the Intermeshing Configuration is Best

[Dave Jackson]

Nick,
>NL- True enough, but it also shows 90% commonality with a co-axial, clearly within the accuracy of our "PPRUNE Engineering" According to the data I looked at today (This web site makes me work on Sunday!!) the negative effects get large at 50% overlap, let alone 90%. While it would be better than a straight forward coaxial, the difference would not be thundering.

I still believe that the lift distribution of the intermeshing configuration cannot be equated with the coaxial. This will be particularly true in fast forward flight. Please remember that we are not talking of the Kaman synchropter. We are talking of a 'head to head' contest between comparable single-rotor and intermeshing-rotor helicopters.

The intermeshing may only offer a 10 to 15% advantage over the coaxial in hover, but in forward flight, the difference will be significant. The following is a sketch showing the lift distribution for an intermeshing helicopter in forward flight. http://www.synchrolite.com/Lift_Distribution.html

This difference becomes even more significant at very high forward velocities, and if flapping is reduced, or eliminated. (ref: Figure 3.15 Helicopter Performance, Stability and Control ~ Prouty). This is where the [intermeshing & ABC] marriage comes into effect.


If you agree with the above, please don't let Sikorsky patent the idea . My long-standing position on this particular idea and any others on my web site is that they are, and will, remain open and available to all.

______
Sketch revised

[ 28 August 2001: Message edited by: Dave Jackson ]

Comments revised

[ 28 August 2001: Message edited by: Dave Jackson ]

[Cyclic Hotline]

Dave,
Getting back to the topic of Intermeshing rotor desynch's (sorry to keep bringing this up).

NTSB Identification: MIA83FA183 . The docket is stored on NTSB microfiche number 22314.

Accident occurred Thursday, July 14, 1983 at NEAR CLERMONT, FL
Aircraft:KAMAN H-43B, registration: N57996
Injuries: 1 Serious.

The helicopter crashed in an uncontrolled descent from a hover. A witness stated that the helicopter was slowing descending to position a 150 ft line for the ground crew when he observed something separate and the helicopter came down in a vertical descent. Investigation showed that the transmission and rotor assemblies separated in flight. The engine continued to operate after the crash and had to be shut down. The pilot sustained a head injury and does not recall the accident.


The national transportation safety board determines the probable cause(s) of this accident as follows.

Rotor system..separation
Rotor drive system,main Gearbox/transmission..separation

NTSB Identification: SEA93LA105 . The docket is stored on NTSB microfiche number 50380.
Accident occurred Wednesday, May 12, 1993 at ANATONE, WA

Aircraft:KAMAN HH-43F, registration: N846D
Injuries: 1 Fatal.

The converted military helicopter was in a hover lifting an external load of logs when the main rotor pylons separated in flight, resulting in an uncontrolled inverted descent into the ground. On-scene examination revealed that the transmission rotor input gear shaft, Pt/no: K774515-5F, had fractured. Safety board metallurgical examination showed that the fracture was characteristic of fatigue failure, and indicated repetitive high loads. The FAA type-certificate, based on military configuration, lists the approved engine as 1100 shp, and the external load limit as 2,300 lbs. The FAA had approved installation of a 1400 shp engine, and operations with an increased external load limit of 4,000 lbs.

The National Transportation Safety Board determines the probable cause(s) of this accident as follows.
Fatigue failure of the rotor transmission drive system, resulting from the improper certification/approval of the aircraft modification by the federal aviation administration.

I cannot quantify the overall number of accidents in commercial operation as I do not have access to the hours flown. However, from a very small fleet, there seems to be quite a number.

The same is true with the K-Max. A recent news report states that the the fleet leader has recently turned 10,000 hours. So with a relatively small fleet and overall low hours, I would not rush to too many assumptions.

H-43 is correct, they are really stout and simple machines - certainly Kaman's trademark, and one which is hard to beat in the real world of making money. The longevity of the aircraft is a pretty fair testament to that.

I have a number of acquaintances who have both flown and operated the H-43. One told me that when firefighting for the State of Washington Department of Natural Resources(DNR) they would always arrive on the scene of the fire at the same time as everyone else left, as they were so slow! (made for a very casual and relaxed summer)

I thought that the funniest comment however, was a mechanic who told me that there was no doubting that the machine was built by a bearing company. "You've never seen so many Kaman bearings in one place before, nor a piece of equipment that can use 'em up so fast!"

Now, about that weird control reversal deal - can't say I've run into that to many times before!

[Dave Jackson]

Help! You guys are ganging up.


tgrendl

>Do you or does anyone know a valid way to model the drag effects at the combined rotor mast/ fuselage area?
I have a feeling that this region may be a "try it and see" area in your testing.<

Your "try it and see" appears to be the answer of the professional designers, as well. All the books seem to mention that the mathematical and the testing methodologies can produce fairly different results. Mind you, some of these books are a few months (years) old and things sure change fast.

There appears to be a strong consensus that streamlining the rotor hubs and associated control linkages is very beneficial in reducing drag. One book mentioned the additional advantages of locating the hub close to the fuselage, then streamlining them together.

Here again, Nick is probably at the cutting edge.
__________________

Kyrilian

You've covered a lot of territory. So here goes a weak attempt at a rebuttal.

Thrust:
There are virtually no calculations available on the intermeshing. Much of the work must therefore be 'guestimates'. The side-by-side configuration is the optimum for thrust. In fact, it has been reported that an adjacent side-by-side give more than twice the thrust of its individual halves. The synchropter will come somewhere between the side-by-side and the coaxial. Hopefully, my sketch to Nick shows that the intermeshing is significantly better than the coaxial.

It might also be noted that in the early forties weight to thrust was very critical and yet Sikorsky and Flettner were able to produce comparable helicopters, with the Flettner being the alleged faster of the two. The image of the Kaman synchropters must be put aside.


>Adding another rotor will increase profile power (more blade area being spun through the air),<

If the two sets of blades are identical then the profile power of a 4-blade single rotor and that of twin 2-blade rotors should be very close.


>from what I've heard the coaxials and intermeshing rotor helicopters leave something to be desired when it comes to yaw control, especially in low/no power conditions.<

I have spoken to the Canadian pilot of a Russian coaxial, which is used for logging. The helicopter uses differential collective for yaw and he makes any minor trim adjustments that are required before taking off. He said that the helicopter was quite responsive and that there was automatic pedal reversal in the event of an autorotation.

I understand that the K-Max has an extended empennage to provide better control that that of the Huskies, and they uses differential longitudinal cyclic in addition to the differential collective. Of course, the pilots of the Huskie can provide the best answers.

It may be of interest to know that the Flettner intermeshing helicopter supplemented it rotor control with elevator and rudder control.

______________

Cyclic Hotline

Oops! Two failures.

Your comments on the drive train and yaw control aren't too good.

Mine you, this is offset by your jokes, which aren't too bad.

[ 28 August 2001: Message edited by: Dave Jackson ]

[tgrendl]

Dave,

Thanks. I've gotten the feeling that Nick was right much earlier (different thread) when he said that a lot of science goes into the design and then a lot of engineering gets applied to it (variable cams, trial and error etc).

It seems as if this is a repeated cycle of development in most helicopters that make it to the flightline. Idea, refinement, mathematical modeling, refinement, scaled modeling, refinement, full scale, testing, refinement, envelope creation, production.

If you have a list of things that are holding you back on yours could you share the particulars? I would guess the people on the forum would be happy (time permitting) to put their brains to use on identified problem areas. Or at least to try.

You never know, you may get something good out of it and I'm sure the problems you pose will help educate everyone.

Always enjoy your posts,

[Lu Zuckerman]

To: tgrendl

I would like to add to one of your statements.

It seems as if this is a repeated cycle of development in most helicopters (or any other complex systems) that make it to the flightline (or the road or, whatever). Idea, refinement, mathematical modeling, refinement, scaled modeling, refinement, full scale, testing, refinement, envelope creation, production and final wringout of overlooked problems by the operator.

[tgrendl]

Hi Lu and you're right. The wringout feedback loop was left off by accident.

I know that Macdac tried to do this with the IKPT on the apache but they still overlooked a few things.

BTW, your helo pilot joke wasn't complete.

It ended by that lady looking down at me and saying "now, who could you make happy with that?"

My answer, of course, was me.

[Dave Jackson]

tgrendl

>If you have a list of things that are holding you back on yours could you share the particulars? <


Thanks for the offer of assistance. It would be hard to think of where to start.

These discussions are very informative and interesting. This specific thread has highlighted numerous concerns, such as mechanical synchronization reliability and a reevaluation of the rotor efficiency.

Nick and many others would be surprised at the number of times their nuggets of wisdom have been clipped and posted in my scrapbook (web site).

[Nick Lappos]

Dave Jackson,
Regardless of what we kibitzers here may think and ponder, the credit goes to the guy who builds and flys the machine! Go and do it, and tell us how it went.

I suggest a scale model, with a good rc system and a tie down phase as a great way to model the aerodynamics. A pair of electric motors (with a simple synch gear set to maintain order) could serve as the power plant. You could measure power consumed through the tether/feed line as you test it.

Good luck

[heedm]

Dave, lots has been said about efficiencies of the intermeshing rotor. One problem I can see is the rotor disks are tilted from the horizontal (12.5 degrees in your design). This means that only a fraction of the lift is countering gravity.

It works out to 97.6% for a 12.5 degree tilt, but that still means there is a 2.4% loss due to design, not yet accounting for aerodynamics. With tail rotor losses of 3-6% I think that this number is significant.

Of course, all rotor disks tilt from the horizontal, but there is a purpose to that tilt. In this case, the lost power just works against the lost power from the other rotor.


Another area where I see a loss for the intermeshing rotor is when you compare it to a single rotor, "head to head", with the same engines, same disk loading, and same fuselage, you would need a smaller rotor diameter for the intermeshing rotor. The loss is found in that there is a greater percentage of fuselage blocking the disk.


I think you may be right that it is a more efficient design, but it won't be any easier to fly. The four axes of control will still be required, the "inherent instability" is a result of the required agility to precisely hover. The only thing that will make it easier is you won't have to change your yaw inputs when you change your power...that part isn't that tough.

The rotor governor will make things safer for engine failures in a particular envelope, but unless the pilot can instantly override it, there are some flight regimes where a governed rotor will kill you in an engine failure. Granted, for the commuter taking off and landing in open area pads, the restricted envelope should suffice.

Time to stop rambling.


Matthew.

[tgrendl]

Dave,

At your target weight a ballistic recovery system (or two) should alleviate some of the concern regarding reliability, at least for test flight.

A well designed safe area for the squishy thing (pilot) operating the controls will help too.

I'd think also that a rotor governer could be replaced by a sprague clutch setup at the right place.

Engine power direct to main gear reduction and then a sprague prior to splitting the mechanical power. The only differance would be that the rotor rpm would have to be adjusted to allow it to drive a small set of gearing in autorotation. This would also allow for any mechanical power taps you needed in growth.

What powerplant(s) are you looking at?
Output shaft speed?
Output torque?
Final rotor rpm?

If you have time, not ganging up on you.

I'm trying to imagine what your helicopter will sound like.

[Dave Jackson]

A general overview.

No single helicopter can be best for all missions, but, based on ease of piloting and a resultant popularity, I claim that the intermeshing configuration is unquestionably best. The intermeshing is the only realistic configuration that can provide the symmetry of an airplane. Even the coaxial does not have absolute symmetry.

The question of the intermeshing helicopter's thrust to empty weight has been raised. The single rotor may well have a slight advantage in this department, but consider the popularity of the automobile. Only 10% of the BTU's that a car consumes go to propel the vehicle, and only 1% of the BTU's are actually use in transporting the occupant. Maybe the Dutch and the Chinese are smarter then most of us since they tend to use the much more efficient bicycle

My positive attitude toward the intermeshing configuration has little to do with the design and functionality of the current synchropters. It is based on Flettner's helicopter and the direction that he and Hohenemser could have taken it.

A gentleman has assimilated a considerable amount of material on the Flettner FL-282. He has even produced the construction drawings of the fuselage and cockpit, with the intent of building a full scale operational replica. He has been very generous in passing on, over a period of time, copies of much of this material. The more I read, the more impressed I became at the technological beauty of this helicopter and its configuration.

Few people would question the technical competence of the German's preceding and during WW II. It might be of interest to know that there was an alleged contract with BMW for 1000 FL-282's. Unfortunately for Flettner, he faced a few obstacles that most of his contemporaries didn't, such as having his manufacturing facilities bombed on two separate occasions, plus being on the loosing side.

I believe that the 3-bladed self-stropping Kellett helicopters and Kaman's use of the Italian servo-flap did little to advance the development of this configuration.

_________________

For those who are still following the 'hype' and would like to dig deeper into the Flettner FL-282, the following page may be of interest: http://www.synchrolite.com/0474.html

_________________

heedm & tgrendl

Thanks for your concerns. Intelligent response coming ~ hopefully.

[ 29 August 2001: Message edited by: Dave Jackson ]

[t'aint natural]

Any MD people on this thread...? Earlier inthegreens and Nick Lappos dismissed the Notar as requiring substantial antitorque power even in the cruise. I always thought the offset vertical stabilisers unloaded the tail in cruise and the compression fan pretty well idled along in flat pitch. Am I misinformed?

[Dave Jackson]

Thanks for the constructive criticism.


heedm

>One problem I can see is the rotor disks are tilted from the horizontal (12.5 degrees in your design). <

This should not be a serious problem. As you mention, the vertical component of thrust is still a healthy 97.6%. The 'theoretical' UniCopter has rigid blades and therefore its current angle is 9-degrees, resulting in a vertical component of 98.8%

In opposition to the western perspective ~ " .... the single-rotor helicopter's tail rotor power consumption accounts for 10-12% of total power." ~ Eduard Petrosyan, Deputy Chief Designer of the Kamov Company


>you compare it to a single rotor, "head to head" .... would need a smaller rotor diameter for the intermeshing rotor<,

This is an important but difficult area to discuss since there is no rotor performance data available on the intermeshing configuration. The downwash on the fuselage is not a serious problem because the intermeshing rotor cutout is quite large. My earlier downwash chart to Nick L. makes it appear that, theoretically, the synchropter is not too bad, particularly in fast forward flight. Ivo, of Ivo Props built a simple little intermeshing helicopter years ago and although it never left ground effect, he was surprised by the small amount of power it required.

The following web page should be informative to anyone who has an interested in the coaxial helicopter, and it may be of particular interest to Nick L. http://www.kamov.ru/news/petr11.htm


> ... it won't be any easier to fly. <

Symmetry of flight controls is a given and cross-coupling should be reduced, but your point is well take, particularly in respect to SynchroLite. It was this concern that prompted the UniCopter development. The intent here is that the rigidity of the rotors will give a faster and more precise response; which is an extension of Nick L. comments on piloting the ABC.


> The rotor governor will make things safer for engine failures in a particular envelope, but unless the pilot can instantly override it,
<

The pilot has the ability to instantly override the rotor governor. My understanding of the 'basic' difference between an engine and a rotor governor is, that with one; pilot input is required to put the craft into autorotation, whereas with the other; pilot input is required to prevent it from going into autorotation. Some additional 'dry' information is available at: http://www.synchrolite.com/Governor.html

_______________

tgrendl

> At your target weight a ballistic recovery system (or two) should alleviate some of the concern regarding reliability, at least for test flight.<

The current method is to hang a St. Christopher medallion. Your idea may work, as long as it is possible to 'get around' the intermeshing rotors.


> I'd think also that a rotor governor could be replaced by a Sprague clutch setup at the right place.<

A Sprague (overrunning) clutch is definitely needed, where you suggest. The rotor governor would serve somewhat different functions and would be a later add-on.

>I'm trying to imagine what your helicopter will sound like. <

Probably like a lawn blower.


> What powerplant(s) are you looking at?
Output shaft speed?
Output torque?
Final rotor rpm?<

Since you asked.
http://www.UniCopter.com/UniCopter_Reciprocating.html http://www.UniCopter.com/UniCopter_P...ccessForm.html
http://www.SynchroLite.com/Reciprocating.html http://www.SynchroLite.com/PowerTrainAccessForm.html

[ 29 August 2001: Message edited by: Dave Jackson ]

[ 29 August 2001: Message edited by: Dave Jackson ]