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To: <murphy-rebel@dcsol.com> (Murphy Rebel Builders List)
From: Bob Patterson <bob.patterson@canrem.com>
Subject: Re: Rotax 912S & props
Message-Id: <E11NdKN-0005gO-00@smtp2.interramp.com>
Date: Sun, 5 Sep 1999 10:31:31 -0400
G'day Ian !
As far as I know, nobody has put a 912-S in a Rebel yet - they're still
relatively new. Should be a great choice, though !
I do have over 980 hours on my Rebel with the old 912 in it - and
just love it ! If the "S" is anywhere near as reliable and low maintenance,
it will be a winner.
I have used the GSC props for most of 9 years - they are
ground-adjustable,
with wood blades with an epoxy leading edge. Very inexpensive, work well,
and you can easily order a new set of blades at very low cost. If you DO
happen to run into something, the wood will break, saving your gearbox &
crankshaft ! (GSC props are less than half the cost of Warp Drive !)
The only suggestion I have is to make up a cloth cover for the prop
to keep the sun off when tied down. Over time, the sun will damage the
varnish on the blades, and let moisture in. At that point, the prop
becomes unbalanced, and start to rot very quickly ! Ours is just a sleeve,
with velcro at the root to tighten it - and should have a small bungee
over the spinner to hold it on in winds. The GSC blades will last at least
3 years - we did have a Collin Walker prop on which the varnish crumbled
in only one summer !
I am amazed that folks with Warp Drive props do not put covers on
them - we fly gliders, and ALL the composite ships are painted white,
with even the registration letters in grey (instead of black), to avoid
any heating of the structure. There the W-D props sit - BLACK, and bare,
with no UV protection !! I'm surprised that more of them don't disintigrate
!
We use a 2 blade prop. The fewer blades you have, the more efficient
the prop will be - only reasons for more blades are: no ground clearance
for longer blades, or the blades are too weak to handle all of the
engine power without distributing it over more blades.
We tried a 3 blade GSC on our Rebel - it disdn't climb as well, and
cruised slower - just NOT as good as 2 blades. Our 2 blade prop is 72"
long - a longer prop is also more efficient, as long as the engine
has enough torque to swing it.
If I had more money, I would go for the GSC Variable Pitch prop -
it's about $1,500. It is variable over about 18 degrees (!), and is
completely mechanical - dead simple ! There is a vernier knob on the
panel, connected to a cable that pulls a bellcrank on the top of the
912. The bellcrank pushes a rod through the center of the redrive shaft,
onto a huge thrust bearing that rotates the prop blade cams. Simple,
inexpensive, and only for the 912, or engines with hollow shafts.
Don't know why they are suggesting the 68" 3 blade - maybe they are
following Warp Drive, who always recommend more blades for more power.
I believe that a 2 blade 72" would be better overall, but only testing
on that engine will tell. The longer 2 blades definitely work better
on our 912 ....
------------------------------orig.----------------------------------------
At 09:59 PM 9/5/99 +1000, you wrote:
G'day from Australia.
Whilst I am awaiting delivery of my Rebel kit, and having nothing better
to do, I am doing some forward planning.
I have a few questions;
1. Has anyone any experience with this engine in a Rebel?
2. The factory offer a GSC propellor as standard. Are these
satisfactory?
3. The 68" 3 blade has been recommended for the 912S. Any comments?
Regards and thanks
Ian Donaldson
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