[Gdeaver]

One problem your going to have is that with that size airframe and power you have almost no electronics payload budget. If you go up in scale and to gas power, there are some off the self options. What I' m thinking off is a pocket PC with a GPS add on. The position, altitude, velocity, heading are available. Use the pocket PC as the main brain. Visual studio Ide can be used to program the pocket PC. The Intel processor has more power than a microcontroller. With the proper cable a pocket PC can out put serial commands. There are servo controller chips based on pic16's that can take the serial command from the pocket pc and generate the hobby servo PWM signals. A rs232 converted is needed. the next part is to use gyro's designed for helicopters and planes. There are single axis units and 3 axis units. They are what stabilizes the RC helicopters. With control of 3 axis, stable straight level flight is possible. These gyro's are designed to take PWM input from the RC receiver and mix these commands with the stabilizing out of the gyro to give smooth control. Release the joy sticks and the plane will return to straight level flight. The Pocket pc controlled servo chip replaces the RC receiver in auto pilot mode. Don't underestimate the magnitude and cost involved with this project.