Blade Pitch

GitItOn

Member
Joined
Nov 1, 2004
Messages
15
Location
Medford
Aircraft
Air Command Gyro / Cessna 172
Total Flight Time
200
What's the theory behind blade pitch? If they are fixed at a grerater angle of attack, I would assume they have more lift, but won't spin as efficiantly, and oppisite for a flat or shallow pitch. What variables are taken into consideration when finding the optimum pitch of the rotor blades?
 
That's basically right, but, if you add pitch, the lift is still the same. Its always equal to the weight of the gyro. The rpm goes down once you pass the optimum angle and the flapping increases with increased pitch(less tip speed to forward speed ratio).
With a lot of pitch, the gyro would tend to go up and down with throttle changes rather than gain airspeed.
For autorotation to occur, the angle of attack has to be great enough to allow enough driving power from the driving section. Too much angle of attack and the rotor won't autorotate and too little and it won't do it efficiently.
The rpm will be maximum when you find the best overall pitch setting. That's when the rotor is most efficient. designing in some twist also helps.
You want each part of the rotor blade to be at the best L/D ratio or glide angle for max efficiency. The angle of attack naturally gets less towards the tips so it is not possible to have a ideal AOA at each point, in fact autorotation requires a gradual change in the angle along the span.
 
Back
Top