It is not necessary to allocate valuable forebody volume to strake-deployment mechanisms.
Inflatable nose strakes have been invented to assist in controlling the direction of flight of an airplane, especially a high-performance fighter-type airplane operating at a high angle of attack. In general, adjustments of the sizes, shapes, positions, and/or orientations of nose strakes gives rise to variations in forebody vortices and, consequently, to variations in aerodynamic forces. These variations can be used for flight control. Hinged, rigid nose strakes controlled by mechanical actuators via linkages have been investigated for use in forebody vortex control for flight control, but they entail a significant disadvantage; the actuators and linkages occupy valuable forebody interior volume that is needed for radar and other instrumentation. In contrast, inflatable nose strakes occupy much less forebody interior volume.
Figure 1 depicts a typical fighter-type airplane at a high angle of attack, equipped with inflatable nose strakes. Each inflatable forebody strake includes an inflatable elastic polymeric membrane mounted in a shallow recess in exterior skin of the forebody. The membrane is held in place by a clamping frame around the edge of the recess. A fluid coupling provides an opening into the volume enclosed by the membrane, for inflation or deflation of the membrane.
When the strakes are not inflated, the outer surfaces of the membranes lie flush with the adjacent forebody surface. When either strake is inflated, the outer surface of the membrane protrudes into the airflow, affecting the forebody vortices. If the strake on the right or left side of the forebody is inflated, the effect on the vortices is such as to give rise to a net leftward or rightward force, thereby causing the airplane to yaw to the left or right, respectively. If the membranes on both sides are inflated equally, the net effect is to generate a longitudinal or a pitch control force.
Figure 2 is a schematic diagram of the system for controlling the inflatable strakes. Any suitable pressurized fluid can be used to inflate the membranes; ordinarily, the preferred fluid is air because it can be handled easily, using equipment that adds little to the overall weight of the airplane. The pressurized air can be obtained via a tap from the airplane engine or from a separate compressor. A valve directs the flow of the pressurized fluid to neither, either, or both strakes. The pilot controls the valve through the airplane flight-control system.
This work was done by Peter T. Zell of Ames Research Center.
This invention has been patented by NASA (U.S. Patent No. 5,326,050). Inquiries concerning nonexclusive or exclusive license for its commercial development should be addressed to
the Patent Counsel
Ames Research Center
Refer to ARC-11979.