Interesting idea..... internal Jet with pop up pipe

Noise? No problem. It is in the air, and you are
on the ground with your remote control transmitter!
But seriously, could it be any worse than a Caproni
A-21J?

Cooling? All in the inlet. You would have to bring
in not only enough aire for the jet, but also to help
in circulating the air to dissipate the heat. Use
the exhaust as the power source for a jet pump to help
in drawing the surrounding air out of the cavity.

Bending the tail pipe? Man, will you ever loose out
big time on thrust. But in a model that will typically
have orders of magnitude more thrust than a full size
plane, you can loose half and still look pretty good.

Best bet is to stick it out into the breeze. It is
small and won't add that much drag while it is being
started. Ask Bob C about how much his Silet performance
degrades with the jets out but not running. Measureable
and noticable, I am sure, but nothing like hanging
an engine and 5 foot diameter prop out there!

But, an interesting thought.

Steve