Indoor Props - Pitch versus Ceiling Height

From: Marty Sasaki <marty_at_mss.tzo.com>
Date: Sun, 15 Apr 2007 20:35:44 -0400

Peter L. Hess writes:
> In general, is there any relationship between the useful or effective
> pitch of, say, an LPP prop and the height of the ceiling in the flying
> venue?
> For example, if I am flying in a venue with a 25' ceiling, would I want
> to use a lower or a higher pitch prop than if I were flying in a 50'
> high venue?
> The question is prompted by an experience I had today flying an LPP in
> a gym with a 34' ceiling (well, rafters, etc., at 34'). I tried a new
> 12" prop with 24.5" pitch on a well used airframe. The prop seemed
> very powerful and efficient judging from the way it hauled the plane
> around while turning at very low rpm. However, it was very difficult
> to control, i.e., to find an suitable rubber size/launch torque
> combination. Using props with pitch of about 20" never gave me so many
> fits.

Good to see you today Peter...

I have to ask this question, if it wasn't broken, why fix it? You've
done well at Glastonbury in the past, why not continue with what you
used before?

I've used LPP props with pitch from 18 to around 24 inches and at the
local sites my times have been about the same after playing around
with rubber to try and match the prop in sites around New England.

Having said that a lower pitch prop, will spin faster and have more
thrust than a higher pitch prop. I think I've read somewhere that a
P/D of 2 is theoretically more efficient than lower pitch, but I'm not
sure if efficiency is all that important with low ceiling LPP
flight. It seems that control of the energy release in the prop is
more important than efficiency. Time(s) will tell.

Having said that it seems to be common practice to use large flaring
blade props in lower ceilings. My latest prop has a prop shaft that is
about .03x.3 inches tapering to .03 x .03. The blades twist up at high
torque. Durig launch the torque causes the prop to twist to a higher
pitch and depending on the launch torque the model will actually lose
a little altitude. As the torque drops, so does the pitch and the
model climbs. Ray Harlan's model had a similarly acting prop.

It is going to take a bit more fiddling with blade size and area and
spar placement to "optimize" the flight to the flying site.

I had a similar prop when I last flew at Lakehurst and even without
any backoff the model never went any higher than about 50 feet. This
prop was definitely not the right one for a high site.

Marty Sasaki
Received on Sun Apr 15 2007 - 17:40:52 CEST