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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
 

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.
 

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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Doug Riley

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Chuck, an odd tidbit on this topic is in the old NACA report about the testing of a 40-foot Pitcairn gyro rotor in the full-size Langley wind tunnel. The authors claim that the rotor blades were built with an aft CG. They state that this produced a sort of constant-speed effect. As long as the blades were loaded and hence coning, a random increase in RRPM would create additional centrifugal effect acting at the blades' CGs. This, they say, would pull the trailing out-and-down, thereby cranking in more twist. It seems that RRPM might still "run away", though, if you flew such a rotor fast enough.
 

C. Beaty

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A tail heavy rotorblade isn’t all that different from a tail heavy airplane; both are unstable vs angle of attack.
Skywheels rotorblades provide a perfect illustration of this; pitch the wrong way in response to gusts and on heavy machines are apt to randomly pitch nose up and do a tail stand.
This characteristic is frequently misinterpreted as high lift or in case of the extended float on landing; high inertia.
 
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