How much thrust would a jet engine need to give equivalent performance on an otherwise identical aircraft?

Question

This plane uses the Rotax 912 engine.

http://www.sporthornet.com/

This link gives the weight and specs of the Rotax 912 engine on page 7 of this .pdf it weighs between 154 and 180 lbs.

http://www.rotax-aircraft-engines.com/pdf/ac%20brochure.pdf

I don't know the take off speed of this airplane. Assuming a runway at 4800 ft on an average day.

Using this engine design tool...

http://www.grc.nasa.gov/WWW/K-12/airplane/ngnsim.html

tweaking settings on a turbofan engine that weighs 23 lbs, can produce upwards of 1060 lbs of thrust at 45 mph and 4800 ft.

What specs would a turbofan jet engine need to give equal performance to the Rotax 912 on the hornet?

If the Rotax weighs over 155 lbs and a turbofan jet could weight at little as 23 lbs and be so much more powerful, why not use a turbofan jet engine and save the weight?

Why are small scale jet engines not more widely used on small planes where weight is so critical?

Answer 1

Probably cost is the biggest drawback to development of the kind you're talking about. Cost to the manufacturer to develop, and cost to purchase, and cost to maintain. Bottom line is you could do it, but nobody would pay the million dollars that it would cost to buy a Sport Hornet equipped with a tiny turbojet engine.

Oh- since the airplane would be a "turbojet" pilots would need a type-rating from the FAA to fly the thing.

Turbine engines are in some cases more fuel-efficient than recips, but they are usually 10-20 times more expensive to purchase, maintain, and overhaul.

There is someone trying a turboprop engine out on a small biplane - google "turbine toucan"

There have been airplanes like the Cessna 206 and Beech Bonanza which have been fitted with turboprop engines, too.

Answer 2

Jet engines operate efficiently at high speeds and altitudes, and by producing large amounts of thrust.

A jet engine would not be suitable for the same airplane a rotax and propeller is useful for.  It's two different worlds.  That's why nobody is doing what you suggest.

Small jet engines are not efficient enough to take advantage of the aspects of jet engine power that make large jet engines useful.