Thank you Gabi.....what an outstanding find!
I can't believe I never heard of this compound helicopter before....
The basic flying abilities of this helicopter is what I wanted with my gyro design.....all thought up by others back in the sixties.
This machine should have never been canceled.

I'd like to view and compare their rigid rotor assembly to my design.

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Thanks Gab .... I didnt realize how "good" the Cheyenne was .... knew it was fast but heard there was a design error .... but after watching the video it appears not .... man , that thing had a stable hover when it wanted to.

Rotoplane .... I remember (part of) your gyro plans/ideas but not the rotorhead .... were you planning a stabilizer/gyroscope/mixer/thingy as part of the controls ?

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Gabor .... are you able to add something like Lockheed AH-56 Cheyenne to the thread title ???

It would be a good place for us to assemble info on it .... especially the rotorhead .... love this stuff.

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Some question I have off the top of my head ....

--- Bell 47 and Bell Huey use a stabilizer bar as a gyroscope/mixer between the controls and blades .... but that is a 2-bladed teetering system .... completely different (use of a stabilizer) than the Cheyenne which is a rigid system ... right ??

--- Cheyenne has a rigid rotor so the gyroscope-affair is mainly to take care of dissemetry of lift .... right ???? .... or does it do more than that ???

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the two big hangars at Oxnard air port held flight test for the x-51 are now RV storage.
In the past they where the storage area for the program flying over the containers counted over 300 in neat rows
and some days you flew over they inspected the contents and I got to see lots of parts & fixtures being preserved

then one day it all got moved out strange-

the Santa Clareta offices shown is now an industrial park the guard shack is gone so you can explore the area
the whirl tower and gun range are on the back lot of the business park it all still looks the same....

the stab bar does the same for both it's the ridged rotor that makes the difference but later they found you didn't need the flybar at all.....the dissemetry lift problem is all in the blades attachment to the hub. ridged attachment had more control power to keep the monkey business to a minimum.

the blade strap system in the x-51 was bought by Hughes for use in the Apache design

No, wasn't planning to use a stabilizer/gyroscope/mixer/thingy.....didn't think I'd need something like that.
I did believe I'd need a rubber dampened lead/lag hinge to keep the in-plane Coriolis force low enough to allow for a less beefy/lighter head assembly.
I wanted to fold two of the blades for transporting or hangering anyway, so the lead/lag hinge serves a double duty.

Instead of twist rotating the rotorblades for rotor control by using the cyclic stick, I decided to have the cyclic move servo-flaps on each fixed rotorblade, which would keep the cyclic control forces low.
The blades are fixed in the hub at 0° and the servo-flap twists the blade instead of rotating them for blade pitch control.
The blades are not stiff in twist/pitch like normal gyro blades and will not pitch hunt due to the stabilizing effect of the servo-flap.

The needed cyclic stick feedback forces come from a quad spring ring that moves fwd and aft depending on fwd speed and/or rotor disk angle.

I can imagine health and safety having a coronary these days if you sat someone on a piece of wood like kids swing, 16' out to the side of a helicopter...

They would crack a mental over here for sure

That chopper is stunning tho... what a shame it never got produced....

What about the mechanic who had never flown a chopper, flew it back to the shop because he couldnt be bothered towing it

I reckon they must have been TOO easy, TOO far ahead of the others... that powerful ones like Sikorski would have shut them down?

You imagine if someone like Sikorski had spent all this time and money building hard to fly helicopters and some whipper snapper comes along with something a mechanic can fly solo on his first attempt.... that wouldn' t go down very well (especially with creditors)

If that chopper was as good as that video showed it.... the only thing that could have killed it was something sneaky

It was a nice looking chopper as well.... considering what else was available then.... for the 60's, it actually looked very 'modern'

Reminds me of the Sikorsky X-2

So what happened to the rigid rotor technology?

The BO-105 uses a rigid rotor.
Perhaps the most significant feature of the Bo 105 is its rotor blades and rotor head. The rotor system is entirely hingeless, the rotor head consisting of a solid titanium block to which the four blades are bolted;[19] the flexibility of the rotor blades works to absorb movements typically necessitating hinges in most helicopter rotor designs.[16] The rotor blades are made from reinforced-plastic glass-fiber composite material; its flexibility of the main rotor allowed for active elements other than rotor pitch changes to be removed, greatly simplifying maintenance and extending blade lifespan.[20] The reliability of the advanced rotor system is that, in over six million operating hours across the fleet, there had been a total of zero failures.[21] The rigid rotor blade design adopted on the Bo 105 has been partially attributed as responsible for the type's agility and responsiveness, it remained an uncommon feature on competing helicopters throughout the Bo 105's production life.[17]

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According to Lu Zuckerman

The Cheyenne was very stable in a hover with minimal impact due to the wings. In a hover the propeller was in flat pitch and the driving power was absorbed by the tail rotor. The pilot would introduce cyclic pitch and the helicopter moved forward in a conventional manner. Once the helicopter was at speed the pilot had a beta control and he increased pitch in the propeller and reduced tail rotor pitch and now the propeller was absorbing the power. The pilot would lower collective and at this point the wings were providing the lift. In this situation the helicopter was an autogyro with flight control being provided by cyclic input.

The pilot could also place the propeller in reverse pitch and this would counter the forward thrust of the rotor system. This allowed the pilot to place the helicopter in an inclined attitude relative to the horizon making the helicopter a very stable weapons platform.

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According to Lu Zuckerman

At high speeds the helicopter rotor system became unstable. This could have been caused by one of two things.

1: Autogyros (certain types) use the rotor system as a means of control and the rotor is at flat pitch. With the introduction of forward cyclic input the blades can go to negative pitch causing the blades to flap down and make contact with the fuselage. This is the situation with the Cheyenne and on two occasions there was rotor incursion and in one case the rotor disintegrated and caused a great deal of damage to a wind tunnel. In the other case the pilot was killed.

2: The rotor blades on the Cheyenne were very stiff as compared to a conventional helicopter blade. The Cheyenne blades were also different from other helicopter blades of that time period. At each blade station the aerodynamic shape of the blade was different which introduced a degree of instability. The changing of the blade cross section coupled with the blade stiffness effected the phase angle of the blade and the pilot would never know where the disc would dip down with cyclic input. This unstable blade condition may have been the cause of the two incidents mentioned above.

It took two years of design development by Parker Bertea and they finally solved the problem of variable phase angles. Although the design changes gave the Cheyenne a very stable and vibration free ride the design was too complex and it contained a large number of failure points that were catastrophic in nature.

The Army cancelled the program and opened bids for the new AAH. This led to the Apache contract won by Hughes.

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According to Lu Zuckerman

It is true that the system was unique and it was completely different from any other helicopter flight control system. Mounted on top of the main rotor was a gyroscope that was driven by a constant velocity joint attached to both the rotorhead and the gyroscope. The gyroscope was made of four tubes in a cruciform shape. Attached to the end of each tube was a heavy weight that looked like a large tin can. A stout cable connected the four arms and kept them rigid and restricted any in plane movement. The gyroscope was installed so that each arm extended between the blades so that they were 45-degrees from the two blades. The gyroscope arms also had a pitch horn the led the control arm by 45-degrees and attached to the blade

The gyroscope under rotation had the capability to exert a very high degree of force if it were nutated by control input. Being a gyroscope it would respond 90-degrees in the direction of rotation when a force had been applied to it. The control inputs to the gyro were pitch rods that ran through the main rotor mast. These rods were in turn attached to the swash plate which was mounted to the underside of the transmission. Pitch links ran from the stationary part of the swashplate to a servomechanism. The collective stick and cyclic stick drove the servomechanism via a mixing unit. The output of each servomechanism was connected to a horseshoe shaped spring, which was connected to the swashplate by the previously mentioned pitch link. The gyroscope had rigidity in space so when the pilot displaced the servomechanism it compressed the spring, which was resisted by the rigid gyro. This applied force causes the gyro to precess inputting a control force on the blades changing their pitch. With rigidity in space the gyro would hold the position causing the rotor system to align itself with the plane of rotation of the gyro. This allowed the Cheyenne to fly like a fixed wing aircraft and not like a helicopter.

Even though the gyro had a 90-degree phase angle the blades did not. Therein lay the problem.

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According to Lu Zuckerman

Early on in the program the Army asked Lockheed to add on additional equipment increasing the gross weight. This taxed the lifting capabilities of the rotor system and Lockheed requested that the Army allow them to increase the rotor diameter along with attendant design changes. The Army refused so the aerodynamicist (Ray Prouty) had to redesign the blades to increase lift. This lead to the multiple aerodynamic shapes at the different blade stations. This coupled with the blade stiffness had a severe impact on blade stability and the shifting of the phase angle. The rest is history.

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According to Lu Zuckerman

One of the things that help kill the Cheyenne was that it had a very low degree of maintainability. It had the complexity of a Century series fighter and the Army mechanics were completely unable to maintain it. The Army did not learn its' lesson because the Apache was even more complex and it too had a very low degree of maintainability.

The Army and Air Force were constantly arguing about what types of aircraft the Army could fly and the missions performed by the Army that were normally performed by the Air Force.

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HINGELESS ROTORCRAFT FLIGHT DYNAMICS
K. H. Hohenemser
Advisory Group for Aerospace Research andDevelopment
Paris, France 1974
http://www.vectorav.com/docs/a007953.pdf
(Lots of info on other hingless systems ... Sikorsky ... Bell .... Westland .... Bolkow)
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Aint that typical

They built something good, then the militery wanted to load it up with killing shit and decided it couldn't lift enough

But why would you build a military piece of equipment without all the killing stuff?
That takes all the fun out of it.



http://www.gifbin.com/bin/032014/139627 ... lares.webm

http://www.gifbin.com/bin/082009/125067 ... e_gun.webm

Very cool interesting stuff in this post!