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06-09-2009 | 12:34 AM

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DarZeelon

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From: Rosh-HaAyin, ISRAEL

RE: Is An OS 55AX The Right Engine?

Spinner,

Let us examine this from the horse-power perspective...

How much more output (HP/kW) do you think are needed, to go twice as fast?...

Let us see; drag must be overcome and it grows by the square of speed... I.e. overcoming drag, while going twice as fast, requires 4 times as much thrust...
Had it been a jet engine, or a rocket motor; rated in lbs thrust, it would be all you need.

But no; this is an engine driving a prop, which must apply this quadruple force...
At twice the speed; this force must be applied at twice the rate per time unit...

So, going twice as fast absorbs (and requires) no less than eight (8) times the horsepower.

Twice the HP would make the same plane (with the same drag) go faster, by the cube root of 2; i.e. only 26% faster. That is all!

So, your notion of having double the HP, no longer looks as appealing to you as it did; does it?

Going 1/4th faster than before is visually noticeable, but is not as easy to see as going twice as fast.
Double the static thrust would double the static acceleration of the same weight, however.

I am not sure flying a model, with a prop as large as the wing-span, would be very appealing... 'Appalling' may be a more descriptive term...[

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'Too much POOOWWWAAAH' is to me, a profanity...

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