Rotor blades higher angle of attack

[jsada]

What would be the pros and cons of setting your gyroplane blades at, say, 5 degrees instead of, say 3 degrees? Slower rpm acceleration on takeoff? Bad autorotation characteristics? Blade stalling?

 

[MikeBoyette]

There is a point at which they will fly so slow that you basically go up and down only with throttle. It’s something that has been experimented with long ago. Depending on the brand of blade but, most that aren’t twisted work best at 2-2.5 degrees.

 

[WaspAir]

High drag and low rpm means higher coning, of course, and the blades must accommodate that.

 

[jsada]

High drag and low rpm means higher coning, of course, and the blades must accommodate that.

What is the AoA in the A and Space 18 during jump takeoff and then while cruising?

 

[WaspAir]

Collective pitch is zero degrees at spin up, about 8 peak at initial climb, and declining to about 4 for cruise as pitch-cone coupling automatically adjusts it. (That's not disc AOA but I assume it's what you were asking about.)

RPM is a slow 240 at average load in cruise (3 very heavy blades, 35 ft diameter).

 

[Eric S]

Collective pitch is zero degrees at spin up, about 8 peak at initial climb, and declining to about 4 for cruise as pitch-cone coupling automatically adjusts it. (That's not disc AOA but I assume it's what you were asking about.)

RPM is a slow 240 at average load in cruise (3 very heavy blades, 35 ft diameter).

Does that mean heavy stick forces, or did A&S gear it down to keep it reasonable?

 

[Jean Claude]

The higher the pitch setting, the slower the speed, all else being equal.
Theoretically, this results in lower blade profile losses, but to avoid greater coning, heavier blades are needed, and the advantage is lost in induced losses.
Only the disadvantages remain, i.e. the need for a powerfuler launch, and divergent flapping at a lower forward speed due to the extended stall on the retreating blade.

 

[WaspAir]

Does that mean heavy stick forces, or did A&S gear it down to keep it reasonable?

It's a swashplate controlled system. You don't tilt the head and blades, but just tilt the swashplate to provide cyclic input and the pitch links follow it like a cam, while the head rotates without tilting. Stick forces for that are normal. The long heavy blades (just over 55 pounds each for three) mean lots of inertia for the jump and little variation in rpm with load.

divergent flapping at a lower forward speed due to the extended stall on the retreating blade.

For the 18A, that's not a problem for takeoff because you prespin to more than 150% of flight rpm. At high speed, you can trim the collective for higher rpm to delay the onset of RBS (felt as a vibration).

 

[Doug Riley]

Unless the blades are appropriately twisted (more incidence at the tip; less at the root), high blade pitch will also result in a larger stalled region at the inboard ends of the blades. This stalled region creates a great deal of drag and relatively little lift.

IOW, too much pitch is inefficient.