HI all
I have an old crash victim of a twin rotor gyro with a short wing.
I am thinking of rebuilding this with no wing and 2x2 blade rotors on a single shaft with them running contra rotating.
I will use the rudder and elevator that is already in place. I was hoping that this would give my a start into gyro flying and some experence before building something with a full functioning dc head.
Any ideas about this , will it work??? any tips?
Many thanks
Rob

Hi Rob

It will work as I have myself performed that exact type of conversion.

I basically copied the layout of the rotor system used on AL'S GYRO which used a co-axial setup.
You need to make the blades non flapping with enough of a coning angle to have the same effect as dihedral on a fixed wing.
If memory serves the lower rotor had 7 degrees dihedral and the upper had 14 degrees, mast was tilted aft at 7 degrees . You will probably have to increase the engine downthrust and definitely the model will need a higher hang angle than a conventional flapping head.

I have some images of mine somewhere which I can post here if I can find them.

Best of luck

Sean

Hi Rob....

For what it's worth....some years ago I experimented with the tandem dual rotor arrangement of "AL's Autogyro". My results were less than pleasing. For some reason both rotors simply would not spin up equally. Reversing the rotors (putting the top one on the bottom and vice versa) didn't help either. One would always be lazy. I don't remember whether it was the top or bottom rotor. In other words, it was the position of the rotor that made it lazy.

My suggestion would be to go to a single rotor, with four flapping blades with 10-12 degrees of "Delta 3". Tilt back and engine thrust angle suggestions from "SpinDizzy" seem about right to me.

Bill

Thanks for the advice guy's!
I might still give it a try as the idea for building a four blade flapping head has me a little worred at this time. The single shaft and contra rotating blades seams easyer so i'll try that first.
Do either of you or anyone else have plans for a flapping head i might be able to use as a guide so i can try that way. Many thanks
Rob

I built a co-axial rotor gyro back in the 80's and it just BARELY flew. If I could get it up and flying in a straight line it would hang in there until I tried to turn it; then it would continue to roll slowly after releasing the rudder input. As I added more & more opposite rudder, it would get into a crossed up slip and finally crash in a knife-edge attitude. I built mine with a larger upper rotor dia. to compensate for the loss of effectiveness due to rotor wash from the lower blades. This is supposed to work, theoretically, but I guess all that was negated by my use of Gorham "Cricket" helicopter rotor blades (heavy!) I've since been told they don't even work on the helicopter they were designed for.

If I were you, I'd take the easy, proven method and use Randy Wrisley's "Gyro Schtick" rotor. Easy-peasey and it flies GREAT!. Just a disc of .032" fiberglass with 3 flat bottomed blades and shims under the trailing edge

Hello Rob

Sounds like the guys here don't go much on co-axial design.

Mine flew superbly and was the most stable and easy to fly gyro I have ever built. Maybe I was just lucky ??

Anyway, here are the images of it. Both upper and lower rotors are of the same dimensions with just the fixed dihedral/cone angle being different. It was actually an experiment with an old fuselage I had and it worked well except it needed more hang angle really. Blades were of flat bottom section set at about -1 degree measured on the flat underside. I double checked and the dihedral angles were 7 degrees each side for the lower rotor and 14 each side for the upper. Even though it was easy to fly and very stable I still managed to destroy it one fine day when I made a stupid mistake........I won't bore you with the details except to say it was 100% pilot error/stupidity.

Currently I am building a small co-axial of similar design for a .09 engine.

Have fun

Sean

Thanks Spindizzy
I will give it a try using what you have said as a guild and see how it goes.
I have not been able to find mush on flapping heads so i'll try your easy approach first.
Thanks
Rob