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12-09-2008 | 04:10 AM

#8

DarZeelon

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From: Rosh-HaAyin, ISRAEL

RE: OS91 FX

Quote:

ORIGINAL: SpeedBoy

You say that the tips of the prop must promote/have smooth shape to produce good thrust right .... and what if I modify the airfoil trying to leave a smooth shape (as the pic below) including the original shape of the tips ??? does it will work ???

What exactly you mean with chopped prop ? .... to shortened .... ???

Why you say that a shortened prop will take ages to produce effective thrust ???

SB,

I hope the prop images below clear up what I meant by 'chopped'...

If the blade tips are 'reworked' well enough, the prop should behave like a production prop, with a high pitch-to-diameter ratio.

As to the last statement; I did not mean a shortened prop. Not necessarily.

I meant any prop that has a high pitch-to-diameter ratio; whether a production unit, or one like you had modified.

Until the 'vortex' builds up, the blades in their entirety are stalled; producing a lot of turbulent air and noise, but very little thrust...
With props that have a pitch-to-diameter ratio, which is high enough, this vortex may never build up in static, or slow flight conditions.

Only as flight speed is increased dramatically, does the prop begin to 'blend in' with its surroundings, becoming much more efficient.

See the full size Mustang, Hercules and Bear and notice the dramatic pitch at their blade tips, in high-speed flight...

At take-off, the pitch they all use is much, much flatter...

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