Radar Cross-Section
Someone mentioned earlier about the visibility of a "microlight" (as it was then assumed to be) on radar.
A few years ago I was working with a Middle-East Government and a N.American company on "Low-Altitude and Low Radar Cross-Section incursion detection" The website for the "light" shows around 200kg empty weight -yes, the engine is probably a fair proportion of that weight but on its own it would have presented a very poor radar X-section and the chances of it being seen reliably by a "regular" (civil or military) radar would not be good.
(Off-topic, but for interest, we were using a 2-metre Doppler-shift type of detection which did not give az-el information, but would be set out in about 1-km "sectors" to allow suitable aerial/missile interception to be launched. A principle that Boeing and I both discovered at around the same time many years ago - but they patented it!)
Maybe there's an argument for "tinfoil" to be incorporated in the GRP panels of such "very-lights"? Just my 2 dirhams worth?