United States Patent [19] [11] Patent Number: 4,739,957 Vess et a1. [45] Date of Patent: Apr. 26, 1988 [54] STRAKE FENCE FLAP Primary‘Examiner-Galen Barefoot [75] Inventors: Robert J. Vess, Raleigh, NC; Attorney, Agent, or Firm-Lynn E. Barber; Paul Dhanvada Rao, Hampton, Va. Overhauser [73] Assignee: Advanced Aerodynamic Concepts, [57] ABSTRACT Inc., Raleigh, NC. The strake fence ?ap is a device which may be tailored to the aircraft to augment the low-speed lift of canard [21] Appl. N01: 860,841 con?gured general aviation aircraft with little or no [22] Filed: May 8, 1986 longitudinal trim change and no cruise drag penalty. The strake fence flap is deployed along the upper sur Int. Cl.‘ ............................................ .. B64C 23/06 [5 l] face of each of the strakes on the canard aircraft. The [52] U.S. Cl. .................................. .. 244/199; 244/213; 244/91 strake fence flap is hinged along its lower edge which [58] Field of Search ........... .. 244/199, 213, 215, 45 R, allows it to be retracted and extended as needed. In the 244/45 A, 91 cruise con?guration, the strake fence flap is folded ?ush with the strake upper surface. For deceleration or land [56] References Cited ing where increased lift and drag are required, the U.S. PATENT DOCUMENTS strake fence flap is extended. The frontal area of the strake fence ?ap becomes exposed resulting in addi D. 266,161 9/1982 Rosenthal ....................... .. 244/45 A tional drag. The geometry and positioning of the fence 2,650,752 9/1953 Hoadley ..... .. 244/199 3,471,107 10/1969 Ornberg 244/199 causes the flow to separate from the upper edge of the 3,744,745 7/1973 Kerker 244/ 199 fence and to roll up into a vortex which trails over the 4,466,586 8/1984 Bumham ........................... .. 244/213 strake. The intense suction which accompanies the vor tex acts directly on the strake upper surface, thereby FOREIGN PATENT DOCUMENTS signi?cantly increasing the lift. 1809593 9/1970 Fed. Rep. of Germany .... .. 244/199 160134 8/1957 Sweden ............................. .. 244/ 199 17 Claims, 4 Drawing Sheets US. Patent Apr. 26, 1988 Sheet 1 of4 4,739,957 FIG. 2 US. Patent Apr. 26, 1988 » Sheet 2 of4 4,739,957 US. Patent Apr. 26, 1988 Sheet 3 of4 4,739,957 \ \\ \ \l g \\ \ \ US. Patent ' Apr. 26, 1988 Sheet 4 of4 4,739,957 18\' 18w 4,739,957 1 2 gravity to maintain longitudinal trim. An aircraft wing STRAKE FENCE FLAP has a strake if its leading edge extends forward toward ' the fuselage, at an angle steeper than the rest of the FIELD OF THE INVENTION leading edge. (Sec FIG. 5.) The strake includes the This invention relates to aircraft lift-enhancing mech portion of the wing from the fuselage to the point on the anisms. In particular, the present invention relates to a leading edge of the wing where the leading edge begins device for augmenting the lift on the upper strake sur to extend forward toward the fuselage, and backward face of canard-type aircraft by vortex generation from to the trailing edge of the wing. For canard aircraft, a retractable ?aps placed behind the leading edge and on strake typically constitutes l to i of the wing span. the upper surface of the strakes. Since strakes usually contain the majority of the fuel load of the aircraft, the strakes represent a substantial BACKGROUND INFORMATION part of the total area of the rear wings. However, these In order for a pilot to effectively control an aircraft in strakes are not very ef?cient in producing lift since their all regimes of ?ight, he must be able to vary the forces large average chord would result in excessive thickness acting on it. This is accomplished by de?ecting various 15 if a normal cambered airfoil section was used. There ?aps on the ?ying surfaces of the aircraft which pro fore, a relatively ?at airfoil section with resultant low duce changes in the pressure forces acting on -those lift is usually used in' the strake region. surfaces. The con?guration of an aircraft and its mission The fact that the strake represents a substantial plan determine the shape, size, and placement of the ?aps. form area near the aircraft center of gravity which does 20 While certain types of ?aps are used to provide roll not generate a corresponding amount of lift is consid ing, pitching, and yawing moments which allow ered a compromise in the low-speed performance of changes in the ?ight path, other types are used to en otherwise cruise-ef?cient canard aircraft. However, hance the low speed lift and drag which determine the these features lend themselves well to other lift en landing performance of the aircraft. In common use are 25 hancement techniques, particularly if the resultant of ?aps which are hinged about the trailing edge of the the augmented lift can be contained in the region of the wing which, when de?ected downward, increase the strake upper surface that is close to the aircraft center of camber or a combination of camber and wing area re sulting in increased lift and drag. Similarly, there are gravity. This can be achieved by the generation of vor ?aps which pivot about the leading edge of the wing tices on the strake upper surface which is the basis of the and increase the camber when de?ected downward. design of the device disclosed herein. Both of these devices allow an aircraft to decelerate Flaps for Vortex Generation quickly, approach an airport at a steep descent angle, and land slowly. Devices which generate or manipulate vortical ?ow are known to the prior art. The invention of Rao (US. Canard Aircraft 35 Pat. No. 4,485,992) discloses a ?ap which is hinged There are some advanced aircraft con?gurations about the leading edges of a highly swept wing which which cannot utilize conventional landing ?aps due to shifts the center of lift on one wing panel to produce a the placement of their wing and tail surfaces. When rolling moment away from the deployed ?ap. This landing, these aircraft are thus forced to make shallower device is designed strictly as a roll control device which angle approaches that those utilized by conventional redistributes the lift generated by the existing leading aircraft. Of primary concern here is a so-called “ca edge vortices which are characteristic of all thin,‘high nard” aircraft. Such an aircraft is generally character ly-swept wings at high angles of attack. ized by a smaller forward wing known as a canard Kasper (US. Pat. No. 3,831,885) presents a device which is placed ahead of the main wing instead of be which is intended to augment lift on low-speed tail-less hind it as is of normal practice. Since this forward wing 45 airplanes such as the one described in US. Pat. No. generates a signi?cant amount of the total aircraft lift, 3,438,597. This device is actually a system of ?aps the resultant of the total lift force (neutral point) acts which work in conjunction to generate and stabilize somewhere between the fore and aft wings. In order to transverse spanwise vortices over the entire upper sur have a longitudinally stable aircraft, the center of grav face of the wing. Thus, the ?aps create an effectively ity (c.g.) must be placed ahead of this neutral point. 50 larger wing pro?le as sensed by the passing air?ows and Therefore, a change in the lift of either surface produces create sustaining aerodynamic lift forces in excess of a pitching moment about the center of gravity. This those which would be created by the cruising airfoil means that if trailing edge ?aps are used on the rear contour beyond stall angles of attack. The object of this wing, they must also be placed on the forward wing and invention is to create the spanwise vortices at an angle de?ected in such a manner to cancel the pitching mo 55 of attack below that at which they would occur natu ment produced by any rear wing ?ap de?ection. In rally on this particular type of wing. practice, the rear wing generates much more of the total aircraft lift than the canard due to its usually larger area. SUMMARY OF THE INVENTION Therefore, the pitching moment produced by any ?ap The strake fence ?ap of this invention is a device de?ection on the rear wing requires a substantial trim 60 which may be tailored to augment the low-speed lift of ming force from the canard which is usually not avail canard-con?gured general aviation aircraft with mini able. It is for this reason that canard aircraft generally mal longitudinal trim change and no cruise drag pen do not use high lift ?aps on the rear wing and, conse alty. The strake fence ?ap is deployed along the upper quently, suffer in the low speed regimes of ?ight. surface (as opposed to the leading edge) of each of the 65 strakes on the canard aircraft. The strake fence ?ap is Use of Strakes on Canard Aircraft hinged along its lower (front) edge which allows it to be Virtually every existing canard aircraft utilizes extended and retracted as needed. The mechanism for “strakes” to distribute fuel and baggage at the center of extension and retraction is well-known in the art of 4,739,957 3 4 aircraft flaps and is not part of the invention. In the or near the aircraft center of gravity and thus to mini cruise con?guration, the strake fence flap is folded ?ush mize or eliminate any change in the longitudinal pitch with the strake upper surface.