Regarding engine choice, I do realize the Lycoming 0320 weighs about 140 pounds more than the 912, but that is really the only downside. Biggest upside of course is the extra power with the 0320. On the cost side, that little 912S new, when you include all the necessary accessories, is pretty close to the new cost of a clone 0320, and a used 0320 would be a lot cheaper.
And despite popular opinion, fuel costs would be pretty well a wash. But with a 150 hp 0320 using reg mogas (like I do) likely cheaper than a 912S that has to use premium. The reason I say this with some certainty, I own and fly another plane with the 912 that also has a fuel monitor, like I have in my Rebel. What I found with testing and monitoring, and determining the hp utilized at different throttle settings, both engines end up using the same SFC ie. lb/hp/hr, which is .45. When leaned aggressively at lower power settings, that old Lycosaurous is surprisingly fuel efficient.
When at the lake in the summer taking people up for rides, I sometimes cruise at only 5.0 US gph, and still do 80 mph (full reflex), by leaning aggressively. I would bet that the 912 would also use 5 gph to do the same speed with that same weight.
And don't get me wrong, the 912 is a nice machine, but I also now have a lot more respect for these old Lyc engines than I used to. Plus you have to admit, they sound better, too.
Walter
----- Original Message -----
From: Bob Patterson <beep@sympatico.ca>
Date: Monday, January 29, 2007 2:28 pm
Subject: Re: [rebel-builders] Rebel - Should you move your firewall back 3"? A letter from Darryl Murphy.
Thanks Darryl !
And thanks, Mike ! This well-reasoned and thoughtful, detailed
analysis of the physics involved will now be in the archives for all
to refer to when making those big choices. I hope everyone will
read it through and think about all the aspects at that point.
One of the great things about the Rebel is that you can just
go ahead and build it - you don't have to decide on an engine
until you get right up to the front end ! At that point, you do
have to decide on the kind of flying you are going to do - and
pick the engine you think will best suit your needs.
For me, the standard Rebel, with a 912-S, will do everything
I need in the flying department. I hope that will be my next Rebel.
I currently fly an O-320 Rebel with the firewall not cut back,
and the empty C of G is 8.1" - very far forward. It stalls
significantlyfaster than I would like when solo.... and would
likely cruise faster
with a further aft C of G. Fortunately, I usually travel with a LOT
of baggage, giving a more rearward C of G, which makes the flying
quality pleasant for my needs. As Darryl says, even if you
don't
make the best choices, the Rebel is still a LOT nicer to fly than
production airplanes ! :-)
The choice becomes especially difficult for those who want
an O-320 now, but also want to go to a Rotax 912 later, if they
have medical problems. My thoughts are: everything takes longer
than you figure, gas prices are rising, you can't register at more
than 1,320 lb. anyway - if you want to go LSA, and health seldom
improves with age, soooooo, when you get up to installing the
firewall, just bite the bullet & go with the 912 !! You will have
a ball flying your Rebel, and save on gas too !!! :-)
OR - cut it back, put in that honking big engine & have fun for
a year or 2, and plan to sell it when things get tough .... :-)
(Anna often reminds me - "There are always 2 choices !") :-)
--
......bobp
http://www.prosumers.ca
http://bpatterson.qhealthbeauty.com
http://apatterson2.qhealthzone.com
-------------------------------orig.-------------------------
On Monday 29 January 2007 20:04, Mike Davis wrote:views onI just received the following letter from Darryl regarding his
moving the firewall back 3". He asked that I share it with all
the builders
on the list. I have also posted this letter as a PDF file in the
file
library.
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