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Jet Glider Sparrowhawk

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Old January 13th 04, 05:55 PM
Mark James Boyd
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Default Jet Glider Sparrowhawk

OK, what the heck. How about a superlight, turbine powered,
short wing, aerobatic, under $40K aircraft that'll
do 100 knots under full power, burn 5 gal/hr at 50 knots
in level flight, and climb at 500+ ft/min gulping
20 gallons/hr?

Prepare for SWAGs (Scientific Wild Ass Guesses)...

Here's what I gathered from





The AMT engines will provide
20 Newtons of thrust (about 4lbf) for one hour with 1 gallon of JetA.

The Sparrowhawk, with a turbine engine extended, has drag of
maybe 100 Newtons at about 50 knots (this is a guess from the
PIK 27 site and windward, and assuming 60lbs fuel on board,
and the extended engine doubling the drag).
Sustained level flight at this speed requires 5 gal/hr.

At 100 knots, the Sparrowhawk should drag 400 Newtons, which
is 20 gal/hr. Or, the Sparrowhawk can climb at 500 ft/min
with the same fuel consumption.

Assuming we have about a 10 gallon tank (gimme some slack here,
yeah, JET A is 6.84 blah, but whatever...) we can climb at
full power for 30 minutes at 50 knots, or cruise at 100 knots
for 30 minutes in level flight, or cruise at 50 knots for
two hours.

This allows (based on published Sparrowhawk gross weight)
a 170# pilot and 30# of engine+accessories + 10 gallons of fuel.

If one wishes to keep it an "ultralight", the tank can be 5
gallons instead (and a 30# heavier pilot) with halved range.

So we get a 170# pilot with a 100NM range or 12,000 ft of
climb, or a 200# pilot with a 50NM range or 6000 ft of climb.

This also assumes two AMT-450 engines (400 Newton max thrust)
or one AMT-1700 (880 Newton max thrust) throttled way back.

I'd believe my guesses are accurate within a factor of two for
everything. If fact is worse than guess, 250 fpm climb for 8
minutes or 15 minutes of cruise at 50 knots is pretty
pitiful. On the other end, 1000 fpm or 120 knots for
an hour is pretty great.

The harder questions a
How to mount the thing?
Will it fit?
Where does the fuel tank go?
Weight and balance?
How about all that heat?
Who wants to fly it first?
Can it take off from under 2000 ft?
Who's got the cash?

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