View Single Post
Old 07-07-2009, 10:21 AM   #21 (permalink)
Finless
Team Taco VP
 
Posts: 34,528
 
My HF Map location
Join Date: Nov 2005
Default

Quote:
Originally Posted by Danal Estes View Post
The "requirement" for negative pitch is a common mis-perception among model helicopter pilots. Full scale does not require negative collective pitch to sustain an auto. If so, a gyrocopter could never sustain flight.

See here
I read through the entire thing. The gyrocopter has a component of forward power that is not being supplied by the main rotor. Thus yes this is very different and look at the angle of attack of the rotor. But read through this and chapter 3 and no where does it say for a helicopter negative pitch is not needed. It simply says reduce collective and maintain a proper head speed. What pitch is used to obtain that no where in here does it say. I understand diagram 16-4 and forward momentum and thus angle of attack BUT what if you have no forward? So while negative is not needed for a gyrocopter due to the forward movement not provided by the rotor, I still argue a heli is not the same and still may use negative pitch to obtain rotor speed. Hey I could be wrong still but it doesn't make sense. Model are not that different.

I agree you don't need much negative to auto and more forward airspeed the less you need to maybe even 0 or +1'ish. In fact I see guys use a lot to drive the heli down thinking this is better. In fact my best auto's are MAYBE -1 where just like this link you provided says. Best auto is maximum glide rate and a slowest decent rate. Makes sense to me from experience BUT does require some negative. I cant believe a real heli would be much different. It's all Bernoulli's principles of lift and drag. But hey... A aerodynamics engineer I am not. So if I am wrong on this so be it.

Bob
Finless is offline        Reply With Quote