On Wed, 25 Jun 2008 10:56:07 -0700 (PDT), pappson@[EMAIL PROTECTED]
wrote in
<f21210b7-96ff-44c6-9b4b-120e489e7682@[EMAIL PROTECTED]
>:
>I'm thinking of a clean glider, one that might weigh 1500 pounds and
>has a glide angle of say 1 in 25. At 50 miles an hour, that would mean
>in an hour's time it might descend two miles (of course scale it
>reasonable numbers, I chose those for ease of calculation). That means
>it's losing about 1500 * 5280 * 2, or about 16 million foot pounds of
>energy an hour.
>
>Now if I add an engine swinging an 8 foot diameter prop, maybe as a
>pusher, the question is, how big an engine for cruise only? A
>horsepower is 550 foot lbs a second, or about 2 million foot pounds
>an hour. If all of that is correct, it suggests with a 50% efficient
>prop a little 16 horsepower engine could pretty much keep this thing
>at constant altitude.
>
>It p***** the reasonableness test as far as I can see. Any serious
>disagreements?
>
It looks reasonable to me, but I'm not qualified to judge.
>For those of you who do things in metric units? I went to school a
>long long time ago, and here in the US I can buy a little Briggs and
>Stanton (spelling?) engine with a horsepower rating, not a kilowatt
>one.
Here's a solution for SI conversions:
http://online.unitconverterpro.com/
[rec.aviation.soaring added]
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