Re: Double springs on a VP hub?

From: Tapio Linkosalo <tapio.linkosalo_at_helsinki.fi>
Date: Fri, 18 Aug 2006 10:20:42 +0300 (EEST)

On Tue, 15 Aug 2006, Bill Gowen wrote:

> I think that the idea is to have the second spring give a fairly quick
> change from a pitch that is too high to sustain level flight to a lower
> high pitch that will keep the model from landing. This would make it
> possible to do a high launch, let the model descend almost to the ground
> and then start from that point with the VP operating in standard fashion
> for the rest of the flight.

I was kind of thinking that it is just the opposite. Like, with a fixed
upper limit of the VP change, you need to backoff n% to get things going.
If you back-off less, you will climb with the set high pitch, and end up
scrathing the ceiling. And if you back-off less AND increase the high
pitch, you end up sinking after a short period of level flight, as the
torque drops off faster than you pitch reduces. All because of prop
efficiency going further down with increased pitch.

With "soft" upper limit you start with the starting point above, but when
you back-off less, you get more torque out of the motor, meanwhile the
second spring kicks in, with _increased_ resistance for the pitch change,
and therefore with the increased torque the _change_ in pitch is less. So
you end up with _less_ pitch to start with than with single spring, and
your model is able to maintain level flight despite the low prop
efficiency, which eliminates the risk of landing right away e.g. due
turbulence.

But then again, this is just theorizing, never flown F1D of double-spring
VP's myself...




-Tapio-
Received on Fri Aug 18 2006 - 00:25:42 CEST