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Hi All,
Thanks for the information, this is a great group, and I appreciate the
help. If I am using Ed's spreadsheet correctly, at 100 hp, fuel burn
indicates 9.3 gph with an air/fuel ration of 12.65, which I would guess is
on the rich side?
I am also debating whether to go to an EAA builders class or using the
experience of the local RV builders group in Houston. There are several
RV's underway here, and this seems to be a generous group with their time
and advise, but ultimately I am responsible for the quality of the build,
and am ambitious to do as well as I can. I view this as a very attractive
challenge, and am excited to be getting close to starting. Any thoughts
here would be appreciated.
Also, Ed you mentioned that you thought your airframe was relatively
aerodynamically dirty, yet from the pictures I've seen, it appears clean,
and is an attractive plane as well as being an award winner. I am curious
what would cause you to make that statement?
Best Regards,
Greg
-----Original Message-----
From: Rotary motors in aircraft [mailto:flyrotary@lancaironline.net] On
Behalf Of Charlie & Tupper England
Sent: Sunday, March 21, 2004 4:15 PM
To: Rotary motors in aircraft
Subject: [FlyRotary] Re: Fuel Consumption Questions
Greg Fuess wrote:
>Hi Fellow Rotor heads,
>
>I am getting very close to starting construction of an RV-7 (much closer
>than last year when I said this! - should start in 8~10 weeks) and very
>interested in the potential for the Renesis engine in this application
>(can't wait for Tracy to get his installed so we can read the performance
>reports). I do have one question that is difficult for me to get my arms
>around. What kind of fuel burn are you guys experiencing that are flying
>your 13Bs? Turbocharged 13Bs? -at various power settings and altitudes?
Is
>there a data reference site anywhere that could provide this information?
>
>Ed Anderson's Rotary Power vs. 2-3-2 Cooling BTU calculation spreadsheet
>indicated 12.4 to 14.9 gph at 5k to 6k rpm (all for 1,500' alt). This
seems
>not to compare well to the lyconosaurus published consumption rates for a
>180 hp engine, though I have read elsewhere on the internet that the rotary
>consumption should be similar. Am I misreading or misusing Ed's
>spreadsheet, or should I get used to the higher consumption rate? Are the
>Lycoming consumption rates bogus?
>
>I am something of a lurker here, but as I get closer to the "date", I am
>getting more and more detail conscientious. Appreciate any and all
>thoughts.
>
>Best Regards,
>
>Greg Fuess
>
Hi Greg,
To add to what Ed & Tracy have already said about the rotary, here are
some real world numbers on Lycs.
A carburated 180 hp Lyc running at 75% power is making 135hp. The best
BSFC you can expect from a stock carburated Lyc is about .45 lb per HP
per hour. Av gas weighs about 6 lbs per gal. If you do the math, that's
135 X .45 / 6=10.125 gal per hour. I can tell you from personal
experience that this is a realistic number for a 180hp Lyc. If you run
the numbers at full power on the Lyc, it's 180 X .55 / 6 = 16.5 gal per
hour. Note that the BSFC is now .55 instead of .45 (& could be worse
than that; required to prevent burning exhaust valves & melting pistons
in a Lyc aircooled engine).
When your buddies tell you that their 180 only burns 8.5 gph (or 8.8, or
whatever), ask them what rpm & manifold pressure they cruise at. If you
get an 'uhhh...', walk away. If they have a fixed pitch prop, don't even
bother to ask the question. :-) Most people flying Lycs tend to run
them at well below 75% power thinking that they are extending engine
life. Most are also afraid to properly lean, because they are afraid of
burning valves & melting pistons. Put the 2 together & you will realize
that most (especially with fixed pitch props) are running at down around
55% power at that 8.5 gph figure. Allowing for less than optimum
leaning & running numbers again, ??hp X .5 / 6 = 8.5gph. Solving the
formula yields 102hp. 102/180 is .5666. Hmmm, what a coincidence.....
The Lyc factory fuel burn charts I've seen are often hard to interpret,
but I think you will find that they agree fairly well with the numbers
above. What does Ed's spreadsheet show for 100hp, & does it allow for
improved BSFC when the engine is leaned for such a low power setting?
Charlie
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