When you have the flaps up fully closed the servos should not hum. You can prevent the servos from having continious load by making sure that the servo horn is parallel with the control rod when the flaps are in the up position. Do the same when with down postion and you will have a strong setup and not eat up your RX batteries. Basically you need to account for the amount of servo travel as the flap's horn travel. Make sence?