On Wed, 19 Aug 2009 07:03:55 +1000, "coriolis"
wrote:

I find the aerodynamics of fixed pitch props relatively easy to understand -
the angle of attack varies with both forward speed and RPM.

However, something puzzles me about constant speed prop thrust. I realise
that the blades twist to give a different pitch, and therefore when you
increase MP to maintain the same RPM the blades will be at a higher helix
angle.

you are one confused puppy. let me correct some of that text.

the blade is twisted to give the same pitch at different radiuseseses.
the twist is something fixed in the shape of the prop blade, for
aluminium, during the forging process used to make the blade.
the pitch angle is a function of the circumfrence of the circle
prescribed by the radius point and the forward advance in one
revolution. the pitch angle = arctan(pitch advance/circumference)
typically the units are in feet. if you have the same pitch along the
blade then you have a helical twist in the blade.

in an inflight adjustable prop the blades rotate in the hub to change
the pitch as the hub is spun through the air by the engine.

you'll find it a lot easier to undersand if you use words more
precisely.

However, won't the angle of attack (calculated by the relative wind)
by the same? Isn't that the idea? If the prop is at the same angle of
attack, why is the thrust higher? Once again, I know the pitch is higher,
but isn't the angle of attack the important thing in generating lift (which
is what thrust is) rather than simply the pitch angle? I've seen texts that
say you get a bigger bite, but that doesn't seem to explain why that matters
since lift is predicated on angle of attack.

now, what dan said in another post.

Stealth Pilot