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Date: Tue, 02 Nov 2010 10:58:50 -0400
From: Ernest Christley <echristley@nc.rr.com>
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To: Rotary motors in aircraft <flyrotary@lancaironline.net>
Subject: Re: [FlyRotary] Re: EM2 Numbers
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Al Gietzen wrote:
>
> No, we sure didn't. In fact, I like going faster than my wallet can=20
> keep up.
>
> Yeah; me tooJ
>
> In doing some searching for LDmax for the Lancair ES, I read the=20
> statement that best economy would be the same as best glide. That=20
> makes sense to me. Probably close enough for our purposes. What say you=
?
>
> I found my data. I think it may be just a bit more complicated. Best=20
> glide will likely give you the lowest fuel burn rate (gph); but since=20
> you=92re going fewer miles in an hour; it=92s not the best mpg. My best=
=20
> glide speed is about 90 kts; but my best mpg is about 130kts - quite=20
> flat from about 140 =96 120 kts. The burn rate was continuing to go dow=
n=20
> at 110 kts; which was as far as I took data.
>
> So minimum trip cost is at max MPG; if you consider your time as free. =

> But my plane seems to have a =91sweet=92 spot at 5500-5700 rpm, and at =

> 10,500 I can go about 170 KTAS at a tad over 10 gph, so that=92s what I=
=20
> do. I could slow to 130 Kts and burn a tad under 7.0 gph; but would I=20
> be happyJ?
>
> Al
>
And just one more factor to keep everyone confused or the conversation=20
going, whichever way you want to take it. The M in that MPG is the is=20
the miles of air your crossing...not the miles of ground. With a=20
tailwind, you'll want to pull the throttle back a little more and let=20
Mother Nature do some of the work of getting you to the destination. If=20
you've got a headwind, you're constantly being pushed backwards. Every=20
extra second in the air requires more energy to get back the headway=20
that was lost, so it makes sense to add some power and force your way=20
through it quickly.

How much to add or back off? Don't ask me. There some computer=20
programmers at the major airlines making really good bank trying to=20
figure that one out 8*)

(It also might make sense to fly at a higher altitude with more of a=20
headwind, because the thinner air offers less drag. The solution to that =

one is also left as an exercise for the reader 8*)