Not much bigger than some of the larger model jets, the SubSonex prototype flew recently.

http://www.sonexaircraft.com/press/r...pr_081011.html

Originally intended to fly with a turbine derived from a model turbine it now uses a turbojet based
on an APU used in aircraft like the L-39 Albatros. - John.

Would be easy to model...

Man it seems like the one thing that is always broken on jets is the stupid APU! I would hate to rely on it for power lol.

But either way its still more reliable then a piston engine.

I see the life of a BD-5 evolving again in the jet-Sonex. Especially in this economy. +1 with gunrad, APU power is scary. I have intentions on building another full-scale BD-5, but with the market of 150+lb thrust turbines for UAV's now, it makes sense to use one of those, more than the APU turbines.

The amount of modification's necessary to make an APU produce thrust and be able to have a throttle, would be outrageous. This has already been done/tried and been a failure on the BD-5. They had to run at 100% power all the time, and had thrust attenuator clamshell's to vary the rearward thrust

Just like my own design jettrainer

http://www.youtube.com/watch?v=R2vbma343eg

Or the jetcap

http://www.youtube.com/watch?v=rUuYsH_9MNI