The stirrer is at it again!!!! LOL

[Aussie_Paul]

The latest PRA Magazine has an excellent article "CarterCopter Technology" written by Troy Schank, Graduate Research Asst. Autorotation is very well explained with excellent schematics and a diagram of length of blade indicating Stall/Driving/Driven regions of the blade. Accompanying this is cross-sectional views of blade relative to the different regions of the blade, with the resultant vectors. Also schematics show the difference between Autorotative Regions of the Disc in Vertical Descent versus Autorotative Regions in Forward Flight. This is probably the best description/explanation I have seen.

I have not had time to digest it thoroughly(if thats possible for me!!)

There are so many times that even experts make the comment that a heli has driven blades, and so twist and a number of other issues are reversed to the autogyro rotor.

We, as in gyroplanes, have driven rotors. They are not driven by the engine, BUT they are driven, so the tips do not know that they are not driven by the engine!!!!!

What do others say about this?

Aussie Paul.

[Al_Hammer]

True, Paul, the tips are driven in both gyro and helicopter. :)
That is, their lift vector is tilted back slightly producing drag, which must be compensated by torque from the engine(helo), or from driving forces on the inboard sections during autorotation(gyro).

In a helicopter, to improve hover performance, the tips are often twisted more negative than the root, like a propeller to even out the distribution of lift along the span.

Negative twist(tips have less angle than root) helps hover performance and actually hurts cruise performance and autorotation in the helo.

The gyro, ideally, has tips twisted slightly positive.
in forward flight, flapping will reduce the AoA on the advancing tip to the point that it will go negative and produce negative lift at higher airspeeds.
Negative twist is the last thing you want in that case.
Hafner calculates the ideal twist as being about 2-3 degrees positive.