"Eric Greenwell" wrote in message
...
Mark James Boyd wrote:

Eric Greenwell wrote:

Mark James Boyd wrote:
At 500 lbs, a notional Sparrowhawk with two AMT-450s

would accelerate at .12 g's (2 knots/second), to 40 knots
in 20 seconds using 1200 feet of runway. Assuming wheel
friction and drag make this figure double, under 2400
feet of runway is still respectable.

Wouldn't that be (500/(45+45) = 0.18 g's ? Or 3.4 knots/second to 40
knots in 10.4 seconds, and about 330 feet? So doubling is only 600 feet.


I avoided the math and safe-sided the heck out of it and
got a way too big figure. Thanks for the extra work


Using one engine, 0.09 g's gives 1.7 knots/sec, 21 seconds to 40 knots,
and 640 feet, doubled to 1280. With all due respect to Mike B, I might
be happy with one engine.
Eric Greenwell


For self-launch, perhaps, but for 100 knot level flight,
or 500 fpm climb, 200 Newtons (45 lbf) may be not enough.
I haven't done the disciplined math for this, nor
do I know the actual drag in Newtons of the Sparrowhawk.
I suppose this can be calculated rather than SWAGed based
on weight and the shape of the polar, eh? Any takers?

That's an easy one. Basically, the weight/(L:d) at the speed of
interest. Sticking with the 500 pounds weight, the drag at best L (36)
is 500lb/36=14 pounds, leaving 30 pounds thrust to climb. 500/30=17 L
climbing; climb rate is [59 knots at best L]/17=3.5 knots 350 fpm. Not
great, but interesting. For 500 fpm climb, a 56 lbf unit would do it.

For a 2000 foot climb:

- 2000'/350fpm = 6 minutes
- 6 min x 460 grams/min = 1200 grams, or almost a gallon liquid.

So, carrying 5 gallons would give you one launch, a 4000 foot climb out
of a big holes, and some travel towards home at 100 knots.

The L at 100 knots ~ 12, so 500/12=41.5 lbf for level flight, so that
goal is met with one engine.

OK, these are a bit optimistic, because I assumed the engine added no
drag. It does show one engine is close to being good, but a 55-60 lbf
engine would be "ideal".

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Eric Greenwell
Washington State
USA

Have you math whizzes figured out how far the wing runner will have to run
before this dog whistle is going fast enough to have aileron control?

Bill Daniels