To VP or not to VP?

From: Tapio Linkosalo <tapio.linkosalo_at_iki.fi>
Date: Sat, 28 Dec 2013 08:01:10 +0200

I've been wondering this recently - provided that you are flying in a
tall enough hall, such that the ceiling is not the limit, would it be
preferable to fly with or without a VP prop?

My thinking has been going along these lines: the common knowledge is
that one should fly with a motor that needs to be backed-off as much as
there are turns remaining, and I interpret this so that the aim to to
reach level flight (close to ceiling) at the "turning point" of the
motor unwinding torque curve, i.e. the flattest part of the curve where
it turns form convex to concave (or, in mathematical turns, the second
derivative is zero). To me this seems to assume that the unwind curve is
symmetrical, that the initial peak is as high as the end-of-the-curve.
Which, obviously it is not, but the torque peak is much higher.
Therefore, with a motor selected as above, but no backoff, the initial
climb would end up quite fast, and take the model so high, that towards
the end of the flight it will run out of turns and deadstick. Or, if you
fit the motor so that it does not deadstick, you end up with a rather
thin motor, and climb quite rapidly to the peak altitude, and then
cruise down for most of the flight.

So my idea was to stick with the thicker motor, that provides the
"turning point" of the flight later, but then, instead of wasting the
initial torque to rapid climb, use higher pitch to slow down the initial
climb, and gain more flight time but less altitude. Then, quite early
onto the flight change into low pitch and spend most of the flight in
that setting.

In other words, my question is: is higher altitude always preferable (if
there is no limit), or can a lower flight pattern be better?




-Tapio-
Received on Fri Dec 27 2013 - 22:01:14 CET