Weight question for C Beaty

skyguynca

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Hi, been a while since we have chatted. I still have a few of your early videos and pictures that you had sent me on your 3 bladed head from your gyro and heli. I was throughly intrigued with both the aluminum plate version with the engine mount blade attachment lead/lag flap arrangement. Also the fiberglass wound head, both show alot of innovation on your part and alot of skill in fabrication.

I just recently started looking at your "Dudely". Again another example of knowledge and skill put to proof of concept. Great job.

In reading your post about the 2 rev and having to use the slider head, reading through all the posts and emails we have sent back and forth I was wondering what was the weight of the Dudely and of the 3 bladed helicopter?

Could a marriage of the two concepts produce a new hybrid of the designs? I was thinking to bring the weight down on the head assy, we had discussed in a old email the 3 bladed design but with something like the Hughes laminate assy but in a simpler form because of the less weight and less complexity.

What do you think? Does it warrant a good old discussion or maybe just the round filing cabinet?

David M.

Oh my email address is still [email protected] if you would like to talk off list and discuss this further.
 
If I ever got the urge to build another 3-blade rotor, I would build a rigid system patterned after the BO-105, using fiberglass bars or rods between feathering bearings and blade roots.

Flapping and lead-lag motion is minimal if mass can be located as near to the rotor center as possible. That requirement pretty much rules out a gyro. The BO-105 mounts engines/transmissions just below the rotorhead.
 
Rigid rotor huh? I can not even begin to think of how to handle the vibrations for such a set up. I have seen the BO105, beautiful head design even as old as it is. Then again it is one of the few aerobatic helicopters out there.

How can the vibrations be handled from the lack of lead/lag abitity and no flapping?

Bo105-Rotorkopf-gross.jpg
 
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If a conventional helicopter had a sliding balance weight that could be slid back and forth, changing fuselage attitude so that the powered shaft axis was always concentric with the rotor tip plane axis, there would never be cyclic flapping or in-plane motion. The swash plate with its cyclic pitch control would attend to the dissymmetry of lift.

A rigid rotor machine does what amounts to the same thing; the rotor stiffness ensures convergence of shaft axis with tip plane axis. The rigidity is not absolute; there is a slight divergence between tip plane axis and rotorhead axis but it’s near enough that flexibility of fiberglass hub bars take care of that.

A rigid rotor machine must avoid large pendulum effects by bringing the heavy stuff as near to the center of the rotor as possible.

Rotor motions are relative anyhow. Viewed along the rotor’s tip plane axis, there is no flapping or lead lag; only cyclic feathering.
 
Weight distribution

Weight distribution

Chuck,
I am a little confused with terminology. By definition, doesn't the tip plane axis coincide with the drive axis on a rigid rotor head?

By sliding a weight around aren't we trying to align the CG with the drive axis?

The BO-105 seats six, with the front seats occupied and a tail rotor that is 12-15 feet behind the main rotor, doesn't that provide a weight distribution that is more spread out than most gyros?

I'm still contemplating a three blade head for my gyro and this is a fairly simple system that looks like it might be lighter than a tilt head with flapping and lead lag hinges.

I am also considering a partially driven rotor and would assume that the same constraints apply. The partially driven rotor complicates the head design considerably for the tilt head, but seems reasonable for the rigid head.

Or am I in la-la land?

Thanks,
Larry
 
If a rotor system was perfectly rigid, Larry, then of course tip plane and rotorhead axes would coincide. But such is not the case; long skinny rotorblades have a certain degree of flexibility and it’s better to have the flexing confined to a fiberglass root extension. Even the Lockheed Cheyenne with stainless steel rotorblades had flexural members as part of the hub.

A floating hub system such as the one I built with fiberglass hub is related to a hingeless system like the BO-105 inasmuch as in the first case, the hub is pulled into alignment with the tip plane axis whereas in the second case, the complete machine is pulled into alignment with the tip plane axis.

Here’s a picture of the BO-105 internals. The torsion pack is shown on top of the hub. I think but don’t know that it’s not really a cruciform section; it’s actually interleaved torsion straps running between opposing pairs of blades. Just looks like one piece in the photo.
 

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That is the 3 blade head that you used on the gyro and on the heli?
It was mounted to the bearing assy by 3 rubber donuts and thru bolts?

I have a few pictures of this one, really nice design, simple. How did it fly on the gryo? What was the weight of this head?

David
 
I don’t remember weights offhand but the fiberglass hub was likely less than 5 lbs. The blade grips had a ball bearing stack and solid steel spindle so were probably a little over 5 lbs.
 
Very elegant design. Few parts and functional.

How did this head fly on the gyro?

I think the video I have of this one on the gyro was a tall tail drop keel benson. In the video I don't think you got more than 50 feet off the ground, flying around the field. I think the text in the video said you used 269 blades too.

How did the fiberglass hub handle the lead/lad loads?

Did you put some time on this head or just flew it a bit then retired it to the shed?

David
 
The drop keel machine with fiberglass hub used a laminated birch spar with balsa afterbody and fiberglass cover.

The helicopter with aluminum hub used cut down Hughes blades, OH-6 if I’m not mistaken. That was during the height of the Vietnam war when Ft. Rucker was churning out helicopter pilots and running out blades in a hurry. I bought a truckload for ~$16/pair.

Both the gyro and the helicopter flew more like a FW than a typical seesaw rotor machine. Minimal lag.

In the case of the gyro, I had bought a box of strain gauges to check stress on the feathering bearing spindles but lost interest before ever getting around to it. Without knowing precise stress levels on anything so critical, I don’t fly higher than prepared to fall.
 
Sounds like fun, thanks for the info Chuck

I for one am very glad someone with your experience in fabrication and design and test flying take the time to show, talk and explain all this to us.

I really do appreciate it alot, thank you.

I am at work today (I skydive for a living) however I have some crude drawings at the house. I will post them tomorrow for you to paruse. I am thinking of a new gyro head, 3 bladed using thing stainless laminates for lead/lag, flap and feather. Sort of what they did with the Hughes 500.

David
 
3 blade head

3 blade head

Thanks for the response Chuck,

Sorry I wasn't more clear in my questions. I wasn't referring to the flexibility in the section but flexibility due to hinges or flexures. I didn't know that flexibility was designed into the BO-105 head. Was that done for aerodynamic reasons, stress control or something else?

On your 3 blade head, is the entire assy fiberglass or just the central spider?

When you flew the gyro with the 3 blade head did you try to drive the rotor mechanically with partial power? From the photos I have it looks like that may have been possible.

I would also appreciate as many additional photos you have of the design and operation of the head. I am particularly intrigued by the arrangement that allows lateral movement of the control stem inside the rotating head without falling out. ( I have the 14 second clip that shows the motion from behind the head.)

Thanks,
Larry
 
The brown part in the photo is the fiberglass, Larry. It was wound from S glass roving with woven filler to provide resistance to splitting.

There was a ball bushing at hub center providing vertical and tilt motions. The ball from a ½” rod end, riding on bronze inserts.
 

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Thanks for the information.

Would you mind sharing some more pictures of the gyro head mounting area?

What is the radial degree offset for pitch input on the gyro head?

Just trying to learn as much as I can from you Chuck.

Thanks
David
 
Cyclic phase was a conventional 90º.

If there was any cross coupling, I didn’t notice.
 

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Sweet, thanks again for the info

David
 
Thanks, got that picture. I have I believe 8 pictures of the head with labeling on two of them and 3 videos.

Chuck, in what instance would you need collective on a gyro? Its benifit? Yes you can increase the pitch of the blades a few degrees but also need a much higher power setting from the engine to get the better climb. Am I missing something of a advantage?

This is the correct airfoil you used with your wood/fiberglass blades?

How does it compare to other airfoils used for gyro blades?
vr7b.gif


David
 
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References for rigid head design

References for rigid head design

I purchased a copy of Gessow & Myers, and while that has a considerable amount on the aerodynamics of the helicopter it is very limited in analysis and consideration of head design. Especially the rigid style we are discussing here.

Chuck, you mentioned flexibility in the root extensions being preferable to blade flex. While I'm not trying to pin you down on that specific parameter, do you know of a book or other references on rotor head design that describes the rationale for that and other such design considerations?

I'm not looking for the formulas for centrifugal force or beam bending.

Thanks,
Larry
 
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