Ground effect in a gyroplane?

Mayfield

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(I actually had a question on ground resonance on my gyroplane knowledge test (PRG)!)
A&S 18A and to a lesser extent the McCulloch J2. When I used to teach in an 18A one of the lessons would be making sure you pattern the blades before starting pre-rotation.
 

bugflyer

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A&S 18A and to a lesser extent the McCulloch J2. When I used to teach in an 18A one of the lessons would be making sure you pattern the blades before starting pre-rotation.
"pattern the blades" ????

smiles,
Charles
 

Mayfield

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"pattern the blades" ????

smiles,
Charles
J.R. (Waspair) would probably answer your question better. The A&S 18A has lead/lag hinges as well as flapping hinges. Physically moving the blade to the rear stop of the lead/lag hinges, before starting pre-rotation, ensures the CG of the disc is concentric with the hub as the blades come up to speed. The blades self center as RRPM increases during spin-up.
 

bugflyer

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J.R. (Waspair) would probably answer your question better. The A&S 18A has lead/lag hinges as well as flapping hinges. Physically moving the blade to the rear stop of the lead/lag hinges, before starting pre-rotation, ensures the CG of the disc is concentric with the hub as the blades come up to speed. The blades self center as RRPM increases during spin-up.
Gotcha, thanks.
smiles,
Charles
 

WaspAir

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As usual, Mayfield has it right. On the 18A, there is an adjustable lead-lag damper on each blade, consisting primarily of a stack of friction discs under compression. These can change slightly with conditions (especially after a big change in humidity). Periodically, I use a fish-scale spring, hooked to the blade tip, the see how much force it takes to break free and get lead motion while the other blades are held still. (Repeat for each blade.) If necessary, a little turn of a nut on top on any out-of-spec damper would set all the dampers to the proper range. Once the damper force is satisfactory, you preset the damper positions daily so that they're all the same before the first spinup of the day. Putting them all against the rear stop will keep good balance until the blades start to sort themselves out with natural lead-lag action.

The J-2 has little oil damper cylinders on each blade. I had little yellow paint stripes on mine that would line up with a cast-in numerical scale so they could all be set the same.

For either aircraft, you set the position by moving a blade in one direction and then rapidly jerking it the other way to make the dampers yield momentarily. With a bit of back and forth action like that you can set them easily to the desired pattern. If you follow this process faithfully, ground resonance is not an issue. If you are sloppy about such things, you might start a prespin with the blades way out of position, and the spin-up will feel like a washing machine spin cycle with all the towels on one side of the tub (signiicant rpm is necessary to get blades flying into their proper spacing naturally). Once the blades are flying nicely, it's all self-regulating and smooth.
 
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WaspAir

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Thanks for your help to all. Will play with the info and see if that helps. Still see the advancing blade rising creating a larger AOA due to relative wind. My sailing days perhaps interfering?
Just pretend you're a 5 year old who wants to fly like a bird. Run forward flapping your arms up and down, and you will definitely feel more AOA on the down strokes (and less lift on the up strokes).

Might be good to do this when nobody's watching, but it works.
 

Doug Riley

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The apparent wind that an individual blade "sees" is the vector sum of its rotational velocity and the aircraft's velocity.

In sailboating terms, the advancing blade's rising path is like the path of a sailboat that's steered so close to the wind that its sails are past the "groove" angle and are starting to luff.
 

WaspAir

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Thanks, Doug. Some of us landlubbers don't know the head from the poop deck.
 

fara

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Just pretend you're a 5 year old who wants to fly like a bird. Run forward flapping your arms up and down, and you will definitely feel more AOA on the down strokes (and less lift on the up strokes).

Might be good to do this when nobody's watching, but it works.

Yeah it will work. Duct tape some cardboard on your arms while doing it and you will really notice it fast
 
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