A question for Chuck Beaty.

joe nelson

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Chuck,

On your three bladed helicopter head, what material was it made from...it looks like it might be fiber glass? If it was, was it built to be rigid or soft in plane. Next question; What did you use for your drag dampers? Thanks!
 

C. Beaty

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The first hingeless rotor Joe, first flown in the 1970s, consisted of a hub made from a 3/8” thick, triangular aluminum plate with feathering bearings at each apex. The hub was made from 4 sheets of 3/32 aluminum, structurally bonded together. First flown on a Bensen derivative and later on a helicopter. There are clips on youtube.

The second, flown in the late 1980s, had a hub made from filament wound “S” glass. There was sufficient flex for coning but it was quite stiff in lead-lag.

The hubs were semi floating, connected to the machines with rubber pads.

If the hub is allowed to align itself with the tip plane axis, there is neither inplane motion nor cyclic flapping.

Picture a shallow sheet metal cone, driven at its apex by a constant velocity universal joint. Does any molecule of metal in the cone try to slow down or speed up? Does it “flap”?

Slit the cone into segments to mimic rotor blades and nothing changes. With individual blades hinged directly to the rotorhead, flap and drag hinges are a geometric necessity to accommodate the differences between the rotor’s axis of rotation and the rotorhead’s axis.

I said CV “U” joint but that really has nothing to do with it. The momentum of the rotorhead is irrelevant compared to the rotor’s momentum.
*************
Google Doman helicopters for more about rotors without flap or drag hinges.
 
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joe nelson

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Thanks Chuck!

Let me see if I have the concept...A floating hub needs no flapping or drag hinges because the rubber bumpers allow the hub to stay aligned with the tip path plane. Is this correct so far? Then the blades are rigidly attached to the cone and controlled through normal blade pitch changes.

Does this type of head with three blades have the same 3/rev vibrations as any other system? What determines the distance between the hub and the rubber bumpers?

When I was looking up your U-tube video, I found some footage of the Doman LZ5. The narative said the Navy was interested in using the Doman system on all of their helicopters. Do you know any of the history behind this? What's your opinion of the system after building and flying it.
 
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C. Beaty

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The biggest difference from a pilot’s perspective, Joe, is the loss of feel when going from tilt head control to swashplate control.

If a gyro is stable, it is easily managed.

An unstable gyro can become very difficult to fly without some form of Bensen offset gimbal rotorhead. I’ve flown an unstable gyro with what amounts a Bell-47 control system and it becomes a full time job just to stay right side up.

There isn’t much difference in vibration between a fully articulated rotor with flap hinges on the center of rotation and a floating hub. Offset flap hinges are a different story.

The Sikorski S-51 had central flap hinges (and identical “mast bumping” propensity to any seesaw rotor):

http://www.b-domke.de/AviationImages/Rotorhead/8951.html
 

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joe nelson

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The semi floating head sounds very interesting but it looks like a nightmare to build. This type of head doesn't need an offset because it's quasi articulated does it? It would be more like the heads on the AS18 and J2 wouldn't it?
 

C. Beaty

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The most difficult design problem in any rotorhead is the feathering bearings.

A stack of tapered race ball bearings, resisting several tons of centrifugal force, with friction no more than a few ounce inches is not a job for amateurs.

The UltraSport series of helicopters were thoroughly professional designs by moonlighting Boeing engineers that used a multistrand loop of music wire embedded in polyurethane for feathering bearings. It was done in by lack of a suitable engine.
 

joe nelson

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I guess that's why the type of head that you used had no hinges? It was mechanically simpler than say a fully articulated one...I'm finding simplicity is hard to design and it has a quality in it's own right. I enjoy working on duplicating different types of rotor systems just to understand the how and why they work. I have been a fan of hingeless systems and elastomeric materials for a long time. I think that I'll kick the floating hub idea around for a while to get a better understanding of the physics of it....thanks!
 

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Chuck- I just wanted to comment on you mentioning the complexity of making the feathering bearings. My Helicycle has elastomeric bearings for the feathering bearings, and they are simply a delight to feather the blades with so little force. You of course don't need to be told that these elastomeric bearings are many layers of metal and an elastic product all specially bonded into a stack that can twist on its axis. To extend the life of these bearings, we Helicycle pilots are instructed to pre set the collective to lock in several degrees of pitch into the rotor blades. When the blades are halfway thru to flight rpm, these bearings are locked in, and now they won't have to flex as many degrees during the flight had the rotorblades been spuun up with full down collective. This does add a little more wear on the drive belts during spinup, as they are also pumping air a little. Stan
 

C. Beaty

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The BO-105’s feathering “bearings” aren’t too shabby either, Stan.

The cross resting on top of the bearing housing is the shim pack. These are individual shims running straight from one blade to its opposite neighbor. Looks like a 4-pole affair but I don’t think so.

In any case, ball bearings are out. Modern stuff uses either rubber or some sort of torsion pack.

But the torsion pack has gone full circle. The Bell-47 used a torsion pack for collective. Hafner, in the UK, used torsion bars for both collective and cyclic in the 1930s.
 

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StanFoster

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Chuck- You are just a never ending well of knowledge. Thanks for sharing so much of that here. Stan
 

joe nelson

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Chuck,

Stan's right! You are definately the go to man! Thanks for your patience with us who ask dumb questions!
 

joe nelson

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I was working on a strap pack for a three bladed head. This strap has been sitting around in my shop until I get a better understanding of hinges. It is made of .018" thick, 316 stainless steel. The number of straps would be determined by the blade weight and be held in place by a cuff like the one on the H369 head. The cuff would hold the drag damper but this is way way down the road! I will eventually make the straps from 355 stainless steel but again way down the road. My intent was to mount a 10 foot wooden 8H12 blades for my test stand but again way down the road.
 

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C. Beaty

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Here’s how a sheet metal cone, driven by its apex would look.

It doesn’t flap, it doesn’t speed up, and it doesn’t slow down, whatever angle it makes with its drive shaft. Each particle of metal in the cone travels in a perfectly circular path at uniform angular velocity.

Slit the cone into segments to mimic rotorblades and nothing changes. Each rotorblade travels in a perfectly circular path at uniform angular velocity.

Now the kicker: Hinge each rotorblade to the driveshaft solely by a flap hinge and blade tips cannot follow the path of the cone rim at uniform angular velocity; tips are forced to speed up and slow down. Drag hinges are required to permit then to rotate at uniform angular velocity.

Drag hinges accommodate an error in geometry.

The nature of the universal joint is irrelevant to this discussion. Certainly a Hooks (Cardan) joint has an angular error but that is normally accommodated by some sort of elastic coupling.
 

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hillberg

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The Bell 47 is all bearings it has no (T/T)strap pack the T T strap was in the Bell 206 ,204 & 205 , Hiller has the strap pack.
 

C. Beaty

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I’m glad you got it, JCC.

A rotor is a difficult problem in spatial visualization, the ability to manipulate 3-D mental images. Men are better at this than women, left handed people better than right-handed people.

Both Isaac Newton and Leonardo de Vinci were lefties.
 

Passin' Thru

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I’m glad you got it, JCC.

A rotor is a difficult problem in spatial visualization, the ability to manipulate 3-D mental images. Men are better at this than women, left handed people better than right-handed people.

Both Isaac Newton and Leonardo de Vinci were lefties.
Chuck, is that the reason you read magazines from back to front? :noidea:
 

J.C.Casabuono

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My first son was some sort of ambidextrous, and he had sometimes wrote in "Mirror" like Leonardo Da Vinci when he start to go to school, it was corrected by some good hits, of course ;)
 

joe nelson

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Watch out, Joe's been down in the shop, lol! This is a miniture image of what I understood. This is a small driveshaft passing through a UHMW piece (bushing) to a universal joint connected to a cone. The blades are attached to the cone and control is done through cyclic control of the blades...right?
 

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