If you are trying to push the flaps beyond what the hinges will allow then you are straining the servo. When you are setting them up restrict the travel to some small amount using End Points then gradually increase the travel until you get to the mechanical limit or to the position you want. The way a servo works is it keeps trying to get to the commanded position. It does this by increasing the current going to the motor to try to get it to move. Eventually, the servo gets to the point that it cannot take any more current and the motor burns out.