has now had to double its power to maintain rotor speed (a governor senses a drop in rotor rpm and puts more fuel into the remaining engine to compensate). You are now thinking 'how can you have 140%??' Simple. Think of the '70%' twin engine torque as 35% in real terms. Ie; its working at 35% of its capacity. An engine fails, it then- in real time, is working 70% (so you still have about 30% to go on one engine before you run out of power on that engine). Thats the theory! With me?

It's just a way of making the indications more readable.


While I'm here, here's another that was buzzing over me:

You hadnt just nicked a Cavalier SRi had you??

[Cron]

wg - bear with me I'm a bit dim.

Genuine Q.

Why don't the gauges just show 35% on each when all is normal and 70% on one gauge when delivering double the power...

I think I'm missing something ..

[Heliport]

There's a mine of information on flying Chinooks here (http://www.pprune.org/forums/showthread.php?s=&threadid=163538).

[wg13_dummy]

Because when both engines are working hunky dory, the max normal power is 100%. I think its all about norms and visual perception.

http://img.villagephotos.com/p/2004-12/915521/CXQHR-BXKCF-IIGIC-DSCF0116.JPG

The gauge is showing no1 engine at 95% and no2 at zero (the picture was actually taken on the ground, power/bty off and the gauges read random values). If this was in flight, and you had other indications of an engine failure, you would expect that under twin engine conditions, you would have been pulling about 45-50% Tq.

Most of the other engine related gauges in the Lynx (that have a % value) read plus of 100%. I think it is because 100% is used to interpret the 'norm'. However, the NR and NF (rotor rpm and free power turbine speeds. Pic below) sit together at about 107% in normal flight. Dunno why.

http://img.villagephotos.com/p/2004-12/915521/YBIEK-DSCF0120.JPG

Thats my spin on it. You would need to ask Westland and Rolls Royce for the definitive. ;)

[amanoffewwords]

You hadnt just nicked a Cavalier SRi had you??

Nope :) - that one was taken at Brooklands during an emergency services day show - it came over us on the way to a shout, did a 360 over the event and buzzed off.. 'twas very impressive.

Here's the buzzing off version:

http://www.ecusb.net/att/police1.jpg

[Max Contingency]

amanoffewwords

When ever you witness an impromptu air display it is always good manners to write a short thank you note to the Chief Pilot of the organisation concerned. Be sure to include comments like

"how nice it was that they turned up completely unexpected"

"how the crew amazed the crowd with such skill at low level"

"how you were previously unaware that a rotor craft could be manoeuvred in such extreme ways"


The aircrews will really appreciate it and it is the polite thing to do. Go on... write today.

Oh... by the way, the technical term for "doing a 360" as you put it, is a "loop". Probably best to use the right terminology in your letter.

:E :E :E :E

[diginagain]

At least it wasn't SilsoSid.


Or was it?

[amanoffewwords]

"And how they endagered the safety of the craft by such pointless manoevres which, as a professional bystander I can further testify, compromised the safety of several large aircraft landing at London Heathrow nearby. The untold panic caused to the attending crowd, which included several pregnant women, a whole contigent of soldiers from Chelsea hospital, several Heads of State, Jimmy Saville and other priceless jewels, is an unquestionable reason for dismissing the crew of this valuable tax-payer owned piece of equipement alas piloted by the equivalent of reckless joyriders, nay, pirates of the air." :*

"In short, bloody good show and can't wait to see it again next year." ;) :ok:

Will that do? http://www.planetsmilies.com/smilies/happy/happy0007.gif

[Farmer 1]

Can Chinooks auto-rotate? can it auto-rotate on one rotor ? I don't think this question has been answered.

Not that I've ever flown one, but I guess after losing one of its rotors a Chinook would autorotate about as well as a conventional helicopter would after losing its main rotor.

[Max Contingency]

The first picture shows quite well how a Chinook's blade paths are inter meshed between the two rotor heads. Failure of one rotor will leave the other one flying unmolested for a maximum of 1/3 of an Nr!


It was a synchromesh problem that brought down a North Sea variant in 1986 with considerable loss of life and ultimately led to the North Sea operators switching aircraft types.

Having only had a 'wee shot' in one, I don't claim to be an expert. However one of my more qualified colleagues told me that they have to self impose a 5000 fpm ROC. The reason for this is that at any higher rates of climb and they would not be able to establish an autorotative 'rate of descent flow' through the blades before the Nr decayed to critical levels in the event of an engine or transmission failure.

[Thud_and_Blunder]

From 1989 to 1998 (my time on the beast) the RoC limit was 3000 fpm. We were told it had nowt to do with establishing autorotation and everything to do with a 3-axis "shuffle" the aircraft exhibited in climbs above this rate. As the shuffle couldn't be explained, it was decided to avoid putting the aircraft into that configuration.

[Agaricus bisporus]

Can Chinooks Autorotate?

YES of course they can. They would never be allowed to leave the ground if they could not!

In fact the Chinook autorotates more gently than any other I have flown, even a LongRanger, in fact it floats like a thistledown with, if memory serves, quite lively Nr. The technique at the end of an EOL is quite different from a conventional helo in that there is no check in the sequence; flare, check, level... in fact you just flare it onto the deck on its back wheels rather like an aeroplane using the collective to control the Nr and it tends to float. float float. Wheels on and keep the nose up until it sinks down onto the front gear too, then use the brakes. This uses up a lot of distance. They may autorotate well, but you sure need some space to stop one one on the ground!

I hope after all these years my memory isn't playing tricks - this is how I seem to remember it!

[Arm out the window]

If it takes up so much distance in the run-on, and the descent's so gentle, why not zero speed it!!!



;)

Just a tongue-in-cheek question; I've got about 0.5 in them thanks to a good mate's generosity, so actually know bugger-all about them really!

[MightyGem]

While I'm here, here's another that was buzzing over me:
Chinooks do anything but buzz!!

[outhouse]

Hi amanoffewwords,
Would have really liked to follow the link you included in your post but it seems under the censorship restrictions operating in Qatar it’s banned and blocked!!! (Good advert for Qtel though) By the internet provider. So if it was not porn it must have been considered controversial? Any hints please.

outhouse

[amanoffewwords]

Hello outhouse,

I'm not providing weblinks, just image links and a couple of smilies linked from another site. Is it the latter that you can't see/access?

:confused:

Cheers
amofw

[outhouse]

Hi again amanoffewwords
Thanks for coming back, all I see at the end of your text after the smiley is the standard Qtel censorship page saying the link is blocked as inappropriate. This censorship system is generally used to block porn and other web facilities that whoever controls the system wish to block. So it can control all aspects, including communication systems (and have at this time) on the web, information gathering and the ability to choose how you use the internet.
Total control, still we are in the year 2005 not 1984? Seems to ring a bell regarding a rather good book.

outhouse

[SilsoeSid]

amanoffewwords,

I see you're not from the Midlands!!!!

While I'm here, here's another that was buzzing over me:

http://www.ecusb.net/att/police.jpg

http://bestsmileys.com/lol/1.gif

Max Con is obviously completely ignorant in the operation of Police Helicopters.

"how nice it was that they turned up completely unexpected"
Sorry, we'll give the crims a phone call in future so they can make a getaway!

"how the crew amazed the crowd with such skill at low level"
It's not difficult to impress the unknowing.

"how you were previously unaware that a rotor craft could be manoeuvred in such extreme ways"
Well, I hope you have now learnt from the experience! Join us on our next inner city pursuit!

I'll just get this hook out from my cheek!!http://bestsmileys.com/fishing/1.gif

By the way, it's not a 'loop', but a low speed route reversal!! ;)


wg_13,

Isn't the torque value based on the gearbox limitation and not the engine!!! Even at a 100% TQ, isn't the engine still only working at about 60% of its capability. It's a powerful engine the Gem!

The Nr & Nf needles are set at '107% Nr' as that is the result of the SSL selection after start up. Bonk tuning?
As your pics show, at 120kts the SSL should be adjusted to give 104.8%. Primarily, isn't this to give 104.8%NR in order to reduce airframe vibration and therefore a smoother flight?

[wg13_dummy]

Slow day at the office SS?:rolleyes:

I was attempting to keep it simple mate.:8

If you wish to have a limitations quiz, give me a shout and I'll send one over. :ok: (I'll make sure you get above 60% this time (30% real time)) :E

It's a powerful engine the Gem!
It is but we work out single eng perf based on PPI not gearbox. :ok:

Tell the rest of the bonk tuning criteria then?? C'mon, you'll not get away that easily!

[SilsoeSid]

Slow day at the office SS? Sorry, I don't know, but I can find out for you! Nice of you to ask though.
memo to self: must remember passwords for tax return, then I won't be drawn towards PPRuNe !

As for the quiz, if you can get one here for Friday in time for my OPC that would be great. It would be the correct type I trust!?

Thanks for the results, I didn't know back then that they were that low! With 'Above Average' gradings back then, I wonder what I would get if I scored higher in the MPQ! :p

By the way, I never got the last question on each MPQ paper corect.
What 'was' the telephone number for Aviation Standards at M.Wallop? I do hope the questions are more relevant these days!

we work out single eng perf based on PPI not gearbox. But surely that is still a transmission torque limitation!!!

:confused: ;)
SS

[wg13_dummy]

Papers in the post ;)

But surely that is still a transmission torque limitation!!!

Forgotten how and why we do a PPI already, Sid??

You've still not furnished me with the rest of the bonk setting criteria:rolleyes:

QHI's.....c*"ts the lot of 'em!:E

[Thud_and_Blunder]

wg13,

Cu*ts are useful and pleasant to be around, aren't they?

Sid,

What's a tax return?! :cool:

[SilsoeSid]

It seems then wg, that my memory is fading faster than a cat can lick it a$$!!

When working out the single engine performance figures, I always used to refer to the charts in the back of the ODM. The figures were based on Temp/Press/Wt. At no time did I go to the BATs office and get the latest PPI figures.


These days, we do a PAC (Power Assurance Check) daily, and still when working out the figures for Cat A Ops, do not go and check the daily PAC sheets. The Performance data charts still only needs a combination of Temp/Press/Weight to give me the required values.

Perhaps it is you that doesn't know why you do a PPI in the first place!

:ok:
SS


Thud,

Time for you to come home, the Sun must be getting to you!!

http://bestsmileys.com/expressions/6.gif
SS

[MightyGem]

memo to self: must remember passwords for tax return, then I won't be drawn towards PPRuNe !
Hmmm...shouldn't that have been done by the end of September?

[wg13_dummy]

Power Assurance Check

And that gives you the limitation for the gearbox??

So you wouldnt use the PPI figures from the 700 to establish where to start on the graphs then? Remember all the different graphs relating to 96% PPI (clean etc), 98% PPI (Clean etc), 100% PPI (blah...).

At no time did I go to the BATs office and get the latest PPI figures.

So why do we bother to go out and do a Comp wash/PPI (comp wash to clean comp blades to give us the best state) if it has no bearing on the figures you calculate each sortie? You are suggesting that all engines are the same and produce the same power with the only variables being wt, press, temp?!?!

Surely the performace of the engine (well, since its last PPI) is quite relevent to what we could expect the engine to produce should the other donk stop?

(........1013 set, S+L, CAC out, friction on, ECL brief, 1 back to check 2, pull to 100 %, allow to settle, read OAT, Alt, NR, TQ, T6, NH....blah..... See if its T6, NH or NR droop limited?? REMES calculate to give the errr Power Performance Index so that we can calculate the errr Sin Eng Perf!!) Jog any memories, Sid?


My, you have been away too long!:rolleyes:




When working out the single engine performance figures, I always used to refer to the charts in the back of the ODM. The figures were based on Temp/Press/Wt. At no time did I go to the BATs office and get the latest PPI figures.

'Above average' eh?

:p :p :p

[SilsoeSid]

Hmmm...shouldn't that have been done by the end of September? Not on line!! 30 December 2005



And that gives you the limitation for the gearbox?? No, the PAC is a means for the pilot to determine, prior to take off, that each engine is capable of developing specification power!!
Running parrallel on this thread, Torque limitations are based on the transmission are they not? An engine can easily overtorque a transmission.

I guess when I said, "At no time did I go to the BATs office and get the latest PPI figures" I must have been thinking about that cat licking its a$$. OK, wrong again, sorry! http://bestsmileys.com/foot_in_mouth/1.gif

Now was that anti-icing and cabin heating off or not? What if I have anti-icing off and cabin heating on? AFCS Height hold disengaged or not?

Anyway, I still stand by "When working out the single engine performance figures, I always used to refer to the charts in the back of the ODM. The figures were based on Temp/Press/Wt." But must add, the chart used was decided by the PPI results found in the 700. But isn't that just for finding MinSELF?

Do/Did you feel safe in an aircraft giving you 94% PPI?

'Above average' eh? Everytime! All types!
You never did make PSI did you? Only now by default!

;)
SS

[wg13_dummy]

Apology accepted. ;)

No, the PAC is a means for the pilot to determine, prior to take off, that each engine is capable of developing specification power!!
I guess its a similar thing for most twin engined helis. But with the Lynx it goes for the most current figure as opposed to what the manufacturer spec says it should be? Is the PAC figure a fixed book figure?

Running parrallel on this thread, Torque limitations are based on the transmission are they not? An engine can easily overtorque a transmission.
Yes quite true. Thats why we have a TQ guage. TQ limitations are set in stone. But with a low PPI engine or a 'bad performance day' there is no guarentee that the TQ limit will be reached before the MSELF. Hot & High it will more than likely be the T6 or even the NH.

When working out the single engine performance figures
But isn't that just for finding MinSELF?
Think youve answered your own question.:E


Do/Did you feel safe in an aircraft giving you 94% PPI?

More than. :ok:

As to your last question......YES! Cheeky git!

[SilsoeSid]

One of those weeks, just trying to get the 3rd thing to go wrong, in order to reset everything.
(This thread seems to have done the trick!)
Thanks for the help________wghttp://bestsmileys.com/kick/1.gifSS________

Is the PAC figure a fixed book figure? Opening up to contradiction on different types here, but I think that the PAC way keeps everything 'tidy'. As mentioned before, the PAC ensures that the engines are capable of developing specification power, if they are producing within spec then all is well. It is a check afterall, as opposed to an index figure.

The check is a monitor for power trends and should a trend develop, indicating power loss, then it is investigated further from that point. Rather than having lots of starting pages (moving posts!!), ie 104%, 100%, 94% anti ice & cabin heating on or off, sand filters fitted, etc.

Wouldn't it be easier in the Lynx to work off one set of charts, lets say the 94% figure, and if you have 104% or 100% PPI, bonus! ?
How about also a system where should an engine fail, the cabin heating (and air conditioning!) automatically switches off in order to utilise maximum power from the remaining engine, with an override for use when back in a safe OEI condition?

Maybe on FLynx!!! http://bestsmileys.com/animals/6.gif


SS exits stage left ________________________ http://bestsmileys.com/eek/3.gif

[wg13_dummy]

How about also a system where should an engine fail, the cabin heating (and air conditioning!) automatically switches off in order to utilise maximum power from the remaining engine, with an override for use when back in a safe OEI condition?

It's taken us nearly thirty years to get an intermitant wiper button on one cyclic!!!

There are even more graphs in the back now, Sid. I think the reason why there is so many is firstly, we operate in slightly more varied environments than was the case 15 or so years ago. I'm talking hot. :ok: And secondly, if we just went for the lowest, it may take away a potential landing site when in fact it could be made. Ie. Taking the lowest PPI, 94%, we may come up with a MSELF of 50 knots (not impossible in some theatres). Having a MSELF as high as that would also give us quite a high run on speed (prob over 30kts). This may push us into a decision to go elsewhere if we didnt have a suitable length or surface of area to run on to. You may think 'well, thats working well on the safe side'. True it is but the greater array of figures and calcs means that we can more accuratly get a realistic figure. Ie, more flexibility.

I'm guessing in the civy side, the PAC gives you a greater safety margin hence it being a set figure?


Maybe on FLynx, I'll let you know. :ok:

[rreijm]

Hi,

I was wondering if anyone here could answer this, or at least refer me to someone who can...

The thing is, for my M.Sc. graduation project I'm trying to implement the Chinook CH-47D AFCS in a Matlab/Simulink computational environment, and currently I'm stuck on the inner workings of the first stage mixing unit.

Apparently, the AFCS pitch control laws have 2 output commands, one to the pitch SAS servo and one to the DASH (differential airspeed hold) servo. These two are accumulated with the pilot control inputs and the other control law outputs (both through the ILCAs) in the first stage mixing unit. This results in two outputs: lateral cyclic and collective pitch (something related to this has been discussed earlier in this thread I believe :) ). My question: what are the mixing equations? I have been able to find some data on the mixing equations of the pilot controls only (from stick input to rotor angle output), but these are unaffected by the DASH and SAS controllers, so there must be a separate set of equations for the first stage mixing.

I don't have a training manual, and I don't know who else I should contact to ask this crazy stuff
:rolleyes:

[heli1]

All this talk of Chinooks..now who can recall the Belvedere...the original aircraft could be flown manual...didn't even had assisted controls 'though they came before ie entered service.Four bladed rotors too and this was the late 1950s !

[Aser]

http://www.147thhillclimbers.org/347~turn.jpg
http://www.147thhillclimbers.org/347~display.jpg
Amazing...:eek:
http://www.147thhillclimbers.org/347~winglow.jpg
More info http://www.147thhillclimbers.org/sound.htm
Regards.
Aser

[Helipolarbear]

I'd say that was one of the Tilt Rotor Platform Test Heli's doing the 'Wing Thing'
Wild looking. Check the static droop of the forward hub rear blade.....wouldn't want any gusting!!!!!

[Ian Corrigible]

HPB,
The use of a tiltable wing allows the high-speed rotor off-loading benefits of a wing to be enjoyed without the traditional loss-of-lift drawback of such configurations (as encountered by the Mi-6). As always, though, the rotorcraft gods demand that a price be paid, in this case chiefly the added weight & complexity (plus in the case of the 347 the reduced rotor-fuselage interface which you've highlighted).
The 347 has dubious distinction of out-living the HLH at Ft. Rucker's museum, and the type's four-blade rotor has long been touted as a feature of the next-generation CH-47X.
I/C

[[email protected]]

I bet it stops really quickly with airbrakes like that!

[Hilico]

Saw a picture of it in Interavia in 1973. In fact, the first picture in your post.

[MerryDown]

What a handsome beast..................

Flying test bed for me.....................


Merry

[widgeon]

more info here.
http://gunsagogo.org/sound1.htm

[CRAN]

Folks i've been asked to prepare a chat for some technical types on vibration/resonnance and am desparately trying to find the video that was posted not long ago on Rotorheads showing a Chinook on ground test shaking itself to destruction. Anyone know where it is?

Many Thanks
CRAN
:ok:

[vaqueroaero]

Here you are.
Side view:
http://www.chinook-helicopter.com/video/Ground_Resonance_Side_View.mpg
Back view:
http://www.chinook-helicopter.com/video/Ground_Resonance_Rear_View.mpg
For other disasters:
http://www.griffin-helicopters.co.uk/videos/

[CRAN]

Perfect, Many Thanks!

CRAN ~ Powered by PPRuNe!
:ok:

[SASless]

For those who are Wokka Lovers....this here is the site!


www.chinook-helicopter.com

http://www.chinook-helicopter.com/Chinook_Jobs/Its_a_living_450x554.jpg

[havoc]

SASLess,

I heard that everyone on the ladder had to bring on board a can of hydraulic fluid.

[SASless]

The ladder was one of those wonderful concepts that look great on paper...but fall a wee tad short of intent when used in the real world of combat.

Hanging about with the ladders down, waiting for the guys to climb up or down, probably explains part of my drinking problem. The locals usually got a bit peeved about all the noise and found ways to lodge complaints.

Ladders rarely lasted more than a single mission. The rotorwash and any wandering in the hover ensured they got hooked over the jagged remains of tree limbs and such and it seemed the Flight Engineer got to cut them away using huge bolt croppers.

http://www.chinook-helicopter.com/patch/tiles/Geronimo_Decal_tile.jpg

[rotorfloat]

Ok, I've viewed the website and closed the browser, why can't I get the music to stop?

[Express Heli]

Talking of chinooks, one just flew over my house..amazing helicopter, love em!

[airborne_artist]

It's a lot quicker if the loady just kicks the grunts out the door ...

I jumped from 800' from a Chinook, three times before breakfast one day in 1986. Only time I went in one - three t/o, no landings. Don't believe that the RAF rig theirs for static line any more, though.

[Vfrpilotpb]

Four favourite noise's.


Wocka--Wocka

UH1 comming in

Nother pint boss?


Yes you can!!!!!!!!!!!!!!!

Vfr;)

[SASless]

Static lines....five minute job to rig each side.

[Rigga]

Dont they use the Ramp Fast Roping Frames anymore?

[BigMike]

http://i8.photobucket.com/albums/a3/Micksphotos/mh47g7ta.jpg

[R22DRIVER]

Awsome Picture BigMike!

Im Sure it will have SaSLess foaming at the mouth! :ok:

[Ian Corrigible]

It's easy to see why the FARE aircraft are called Fat Cows...! :E

I/C

[SASless]

http://www.chinook-helicopter.com/chinook/images/64_13149.jpg

Four ACH-47A's were produced....named "Easy Money, Stump Jumper, Birth Control, and Cost of Living". Easy Money is the sole survivor...the other three were lost in combat operations in Vietnam.

Armament consisted of five .50 Caliber Browning M-2's MG's, two 20mm cannon, 2.75 inch Rockets, and a 40mm Grenade Launcher.

[g-mady]

Couldn't agree more...First picture is awsome!
MADY

[SASless]

http://www.chinook-helicopter.com/news/Afghanistan/Cobra_b.jpg

[BigMike]

Is this a new self defence mod?

[albatross]

SASless and BigMike
Would you be so kind as to let me steal those photos in order to post them here?
Thanks
Albatross

Fine Scale Modeler Helicopter forum

http://www.finescale.com/FSM/CS/forums/601144/ShowPost.aspx

[BigMike]

albatross, photo is from a thread on the 160th SOAR on militaryphotos.net

http://www.militaryphotos.net/forums/showthread.php?t=40746&page=4&highlight=160th

There is a some great footage of the SF guys driving an inflatable into the back of it, while they hover in water. Its on a video link posted there.

[BigMike]

http://img89.imageshack.us/img89/3537/zodiaclaunch0wh.jpg

[SASless]

Best we ever did was pull water skiers at Lake Tolocco....smack dab in front of the Base Commander who was not amused. Very short, succinct briefing by the Multi-engine Branch commander (a full Colonel) who was even less amused. Hand Salute...about turn...back to work sitting a lot lower in the seat.

[Thomas coupling]

http://onfinite.com/libraries/834916/240.jpg

[SASless]

Pretty darned good camo that....even Bloggs looks fuzzy!

[Droopy]

I wonder why they bothered with the chocks...

[Robbo Jock]

TC,

What's the drainpipe strapped to the side of the beast ? Early version of SkyShout ? Outside loo ?

Ta.

[SASless]

I just dig the shiny white aiming points on the flight suit....that would come in real handy in an E&E situation! I guess you stop...call a time out and then start de-rigging yer pickle suit for the neo-tactical look.

[Thud_and_Blunder]

Pull up a sand-bag, swing the lantern...

The drainpipes were the ejection chute for the M134 (dodgy arms-market purchase; GE man spent some time at the FOB helping to get them working). The det's 5 RAF Regiment gunners became the port-side operators for all ops after these were fitted, the other position shown here being manned by the No.2 crewman.

After the first night's tasking it was abundantly clear to all concerned that the IRR desert cam paint glowed in the dark. Our excellent JNCO engineers were given the task of nipping down to the local souk and obtaining all the dark paint they could get their hands on. I can't remember exactly how much they found, but it wasn't enough for a full repaint even when the stuff was fully thinned-down. Hence the stripe effect. While they were painting ZA712 'R' one of the lads kicked the paint bucket while they were doing the cabin roof - that aircraft ended up with a mixed pattern with WW2-style broad stripes as well as the small dashes.

SASless - looking at the scenery, I'd say this shot was taken post-GW1 during the operation to assist the Kurds in Turkey/ NW Iraq. You can rest assured that Mk14s with kneepads were never worn on Op Jena tasking.

As an afternote, one of these aircraft was still in this paintscheme several months later when it went over to do its share of tasking in N Ireland. The cam was surprisingly effective there too, although the dept of the MoD then carrying out the Wessex paintscheme trials (Light Dove Grey Walters seemed particularly unpopular with the customers...) were deeply unimpressed. It seems local initiative on the part of our Gulf groundcrew was seen to undermine their all-embracing remit to decide UK Armed Forces paint jobs. Still, these aircraft weren't the first to use non-approved schemes - anyone from the AAC care to recount the 'thinking' behind the change from black/green to light grey/grass green? Scientific selection didn't exactly come into it...

[Blind Bob]

Sorry Thud and Blunder, but the selection of paint schemes on Army aircraft was very scientific!
The RAF boffins came over to Hildesheim, Germany in 1983/4 with lots of Motorola cameras and tape recorders and a couple of Pumas. We painted some aircraft (lynx & gazelle) in the light grey and green, and left others in the black/dark green. They all had camera mount fitted to the skids and the recorder inside. The aircraft then flew pre-selected routes and heights against each other until either was seen. The tapes would then be played back to confirm what gave the opposition away! After 2 weeks fun and games the light grey/light green was the best all-round in the low level environment. The black /dark green was great against the tree line, but most were detected when breaking the skyline or crossing light coloured fields.
PS. The Pumas would have been best painted light grey for the altitudes they were flying at! Only joking, they did a great job and we all missed each other!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

[Thud_and_Blunder]

Hi Bob,

Good to hear from someone directly involved. The trial, as you say, involved a choice between the 2 schemes. It was the way the new scheme was devised which wasn't exactly scientific; STANOC (which IIRC stood for Surveillance, Target Acquisition, Night Observation and Countersurveillance) suggested a blend of green tones very similar to what adorns the Harrier and Chinook fleet these days. Similar trials using the RAF's route-recce Gazelle (used for several years by 7 and 18 Sqns) wearing that scheme showed it to be a better all round cam cover than the stripes. Not of course that the RAF would ever stoop so low as to blame all low-flying complaints about green Chicken-Legs on the AAC...

Word on the street when I taught at Wallop in the mid-80s was that the Brigadier wanted grey and green to match the new urban-centric doctrine, but it had to be different from the Crab colours!

[pumaboy]

Hi Big Mike

This has to be the coolest Chook I have ever seen.

And I'm a big Chook fanatic!!!!::

:)

[thecontroller]

the other night a chinook landed at our airport. the wind was 28 kts and it landed directly downwind. is this normal practice? is the chinook so powerful you can ignore the wind direction on landing?

[Shawn Coyle]

Essentially, the tandem design is nearly immune to wind direction. At light weight, there is so much power that it's easy to take care of a downwind approach and any performance aspects it may have.
And the rotor brake is extremely powerful.
Must have been interesting for the crew - lot of wind when the ramp went down, and I don't imagine the landing was too much rear wheels first.

[SASless]

Essentially, the tandem design is nearly immune to wind direction.

Errrr.....Shawn....which Tandem Rotor beastie would that be?

[Hughesy]

Another question about Chinooks, or any tandem rotor helo.
How do they do a turn in the hover?

Hughesy

[Fg Off Max Stout]

Yaw control is achieved through differential cyclic. Pedal input is as for any helo but the control mixing box then causes a lateral cyclic input to the left on one rotorhead and to the right on the other.

Wind direction is rarely a big deal for the Chinny because it mostly has loads of spare power and doesn't have the wind direction issues associated with tail rotor configurations. The only time it's a big deal is when the wind is really strong or the cab doesn't have much power in hand due to weight or density altitude.

[Heliport]

Thanks to Wokkaman for these pics -


http://img.photobucket.com/albums/v140/Rotorheads/ChinookBiggin.jpg


http://img.photobucket.com/albums/v140/Rotorheads/bfa372b6.jpg


http://img.photobucket.com/albums/v140/Rotorheads/9c0c364e.jpg


http://img.photobucket.com/albums/v140/Rotorheads/chinook98.jpg


http://img.photobucket.com/albums/v140/Rotorheads/Chinook_Sunset_2_b.jpg



And last, but not least .........

http://www.chinook-helicopter.com/chinook/images/160_fuel_probe_a.jpg



and a video ..... Chinook in Afghanistan (http://blog.siegnet.us/vids/Exfill.wmv)

[ems300]

just trying to work out what those girls are trying to re-fuel?:E

[SASless]

Great Photos!:D

Does an old Chinook pilot's heart proud to see them still out there doing their thing.

[allyn]

...boom.....


.....what's the penguin doing there? :p

[Flingwing207]

.....what's the penguin doing there?I'll tell you later.

[soupisgoodfood]

Someone linked to the site about the 347. In one photo, it looks like there is a large tandom rotor heli in the background, much bigger than a Chinook. Anyone know what it is?

http://www.147thhillclimbers.org/347down.jpg

[SASless]

Soup,

The aircraft you mention was a mockup of the Boeing-Vertol Heavy Lift Helicopter (HLH). Alas, Sikorsky convinced Congress that the CH-53E Sea Stallion should be the "heavy lifter" for the military.

* While the Chinook is a big brute of a helicopter by American standards, it is dwarfed by the huge Soviet-Russian heavy-lift helicopters designed by the Mil organization, and for a long time Boeing and the US military had an urge to match or top the Mil heavy lifters.

In the late 1960s, Boeing came up with designs for machines with broad similarities to the Sea Knight and Chinook, but about twice the size of the Chinook in terms of linear dimensions. Proposed machines included the "Model 227" transport and the "Model 237" flying crane.

Following award of an Army contract for a prototype of a "Heavy Lift Helicopter (HLH)" in 1973, Boeing did move forward on building an oversized flying crane machine, the "XCH-62". Rotor diameter was to be 28 meters (92 feet), fuselage length 27.2 meters (89 feet 3 inches), and footprint length 49.5 meters (162 feet 3 inches). Its widely spaced landing gear would allow it to straddle heavy cargoes such as armored vehicles, and still carry twelve troops in its slender fuselage. Boeing also considered selling a commercial version, the "Model 301".

The XCH-62 prototype was in an advanced state of assembly in 1975, being readied for a planned initial flight the next year, when the US Congress cut funding for the program in August. The Sikorsky CH-53E Super Stallion was felt to give adequate heavy-lift capability for US forces.

The incomplete XCH-62 prototype was mothballed, to be pulled out of storage in the mid-1980s when the Army, the US National Aeronautics & Space Administration (NASA), and the Defense Advanced Research Projects Agency (DARPA) collaborated on a scheme to finish the XCH-62 for experimental flights. However, Congress put their foot down again and it didn't happen.

This link discusses the "final" end of the mockup.

http://www.aero-news.net/index.cfm?ContentBlockID=d07b9f97-11df-4fae-be11-93e7f7b4c58f


http://www.pilotfriend.com/photo_albums/helicopters/images/h62.jpg

[John Eacott]

This video (http://www.youtube.com/watch?v=Tyqrc5sER3Q&NR) on YouTube makes me wonder how bad the track & balance has to be before someone says something!

[Hilife]

When the cabin shakes so much the sidewalls begin to blur is a good time to think about track and balance.

[Tandemrotor]

The one thing I will say, looking at these pictures. It reminds me that this helicopter is a beast. A machine of war if ever there was one. Some great times, some absolutely desperate times, but glad to have had the experience.

[Dave_Jackson]

Do any commercial operators use Chinook helicopters or are they only used by the military?

If they are only used by the military, or only produced for the military, what would be the reason for this?

Thanks,

Dave

[HeliEng]

Dave,

Try this link

http://www.colheli.com/colheli.html

[Shawn Coyle]

Dave:
The Chinook is primarily used by the military. It has had some commercial uses - as a passenger machine for British Helicopters and then an Alaskan operator. These were used for longer distance, large crew change operations. The UK operation had at least one accident which destroyed faith in the machine, and I think the long-range offshore work in Alaska dried up. Now the main use for civil Chinooks is either logging or heavy equipment moving.
Not a lot of call for a machine that can lift 12 tons with commensurate fuel burn in the civil world.
The militaries that operate the machine love it - a great example of evolution in terms of reliability and growth in transmission and engine capability, as well as the use of fiber-composite rotor blades.

[Boslandew]

Dave

I flew the Civilian Chinook for British Airways Helicopters in the '80's. It was used for long range flights when the major off-shore installations needed large numbers of passengers moved. Our most distant destination from Aberdeen was the Magnus field, the most northerly platfom in UK waters. The Magnus was some 294 nautical miles from Aberdeen and a round trip without shutdown was about five hours. We almost always carried the full 44 passengers and the operation became very efficent. The BAH Chinooks had an excellent avionics fit with area navigation and ILS approaches could be flown with coupled Flight Director, a big step forward for those days for helicopters.

Sadly a serious accident saw the end of their service with BAH. They were undoubtedly expensive to operate and only succeeded because they fitted the oil companies requirements for specific routes and installations. It is difficult to see how they could be used profitably elsewhere in the UK but have found a role logging and heavy lifting in other countries - I once lifted ten tons on the hook and that was the absolute limit for the aircraft for that days ambient conditions

[Graviman]

A couple of Chinook tech questions, i never got around to asking before:

What sort of drive shafts does Chinook use? Clearly driveshaft failure would force an auto, but it is something i've never heard about failing. They must be some weight, despite the front gearbox.

Does the front rotor have a more forward inclination angle than the rear rotor? If so how does this affect handling? I don't know if there is fore/aft cyclic for each rotor, but imagine that negative longitudinal dihedral would reduce cyclic movement in forward flight.

Mart

[Boslandew]

Mart

The Chinook transmission is very complicated. Each engine drives a nose gear-box which drives into central combining gearbox. From there shafts called synchronising shafts drive to the forward and aft main gearboxes. Synchronisation is considered to be even more important than power transmission because the two rotors overlap and it would be catastrophic if they were not in phase. Autorotation in training with both engines out of the governed range were standard and in the simulator, full engine-off landings were achievable with a little practice. One anomaly that the simulator threw up was achieving vortex ring on one head and not the other. The recovery was violent!!

The fore and aft gear-boxes are mounted at slightly different angles for technical reasons that escape me but that makes no difference to handling. Longitudinal aircraft pitch changes are made by increasing collective pitch on one head and reducing it on the other. Laterally both heads tilt in the required direction and yaw changes are made by tilting one head in one direction and the other in the opposite direction. Handling however is completely conventional and anyone who can fly a helicopter would have no problem in handling a Chinook. Understanding the systems is something else.

[slowrotor]

A native tribe just hired Columbia Helicopters big Chinook to place logs in the local river for salmon pools.
Usually, the logs are flying one way out of the woods.

[Flying Bull]

Hi Mart,

A couple of Chinook tech questions, i never got around to asking before:

What sort of drive shafts does Chinook use? Clearly driveshaft failure would force an auto, but it is something i've never heard about failing. They must be some weight, despite the front gearbox.

Does the front rotor have a more forward inclination angle than the rear rotor? If so how does this affect handling? I don't know if there is fore/aft cyclic for each rotor, but imagine that negative longitudinal dihedral would reduce cyclic movement in forward flight.

Mart

I'm not a Chinook-jockey - but I think, it depends, from which drive shaft you are speaking.
Engine - the helicopter has two - so normally not that a problem, except in hover.
Drive shaft between the gearboxes? That's why the Banana is also called flying coffin...
It tends to tangle the blades from front and back, when die dirve shaft goes.....

Much less chance than surviving a tailrotordriveshaftfailure in a normal helicopter....

Greetings Flying Bull

[Dave_Jackson]

HeliEng & Shawn, thanks for the replies.

http://www.boeing.com/rotorcraft/military/ch47d/images/ch47art.gif
The reason for asking has to do with vibration. The Chinook has a rotor-to-rotor interaction, plus it has a relatively large fuselage area under the two rotors. I was wondering if these features result in a high level of vibration. A vibration that might be acceptable for transporting armed services personnel but not acceptable for transporting commercial personnel.

Is the vibration in the Chinook higher than that of other large helicopters?

Dave

[Boslandew]

Dave

The vibration level in the Civilian Chinook was quite high, certainly higher than for example the S61 or S76. Because of that both pilot seats and the entire passenger cabin were mounted on dynamic vibration absorbers. When levelling into the cruise the rotor revs were reduced slightly and that change of rotor speed induced extra vibration that the seat absorbers might take as much as two minutes and more to absorb. When the first Chinooks were received we found that vibration was usually what determined the cruising speed regardless of what the book said. Typically on departure from Aberdeen the book cruise might be 120 knots. The aircraft was accelerated until the vibration level became uncomfortable and the speed was reduced a couple of knots which speed then became the cruise. On the inbound leg minus 10,000 lbs or more of fuel up to 135 - 140 knots was usually possible

[Graviman]

It tends to tangle the blades from front and back, when die dirve shaft goes.....

Much less chance than surviving a tailrotordriveshaftfailure in a normal helicopter....


Thanks Flying Bull. This already tells me the shaft would have to be designed to handle full rear cyclic, and full collective, more-or-less as a fatigue loadcase. By this i mean that the shaft stresses at this torque would be low enough for the the shaft to never fail during its design life, since clearly failure would be catastrophic.

I would imagine that shaft will be carbon composite, and very substantial. The other problem is that the surrounding structure has to be stiff enough to avoid torsional and flexural resonance problems. At high rpm any initial flexure in the shaft would soon lead to catastophic failure.

Hmmm, them Chinook boys must trust the ground crews. :uhoh:


Dave, have you ever heard a chook fly overhead? Vibration from ground level is pretty high. Every rotation each blade intersects the vortices from the opposite rotor set, so you get persistent blade slap. Great noise though.

Mart

[brett s]

What sort of drive shafts does Chinook use? Clearly driveshaft failure would force an auto, but it is something i've never heard about failing. They must be some weight, despite the front gearbox.

They are actually pretty light (reasonably large diameter, 6" or so from memory but it's been a while & they are of course hollow - can't remember what they are made from) - between the fwd & combining (center) transmission there are 7 sections with flex plates between them, between the combining & aft there are two. If any of those fail you're toast, no way around it. The two engines have shafts connected to the combining transmission, which drives the fwd & aft transmissions.

Does the front rotor have a more forward inclination angle than the rear rotor? If so how does this affect handling? I don't know if there is fore/aft cyclic for each rotor, but imagine that negative longitudinal dihedral would reduce cyclic movement in forward flight.

Yes, the fwd rotor is tilted more (9 degrees vs 3 or 4 for the aft)- and it uses differential collective pitch rather than fwd/aft cyclic. There's a bit of fwd cyclic pitch added automatically by an electric actuator based on airspeed to reduce stress, but that's it.

For Dave, they aren't any worse to me - if tracked & balanced properly of course. The older metal blades were a lot easier to get smooth back in my days but you could also get the composite ones just as good - just took longer! The minumum standard used to be .2 IPS, which isn't particularly smooth to me - this was 20 years ago, who knows what the story is now.

[Dave_Jackson]

Boslandew, brett s & Mart

Thanks for the remarks about vibration, particularly since it is related to a craft with twin-rotors.


Mart,

Nick has said that the noise is intentional. He mentioned an old documentary called 'Apocalypse Now'. Nick said that the noise caused the enemy to **** their pants. Then the helicopters could catch the enemy with their pants down. ;)


Dave

[Graviman]

Boslandrew,

I only just spotted your very informative post. Apologies - put it down to quick lunch time posting...

Interesting that Chinook had no peculiarities in handling. Still the idea of VRS in the rear rotor is not pleasant - i guess you had to roll the machine sideways to recover. Prouty commented that they climbed best flying slightly sideways, since this increased the rotor area to flow. I must admit to having tried to work out if there was any reason other than blade clearance for the 5 or 6 degree difference in rotor g/box mounting angles.

I'm not suprised about the vibration being the main constraint though. There are lots of opportunities for the tip vortices to impinge other rotors and structure. The other vibration source would be drivetrain eigenmodes, which i imagine are not insignificant (massive rotors and flexible drivelines). I'm also slightly suprised that they haven't followed the trend and moved to 4 blade hingeless rotors.

Still, good bit of versatile design - it clearly delivers.


Brett,

Thanks for the driveline details. I'll have to do some googling to come up with weights and materials. I imagine the guy that did the original layout (based on Piasecki's concept drawings no doubt) lost a lot of sleep about getting the stress calcs right - i know i do! :ugh: From Boslandrew's comments i would imagine that the cost of maintaining such a complicated powertrain is a disadvantage.

Do the electric trimmers bias the forward thrust in any way, or are they just there to compensate for flapback?

Mart

[Shawn Coyle]

A couple of points -
The whole Chinook flight control system is very complex. There is collective and lateral tilt on the swashplates, but no fore-aft tilt through the mechanical flight controls. The fore-aft tilt is done only through the Longitudinal Cyclic Trims (LCT) which program as a function of airspeed and density altitude. They must be extending by 60 knots, and the Vne with the aft one not extended is 100 KIAS. The reason for this is the aft shaft from the transmission to the rotorhead would be under way too much flapback beyond 100 KIAS. In fact, the alternate way to tell the aft LCT isn't programming is that 100 KIAS, it got quite smooth as the aft head was now not intermeshing with the forward head.
The LCT system is how the fuselage stays level in all flight attitudes - an interesting system.

As for the system being more efficient with some yaw, the Canadian Air Force version of the CH-46 had a gauge for most efficient yaw angle to be used following an engine failure. Only instance I know of this being measured and used. The yaw angle came from the AFCS which measured and controlled yaw with differential sideslip from the things on the front that look like static ports.

Confused yet?

[IFMU]

Dave
The vibration level in the Civilian Chinook was quite high, certainly higher than for example the S61 or S76.
I suspect a big part of that is the 2 3-blade rotors. More blades = more smooth.

-- IFMU

[Graviman]

Shawn,

Thanks for detailing the LCT. By extending do you mean that the LCT is out of trim by 60 KIAS, to get the forward thrust component while maintaining level attitude ?

A wealth of wisdom - one copy of C&C winging it's way to me as we type... :ok:

In fact, the alternate way to tell the aft LCT isn't programming is that 100 KIAS, it got quite smooth as the aft head was now not intermeshing with the forward head.

Interesting fact - Dave, you might like to take a note of that.

Mart

[Boslandew]

A lot of the vibration stemmed from general interaction between the two rotors not helped by the three blade system. If the blades were tracked and balanced properly the vibration could be minimised. However, speed and weight affected vibration enormously. We had a graph produced showing vibration against weight at VNO and it was a gentle slope up to 45000 lbs but then curved sharply up between 45000 and 48500, the civilian MAUW.

As regards increased performance from yawing the aircraft slightly, the BAH aircraft were operating to Public Transport standards so Performance 'A' standards were required which did not allow the technique. However, operating empty on one occasion for underslung work, we made a take-off into wind but with the aircraft yawed thirty degrees to starboard putting the rear disc in clearer air. There were no handling problems and it went up like a rocket.

[Graviman]

Boslandrew,

Interesting that vibration increased non-linearly above 20.4 tonnes MAUW. It may just be that the orginal design was pushed up from this, with parts beefed up as required. The higher disk loading probably pushed blade pitch away from ideal, using more dependancy on vortex shedding to provide retreating blade lift. Basically a stalled wing will briefly increase lift as the circulation breaks away - in a helicopter this can be used every revolution. It would explain why vibration increased with speed too.


Did you find that having two rotor sets on the one aircraft worked out more expensive to operate? I realise a machine with a MAUW just shy of 22 tonnes would be harder to achieve with one rotor, although the obvious example is the MIL26 (payload ~ 20 tonnes). I just wondered how often the synchronising driveshaft and nose/combining/forward&aft gearboxes needed overhauling. My experience (albeit not with helicopters :sad: ) it that complexity normally introduces cost, both investment and operation.


Mart

[ShyTorque]

Vibration? Ask a Chinook pilot a question about it and he will nod a reply.

He will keep on nodding, even after he's given his answer.

The day after that, too..... ;)

[Granny]

Shy Torque-
what a crock of ****

[ShyTorque]

They're not that bad....

...can't take the banter?

[Boslandew]

I sometimes think that what this site needs is a Forum just for intolerant comments and the sort of remark that people wouldn't dream of making other than from the safety and anonymity of the Internet. This thread has hitherto been very informative and friendly. Couldn't we keep it that way?

You're right, Sky Torque, about the vibration. I once flew nearly nine hours out of Aberdeen without a shut-down on a Christmas Special and was still vibrating the next day.

As regards the economics Mart, I have no direct information - the figures were kept confidential. My only memory is that the oil companies said they had to fly the aircraft full to make it pay - rarely did we fly with less than a full load. The servicing cycle for the transmission was no more frequent or demanding than for, say, the S61. It was a well-proven airframe from military service. Having said that with five gear boxes as opposed to two or three it was an expensive aircraft to operate.

[Shawn Coyle]

The Chinook is a relatively old design - remember it started with metal blades and a maximum weight of much less than it has now.
There have been significant, incremental improvements in the machine over the years - fiberglass rotorblades made a huge difference in vibration and noise, hydraulic system completely redesigned for reduced maintenance, and so on.
It keeps getting improved, and I see that yet another refinement has just flown at Boeing's works in Philadelphia.
It would be very unfair to make comparisons of the machine to other helicopters based on the early version - remember it was nearly 25 years ago that it was used in passenger transport. A lot has changed since then.

[Graviman]

Having said that with five gear boxes as opposed to two or three it was an expensive aircraft to operate.

This was my concern Boslandrew. I was once amazed when an RAF S61 engineer told me that they replaced the main g/box every year! Then again they also did a 5 to 10 man-hour walk around before every flight. :eek:

It would be very unfair to make comparisons of the machine to other helicopters based on the early version - remember it was nearly 25 years ago that it was used in passenger transport. A lot has changed since then.

Good point well made, Shawn.

Mart

[Dave_Jackson]

The previous posting was deleted because the helicopter would not vibrate.
If anyone wants to see what the intended effect looks like Click on this link and then click on the 'Vibration Analysis' link. (http://www.unicopter.com/SynchroLite.html#Primary)


The information posted on this thread is much appreciated. Thanks.

Dave

[Boslandew]

All the major components on the Chinook, like all aircraft, were 'lifed' after which they went off to be re-conditioned. I think the gear-box lives were 1200 or 2400 hours and the engines the same. The BAH Chinooks often flew ten hours a day/five days a week/2500 hrs a year so gear-boxes and engines were probably changed more than once a year. Maintenance was done on an on-going basis, a gear box change here, an engine change there, hydraulic systems and generators, all highly regulated but done to ensure that the aircraft wasn't down for too long at any one time. Major servicings were done at required intervals when the aircraft might be in the shop for a few days.

Daily pre-flight and after flight inspections were carried out on top of that. An engineers inspection might take half an hour but only after any scheduled work had taken place overnight.

[MightyGem]

Some pretty extreme vibration here!! (http://www.chinook-helicopter.com/video/Ground_Resonance_Side_View.mpg)

[GWidgery]

Wow, that is one awesome self destruction video! Any idea whose Chinook it was, or where that happened?

[wheatbix]

A perfect example of ground resonance!

I think they were just testing to see what happened and do some analysis, AFAIK that chinook was due to be decommissioned anyway.

[Graviman]

All the major components on the Chinook, like all aircraft, were 'lifed'...

Serious thanks for input Boslandew. Not being in the industry (at this time), this is the best way i can gain heli design "experience". :ok:

Mart

[Heliport]

RAF Chinooks assisting in the evacuation from Beirut during the Israeli war on Lebanon, July 2006.


http://img.photobucket.com/albums/v140/Rotorheads/Gallery/RAFChinooks_LebanonJuly06.jpg


http://img.photobucket.com/albums/v140/Rotorheads/Gallery/ChinookBeirut2.jpg


http://img.photobucket.com/albums/v140/Rotorheads/Gallery/ChinookBeirut.jpg

[Senior Pilot]

There's an interesting article on a Chinook repair in field,Widow Maker: stuck between a rock and a hard spot (http://www.chinook-helicopter.com/history/aircraft/C_Models/71-20955/71-20955.html) :ok:

A couple of photos from the story:

http://www.chinook-helicopter.com/history/aircraft/C_Models/71-20955/71-20955_e.jpg


http://www.chinook-helicopter.com/history/aircraft/C_Models/71-20955/71-20955_b.jpg

No doubt they all wore Safety Vests, which protected them from falling down the cliff ;)

[CheekyChopper]

I now understand more thanx.
I am 50-ish and have been befuzzled since I started flying at 16. How does the mixer-linkages work in the control system. I dont want to hear how the concept works again? I want a schematic if linkages. :)
Why doesnt something brek when you apply left cycli and right rudder?
Help me. I wont die before I know and I dont want to live forever!

[SASless]

The video of the Chinook experiencing ground resonance was taken of a ground run test of the aircraft at the Aberdeen Proving Grounds. The aircraft was there to be shot at by various weapons to determine what resistance it had to various size rounds and when hit in various sensitive places.

Unfortunately, the aircraft was chained tightly to the hardstand and during the remote run test the aircraft was unable to move naturally and encountered ground resonance which led to the aircraft shucking the aft rotor, gearbox, and vertical fin area.

Chalk up another success to the Army!

[Rigga]

CheekyChopper,
Download the following pdf file:


http://chinook-helicopter.com/Publications/CH-47D_Technical_Publications/23_Series_P_Manuals/TM_55-1520-240-23P-3.pdf

and go to Page 126 of 511 (or Figure 392 (Sheet 1 of 5))
for a picture of what the Chinny Mixing Unit looks like.

If you can pick out the lower assembly (to the Left of the words "Detail A") that is what a 'normal' Mixing Unit may look like!

If you can find manuals for a Whirlwind (S-55) or Wessex (S-58) they have really simple examples.

[Robin Clark]

..what happens if one of the rear undercarriage units still show in contact with the ground after lift off........????.......do you have to touch down again to sort it out......???????.....
.....what happens if the indication occurs during flight.........????....

regards Robin......

[joe nelson]

I am working on a project of a 10% scale model of a tandem gyroplane and I'm looking for a little help from the experts here on this thread.

This project has been on my bucket list for nearly twenty years and now that I'm retired I have the time to work on it but lack some tandem expertise. I hope some of you can help.

Today's problem is the use of gimbal heads and can DCP be acheived by making the front and aft rotors work opposite to each other...pitch up on the front and down on the aft rotor ect?:sad:

[SASless]

DCP should work as you describe.....for pitch control. In order to level the fuselage in flight for better aerodynamics gets much more complicated. Read up on "Speed Trim" on the Chinook series....and you will understand why that is so.

Search for photos of the "SAS Closet" (left side of the companionway leading to the Cockpit) to get an idea of how complicated the bell crank system is for the flight controls.

I wish you ever success.....as when you get it worked out you shall be a genius on your own right!

[joe nelson]

Thanks SASless,

I have three flights under my belt so far. All three ended in an an abrupt loop crashing nose first. The aft rotor appears to not to be generating enough lift or the AOA of the aft rotor is too shallow. Maybe the differiential movement is too much for a good take off. Who knows? I guess I'll find out soon enough!:ugh:

PS I'm using a 1/1 unit ratio for my DCP changes between my rotors...is this too much?

[SASless]

What is the CG of the aircraft? Perhaps there is an issue there that might affect the necessary lift from each head.....which might change that ratio.

I am purely guessing on this.....but it would seem "airspeed" would have to be a function of pitch angle of the airframe as you have no way to level the fuselage by using speed trims.

Would reducing the sensitivity of the collective inputs make the aircraft less sensitive and perhaps more stable?

I bet it is a thrill trying to work all this out!

There was a really sharp guy that built a Huey helicopter complete with turbine engine that did some flights where Huey 509 was based several years.

I will send you a PM on a way to get in touch with him.....hopefully.

[joe nelson]

SASless,

The first flight was with the CG located at the 25% station and was moved forward 5% after each attempt. The longitudinal rotation did slow somewhat with each change. Now, I'm looking at the DCP ratio. Maybe, the aft rotor need to move more than the front due to flying in the wash of the front rotor. A ratio change, as you suggested, to say 1/2 might be in order here...it's easy enough to do with a change in the linkage position on the aft bell crank.

Yes, It's great fun doing this. My grandkids love to help on Sundays, after church, by being my "ground crew". They each have a job doing camera work and picking up the pieces, lol. The most enjoyable part is the experimentation. I have made blades with BERPs and even servo flaps...Kaman style. Now, I'm playing with blade twist but it seems to be above my skill set, for the moment.

I will certainly give the Huey fellow a shout. I love to talk "helicopter" with anyone!

joe

[SASless]

On the Chinook the CG limit spread is a staggering 144 inches (as I recall anyway....) which is very forgiving as compared to a Single Rotor helicopter.

Enjoy the time with the young un's.....must be good fun as they laugh when the pieces fly! I reckon that can turn into a real scavenger hunt at times.

[JohnDixson]

SAS, maybe the BV marketing troops thought it was 144 inches.

People evaluating the CH-47 vs the CH-53 ( thinking UK, Israel and Germany ) always got a surprise when they found out that the CG ranges were almost identical. I know the 53A/D went from 328" to 352" and I just looked up the CH-47D on an Army wt and balance presentation and at 42,000 lbs, their CG range went from 316" to 338". Pretty close.

Thanks,
John Dixson

[Rigga]

Might it be the rotor head angles?
Most tandem rotors are biased away from each other by approx ten degrees.
Don't forget that Chinook swashplates (LCT's?) change each Rotor Head's path/angles relative to forward flight speeds.

[SASless]

John,

I stand corrected....too many Pints of the foaming Ale I presume!

I found a CG chart for the A Model Wokka.....which shows a 48 inch travel at 27,500 Pounds MAUW and 23" at 33,000 Pounds.

I know you can set a full pallet (about 4,000 pounds) of Cememt Mix on the Ramp....sling a huge Yellow Concrete Mixer bearing Blue Air Force markings and still have sufficient cyclic control. As haste was of the essence....and it being Midnight at Bien Hoa AFB....there was not a lot of planning involved.

Having a Cargo Winch, Ramp with extensions, and a Cargo Hook made Midnight Requistioning great fun....with virtually unlimited possiblilities. Having the ability to carry an M-151 Jeep with FM Radio for scouting and coordination opened up places not usually accessible.

The trick was to get the Yellow covered up with Olive Drab and place Black US Army numbers all over the Mixer.....and dryed before OSI, CID, or the MP's made it to our unit area!

[JohnDixson]

SAS, should I have written: " sorties "? BTW, you are entirely correct about the local license applied to that subject.

Flying in a unit ( 119th Avn Co ) that had UH-1B guns and slicks in 65-66, not only didn't we have the performance to steal anything of use, but stationed at Camp Holloway we didn't have anyone nearby who had anything worth taking anyway.

Prior to that however I was at the Army Test Board ( as a 2nd Lt out of flight school ) and our three CH-47A's were having problems with resonant, self-destructing nose gearboxes that shed pieces thereof into the T-55 immediately aft, resulting in landings at the golf course and other places that got attention. Anyway, the older heads tended to avoid getting on the CH-47 schedule, so within two months or so I was an IP, which made me available ( read as " expendable " ) for an interesting mission.( Boeing changed the operating Nr from 204 to 230 which avoided the resonance ).

They wanted to know how vulnerable the UH-1 was to the sort of ground fire expected in RVN, so a full scale wooden UH-1 was built with a double metallic foil skin in 30-40 sections, each attached to an electrical feed to a tape recorder. Proposition: sling this model at the end of a 2000 ft long cable at night and shoot live ammo at it as we flew various courses and altitudes under radar control at FT Bliss. If a bullet pierced the skins, electrical contact would be recorded for that skin section on the recorder. Good job for a 2nd Looey.

To pick up and return the model without banging it around, we had a very powerful AA WWII searchlight whose beam was aimed skyward at the vertical. So after they had run out of the prescribed amount of ammo, one would come back to a hover at 2000 plus 3-500 ft and listen to another crewmember talk us down the beam to a gentle touchdown.

Did this for about a month until we got some new gunners on the ground and the cable got parted 200 ft from the CH-47. At the time, they had increased the ground fire caliber to 40mm ( no typo ) so the test was declared over.

Always thought the CH-47A, now I'm talking about 1963-5, was easy to fly, and actually the Army and Boeing managed that program pretty well over the years.

Thanks,
John Dixson

[Dave B]

In accordance with the original thread title, here is something other than you Chinook. 22000 lbs A.U.W., no Auto. Stab., no rotor speed governing, and manual throttles. Pilot was F.O. Nast, who wanted to see if the beast was good for roping.
http://i866.photobucket.com/albums/ab221/MountKenya/Belvedere60001.jpg?t=1311871226

[msuldo]

Navy H-46 (BV107). I was flying over mixed land and water about dusk at 1300 ft when the DCPT actuator in the control closet came disconnected due to a cotter pin not installed in prior maintenance about 10 flight hours before. A/C did a high G uncommanded loop and blades meshed at about 1800 ft upside down at the top of the loop. Broke into 3 sections. Very violent. On the way down I was hit in the head (concussion) by the overhead circuit panel coming loose and knocking me into the cyclic (besides having both lower legs broken by the bottom of the instrument panel) was unconscious when we hit the water and woke up about 20 feet down. Egressed and bobbed up next to the copilot (broken back) who thought I had died (had his footprint on my kneeboard where he stepped on me leaving - still friends!). Unfortunately the 3 crewmembers in the back perished. Lots more to the story - buy me a beer sometime if you want to hear the rest.
Still - with 2000 hours or so in them, it's the best helo I've ever flown for power and all around fun. Nothing like doing a head on approach to an underway ship with an external load and doing a button hook, rotating around the nose as you came abeam in a 180 turn and ending up placing the load right on the deck as you swung through.. Although, for a long time, I got a bad feeling in my stomach when the co-pilot would pull back on the cyclic quickly without saying something.
Mike

[http://img89.imageshack.us/img89/8718/46photo.jpg (http://imageshack.us/photo/my-images/89/46photo.jpg/) Uploaded with ImageShack.us (http://imageshack.us)

[SASless]

Mike,

I defy anyone to top that story.....you are one very very lucky fellow!

Perhaps we need to start a "There I was....." thread telling of our very lucky escapes from bad situations!

There are some corkers to be told.....and as yours....all true!

By the way.....you got a lucky Lotto number you wish to share?

[birrddog]

Amazing what a small world this is. I was with a friend at the Intrepid Museum on Saturday, and there was a Piasecki H-25 Retriever.

Thought this was a coincidence in name though didn't think anything of it again, until I met with a friend/colleague this week, and it turns out that was his father!

Reading his obituary it turns out he was also the first helicopter pilot to get an helicopter license without having a fixed wing license.

An interesting man indeed.

[joe nelson]

Dave B,

What made the Belvedere so stable as not to need a SAS?:confused:

[Good Vibs]

Did not the RAF say to the Belvedere: Two engines,two rotors, two pilots, too much trouble!
All you RAF types can confirm this if true!

[Peter-RB]

Msuldo,

Ages ago when I started this thread, I never expected to read something like you have written, dropping in from such a height would seem like a certain one way ticket, was it just massive bulk bodywork that saved you and your pal.

thank you for that short but very gripping piece of your flying history.

Peter R-B
VfrpilotPB

[heli1]

AAAAHHH Belvedere !
Stable because Raoul Hafner ,the designer didn't believe in power operated controls,although they were fitted after a few flights,one engine at each end because it was born as a piston design but modified for turboshafts when they first arrived on the scene in the mid fifties ,able to fly at AUW on one engine (with an auto doubling of power if one failed) but never intended for the RAF who got the short straw when the original customer ..the RN cancelled in favour of the Wessex ,hence the lack of cabin windows,the stalky front landing gear,and the overall fuselage dimensions.
Mind you Belvedere Mk 2 would have beaten the Chinook hands down if Bristol's had been allowed to build it.Aft mounted Gnome engines(3 or 4),rear ramp,four blade rotor system ,cabin plug option for civil use, but cancelled because the short sighted government didnt see any use for large helicopters once they withdrew from east of Suez.
Hindsight is a wonderful thing !

[SASless]

Three or four engines.....long ladder to get into the cabin....narrow as a sausage....oh yeah right it would have beat the Chinook! Even the RAF is celebrating thirty years of flying the Chinook.

Some of us are celebrating 44-45 years of flying Chinooks....and in the future there shall be Kids celebrating 90 years.

We should also recall the Wessex was originally designed by Sikorsky and some variants are still flying in commercial service today fifty plus years later.

[joe nelson]

The Chinook is a great aircraft even with all of it's warts and blemishes. The Belvedere did enter production and service in the RAF. My interest is their aerodynatics. Why does one reqiures supplimental stability controls and the other doesn't. Is it pilot training or a fix to the airframe?:confused: I would like to understand the tandem rotor helicopter not cause an argument between rotorheads.

[SASless]

Designers learned as they went....the "A" model Chinook had a very sharp end to the Aft Pylon and was quite sensitive in Yaw. The subsequent models had a squared off end to the Aft Pylon which provided the equal of about 37 feet more fin or some such number....and was much more stable in Yaw. The A and B models had dual channel three axis SAS systems.

Starting with the "C" model the aircraft were equipped with an additional Pitch SAS system.

The earlier Piasecki CH-21 has no SAS but did have stabilizing fins on the Aft Pylon.

The H-25 or HUP had neighter SAS or Fins..

[FH1100 Pilot]

http://boeing.com/history/boeing/images/hup.jpg

SAS:The H-25 or HUP had neither SAS or Fins..
Uh-oh! Don't mean to be disrespectful, SAS, and I certainly could be wrong about this...but I believe the HUP did have *both* of those things, depending on model.

HUP-1 had fins on the side of the aft cowling.
HUP-2 had no fins and a crude SAS.
HUP-3 had a more sophisticated SAS (that could, I've been told, autohover).

My dad flew the HUP-1 and -2. Said they weren't very pleasant to fly.

[joe nelson]

SAS and FH1100,

Thanks for your input! The best information comes the guys who drove these machines. Please forgive my ignorance, I drove OV-1's while in the Army but escorted a few Chinooks into some bad places.

[Fareastdriver]

Belvedere Development.

The turbine powered version bore no relation to the ship borne torpedo firing botch-up that the British Navy wanted. It was similar in appearance, though larger, and more importantly, earlier than the Chinook. I cannot find any drawings of it at the moment but the ones I have seen were very impressive.

However, shoveling money into the back pockets of benefit scroungers, illegal immigrants etc, had a far higher priority for public money so the project was scrapped.

[heli1]

The Belvedere Mk.2 was nothing like the original version SAS less...it had a level undercarriage ,larger cabin and was very Chinook-looking ,even though the design predated the Boeing aircraft.No coincidence that after it was cancelled some top Bristol designers emigrated to Philadelphia ?!

The success of the Chinook since just shows what a world beater the Brits would have had if the government hadn't cancelled it ...

As for the S-58 the British conversion to twin turbine power turned a heavy poor payload aircraft into something that could fly OEI at max AUW.

[SASless]

I was more familiar with the Army version....which in those days...helicopters were considered more in line with Jeeps and Trucks than aircraft.

The CH-34 had "ASE" , and auto pilot system with a Barometric Altitude hold feature....which did not find its way to the Huey or Chinook. It is no surprise the HUP was far better equipped than the H-25.

As in most helicopter designs of the US Military....there are many different models of the same aircraft.

http://www.flugzeuginfo.net/acimages/hup2_edwardgronenthal.jpg


From the US Army Aviation Museum at Fort Rucker, Alabama.....

http://upload.wikimedia.org/wikipedia/commons/thumb/f/f3/Piasecki_H-25A_116616_Fort_Rucker_AL_14.12.02R_edited-2.jpg/220px-Piasecki_H-25A_116616_Fort_Rucker_AL_14.12.02R_edited-2.jpg

[Dave B]

This may be of interest, picture taken from the RAF news, showing Belvedere picking up a crashed Lightning. The Lightening crashed after the Pilot ejected, after an undercarriage failure. BAC wanted it back for examination, as it was by the sea, and the tide was coming in.

Aircraft was flown by Flt.Lt Youngs, and Flt.Lt. (Bunny) Austin, with me as crewman. After we managed to get it back, we found it was full of sand, and seawater, so was way over the 6000lbs hook weight.http://i866.photobucket.com/albums/ab221/MountKenya/Belvedere40001.jpg?t=1312388386

[Senior Pilot]

There never seemed too much concern about what was slung under a helicopter back then: and always a short strop, too ;)

http://glostransporthistory.visit-gloucestershire.co.uk/images/AirHeli%20Belvedere%20and%20Wessex.jpg

Bristol Belvedere XG 456 of 66 Squadron - based at Seletar, Singapore - recovers Westland Wessex XS 117 of 845 Naval Air Squadron.

[Tallsar]

Bet that was a fun load to fly Dave....Not! Just as well it was more dense than anticipated.

Heli 1, while it probably would have garnered a few orders, i am not convinced a Belvedere Mk2 would have done that well. Just as many other UK designed ac of the 60s didn't - many foreign air forces were already buying US or Soviet ac due to their lower costs and better availability, never mind the hidden cold war subsidues. Most CH 47s have been bought by the US Army, so do you really see them buying from us rather than US built...? Coupled with the fact that the RAF would probably only bought about 30 , the production line would have probably closed 1970 before we woke up to the real value of such beasts as we have now.

[heli1]

Tallsar.
Of course the US Army wouldn't have bought it.US politics would have seen to that ,even if it was twice as good,but when you look at UK purchases of Chinook since then,now close to entering three figures, and a few other possible overseas sales..Canada,Australia etc it would have been a decent run and justified the millions spent on Belvedere development.

Like many British projects,it was just ahead of its time.

[Peter-RB]

Heli one,

like the Spitfire, RR Merlin and more, then the Jet Engine, the turbine, the fully flying tail components, The Buccaneer, other supersonic designs, Concord/TSR2, to name just a few:D

if our politians had had brains then,.. the UK Inc would be in a good state now !

Peter R-B:ugh:

[Dave B]

Tall Star
Yes it was tense, as the pilots were not aware that it had been slung wings down, so I had to keep saying "you must get some more height", as the wings were in danger of clipping the ground. Trouble was they were using all available power.

Here is a picture of why it could never enter Naval service. Embarking on HSM Albion, en route to the far east.

http://i866.photobucket.com/albums/ab221/MountKenya/Belvedere10003.jpg?t=1312471087

[JohnDixson]

Heli One, you had written that the MK II would have 3-4 engines. It sounds as if the design was conceptual in nature. To exceed the performance of the CH-47A, which had 2 X T55-L7's at 2650shp each ( or to address beating the CH-53A which was on the scene as well with 2 X GE T-64-6B at 2650shp each ), it would have needed the four engines I suspect.

I certainly concur with your remark re the talent available. Sikorsky as well as Boeing were very lucky to sign up UK engineers, who were hard working, extremely talented and an asset of immense importance. And they certainly added a note of civility to our often loud and noisy design decision meetings.

As I believe SAS was getting at, however, the task facing Bristol in starting with the model 192 and coming up with a product that exceeded the built in capabilities of the 47A and 53A, was funding an an investment that probably wasn't justified by the total expected sales revenue ( whether the money came from Bristols or UK Gov't funds ).

Thanks,
John Dixson

[Tallsar]

Hel1 - i think you missed my point. In the 60s, the RAF only ever had a requirement for 15 Chinnook. It was not the late 70s that some cash was found to buy the 33 to meet a new BAOR task ... And then reluctantly. In other words, there simply was not a requirement for enough Uk built ac for our own services to sustain profitable production. Why would Australia and Canada then buy an overly expensive Belvedere 2 compared with the small number of more cost effective CH47s they would have found cheaper and more supportable. Had the RAF and the Army had the vision to want a lot more in the first place, then maybe a sustainable and cheaper product could have been made. Forget not that with the Defence budget as always under great pressure, all the money in that era was going on Polaris, TSR2 and the reequiping of BAOR with hundreds of tanks etc. You would have found very few voices supporting spending precious R&D money on a large helicopter...and thats in the military staffs, not the government.

[heli1]

Hmmm Tallsar...since when in the 1960-1970s did we ever base military orders on sustainable production ? I'll leave others to produce a list !

Instead I will comment on the proposed Type 191/193 naval variant ,which as the Belvedere picture on Albion shows ,was overly ambitious .However it was sized for the larger HMS Eagle class carrier lifts.As the picture shows there was a novel way of fitting the rotor blades if removed but the 191 had blade folding ,using chinese scaffolding I think to stow the rear set! Certainly I wouldnt have wanted to be working on them on deck in a sea state 5!

Three 191s were virtually completed when the contract was cancelled ,with a vee tail unit (fitted the lift better) and a Wasp type heavy duty landing gear.None were fitted with the intended Leonides Major piston engines and instead were used as Gazelle turbine engine and transmission test rigs for the Belvedere.One eventually ended up in the pit at Ternhill.

The similar Type 193 for the Canadian Navy was cancelled before any were completed and reallocated to the RAF order.Canada went for the CH-124 Sea King instead.

I admit that the whole 191-192 programme was financially a disaster,with all the investment lost , but in terms of keeping the UK at the head of the technology game and independent of foreign powers it was successful. Sadly its demise saw the breakup of a very good design and engineering team and although some of the specialism went to Yeovil to work on Lynx and future projects (including tilt rotors and tilt wings) the tandem rotor expertise withered away.

[Dave B]

The Belvedere had a very interesting starter system for each engine. Their lordships of the Air Council decreed that the aircraft should be independent in the field, of any external starter aids, so the BTH cartridge initiated Avpin system was fitted.

The only trouble was, the Avpin tank was above the cartridge breech, so if there was a seal leak over night, Avpin would fill the cartridge chamber.

The result of this, was that when you went to do the first start in the morning, the whole thing would explode.

The fix for this was to armour plate the co-pilots seat, the rear engine was no problem, as you had enough time to evacuate.

[Paul Cantrell]

Some people posted some really impressive photos of CH47s from the outside, but I didn't see any interior ones, so I thought I'd put up a handful.

http://photos.copters.com/img/v29/p522049218-4.jpg

As a HHGTTG fan, I love:

http://photos.copters.com/img/v33/p452390857-2.jpg

http://photos.copters.com/img/v34/p514080265-3.jpg

http://photos.copters.com/img/v29/p1045095242-3.jpg

Sorry for the poor quality, it was a quick grab of some photos...

These are exterior and not very exciting, but perhaps of some interest:

http://photos.copters.com/img/v30/p571188093-4.jpg

http://photos.copters.com/img/v34/p1048755157-5.jpg

[Rigga]

Wow! After all the development that went into making the 47D/E and they didn't even change the locking wire on the rotor heads!

Nice to see they haven't changed - I used to build 'em at ODI.

[The Sultan]

The Chinook: big, slow, noisy and with a critical flaw. If you hit the interconnect shaft game over as the rotors collide and destroys the aircraft. On the V-22 take out the interconnect shaft and you get a caution light.

The Sultan

[SASless]

So......Sultan.....why have it at all then if it is excess to need? Would the Osprey not be much cheaper to build it did not have one? Is this a Bell way of upping the price much akin to the 500 Dollar Toilet seat or 700 Dollar Hammer we have heard so much of in the past?:ugh:

I guess you shall try to convince us there is no way an RPG could hit an Osprey and not take out an engine and the shaft at the same time....eh?:rolleyes:

Spent a lot of spare time thinking up these kinds of comments during your time off?

I cannot but wait to hear this explanation!:rolleyes:

[HueyDog]

You know, I remember the scandal about those 500 dollar toilet seats and 700 dollar hammers when I was in school and was outraged. Now that I have had plenty of years in aviation and am aware of the cost of aviation related tools and components I realize all of the complaints about those prices were from media idiots and political grandstanding. You can barely buy a nut or bolt from Sikorsky or Bell for those prices and that is on the commercial side, nit the military.

[SASless]

Huey,

Along about that time I was involved in Fraud Investigations for what is now NCIS. In a training class at the Navy Supply School in Athens, Georgia....an Officer there tried to explain away how all that so innocently happened and how there really wasn't a problem and there was no attempt to cheat the Navy.

His example was the accounting method used to figure the costs of each line item within the contract. At the time he was speaking I happened to have a General Services Catalogue on the desk next to my notebook. As he talked, and I was taking notes of what he was "teaching" us.....I keyed on something he said having made the note.

He was talking about hand tools....and how the accounting method was really the problem. He flashed on the viewing screen part of the contract that applied to what he was saying. In that list was a thing called "Device, Impact, Manually operated". A layman would have called it a "Hammer" and a Specialist would have called it a" 12 ounce Ball Peen Hammer".

I went to the GSA Catalogue and roamed through the Hammer section and found literally hundreds of different kinds of hammers, wedges, mallets, ball peen hammers, tack hammers, roofing hammers, claw hammers, sheet rock hammers, brick hammers....you get my point.

He was dumbstruck when I told him of that and the fact at no point was there an entry for "Device, Impact, Manually operated" anywhere in the GSA catalogue.

He got really flumoxxed when I asked him why the builder of the F-18 did not just call it a fecking hammer instead of what they did if they were not trying to pull a fast one?

A hammer is a hammer is a hammer.....is it not?

One outcome of those investigations was a program called BOSS....Buy Our Spares Smart....that encouraged employees to challenge any questionable pricing and rewarded them with percentages of the savings made. A simple practice borrowed from the private sector historically unknown to government.

[joe nelson]

I think, that I have discovered the reason why my tandem loops on take off! I just want to see what the experts here on the forum think... The flapping hinges are too weak that allows the advancing blade angle to pitch up and with precession the result is a pitching up moment at the front of the rotor disk. What do ya think?

[joe nelson]

Guys,

I didn't mean to poo-poo your thread...I was enjoying the war stories very much. I promise not ask any more technical questions!:sad:

[riff_raff]

I think, that I have discovered the reason why my tandem loops on take off! I just want to see what the experts here on the forum think... The flapping hinges are too weak that allows the advancing blade angle to pitch up and with precession the result is a pitching up moment at the front of the rotor disk. What do ya think? Admittedly, I'm no expert on rotor aerodynamics. But I believe the purpose of rotor hinge joints is to make them flexible, not stiff. Blade pitch itself is controlled separately by the swashplate linkage, and not much by the flap hinge. As for asymmetrical lift between advancing and retreating blades, there shouldn't be much in hover/TO.

As for Sultan's comments about the CH-47 being big, slow, noisy, etc., I would not necessarily call the CH-47 slow. I believe it's as fast as the current CH-53, and a bit faster than the current UH-60. The fore/aft driveshaft on the CH-47 is indeed much more critical than the interconnect shaft of the V-22. The forward rotor of the CH-47 is driven by this driveshaft alone, so a failure here would mean a loss of the aircraft.

[The Nr Fairy]

A civilian Chinook was lost near the Shetlands because of this - wasn't the shaft, but the forward gearbox corroded and failed (from memory, correct me if I'm wrong, someone). See AAIB report here (http://www.aaib.gov.uk/publications/formal_reports/2_1988_g_bwfc.cfm).

And as for speed, RAF Chinooks in Afghanistan have been known to outrun their Apache escorts if they need to get back to the medical facilities at Bastion in a hurry.

[joe nelson]

When I was in Vietnam, we routinely had to asked the Chinooks to slow down! :ok:

rif raf,

I was using different hinge materials at that time. I was never sure if it was the design or poor material choices. I later disovered what the problem was...it was my choice of airfoils. I was using an 8H12 airfoil blades that has an up reflex to it. When the blade start to advance, the up relex made the blade pitch up uncontrollable. Over time, I had changed the head design several times but still had the pitch up problem. The only common factor was the 8H12 airfoil. Then I changed the blade airfoil to a profile with a slight down relex...it now works better. The model still pitches up but not to where it's uncontrollable.

Now I'm working on the control mixing. At this scale, any change is difficult. To begin the work on the controls I'm using the MC-4 tandem helicopter's lay-out as a refence. It's the simplest control system that I can find.

[joe nelson]

Nr,

Does the Chinook have a chip detector in the front gearbox? I would have thought that for something as serious as a gearbox failure there would be some indication like a chip light.

[Rigga]

ISTR 5 Mag-Chips - Each Engine Nose Box, Aft & Fwd Boxes and finally the Combiner - all with Fuzz-Burners (well they did in my time!)

Any "Light" deserved a short notice landing - Nowadays I suppose there must be an ultra-serious think about carrying on for more than the current height!

[Hooker47]

I'll have to see if I can dig up some of the cooler pics I have laying around. Of the more unusual are a few of me slinging another Chinook which got shot down while we were in Afghanistan. The bird I was flying was your typical OD green while the dead bird was the new desert tan junk. I'll leave it up to you to determine if this paint scheme is worthy.

[SASless]

Actually....neither paint scheme is worth a damn.

As we do not have to worry about Oppo Air.....thus no need to blend in with the terrain beneath us....why not paint them to blend in with the sky above us as that is the direction the bad guys are looking (generally). If they are looking down at the aircraft....it is from a hill/ridge/mountain and thus close enough to make out the aircraft no matter what color or pattern they are.

[Peter-RB]

Since I started this thread , it seems Ive grown very old, and yet only just seen the pictures of the business end of a 47, looking at the cockpit end it looks and seems just like that of any other large Heli, so how quickly can an existing Heli pilot get to grips with the physical side and fly one away, a Ch47 that is.

Thank you for all the input I have just re-read many of the entrys, and I am still MAD KEEN to get in one and see what happens, I am also green with envy when my boy tells me how good they are in the Afghan area.

Peter R-B
formerly VfrpilotPB

[wokkawarrior]

Evening, does anyone know of any books that deal with tandem rotor P of F?

Ww

[Rigga]

P of F?

And I have to put some other words in to make up some numbers...

[SASless]

The trick to flying the Chinook is learning how small it is.

In time...some folks can get the "feel" for where the Cargo Hook is and how high off the ground the aft gear are....but it is a rare pilot that can also "feel" where the Aft Gear is.

When it came to putting the Aft Gear down on a Rice Paddy Dike....that took some doing. Putting the Cargo Hook into the Hook Up guy's hands was no mean trick but even some never got it figured out.

Pitch Attitude and knowing which particular Pitch attitude was needed or what Cyclic Stick Position was needed when doing maneuvers with the aft gear or sometimes forward gear in contact with the ground took some getting used to as once the gear were on the ground....two inches of aft cyclic glued the gear and then all pitch attitude control was done by use of the Thrust Lever (Collective Lever).

[Madbob]

P of F = Principles of Flight to me. :ok: ISTR that AP 3456 Vol. F might be the fount of such knowledge......

MB

[Rigga]

As I am a mere Rigga; maybe someone could tell me the difference between Theory of Flight and Principles of Flight?

Have I read the wrong books? Or is it just the wrong language?

[Rigga]

Aha! Looked it up on here:
CH-47 Chinook helicopter - Free Maintenance Manuals, Technical Manuals (TM), Study Guides, and other Publications. (http://www.chinook-helicopter.com/Publications/Publications.html)

As I thought it was a language thing (to me)

Near the bottom of the page "Theory of Operation". It doesn't explain/show how the double Mixing Unit works, but it does show how the disks move.

[stilton]

Two questions:


Why is the Chinook so much faster than 'conventional' helicopters ?


Why are there only two wheels at the rear instead of four, surely it would be better to have the opposite arrangement with touchdown on the rear wheels ?

[SASless]

The Chinook originally had two small wheels per landing gear on the rear. When it went to the steerable rear wheel system the Single Wheels were installed in lieu of the double wheels. The much larger tire gives better handling.

The Chinook is fast for several reasons....sheer horsepower is one. Tandem Rotor systems are more efficient than single rotor systems as well.....no loss of power to merely counteract torque of the Main Rotor system.:ok:

Third....the top and lower thirds of the fuselage usually have some hydraulic fluid smeared all over them so it is slippery as an eel.;)

[Brian Abraham]

the top and lower thirds of the fuselage usually have some hydraulic fluid smeared all over them so it is slippery as an eelAnd then there was the indoor shower as well. Wouldn't ever have corrosion problems.

[SASless]

Ah the memories of hot hydraulic fluid, cold hydraulic fluid, pink sticky residue on everything, red hued goat gizzum overing the ramp when doused with rain water made for a skating rink....red tinted flight suits....but she wuz the Queen of the Skies....and still is for kids that could be my Grand Kids.

Except for an EPA waiver....the old girls would require an Environmental Impact Statement for every time they landed somewhere.

[JohnDixson]

Now SAS, this is an interesting thread about a truly terrific machine, but can an early ( 1963-1965 ) driver share just a few recollections?

We had three pre-prototypes at the Test Board at Ft Rucker, and they all shared a common hydraulic system reality, which was about an inch of 5606 red stuff being not-so-gently , " shaken, not stirred " by the not inconsequential 3P vibration levels.

Then there was the speed, with a red line set at 130. Fast forward to June 1966 and I started flying a production CH-53A, every one of which was flown to 170KIAS. It held altitude, ( baro or radar ), heading, and attitude, while in the Chinook, one did all that stuff the old fashioned way. My recollection is that it took decades for the CH-47 to catch up, but catch up they did, and in fine style. An effort by Boeing and the Army which we at SA for the most part watched with a little envy, while we limited improvement of the CH-53 to engines, and one gearbox update, until the 53E.

Oh, almost forgot to mention something that surprised me when it happened. After Desert One, and the Army decision to address the special ops requirements in all phases, we saw the development of the MH-60 and MH-47, at 24500 and 54000 lbs respectively. What surprised me was that, at the time they came out, the Hawk had 2-3 kts on the Hook. I cannot comment on what the MH-47 number was based on. I was surprised because at 24000, that Hawk wasn't what one would term.....speedy!

One of my all time favorite helicopter pictures is the CH-47 in Iraq (Afghanistan? ) with it's rear wheels on the roof of a small mountain-side building, while the cockpit is hanging out over the slope to the valley floor. Certainly speaks to the quality of both the aircraft and those indomitable Army pilots.

Thanks,
John

[Matari]

John D,

This must be the pic you refer to. Lots of nice pinnacle landing shots here (http://www.chinook-helicopter.com/Pinnacle_Landings/Pinnacle.html).

http://www.chinook-helicopter.com/history/aircraft/D_Models/91-00264/91-00264_pinnacle_a.jpg

[JohnDixson]

Matari, those are some very impressive shots in your link. Looks like a lot of talented aviators in those Guard units.

Thanks,
John

[SASless]

John,

I would say that despite the US Army...the Chinook became a graat helicopter.

The CH-34/CH37 had a great autopilot in the thing....but the next generation of helicopters, the UH-1/CH-47 were not equipped with any autopilot....and the great leap forward in the 47 Series....the C Model only added a Pitch Sas Channel that had some sort of Pitch attitude hold capability.

It was not until the advent of the MH-47 did the Army get its head out its ass and consider the Chinook as being something more than a flying Five Ton Truck.

When the UH-60's arrived....they did so without an Auto-pilot. They had a Flight Director system....but it was hand guided.

It took Aviation becoming its own Branch....and Officers being dedicated Aviators rather than Cannon Cockers, Grunts, and worse of all....Truck Drivers....seconded to Aviation for the Army to really progress and begin to embrace technology to improve the capability of the helicopters.

If you remember the wonderful "Tactical Instrument Rating" created by a General Tolson....I once got to remind him of the limitations of that system in a pickup truck ride from halfway between Charlotte and the Adjutant General's office in Raleigh one rainy, murky, ugly day after we parked a Huey in a cow pasture. Shortly after that we began to get all sorts of slots at the Instrument Flying Course where we obtained "Standard Instrument Ratings".

[JohnDixson]

Yes, SAS, I do recall the Tactical Instrument Rating, which came after I graduated from flt school. We got 6 hrs of hood time in an H-19, but luckily, I had a great mentor at the Test Board and the opportunity to practice instruments in our three Chinooks, and I think I could have passed a checkride, but that was beyond the flexibility of the Army system.

Good thing I did that too, because a few months later, due to a tactical emergency situation, our company commander at Pleiku had us saddle up and he led the company out into the monsoon, where 15 minutes later, all 22 of us were in the clouds executing that inadvertent IFR procedure. That nobody died I always considered as one of the missing Augustinian " Proofs for the Existence of God ". ( Another one being that the Pope wasn't killed when he took a ride in the Phillippine UH-60 ).

Thanks,
John

[SASless]

Remember all those hours practicing a Tactical Figure Eight Instrument Approach.....that no one ever...ever dared try as it was absolutely certain you would get Vertigo or get lost in space in some dark, foggy, nasty place?


Re the photo of the Chinook landing on the roof top.....it actually is much easier than it appears.

You position the aircraft over the landing spot so the rear wheels hit the right spot.....lower the Thrust Lever....Collective to the Not Knowing....until the gear touch....bring the cyclic back to the "Two Inch Mark" on the Cyclic Stick Position Indicator (actually about two inches aft cyclic or so....) then simply maintain pitch attitude with the Thrust Lever and yaw control using pedals.....a piece of cake as it replicates the takeoff from the ground maneuver where you do exactly the same thing in reverse.

We used to ground taxi using that method to include backing up....kinda like making Jumbo dance at the Circus....it happens slowly and with some good delay between inputs and outcomes.

The only trick to the landing is if you are sitting out over the wide, wide World on a mountain top or atop a cliff....and then as you cannot see behind you to know where you are relative to the ground....it can get a bit interesting....but that is why you have to trust and rely upon the Crew in the back to help you out by talking you down.

[JohnDixson]

SAS: Tactical Instrument Approaches? In an H-19 with a 2.5 inch, pull to cage attitude indicator and a 6 inch diamer compass card? The 6 hours was spent trying to keep the greasy side down!

This is way off the CH-47 thread axis, but in 1964 I had to ferry an Army H-19 from the West Coast back to Alabama, and got stuck at the San Diego Coast Guard station, where they flew their H-19's IFR. But their instrument panel and radio/nav equipment was far different than what I had. In fact the USCG pilots seemed to be amazed that anyone would actually operate a machine such as I had.

Thanks,
John

[Shenanigan]

Just out of curiosity what was a Tactical instrument rating? Or a tactical figure 8 instrument approach?

[JohnDixson]

SAS or some of the younger guys better answer this as to the details.

All I can add is that beginning in 1966, the new pilots right out of Ft Rucker had this training, and from personal observation, the training in basic instrument flying was very sound. If one had a new kid for a night flight, no moon and iffy weather, and assuming it was ash and trash or something non-adversarial in nature, so to speak, you put the new guy in the right seat and treated the situation as if you had an audio-command auto-pilot. My sense was that it was the basic IFR flight tasks from a standard ticket type of training syllabus, but less the civil nav and approach tasks.

Discussions about this rating tended to be loud and polarized, in my failing memory.

Thanks,
John

[SASless]

The basic difference was the Tac Ticket got no ILS training and very little VOR work but lots of ADF, GCA, Holds, IMC takeoffs from the ground (No outside reference at all)....and standard NDB approaches and lots of Tactical NDB approaches that included NDB and FM Homing Figure 8 approaches.

For the sake of a few hours training on ILS's and a few hours less on the Figure 8 approach....we could have all had Standard Instrument Tickets.

Standard Instrument Ratings were usable in Civilian Airspace....Tactical Instrument Ratings not. In Vietnam did not mean much but once back in real World environments....it meant a huge difference.

The figure 8 approach was one where you did a figure 8 pattern with constant heading segments 15 seconds long after passing overhead the Beacon or the FM radio location (think down to Platoon Level untis using back pack radio's and keying the Mike for you to home to.

You descended all during the approach to arrive at decision height as you approached the beacon or homer transmitter.....200 feet was the minimum as I recall. Visibility was not a factor. Either you could see to land or not....and visual guidance would be assisted by Smoke Grenades, Flares, Flashlights, Zippo lighters or sometimes guys laying on their backs in small holes waving an index finger if it was a really Hot LZ.



I preferred to find the trees....and then home to the location or map read to the place or in extremes do the old "You are getting warmer talk down method".

[John Eacott]

One just for SASless :cool:

http://www.eacott.com.au/gallery/d/6087-2/Chinook+cartoon.jpg



Larger image here (http://www.eacott.com.au/gallery/d/6086-1/Chinook+cartoon.jpg)

[SASless]

Thank you John.....but you ruined my evening! Mere sight of the "Ladder" sends shivers down my spine yet today!

They were one of those grand ideas that Engineers come up with that should never make it past the pipe smoke!:=

By the time you found a clearing big enough to safely use the things.....you could land the Chinook to the ground instead of using the ladders.

Drop the darn things off the Ramp and stick them down into a hole in the Jungle....usually one that had been made by some sort of Explosive device....with all the attendant broken Tree Limbs sticking out in all directions....and odds were you would leave them there as you left.....having cut them away with Bolt Cutters.

The Ladders looked so festive decorating the Trees around the LZ.

Also....imagine the Troops climbing up the darn things...hot, tired, scared, and some rather anti-social locals shooting at them as they clamber up the thing.

All the while....there we were....looking at sure signs we were disturbing folks in the area.

Then for real kicks....do that at night!:ugh:

People wonder why I drink!

Dropping Para's was always fun.....for us.

Slow right down....just above ETL....with all that rotor down flow pouring down behind the Chinook....very interesting parachute openings to be seen! I am sure I have converted some Heathens to Religion doing that!

Advice to you Para's....always make sure the Pilot knows you mean AGL.....not MSL!

[Samaritan]

I have always wanted to know why is there a 100 kts limitation on the CH47 when operating on single AFCS. Any instructors can enlighten me please?

[Boudreaux Bob]

That Limitation is similar to many aircraft with two AFCS systems....the airspeed limit might vary but the concept is the same.

In the "A" model with the "sharp" ended Aft Pylon...when you lost SAS the Yaw Divergence could be extreme particularly if in a turn and out of trim to some degree. The subsequent Models with the "Blunt" end to the Aft Pylon were much more docile but still required some attention when SAS was lost.

Supposedly, the Squared off Aft Pylon gave the aerodynamic effect of 31 feet of Tail Fin in yaw stability. It was very noticeably different than the A Model.

The Bell 412 for instance, has a similar limitation re AFCS.

In the early A Models of the Chinook, it was not all that uncommon to hear the Droop Stops pound when "skidding" after the SAS was turned off with no Warning. Usually, an Instructor only did that once in his career and afterwards there was plenty of warning to the Student. Few of us were really Suicidal or that Masochistic to do it on purpose after a really good fright the first time.

[chinook240]

Until recently, certainly in RAF use, the 100 kt limit applied to single AFCS flight, but if you switched the 'good' system off ie AFCS out, you could use the VFR speed limit ie 150+ kts. Not sure how this fits with the Yaw divergence of A models, but I thought it was to do with the protection against DASH runaway. On a single system you don't have the protection of the other DASH backing off in the event of a runaway, hence the 100 kt limit. If you have no DASHs to runaway then the speed could be unlimited but very tricky to keep under control. What model are you flying?

[Samaritan]

Thanks for both replies, i am flying the CH47D model.

Not sure if i understood correctly but the comments about why there is a 100kts limit with single AFCS operating are

1) 100 Kts is the maximum speed that flight augmentation can be controlled by a single AFCS based on fuselage aerodynamics

2) 100 Kts is the maximum speed that a single DASH actuation motor can compensate for cyclic stick giving enough negative stick to make necessary speed reduction should the need arises since one of the 2 DASH actuaion motors are inoperative?

[The Sultan]

Can anyone point me to the accident report for Columbia's 234 crash in Jan 2013? Interested on why the rotors intermeshed 5 minutes after takeoff. A very intolerant design.

The Sultan

[Boudreaux Bob]

Sultan, you ever heard of Google?

The Report can be found there......how's that for a pointer?

[chinook240]

"100 Kts is the maximum speed that a single DASH actuation motor can compensate for cyclic stick giving enough negative stick to make necessary speed reduction should the need arises since one of the 2 DASH actuaion motors are inoperative?"

Not quite, it's more to do with the speed that the DASH can move, with both operating a single runaway is counteracted by the good DASH running in the opposite direction giving the pilot time to intervene. With one system failed this can't happen, and in a DASH retract at low level, it might not be recoverable at higher speeds.

[The Sultan]

BB

So defensive, sound like SASlass when the Chinook is shown to be a flawed design. I did find this on Google before:

https://www.federalregister.gov/articles/2014/06/30/2014-14800/airworthiness-directives-columbia-helicopters-inc-type-certificate-previously-held-by-boeing-defense

but it is just the clean up actions. I was looking for a report like the AAIB puts out where the facts are detailed.

From the above. The blades voided, probably had water in them, high 1/rev, causing fatigue failure of the aft pylon. Result the same as on a lot of CH-46's with the same result.

The Sultan

[Boudreaux Bob]

Sultan, Christmas Turkey's have nothing on you.

I dare say Barrack Obama has more credibility than you.

It seems you think your keel hauling here at Rotorheads has been forgotten.

You got run off before, you trying for a Trifecta or something?

[Samaritan]

Thanks Chinook240,

I think i kinda get it but could you elaborate on how a DASH runaway in low level and high speeds with one AFCS operational lead to the pilot not being able to have sufficient control of the cyclic to recover? I have never been on any flights where there were training on low level high speed recovery flight.

Thanks for the knowledge

[Samaritan]

Hi,

DASH on the CH47D is supposed to provide positive stick gradient to the pilot on controls can anyone define what is positive stick gradient and explain the concept to me pls.

I understand positive stick gradient as the DASH actuators consistently giving the cyclic/pitch axis more movement travel as the speed of the aircraft increases without requiring the pilot to move the cyclic stick forward. In that way even at high speeds, the pilot will not run out of aft stick when the need comes for a quick deceleration?

can someone do me the favour by verifying my understanding?

[chinook240]

It's not sufficient control movement but rate of control movement that you are guarding against. I don't have access to the manual at the moment but there is a Boeing graph showing stick position with the DASH fully extended and retracted vs speed which would help here.

[Peter-RB]

In 2001 when I started this thread, it was to find out more about the Chinook for it really is a helicopter that always grabs my attention , I will even now pull over and watch them until they disappear from sight, also I am still trying to blag a ride, older and wiser but still like a big Kid when I see them.

A lot of very interesting posts on here, and obvious good knowledge from you lucky people who have steered them.

Peter R-B formerly due to computer cock up VfrpilotPB ;)

[Boudreaux Bob]

Positive Stick Gradient means the Cyclic Stick position is directly proportional to the Airspeed....the faster you go the more forward the cyclic stick will be.

It is more a certification issue than a handling issue.

[Samaritan]

Hi BB,

Thanks for your reply, can i safely assume now that negative stick gradient means there is a chance the crew on flight controls may run out of aft cyclic to retard speed when needed especially since now they will have to pull aft cyclic, bring it back to neutral and pull back again?

Does that define negative stick gradient? and similarly does negative stick gradient also means the characteristic of gaining more speed requires the pilot to push stick fwd, pull back to centralise and then push forward again?

trying to get these basics right

[chinook240]

Doesn't answer your question but a useful link for understanding D model AFCS.

http://usarmyaviation.com/studyguides/index.php?folder=Documents/CH-47%20Chinook%20Specific&download=AFCS.pdf

[Samaritan]

hi Chinook240,

I have read these training manuals as well.

Thanks

[Shawn Coyle]

The difference in maximum speed with only one AFCS operational is due to pilot intervention time if an AFCS runaway happens. With two systems working, if one fails (let's say a roll actuator suddenly goes to full right roll), the other system can take out part of the effect - the pilot has to be 'warned' of the failure - which, like engine failures, will take some finite time to be recognized and then for appropriate action to be taken. It''s much worse if you only have one system working, and it decides to runaway - the pilot recognition and reaction time will be the same, but there is no other AFCS to counter the effect of the runaway - at higher speeds, the failure could be more than entertaining - hence the lower maximum speed.

[stilton]

Can anyone explain this, I understand how a tail rotor equipped aircraft is yawed but what happens when a Chinook Pilot inputs 'rudder' ?

[Tailspin Turtle]

Differential lateral cyclic. With a right pedal input, in effect the forward rotor tilts to the right and the aft rotor tilts to the left.

[stilton]

Ok, understood then, correct me if i'm wrong but neither rotor can tilt forward and aft like a 'conventional' helicopter or it would risk having the blades hit each other ?


Interesting that isn't an issue with the rotors tilting left and right.


So when you input forward cyclic the desired affect is achieved by increasing the pitch on the rear rotor and decreasing on the front and vice versa on rearward cyclic ?

[SASless]

The early models had "Speed Trims" were electric actuators that tilted both Rotors forward as Air Speed increased from 60 knots in order to level the fuselage and reduce drag. As the airspeed decreased the actuators reversed that input.

If the Speed Trims stayed extended....and the aircraft slowed it put excess strain on the Aft Vertical Shaft that connected the Aft Transmission to the Aft Rotor Head.

There were Manual Switches for use in that case that allowed the Pilots to manually retract the Speed Trims.

[Ascend Charlie]

Stilton, look at a photo of a Chook - the blades intermesh and are very unlikely to bump into each other. There is fore-aft movement available.

SASless, there was an interesting accident in Oz back in 75 or 76, the right engine turbine blew out, went through the centre pylon and lodged in the left engine. Along the way it cut through hydraulic and electrical lines. The Chook was carrying 3 bladders of water on a training run, and the pilots tried to pickle the load, being under severe OEI conditions.

But with no electrics, could not pickle load. Loadmaster tried to move through the cabin to do manual release, but slipped over in the gushing hydraulic fluid. Machine could not hold height, and they did a running landing on a flat field - the squishing of the water bladders was a lot more convenient in cushioning the impact than landing on the big truck they normally used.

On rundown, with no electrics, they could not use the sped trim to level the rotors, so the back rotor started to slice through the transmission tunnel and fuselage as it slowed down.

[SASless]

That must have been an exciting few minutes!

Actually they were very...very...very lucky and not for the reasons One would immediately assume.

We had a rash of C Model's with the L-11 Engine without Shot Peened Power Turbine Wheels....that when the Turbines came apart tried to saw the aircraft in half and while doing so....severed the Main Fuel Lines which had (if memory serves me right) about 430 PSI shoving lots of Jet Fuel through some very big Lines. To say that creates a very large fire instantaneously is some understatement.

One aircraft was about 300 feet off the ground and burnt in half before it hit.

For a while we had what we called C- versions....that were retrofitted with L-7C engines which the upgraded A's and regular B's used. That was a very good engine.

[horlick97]

What do you think of this idea:
To have coaxial tandem rotor for the chinook.
The objective is to reduce the rotor diameter, and hence footprint of the helicopter.
With coaxial and the reduced rotor diameter, the vertical gap between the levels of rotors in an coaxial can also be reduced with reduced drag.
Is this worth exploring?

[Watson1963]

Stilton,
The first few pages of this pub show in pictures how the different control inputs are used:
http://www.chinook-helicopter.com/Publications/Theory_Of_Operation/CH-47_Theory_of_Operations.pdf
48mb, but worth a look if you're interested in the Chinook

[SnowFella]

Might not be a wooka but tandems can be darn nimble by the looks of things.
https://youtu.be/xtZpcUj_wqQ
Guess this display would be out of bounds nowadays to say the least!

[Bravo73]

Guess this display would be out of bounds nowadays to say the least!

Why?

There didn’t seem to be anything particularly extreme (or aerobatic) about the display. Modern Chinook displays are far more ‘dynamic’.

[Ascend Charlie]

To have coaxial tandem rotor for the chinook.

Ummm... you can be coaxial, or tandem, but not at the same time, unless you have 2 coaxial rotors at the front and 2 at the back. Somewhat unlikely.

[SASless]

Ok, understood then, correct me if i'm wrong but neither rotor can tilt forward and aft like a 'conventional' helicopter or it would risk having the blades hit each other ?


Interesting that isn't an issue with the rotors tilting left and right.


So when you input forward cyclic the desired affect is achieved by increasing the pitch on the rear rotor and decreasing on the front and vice versa on rearward cyclic ?


A unique result of such a dynamic is upon arriving in a high nose high attitude and gross weight approaching the limits of power.....as you try to lower the nose by applying forward cyclic...you are reducing lift in the forward head and demanding more from the aft head that might not be available.....and the aircraft "Falls Through"....which can result in an unscheduled landing.

The various techniques of flying a Tandem Rotor design, once learned, facilitate takeoffs and landings that in a single rotor helicopter would just not work.

In the Chinook an aggressive combat landing with good visual reference, includes a sideways flair which uses the huge flat belly of the aircraft and the rotor system as "speed brakes".

Rotating the Aft Head outside of the disturbed air of the forward head enhances performance....and if is done with a fair bit of boot at the right time will actually accelerate the aft head transition into translational lift.

The one thing that always caused me to smile was the way the Chinook felt like a Truck driving over a street curb when encountering Thermals....the forward head hits the uprising air and moves up...followed by the aft head which then does the same thing a moment later.

Water landings are the real hoot.....as was pulling water skiers....but the last is a story for another time.

[CobraDriver]

The guys that I know that fly the hook love em, otherwise forget about it. Back when I was at Ft Drum they were trying to give away transitions into the aircraft and the poor guy tasked with going around asking wouldn't even stick his head in the door because he knew books and whatever was nearby would come flying at him for doing so.

[SASless]

I have told this story before:

To convert a Huey/Cobra/Blackhawk Pilot to a Chinook Pilot is simple.

During the first flight for the newbie....one does the old Fort Rucker Instructor Pilot chat while demonstrating maneuvers....the boring kind....and using the most boring tone and cadence of speaking....until the aircraft is light on fuel and you see the Student's eyes glazed over with boredom.

When you know he is no longer listening to you and is day dreaming about being anywhere but where he is....you keep up the boring chat and mention Confined Area Operations....giving the Fort Rucker chat until the aircraft is setting on the ground in the confined area.

Then you begin the Fort Rucker explanation of how to do a Confined Area Takeoff....and at some point the Student gets to say "Clear Right and Up!" as part of the procedure....but he is by now....very...very...very bored.

Then you apply Maximum Takeoff Power....right to the limit....rapidly......and ascend vertically....with your Left Foot stuck well out into the Chin Bubble causing the aircraft to rotate about its vertical axis.....climbing like a Rocket....with some pretty impressive "G" forces due to the acceleration upwards.

As the Student tries to get his chin out of his lap....and finally gets to where he can see out of the Windscreen.....by the time you stop the climb and rotation at 3,000 feet AGL.....you have created a Chinook Pilot!

The sheer power and performance of an empty Chinook is mind boggling!

The rest of the demo is to descend vertically turning to the right....back into the Confined Area and let the new guy try that takeoff for himself.

They are then are properly "hooked".

[JohnDixson]

Correct me if I err, SAS, but a pilot gets signed off in a CH-47 after he/she can demonstrate credible taxi 360’s with four wheels on the ground, without using the left rear power steering ( just unlocking the swivel locks ) and without knocking the droop stops off. oops, now that I think about it, once the rear left power steering appeared, one had to use it.