RCU Forums - View Single Post - Does prop-pitch increase thrust ?
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Old 11-29-2002 | 02:12 PM
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JimTrainor
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Default Does prop-pitch increase thrust ?

I certainly agree with the opinion that you have to experiment to figure out what's going to work best.

At the risk of complicating matters...

My formula was a just back of the envelope estimate. All I did was assume the prop was a wing with varying velocity across the radius.
Velocity = w*r,
Lift = Cl*(w*r)^2
integrate w.r.t. r and you get Cl*w^2*D^3

w = rotation speed (rpm)
r = radius from root to any point out to prop tip at Diameter/2
Cl = a lift coefficient representative of the pitch

I dropped all constants along the way since I didn't care about an actual number. AND, there is no accounting for air speed that will reduce the prop's angle of attack in flight (which will affect Cl), AND, of course, it says nothing about the engine.

I am curious why you say the prop is stalled at zero air speed? If it was a very high pitch prop, then I could see that it could very well be operating past the airfoil's peak lift coefficient (i.e. too high angle of attack) hence one might say it's stalled. If that is not the case, I don't see why it would be considered stalled.

By stalled, in this case, do you mean it's doing no useful work since the plane is not moving?

So, how about ThrustHP - which is so often mention here (i.e. RCU)? It's thrust estimate doesn't change *at all* with pitch, only diameter has an affect. Just seems wrong to me.