Re: Indoor Props - Pitch versus Ceiling Height

From: Peter Hess <hesspl_at_comcast.net>
Date: Mon, 16 Apr 2007 10:12:17 -0400

Marty:

It was great to see you after such a long time in Glastonbury yesterday. And, thank you for your suggestions about how to control the unruly beast of an LPP that I was trying to tame.

You asked: "[I]f it wasn't broke, why fix it?" Well, I, too, have read that a P/D of two is probably most efficient for indoor duration models and I just wanted to try it. Also, in constructing the prop I wanted to achieve flaring at launch torque and for this purpose I used a blade shape similar to that used in the classic Cesar Banks design but with slightly larger blade area and approximately 75% of the blade area in front of the prop spar. I hoped that the spar was sufficiently flexible to assist in permitting flare at high torque. From your post I gather that I was attempting at least to accomplish the right things.

However, after reading your post and reflecting on what I observed when Ray flew his LPP yesterday it seems clear that I was not successful. What I observed when Ray's plane flew was that for what seemed to be the first 45 or 60 seconds of the flight it barely climbed at all. In fact, the first time I observed it I thought that there must be something wrong until, that is, it started a very slow climb to cruising altitude and then just floated aroung, all just as it's supposed to happen. This behavior was similar to your describing that your plane with a highly flaring prop, at times, even lost a little altitude.

In contrast, with my prop the plane started climbing immediately upon launch. It was not a blast off kind of climb, but it was pronounced. So, without any data to support this, my suspicion is that my blade/spar combination was too stiff to be able to control the torque. I also suspect that, with the high pitch, flaring sufficient to absorb/control the launch torque would have caused the prop to stall, but there certainly was no evidence of that.

Based on this speculation, my very inexpert conclusion is that for the low ceilings in which I fly I should go back to lower pitch props - - probably about 20" - - and strive to build props that will flare more than those that I have, so far, been able to build. And, as you said, time and times will tell.

Thanks, again, for your help. Be well!

Peter

 

[Non-text portions of this message have been removed]
Received on Mon Apr 16 2007 - 07:08:28 CEST