Is it possible to build a rc model plane that can fly up to 2-3 hours at high alt.?

GPS would be out of the question due to the amount of electronic gear necessary unless you simply used it to set your current level above sea and position at the beginning of flight. From there, to not lose your plane entirely, you'd have to build in some sort of real-time gyro-based control feedback system (I did this for missiles for TI), which is not for non-engineers as it presents a bit of task for us even when trained. The easiest way would be to simply have a GPS base on the ground that would tell the plane how far up it is and how far it is (in Euclidian coordiantes) from the GPS, so that it knew where it's "boundaries" were. I'd use a Zilog or other uProcessor but you can do it with an FPGA or any of the (now) majorly packed logic gates, as most of it will just be a large nested if-then set of conditions. As to the flight level, remember that air thins as you go up, so you will have a max flight level for your current plane, probably less than 2000 feet. If you don't want to either find or hire someone nerdy enough to do all of this, I'd look instead at a home rocket based system with a very good parachute. They can get pretty good flight heights and are fairly stable with pictures if you can use a fast ISO and shutter speed. Much luck, Shawn Harvey, EE

It's technically possible, but not with the kind of stuff that you can buy in your average hobby shop. You'd also need to be an MIT student just to put it all together and it would cost thousands of dollars. The US military and police force have been doing this kind of stuff for years, but you're average citizen neither has the money nor the skills to do it. You'd also have to be VERY careful legally because if you fly too high or start spying on people you're going to get arrested. People tend to get very shirty if you hover an RC plane over their hot tub to spy on them. Expect gunfire, then a law suit.