Control force

wolfy

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For what it's worth, my last single seater had a lot of different rotors. Some heavier and some longer and some both, without anything else changing the longer and heavier rotors from memory absolutely had a heavier stick.

wolfy
 

XXavier

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In case it may be of some help, in this book:


there's a description of the control forces of an MTO gyro, stick forces included. Pages 105 ... 161 Yes, it is in German, sorry... To my knowledge, this interesting book hasn't been translated yet...
 
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jm-urbani

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For what it's worth, my last single seater had a lot of different rotors. Some heavier and some longer and some both, without anything else changing the longer and heavier rotors from memory absolutely had a heavier stick.
all what you say is worth Wolfy you belong to the people who never speak to speak
so the longer the rotor the heavier the stick
as tandems have longer rotors it seems normal that they have heavier stick because the lift being more important , the twisting force is more important making the stick heavier ... is it something that we could considerate as true ?
 

jm-urbani

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In case it may be of some help, in this book:


there's a description of the control forces of an MTO gyro, stick forces included. Pages 105 ... 161 Yes, it is in German, sorry... To my knowledge, this interesting book hasn't been translated yet...
unfortunately I don't speak german at all, the only thing I understand in german is the refrain of the lili marlen song (((-:
 

C. Beaty

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Stick force for a given control arrangement depends upon the following rate of the rotor. The greater the rotor lag, the heavier the stick.

The higher the rotor inertia, the greater the lag but that’s only the tip of the iceberg; design errors along with torsional stiffness play a much greater role.

Tail heavy and torsionally flexible rotors such as Skywheels have a form of built in power steering; pulling the stick back tilts the advancing blade in a nose-up direction and the resulting aerodynamic force twists the blade more nose-up, amplifying the control input, yielding a very light stick. The built in collective pitch also increases the “float” during the landing phase. An upward gust causes a nose up pitch, an unstable response; often misinterpreted as “high lift.”

And of course nose heavy and torsioally flexible blades such as Magni produce the opposite effect. Pulling the stick back causes the advancing blade to twist nose down, partially nullifying control input, increasing lag and thereby stick force.

Correct design requires that the blade CG and aerodynamic center coincide. Professional designs, beginning with Cierva have always used rotor blades with coincident CG/AC.
 

jm-urbani

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hi chuck , thanx a lot, but before I try to understand , could U explain what do you mean by rotor lag ?
 

XXavier

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unfortunately I don't speak german at all, the only thing I understand in german is the refrain of the lili marlen song (((-:
Wie einst, Lili Marleen,
Wie einst, Lili Marleeeen...
 

C. Beaty

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I, Linux and this forum just don't get along. Try as I might, I can't reduce the size of that sketch.
 

jm-urbani

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Thanks Chuck,
a lot chuck .

my blades are made of extruded aluminium, and I think that it is not easy for the makers to drag back the CG in order to locate it under the AC

on my monoseater I really don't have any effort to make to hold the stick which is very light, I flew tandems (jyro and xeeleex) with the same but longer rotor (8.7m) and I have noticed the stick was much heavier (but not like a magni) and I still wonder why ?

hence this thread
 

C. Beaty

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It’s a matter of blade loading, JM. If the gross weight is 2x as great, the rotor diameter must be increased by a factor of 1.414 to keep the disc loading the same but blade loading has increased by that same factor. Heavier blade loading increases blade twist.
 

hillberg

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Tested rotor blades of different weight on the Mouse from 16 lbs up to 60 lbs ea. No control force difference. (profiles same)
The heavier blades were great at hovering autos from 10 feet, but were slower at spooling up from after drooping - No other issues
 

jm-urbani

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Tested rotor blades of different weight on the Mouse from 16 lbs up to 60 lbs ea. No control force difference. (profiles same)
The heavier blades were great at hovering autos from 10 feet, but were slower at spooling up from after drooping - No other issues
thanks for your testimony it is really interesting,
could you tell me what you mean by "hovering autos from 10 feet" ?
 

C. Beaty

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Heavy stick Magni:

Magni originally thought the heavy stick was the result of control pivot friction, issuing a service bulletin entitled “Fictionalizing the Controls.”

I didn’t pay much attention to the heavy stick issue, having previously heard the first US Magni dealer, Bill Parsons bitch about the heavy stick and blaming it on the horizontal stabilizer. Bill thought horizontal stabilizers were dangerous, believing that a strong gust could blow the tail up and into the rotor.

A number of years later, Aussie David Bird (Birdy) flew one and also bitched about the heavy stick. Greg Gremminger informed Birdy that the heavy stick was the result of control pivot friction pointing him toward the Magni service bulletin. Birdy replied, “Where does the friction go when the gyro is on the ground with rotor stopped?” At that point I jumped in and suggested the heavy stick was the result of nose heaviness. Greg replied. “not so,” producing a blade sample section cut from mid span that was properly balanced chordwise.

Then Averso posted photos of a Magni rotor cross section at both root and tip ends showing the heavily tapered spar that made the rotor quite nose heavy at the tip end. The tapered spar isn’t all that relevant; lead or brass internal nose weights near the tips could accomplish the same thing.
 

hillberg

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thanks for your testimony it is really interesting,
could you tell me what you mean by "hovering autos from 10 feet" ?
More inertia from 60 lbs each blade as the engine power was removed the helicopter will settle to the ground as main rotor RPM drops.

With the 16 lbs I could do a hovering auto from two feet any higher I have to slightly lower collective to conserve RPM before a vigorous pull to soften the touch down.

With the heavy blades the helicopter would settle from ten feet with no collective action all the way down vertical to a soft landing.

turning weights take energy -turning weights give energy
 

C. Beaty

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The Bensen rotor system with fixed pitch rotor blades and tilt head cyclic control is quite tolerant of improperly designed rotor blades whereas rotorcraft with feathering bearing/swashplate cyclic control are not. In the case of helicopters and gyroplanes such as the A&S 18A and McCulloch J-2, misaligned CGs and pitching moments create intolerable collective control pressures.

As it turned out, only Dragon Wings as used on the Mosquito helicopters were suitable for swashplate control. John Uptigrove, the Mosquito’s designer, was one of the very few hobbycopter designers with formal engineer training.
 

jm-urbani

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Hi Chuck,
one more question : when we are flying a gyro we need a feed back force acting on the stick , in the case one uses blades with coincident CG/AC will the feed back provided only by rotor lag be enough ?
 
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C. Beaty

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Check the rotorhead sketch in post #28, JM. That sketch illustrates a standard Bensen offset gimbal rotorhead.

The rotor thrust vector, the line of rotor thrust, trails the pitch pivot, producing a nosedown force in the cyclic control system that is normally balanced by the trim spring. An upward gust produces an additional nose down force in the control system, overpowering the trim spring. This nosedown force and the resulting rotor tilt tends to keep the gyro headed into the relative wind.

The stabilizing force thus produced depends upon trim spring rate and the pilot’s grip on the control stick. Fledgling pilots with a death grip on the stick defeat the stabilizing effect as does a trim spring with too high a rate. The need is for a long, soft spring and a light grip on the stick.

Bensen’s first rotorhead, the “spindle head” provided feedback in an unstable direction.
 

C. Beaty

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The Bensen plans for the B-8 Gyrocopter included drawings for the spindle head but not the gimbal head; it was available only as a finished product.

Dave Prater, an early gyro builder/pilot once related the story of his experience with the spindle head; Dave had a spindle head on his gyro while flying buddy Bill Parsons had a gimbel head on his gyro.

Dave said that when flying together, he was all over the sky* while Bill was rock steady. Dave said that initially, he believed the difference was the result of Bill’s superior flying skills but after going for a spin in Bill’s gyro, realized the difference was due to rotorheads.

That tale was posted here on the forum several years ago.

*all over the sky was an exaggeration; I expect a more descriptive word would have been "bobble"
 
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