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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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