Swedish yoke

wolfy

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To Chuck, Jean Cluade etc,
I am just starting to get back into gyro's and was hesitant because of having to deal with the very annoying 2 per rev shake.
So I am wanting to try my version of the Swedish yoke. I can't find any pictures of Joe Pires version (can anyone point me to them) but have seen Mad Man Mike's version.
My thought's are to just make doublers on top of the blade retention straps, but the doubler would be as wide as possible (span wise) out near the end of the blade strap.
So I would have the drag struts out near the last bolt hole in the straps and in front of the leading edge and behind the trailing edge.
The drag strut would be from the leading edge of one blade to the trailing edge of the opposite blade.

My concerns are that I may introduce a local hard point at the ends of the blade corresponding with the drag strut, forcing the blades to flex (lead and lag) instead of the hub bar flexing as they do now. Is that something that I need to worry about?

Any thought's ?

Wolfy
 

wolfy

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And another question, I already have a long limber mast.
Is it possible to soften the mast too much? eg, long mast plus a slider head.

thanks wolfy
 

C. Beaty

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With a long, flexible round tube mast, you’d have freedom from 2/rev vibration even with a drag hinged rotor. That’s because with several tons of centrifugal force holding the rotor straight, the mast wouldn’t be stiff enough in any direction to knock the blades out of pattern.

Joe Pires’ drag struts were very much like MM Mike’s.

A mast can’t be too limber so long as it doesn’t collapse in normal flight.
 

wolfy

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Thanks Chuck, it wont be possible for me to incorporate a round mast into this current gyro. it has the standard Australian 2x 2.5" rectangle.
I have flown plenty of rotor's on the last gyro with some of them being extremely smooth (the light rotor's), but this new machine will have heavier rotor's.
Mmm maybe I should look into adapting a round mast.
Is there any benefit from making the Swedish yoke wider (span wise) than the inboard end of the rotor, as per MM Mike's?

wolfy
 

C. Beaty

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Wolfy, 2/rev shake results from the rotor being forced out of pattern. With 2 blades, out of pattern means that the rotor’s CG is offset from its center of rotation; that’s what triggers the shake.

Drag struts, Skywheels hub and the like are mainly to keep stiff rotor mounts from forcing the rotor out of pattern.

As mentioned previously, with a sufficiently soft mast, centrifugal force will keep even a drag hinged rotor in pattern.

My first gyro was built to Bensen B-8 dimensions, using 2.5” diameter x 0.120” wall 2024 aluminum tube. It was free of 2/rev vibration with a drag hinged rotor and I was too dumb to know why. That was in the 1970s.

If I was building a gyro today for yanking and banking while chasing feral hogs around Florida bayheads,* I’d use 2” round 4130 steel tube mast.

*A Florida bayhead has nothing to do with saltwater bays; it is a depression in otherwise flat ground, usually circular with a diameter of a mile or so overgrown with bay trees.
 

C. Beaty

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Off the top of my head, without running the numbers, my guess is 1/16” (0.062”). I’m not sure if that’s a standard wall thickness, need to check the catalogs.
 

wolfy

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Thanks Chuck, something to consider. I guess it's not too hard to make up some adapter's to adapt to the cheek plates.

Cheers wolfy
 

C. Beaty

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Those photos appear to be MM Mike’s gyro. The use of Bensen’s “redundant” (twin 1x2 tubes) mast exacerbates the 2/rev shake problem.
 

Mac

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Dropkeel KB2, EA81, 2.19:1, 68"Warpdrive, 24'Dragonwings, talltail
Pulled up Aircraft Spruce round 2" seamless 4130 tubing
 

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Mac

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Messages
247
Location
Amarillo, TX.
Aircraft
Dropkeel KB2, EA81, 2.19:1, 68"Warpdrive, 24'Dragonwings, talltail
2" 4130 seamless tubing with heading
 

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C. Beaty

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Thanks, Dar. That’s Averso’s drag link rotor hub from his days of fighting 2/rev. I understand that he was able to internally stiffen the blade roots enough to be able to eliminate that hub.

It amazes me that you’re able to find all this stuff; I had saved a copy of that hub photo on a CD or hard drive but gave up hunting for it after a while.
 

C. Beaty

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This image, from "Cierva Autogiros" by Brooks shows a C-30 autogiro making a jump with a 2 blade, drag hinged rotor.
Cierva's jump design using inclined drag hinges would only work with 2-blade rotors because they did not require the strong drag dampers of 3 blade rotors and thus would assume jump pitch quickly and with less loss of RPM.
However, Cierva could never solve the severe 2/rev vibration problem of 2 blade rotors.
I stumbled across the solution in the 1970s; a round tube, flexible rotor mast without realizing it at the time.
But I'm too dumb to master picture posting along with text on the current forum setup.
 
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