It's been done before, 3 or 4 years ago. It was a university project with some funding from industry, with remote weather sensing as the excuse. Aerosonde or some such name. They launched 3 aircraft with approx 10 ft wingspan, crashed one on launch (which was from a car roof rack), one headed off into the Atlantic and was never seen again and one made it to Scotland. From memory it had a 9kg payload and used 6 litres of fuel in a 20cc engine.
Still, good luck to the amateurs.