Innovators at NASA's Armstrong Flight Research Center are experimenting with a new wing design that removes adverse yaw and dramatically increases aircraft efficiency by reducing drag. Known as the PRANDTL-D wing, this design addresses integrated bending moments and lift to achieve a 12 percent drag reduction. The approach to handling adverse yaw employs fine wing adjustments rather than an aircraft's vertical tail. The technology has the potential to significantly increase total aircraft efficiency by optimizing overall aircraft configuration through the reduction in size or removal of the vertical tail as well as the reduction of structural weight. Similar improvements have been applied to propellers to achieve significant efficiencies with rotating machinery.
The Armstrong team (supported by a large contingent of NASA Aeronautics Academy interns) built upon the 1933 research of the German engineer Ludwig Prandtl to design and validate a scale model of a non-elliptical loaded wing that reduces drag and increases efficiency. The team also applied these concepts to improve propeller blades.
The wing design sought to reduce adverse yaw, which is the adverse horizontal movement around a vertical axis of an aircraft; the yaw opposes the direction of a turn. As an aircraft turns, differential drag of the left and right wings while banking contributes to adverse yaw. Proverse yaw—yawing in the same direction as a turn—would optimize aircraft performance. Initial results from flight experiments at Armstrong demonstrated that this wing design unequivocally established proverse yaw. This wing design further reduces drag due to lift at the same time.
The key to the innovation is reducing the drag of the wing through use of an alternative bell-shaped spanload, as opposed to the conventional elliptical spanload. To achieve the bell spanload, designers used a sharply tapered wing, with 12 percent less wing area than the comparable elliptical spanload wing. The new wing has 22 percent more span and 11 percent less area, resulting in an immediate 12 percent drag reduction.
Furthermore, using twist to achieve the bell spanload on an aircraft wing produces induced thrust at the wing tips. This forward thrust increases when lift is increased at the wingtips for roll control. The result is that the aircraft rolls and yaws in the same direction as a turn, eliminating the need for a vertical tail. When combined with a blended-wing body, this approach maximizes aerodynamic performance, minimizes weight, and optimizes flight control.
For propellers, a similar approach resulted in a technology that modifies the spanload using a non-linear twist. This twist dissipates the tip torque, reducing power required while maintaining thrust. Quieter performance results from reduced load and torque at the tip.
Conventional aircraft make use of elliptical loaded wings to minimize drag. However, achieving aircraft stability and control in conventional elliptical wings produces a strong adverse yaw component in roll control (i.e., the aircraft will yaw the opposite direction with application of roll control). Therefore, a vertical tail or some other method of direct yaw control is required, such as split elevons for use as drag rudders. The use of elliptical wings also results in a suboptimal amount of structure to carry the integrated wing bending moment.
Adopting the bell-shaped spanload change results in an immediate 12 percent drag reduction. In addition, optimization of the overall aircraft configuration is projected to result in significant overall performance increases.
In propeller systems or other rotating machinery, first-order analysis shows a more than 15 percent improvement in power consumption while producing the same thrust.
The benefits offered by this innovative wing design are not limited to aeronautics applications. For example, students at California State Polytechnic University, Pomona (Cal Poly Pomona) have leveraged the technology to develop a redesigned blade for industrial fans. The blade is 11 percent more energy efficient than typical blades and significantly quieter. This, in turn, reduces energy consumption, noise pollution, and carbon dioxide emissions as well as health hazards for workers. This work is being done in partnership with Armstrong’s Technology Transfer Office.
Armstrong has one patent issued (U.S. Patent No. 9,382,000) for this technology and has applied for a second patent (U.S. 15/239,293).
This technology is part of NASA's technology transfer program, which seeks to transfer technology into and out of NASA to benefit the space program and U.S. industry. NASA invites companies to consider licensing the Integrated Minimum Drag Solution (DRC-012-027) and/or the Integrated Minimum Drag Propulsion and Power Production technology (DRC-012-026) for commercial applications.
If you would like more information about this technology or about NASA's technology transfer program, please contact:
Technology Transfer Office
NASA's Armstrong Flight Research Center
PO Box 273, M/S 1100
Edwards, CA 93523-0273
Phone: (661) 276-3368