Re: Prop efficiency at high pitch (was: News from Roman...

From: Tapio Linkosalo <tapio.linkosalo_at_helsinki.fi>
Date: Tue, 20 Mar 2007 06:54:13 +0200 (EET)

On Mon, 19 Mar 2007 dgbj_at_aol.com wrote:

> "This seems to come quite close to Fred's observation, that in the salt
> mine the question is not how to get to the ceiling, but how to get there
> with the smallest number of turns used. Sounds to me that this is
> precisely the same thing, how to keep the prop efficiency up at the high
> pitch setting. Am I right if I speculate from these messages, that a
> flaring prop might have a better efficiency at high pitch than a VP? If
> so, why?"
>
> The important question for prop design is not about using it to control RPM,
> but using it to convert torque energy into altitude energy with the greatest
> efficiency. It is not getting there with the smallest number of turns, but
> getting there with the smallest energy. If the plane climbs too fast with an

Gary,

thanks for your words of wisdom. Of course I am aware that prop efficiency
is important, after all, indoor flying is all about prop efficiency. My
point was, however, that it seems in outdoor models that VP does great
harm to the prop efficiency, and if this same analogy is carried to the
indoor models, then VP is there used (in low flying sites) just to kill
the climb.

Going to a thinner rubber as you suggest is not the answer, as then your
model would not maintain altitude during the cruise phase of the flight.
Things would be as wonderfully simple as you suggest if we had rubber that
delivers energy at constant torque throughout the flight. Unfortunately
reality sucks, and thus we need to play with all sorts of gadgets like
VP's and flairing props.



-Tapio-
Received on Mon Mar 19 2007 - 22:00:38 CET