An improved secondary wing system of the canard type has been invented to improve performance and increase efficiency of airplanes capable of flight at supersonic and high subsonic speeds. Canards, including small forward-mounted secondary wings, are used to increase the total wing surface areas of airplanes in order to improve their low-speed lift-to-drag ratios and trim characteristics. Although canards have been used on supersonic airplanes to increase low-speed performance, heretofore the designs of canards have not provided for optimal high-speed performance and aerodynamic efficiency.
The present secondary wing system includes a single canard that can be pivoted about a vertical axis at its spanwise midpoint (see Figure 1). By such pivoting in conjunction with retraction or extension of fairings, the canard can be either (1) deployed to augment the lift, stability, and control of an airplane during lower-speed flight or (2) retracted conformally into the fuselage in order to minimize drag at higher speeds. The canard is equipped with leading- and trailing-edge control surfaces to enhance the aerodynamic performance of the airplane during use of the canard at low speed.
This invention is applicable to an airplane, the fuselage of which is area-ruled and includes a bulbous forward portion. A unique feature of this secondary wing system is that the secondary wing has a quasi-elliptical planform shape derived from an imaginary horizontal planar cut through an upper portion of the bulbous forward portion of the fuselage. The elliptical planform shape favors aerodynamic efficiency at low speed, thereby making it possible to reduce the engine power (and thus also noise) during low-speed operations, including takeoff, climb, and landing.
The lower surface of the canard is substantially flat as defined by the imaginary cut through the fuselage. When the canard is stowed, the upper surface of the canard (except at its edges) constitutes the surface of the upper portion of the fuselage from which the canard planform and loft was derived. When the fairings are extended at the leading and trailing edges of the canard to complete the stowage of the canard, the combination of the upper surface of the canard and the fairings define a streamlined surface contour that blends smoothly with the surface contour of the rest of the fuselage (see Figure 2), thereby promoting aerodynamic efficiency in high-speed flight. The characteristic fuselage shape that results from designing according to the area rule makes it possible to incorporate a canard that can be used at low speed and conformally stowed in the fuselage without incurring a significant wave-drag penalty at high speed.
The canard is connected to the fuselage by a ring-and-track mechanism, which includes (1) a submechanism for rotating the canard about a vertical axis for deployment or stowage as described above and (2) an actuated hinge submechanism that can be used to vary the angle of incidence of the canard when the canard is deployed. The design of this mechanism is such as to minimize its intrusion into the interior volume of the fuselage. The secondary wing system can include additional mechanisms for securing the tips of canard to the fuselage when stowed to prevent flutter and flutter-induced damage that could otherwise be caused by the aerodynamic loads that are present during high-speed flight.
Figure 1. The Canard Is Deployed by rotating it so that its spanwise axis lies perpendicular to the longitudinal axis of the fuselage, and is stowed by rotating it so that its spanwise axis lies parallel to the longitudinal axis of the fuselage.
Figure 2. The Upper Surface of the Canard and Fairing blend conformally with the adjacent upper fuselage surface.
This invention has been patented by NASA (U.S. Patent No. 5,992,796). Inquiries concerning nonexclusive or exclusive license for its commercial development should be addressed to the Patent Counsel, Ames Research Center, (650) 604-5104. Refer to ARC-14122.