Boosting aircraft efficiency by reversing the load on the horizontal stabilizer

Abstract

This work aims at finding how reversing the direction of THS force improves aircraft performance. In most airplanes, the trimmable horizontal stabilizer (THS) is subjected to downward air force. This downward force acts in the same direction as the weight and opposite to the lift. The produced extra lift can be used to increase the payload or extend the range of the aircraft by carrying more fuel. The proposed design is based on shifting the wings location forward in order to make the force on the THS upward instead of downward. However, the stability of the airplane will be adversely affected. To address this issue, modern control theory is applied to the airplane elevator so as to maintain longitudinal stability. An airplane model based on longitudinal dynamics was used to investigate the stability of the airplane. Both current and proposed designs are simulated first without controllers and then with active controllers. The longitudinal dynamics’ equations are used to design the controllers so as to make the aircraft stable. The payload gain due to the proposed design is calculated; For a typical airliner, it is found that up to 21% increase in payload can be achieved using the proposed design. The proposed design where the load on the THS becomes upward instead of downward results in improving flight efficiency; that is, we can choose between increasing payload, extending the range, reducing the thrust, or using a smaller wing, or any combination of these benefits. In all these cases, there is an operational advantage. This advantage is translated to cost savings or higher revenues.