With the F-5E-3, you have the option of selecting flaps to AUTO, in which (central air data computer, I guess) will position the flaps optimally for your AOA and airspeed; or manually set them to UP, FIXED (an intermediate position), or FULL. And if the landing gear is down, I think the flaps are automatically set to FULL when AUTO is selected. I think manual mode, UP position is the default setting. If you choose AUTO, then you get what the plane thinks they should be. If you get into PIO (pilot induced oscillations - porpoising), the AUTO flaps may go a little nuts trying to set flaps for whatever you are trying to do, because your PIO has the AOA bouncing up and down. As mentioned by randomTOTEN, make sure your fuel is balanced. There's a switch to have the fuel system balance it for you, but you have to start it early in the flight. BTW, left and right fuel tanks are really front and rear internal fuselage tanks. So an imbalance affects CG and longitudinal stability. The F-5 wings are too thin, I guess, for internal wing tanks. So, setting flaps to manual - UP, I think you can take off and land with flaps UP, if you wish...might need a long runway, though. I like to set them manually, myself. But don't forget to raise them to UP (or AUTO) after takeoff. :) Also, don't forget to raise the gear after takeoff...and close the speed brakes before takeoff! I have taken off a few times with the speed brakes out. Checklists are a real good thing. Hope that helps. (or read the manual and study the flaps switches on the throttle and next to the throttle)