I spec'd out the F80 motors for a VTOL plane weighing 3kg. I couldn't get the endurance I wanted. After a bunch of ecalc iterations, I choose to use 4 t-Motor antigravity 4006, KV380 motors. http://store-en.tmotor.com/goods.php?id=440
With a 8,000mAh battery, ecalc estimates more than an hour in plane at max efficiency. Obviously, that doesn't include the power required to take off and transition to plane and back to copter for landing. But I am estimating i'll get at least 30 mins in plane with a nice reserve, which will allow me to map several hundred acres per flight
This is all theoretical as I haven't completed my build. I got side tracked repairing a crashed drone.