Drag control system for flying machine, process for estimating drag of flying machine, boundary layer control system, and boundary layer control process

1. Field of the Invention The thrust T of an airplane is estimated by a thrust estimating device, and the motion state (the speed, the angular speed, the attitude angle and the elevation angle) of the airplane is detected by a motion state detecting device. Then, a drag estimating device estimates the drag D of the airplane, based on the thrust T and the motion state of the airplane. An operation-amount calculating device converges the steering angle into a target steering angle at which the drag of the airplane is minimized, by repeating the operation of varying the steering angle of a flap by a very small angle by an operating device, and further varying the steering angle by a very small angle, while monitoring the increase or decrease in drag resulting from such variation. Such a drag reducing control is carried out, while monitoring the actual drag and hence, is extremely effective, and also can exhibit an effectiveness, irrespective of the motion state of the airplane.