Re: Increasing duration in F1D - prop settings and back-off

From: jannis1indoor <jannis1indoor_at_yahoo.com>
Date: Tue, 20 Mar 2012 02:47:03 -0000

Tapio,

If your VP is properly setup you shouldn't have to backoff any turns. The main reason that I developed the first VP more than 40 years ago was so that I could keep the model just below the rafters and not have to backoff much on the turns. You probably need a higher pitch and the pitch should also change more throughout the flight which would imply a stiffer spring with less reload. My original props would change pitch continuously throughout the flight. Sometimes if required, I would add an upper pitch stop or lower pitch stop. I don't think that you want your prop to change from a high pitch to the low pitch setting like a switch or step function. You could do some static rundown tests and measure the rpm every minute by counting 10 revs and timing with a stop watch. Plot these static rundown results and scale to what you expect for your cuurent flights. Then experiment with different prop settings and do the same static rundown tests. Good luck on getting the prop setup.

Jeff Annis

--- In Indoor_Construction_at_yahoogroups.com, Tapio Linkosalo <tapio.linkosalo@...> wrote:
>
>
> Last night when making motors (for F1B...) my thoughts turned to
> Belgrade, again. Started to wonder what to do to climb up the ladder of
> duration (I'm currently at 26 mins, so next target should be closer to
> 30...)
>
> Comparing my flight profile to the one that John was flying in 2010, I
> was surprised to see him taking almost 20 minutes to climb to the
> ceiling. My model was at the apex of the flight profile in 10 mins... So
> obviously this is where the missing flight time lures. One thing that I
> need to fix for next summer is to modify my VP's to take higher max
> pitch, currently I'm against the top stop (cannot adjust any further),
> and need to take backoff to avoid hitting the ceiling.
>
> So this is the first question: should I aim to fly with no backoff at
> all, and just add the max pitch to control the amount of the climb?
>
> Second, my props use a "soft" spring with multiple turns. Thanks to very
> informative discussion with the Brits last summer, I now understand that
> this kind of spring works with a rapid movement from high pitch to low,
> and indeed this was showing in my flight profile last summer: after the
> apex at 10 mins, the model started descending, until at around 14 mins
> the pitch changed, resulting in a shallow second climb and then cruising
> down for the rest of the flight. Maybe a "harder" spring of fewer turns
> would enable similar action as Treger was showing, with a long cruise
> not changing much altitude throughout the middle parts of the flight? I
> suppose this would, however, make the adjustment of the spring
> pre-tension much more sensitive than with a softer spring?
>
>
>
> -Tapio-
>
Received on Mon Mar 19 2012 - 19:47:07 CET