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Old Mar 05, 2007, 04:16 PM
Mickey from Orlando. Really.
Joined Nov 2004
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Quote:
Originally Posted by Wildman
what type of rotor heads did Cierva and Pitcairn use?
I have seen pictures of the aircraft but nothing describing the rotor head.
And how did they acomplish a "jump takeoff" there has to be more to it then a pre-rotater and cyclic pitch, right?
Wildman
All but the last models used a tilting spindle ("direct control") at the very end they went to a swashplate.
To do jump takeoff they had collective pitch which meant the blade holders had to have feathering bearings.
Cierva incorporated swashplates at the end. The british Cierva company licensed Cierva's designs (after his death) to Focke and Flettner in germany making their helicopters possible.
Sikorsky worked very hard to overcome cierva's patents in the USA (held by Pitcairn). During WWII Pitcairn patriotically gave license to sikorsky to aid the war effort, thus making Sikorsky's machine possible. Many of Sikorskys experiments (like three rotor tails for roll and pitch control) were trying to find a way around some 39 Pitcairn/Cierva patents, including cyclic pitch with feathering, etc. Pitcairn never intended the free use after the war. Sikorsky and Bell built helicopters anyway. Pitcairn sued sikorsky. Sikorsky whined and the army stepped in to defend him, forcing Pitcairn to sue the US government. Pitcairn sued the US government and the case was finally won by Pitcairn's family in 1977. His estate was awarded 32 million in back license fees, etc.
Remember that Cierva had tried feathering cyclic pitch in the beginning but his method was clumsy.
I believe that Cierva and Pitcairn had realized that to perform jump takeoff with collective and pre-rotation the swashplate was much easier to implement than the tilting spindle. There are also references to engineering the giant spindle bearing as being difficult as well. Once you go to the trouble to put feathering bearings on the blade holders for collective pitch for jump takeoff, it doesn't make much sense to retain the tilting spindle, just tilt the part that needs tilting, that being the swashplate and let the shaft be rigid. Then getting power to the shaft is easy anywhere along the shaft.
The tilting spindle died for a while until Bensen revived it on his gyrocopter. He states that he did this because he was trying to design a homebuilt and the tilting spindle was easier to home build than a swashplate. Bensen wasn't trying to build a homebuilt for himself, he was trying to design a homebuilt design to sell, hence the ease of manufacturing. His business plan was to take advantage of the recent availabilty of Alcoa aluminum to the average person on the street.....

When you start looking at how to do collective pitch and pre-rotation on a tilting spindle you can begin to realize how difficult it is, taking many complex joints and assemblies. It's like the difference between front wheel and rear wheel drive cars. When you transmit power to the non-steering rear wheels the axle can be simple. When you transmit power to the steering front wheels you have to have a constant velocity joint to avoid vibration. A CV joint is a fairly complex assembly. It results in a lighter overall assembly to let the shaft be rigid and turn it from below and put the universal joint in the non torque carrying swashplate. To do pre-spin you have to have a u-joint somewhere, either in the head where it is torque carrying or in the swashplate where it isn't torque carrying.
If you've read this whole thread you realize by know that the rotor is steered by cyclic whether you tilt the spindle or the swashplate. Once pre-rotation comes into play it makes better mechanical engineering sense to not try to carry torque through your control mechanism if there is another way.....
When I became interested in gyrocopters I started out with tilting spindles, but put them them aside. I came back to gyrocopters after the availability of inexpensive helicopter assemblies where I knew it would work and adding pre-rotation would be easy. I kind of had a light bulb moment one day while flying a fixed pitch piccolo heli and noticed that it autorotated just fine for a while with the motor off using like90 non twisted blades set at low pitch.....
There are some purist who think that the only gyrocopter is one with a tilting spindle. I see that Cierva started with wings and an uncontrolled rotor. Progressed to a controlled rotor, then lost the wings. Then went to mechanical pre-spin, then went to collective pitch and finally arrived at swashplate controlled, cyclic and collective pitch with mechanical drive. He invented the helicopter in every way but the tail rotor. So my view is that tilting spindle was just one step along the way for Cierva, not the end.
Any a long and windy post. An apology to my critics.
But the history/engineering is interesting to me.

mick
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Last edited by mnowell129; Mar 05, 2007 at 04:31 PM.
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Old Mar 05, 2007, 04:19 PM
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Kansas city MO
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Is this the gyro from France you mentioned?
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Old Mar 05, 2007, 04:31 PM
Mickey from Orlando. Really.
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Yes
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Old Mar 05, 2007, 05:28 PM
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Wouldn't a lot of tip weight in the blades make a 2 bladed head possible? I would slow the following rate, and contain more energy in the rotor. I know thats how we got the first CP hornets to fly, even thought they were a hand full in the wind.
It would be cool to see a two bladed gyro fly with no flybar, especially at the size of your gyros, or just a bit smaller. I have some old fixed pitch Hornet stuff laying around, I might have to experiment.

Scott
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Old Mar 05, 2007, 05:46 PM
Mickey from Orlando. Really.
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Yes. I've indicated before that a lot of tip weight solves the problem. The question is how much.
I don't know if tip weight helps the teetering rotor problem as it has no inherent damping.
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Old Mar 05, 2007, 06:06 PM
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Yeah, we added little music wire springs to that head for damping. Otherwise, the heli would bobble under the rotor head, with no so much control power.
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Old Mar 05, 2007, 08:31 PM
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Here is a head I am tinkering with. Its not a true teetering head, but it will allow collective pitch, and I can test how much tip weight is needed for the blades. It does teeter a a bit, damped by a piece of rubber band.
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Old Mar 05, 2007, 10:35 PM
Mickey from Orlando. Really.
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Yes I have a collective and fixed pitch hornet laying around somewhere. I think with the right tip weight you can make it work. It will still probably be "twitchy".
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Old Mar 05, 2007, 11:29 PM
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thanks for the engineering and history lesson very interesting, and all this time I thought Sikorsky solved the cyclic problem.
Okay I will give you a break for now Mickey and some day you can explain the power pusher over and what happens when the blades are unloaded in negative G's.
so much for the break.
Wildman
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Old Mar 06, 2007, 08:41 AM
Mickey from Orlando. Really.
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Interestingly Sikorsky didn't believe in the the 90 phase lag of the cyclic system. So despite his engineering's staff advice he rigged the control system without the lag adjusted for. Only after he had become convinced himself did he accept the 90 shift.
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Old Mar 06, 2007, 09:00 AM
Mickey from Orlando. Really.
Joined Nov 2004
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Once you see that a teetering rotor cannot put a torque on the shaft you can see the negative G problem. The copter with a teetering head just hangs from the positively loaded rotor. To steer, you tilt the rotor and the body slings along. If you accidently push over to 0 G the rotor can no longer do anything to move the body. How can it as the rotor is making no thrust and the teeter prevents the rotor from putting any force on the shaft? Further once you go to negative G's and the rotor is loaded down, not up, when the rotor is tilted back it puts a nose DOWN force on the body, thus creating a control reversal.
I haven't studied the problem carefully but I think what happens is the pilot applies too much power, over corrects with nose down. The rotor goes to 0 G. The pilot sensing his overcontrol applies nose up as the rotor continues on to negative G. Once the rotor is negatively loaded but in a nose up condition the rotor pushes the nose down. The pilot pulls back aggressively worsening the nose down force. The rotor slows, stops and/or folds and we know what happens next.
The basic problem is the teetering rotor, complicated by extra power. I think its odd that the full sized community hasn't dealt with this. What you have to do is allow the rotor to apply some torque to the shaft. You could use rubber snubbers or a piece of leaf spring in the teeter or move to offset hinges rather than a single teeter. Then at 0 G the rotor will still apply the correct force to the shaft to correct the attitude.
I think this was Bensen's great failure in design that killed some people. He was a good enough pilot that he could avoid the situation, but other's weren't. The Flapping head with offset hinges always has control power at 0 G because the blades can supply a centrifugal force generated torque to the shaft. Any aircraft that has no control power at 0G and a control reversal at negative G, scares the poop out me, it's why I won't set foot in a teetering rotor gyrocopter.
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Old Mar 31, 2007, 07:55 PM
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hello,
is someone have already build the "2d" of autogyro compagny of aryzona.?im searching for information because i have never succeed to fly with it.
thanks you
christophe from france
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Old Apr 15, 2007, 07:40 PM
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Sedona, Az
Joined Sep 2001
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Mickey,
Could you help me understand how the depron auto's fly? I understand the whole airfoil lift thing, but how does a flat plate with negative pitch produce lift? Does it have something to do with how the blade still has positive pitch relative to airflow? Thanks alot.
Scott
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Old Apr 15, 2007, 08:51 PM
Mickey from Orlando. Really.
Joined Nov 2004
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Busy for a day or two but I'll get back to this.
Short answer, mast tilt plus forward motion = positive angle on the blades, with respect to the blade's axle.
It is confusing and doesn't look like it should work but I'll try to diagram it simply.
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Old Apr 16, 2007, 09:52 AM
FPV really is fun.
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Thank you.
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