Analysis of Different Stabilizing Control Systems for Aircraft with Automated Cruise Flaps

Cruise flaps are a promising method of increasing aircraft performance by reducing drag, but their use is restricted to applications where increased pilot workload is not a significant detriment. Recent research has focused on automating the cruise flap to achieve low drag without the increased pilot workload. In this paper, a flap controller developed in an earlier research effort is revisited and is compared with a new controller developed in this effort. The earlier controller uses the current lift coefficient to adjust the flap angle towards the optimum value for minimum profile drag. As shown using static-stability analysis in earlier research, such a controller is unstable unless it is accompanied by an elevator controller that maintains the lift coefficient. The current work revisits this controller and confirms the earlier results using dynamic-stability analysis. A new controller is developed in which the flap angle is adjusted to achieve a desired lift coefficient, leaving the elevator controller to achieve a desired angle of attack as needed to minimize profile drag or any other objective. The new controller has the advantage that it can be implemented to automate multiple flaps along the span of a wing. Dynamic analysis of the aircraft with the new controller is explored in this paper.