Augments Control of Lifting Forces by Regulating Flow Reattachment Using Miniature Adjustable Surfaces Affixed to Wings or Fins
This miniature sliding control surface fixes to the leading edge of a lifting surface to improve precision maneuverability in aerial and underwater vehicles as well as sailboats. Manned and unmanned aerial and submerged vehicles benefit a variety of industries and have key applications for military defense. The unmanned aerial vehicle (UAV) market alone should to reach an estimated $52.3 billion by 2025. Aerial and submerged vehicles must often perform precise maneuvers at low speeds to complete operations such as takeoff, landing, surveillance, docking, and turning. During these maneuvers, the forces and moments generated by lifting surfaces operating at high angles of attack must be controlled. The boundary layer separation that occurs during these operating conditions stalls fluid flow over the control surfaces, making handling difficult. Available control augmentation solutions utilize flow control or leading-edge flaps. Flow control systems tend to be expensive and bulky due to their need for external power/reservoirs, and they are generally difficult to incorporate into existing designs. Leading-edge flaps elicit undesired transients when deflected and are large compared to the lifting surface requiring a significant amount of energy to operate.
Researchers at the University of Florida have developed a high angle of attack control augmentation surface that is miniature, low-cost, lightweight, and low-power. This control surface mimics the design of a bird’s alula to improve stability and precision handling at low speeds.
Application
Sliding control surfaces for air and water craft that enhance stability and maneuverability
Advantages
- Can be configured to any air or underwater vehicle with a lifting surface and sailboats
- Enhances lift during low speed and high angle of attack conditions, increasing vehicle control takeoff, landing, and surveillance scenarios
- Restores roll control authority in post-stall flow conditions
- Adds little extra bulk to wings of craft, reducing the cost and weight of control augmentation
- Can be stowed during off-design conditions minimizing drag penalty
Technology
This control surface operates similarly to the alula on a bird’s wings, which act as small control surfaces on their leading edges. It aligns with the leading-edge of the lifting surface and protrudes upwards at an angle when deployed. Its leading surface is flush with the leading surface of the lift structure or offset from the leading edge. The control surface is considered miniature as its length is less than 20 percent of the length of the lift structure, and more than one may affix to the same lift structure. The control surface’s distance from the side edge of the lifting surface is critical to its performance. Two different configurations are possible: stationary or sliding. The stationary control surface acts as a passive lift enhancement device resulting in a fixed amount of lift augmentation dependent on the spanwise distance of the control surface from the side edge of the lifting surface. In the correct location, a stationary pair of control surfaces is shown to enhance the lift of the lifting surface up to 25 percent in a post-stall flight condition. Importantly, the wetted area of the control surface is only 2 percent of that of the lifting surface. The sliding configuration utilizes a mechanical system to translate the control surface along the span of the wing to actively control lift augmentation. Asymmetric translations of two control surfaces can control rolling moments. The roll control effectiveness of the sliding control surface in post-stall conditions is comparable to that of a conventional flap-aileron operating in an attached-flow condition. Notably, the wetted area of the alula is one order of magnitude smaller than that of the referenced aileron.
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