Dihedral in twin-rotor winged autogyros

[iter]

Gyrace has a dihedral built into its short wing. Many of the other
twin-rotor winged autogyros I've seen have a dihedral as well. What
would happen if you built one with a completely flat wing? would it be
instable in roll, unresponsive in yaw, both, none?

[mnowell129]

Gyrace has a dihedral built into its short wing. Many of the other
twin-rotor winged autogyros I've seen have a dihedral as well. What
would happen if you built one with a completely flat wing? would it be
instable in roll, unresponsive in yaw, both, none?
The answer is yes to both, unstable in roll and unresponsive to rudder. This would be fine if you also had ailerons but without you would lack any kind of roll control. Further, the rudder/dihedral control probably works at lower airspeeds than an aileron controlled flat wing version. For comparison the direct controlled models work all the way down to 0 airspeed, as long as the rotor is turning.
The dihedral works because the rotor that is yawed forward gets a higher presentation to the incoming air and speeds up/makes more lift. The rearward one the opposite. This creates the roll to turn with rudder. When you get a slip, the rotor toward the inside of the slip sees a higher presentation to the wind than the one to the outside of the slip. Same effect as the inboard rotor speeds up/makes more lift and picks up the inboard wing, just like dihedral on a plane. If they were both flat, both rotors would see the same presentation change with yaw or slip and would never create the different lift needed to create the roll forces needed.
mick

[iter]

Thanks for the answer. I'm not sure if I was clear enough in my question. There's the dihedral of the wing itself, and there is an angle between the two masts. They are quite independent of each other. So my question was about a flat wing with turned-in pylons, i.e. dihedral on the rotors but not on the wing.

Ari.

[mnowell129]

Thanks for the answer. I'm not sure if I was clear enough in my question. There's the dihedral of the wing itself, and there is an angle between the two masts. They are quite independent of each other. So my question was about a flat wing with turned-in pylons, i.e. dihedral on the rotors but not on the wing.

Ari.
Yea, that'll work aerodynamically as long is the wing is not contributing most of the lift, it just creates mechanical problems. What this does is increase the length of the mast needed because now as it is tilted in, you have to clear the wing inboard section or fuselage. The value to putting the tilt in the wing is the mast stays short (stronger) and the rotor/wing clearance stays the same.Of that genre, the shoulder mounted, dihedral wing is pretty optimum for getting the most rotor in a given span.
As an aside, keep in mind that the center section on a twin gyro is much more loaded than a wing of the same sized plane. In a wing the lift is distributed, with most of the lift inboard. With the gyro all the lift is a point at the wing tips so the center bending load is high.
mickey

[iter]

As an aside, keep in mind that the center section on a twin gyro is much more loaded than a wing of the same sized plane. In a wing the lift is distributed, with most of the lift inboard. With the gyro all the lift is a point at the wing tips so the center bending load is high.
Right. That's why I was thinking of a straight wing, with a single spar that would not have to be cut in the middle. You saw my carbon-frame attempt, right? I thought if I added a little bit of wing to it, maybe it would fly (otherwise I think I'll need to ask DWE to come up with a 75MHz version of their Rx to stay legal). Putting dihedral in that carbon rod is a bit of a hassle and would certainly make it weaker.

Ari.