Swedish yoke

C. Beaty

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OK Wolfy, but bear in mind that a flexible mast only solves the 2/rev problem.

A flexible mast does nothing for 1/rev vibration; -out of balance, out of track or out of pattern.
 

wolfy

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Absolutely Chuck, I/rev is easy to deal with 2/rev is the real demon.
I also have a two blade helicopter and balancing equipment, I am extremely fussy about stick shake so have played lots and understand the difference. Short of having perfect track there's not a lot a balancer will help with two per rev.

wolfy
 

DangerBird

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Very informative thread, Thanks.
I have one more question for Mr. Beaty, What would you use for a mast on a heavier 2 place to cut back or stop the shake?
 

C. Beaty

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With a Bensen style layout where the mast points about in the same direction as the rotor thrust vector, I’d guess 2.5” with an 0.083” wall. But that’s only an off the top of my head guess; the calculation isn’t difficult but it takes a bit of time. For Eurotub style gyros where the mast leans forward, it’s probably best to avoid flexible masts and go to some kind of flexible rotorhead mount.
 

C. Beaty

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Wolfie, say the gyro weighs 1.000 lbs and the vertical mast is 4 feet long from the last brace, normally the top engine mount. The rotor thrust line is tilted toward the rear at about a 10 degree angle. The bending moment arm is then: (tan 10 degrees) x 48 inches = 8.5 inches. The bending moment is then: 1000 lb x 8.5 inches = 8,500 inch/lb = 708 ft/lb. Takes a pretty stiff piece of pipe not to bend.

That’s the reason it’s best not to stray too far from Bensen.
 

wolfy

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Mmm got me worried now, mine was a vertical mast before the modifications started and had to stay vertical.
Hopefully I will get away with it as a compromise?

wolfy
 

C. Beaty

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Pioneer aviators, beginning with the Wright Bros, flight tested their own designs.
You’re a pioneer aviator, Wolfie.

Also, if balance requires that the rotorhead be offset to the rear of the mast, the bending moment arm is shortened by that amount. Can your single place gyro really weigh 1,000 lbs?
 

wolfy

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Haha don't want to use a flight test to find out the mast isn't up to the task though:).

Shouldn't be anywhere near 1000 lbs, and yes I am guessing the rotor head will be offset to the rear.

Thanks wolfy
 
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