Marty, i was referring to the JetCats in the Avonds F-15 with pipes...that really sounds vaccum-cleanerish. Heard the eurosport with pipe, too....also not convincing, but better.

But why ultra light engines? 2 KJ-66, right back in those nozzles, no pipe, no hassle...put the batteries in the nose and off you go.
See here:
[link=http://www.jo-schaeffler.de/Jetmetting%20Cham/picture-0005.jpg]Twin F-15 no pipes[/link]

PS: twice as many components to fail, but infinetely small probability of a full failure on both systems in 1 flight...