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There was a fairly long discussion about this on the other list about
a year ago. If you look at the BSFC charts, there is a little island
where BSFC is lowest, and it increases every where else. If you are
careful to arrange your speeds correctly, it's possible to come out
ahead. The trick is to run the engine in an effecient regime while
climbing. Then while descending, even though the BSFC is worse, the
amount of fuel usage is less. Attached is a chart I did based on a BSFC
plot for an NSU KKM 502 engine (which was published by Paul L.) The values in green are places where less fuel was used climbing and
descending as compared to level. The BSFC map I used to generate this
table is about 110K. This plot was for an engine in a car. I can
upload it if anyone is interested.
Bottom line is that under some conditions, climbing and descending can
result in less fuel usage. (As you have measured.)
Bob W.
On Wed, 2 Nov 2005 17:37:24 -0500
"Tracy Crook" <lors01@msn.com> wrote:
(Bottom posting this time)
Subject: [FlyRotary] Re: Shady Bend / economy test
Tracy Crook wrote:
> At 9.5 GPH and 100 MPH I was climbing at 1500 fpm and getting 10.5 > MPG. It took 40 seconds to climb 1000 feet. Hmmm, I thought, what > is the average MPG if I get 10.5 MPG for 40 seconds and 55 MPG for the > next 5 minutes? I think the answer is around 48 MPG but that seems > to be too good to be true. Seems like some one would have used this > technique long ago if it would give a 60% increase in fuel economy. > The error in the EM2 fuel flow readout may be higher at this low flow > but nothing like 60%. Any math majors out there see a flaw in my math > or logic? Or maybe I was in a giant thermal at the time? I repeated > the test twice so I don't think so.
> Were you decending at 100mph? If not, then it is an apples and oranges comparison, isn't it?
You went 1.1 miles at 10.5mpg, using .105 gallons.
Assuming a decent speed of 100mph, you went 8.3 miles at 48mpg, burning up .174 gallons.
In the total 9.4 miles, you used .279 gallons, for 33.7mpg.
Does that sound closer to reality?
www.ernest.isa-geek.org<http://www.ernest.isa-geek.org/>
Actually it was 55 mpg during the descent portion of flight. I was looking at MPG averages so speed never entered the picture in my quick & dirty look at this. But you suggest another way of cross checking the results. Let's see, I think I agree with your miles traveled calcs so lets look at it this way. I burned .106 gal in the 40 seconds of climb and .125 gal during the 5 minutes of descent for a total of .231 gal.
9.4 miles divided by .231 gal gives 40.69 MPG. Not as good as I got by averaging the MPG during each unit of time (48 mpg result) but still a pretty good bump up from 30 mpg in level flight. Not sure where the error is coming from.
Naturally my test results will have to be repeated many more times before I accept them as fact.
Tracy
--
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