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For the real engineers here
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 passes the reasonableness test as far as I can see. Any serious disagreements? 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. |
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