Message-ID: <405E13D1.8070002@netdoor.com>
Date: Sun, 21 Mar 2004 16:14:41 -0600
From: Charlie & Tupper England <cengland@netdoor.com>
Reply-To: cengland@netdoor.com
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To: Rotary motors in aircraft <flyrotary@lancaironline.net>
Subject: Re: [FlyRotary] Fuel Consumption Questions
References: <list-3110936@logan.com>
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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