United States Patent [11] Patent Number: 4,485,992 Rao [45] Date of Patent: Dec

United States Patent [11] Patent Number: 4,485,992 Rao [45] Date of Patent: Dec. 4, 1984 [54] LEADING EDGE FLAP SYSTEM FOR 4,161,300 7/1919 Schwaerzler et al. ........... 24/90 R AIRCRAFl' CONTROL AUGMENTATION 4,182,503 1/1980 Muscatel1 ............................ 24/219 4,267,990 5/1981 Staudacher ......................... 244/199 [75] Inventor: Dhanvada M. Rao, Hampton, Va. 4,293,110 10/1981 Middleton et al. ................. 24/214 [73] Assignee: The United States of America as FOREIGN PATENT DOCUMENTS represented by the Administrator of the National Aeronautics and Space 517422 1/1940 United Kingdom ................ 24/214 Administration, Washington, D.C. Primary Examiner-Galen L. Barefoot [21] Appl. No.: Attorney, Agent, or Firm-Howard J. Osborn; John R. 522,628 Manning [22] Filed: Aug. 12, 1983 [571 ABSTRACI- Related U.S. Application Data Traditional roll control systems such as ailerons, elevons or spoilers are least effective at high angles of [63] Continuation of Ser. No. 301,078, Sep. 10, 1981, abandoned. attack due to boundary layer separation over the wing. This invention uses independently deployed leading [51] Int. (3.3 ................................................ B64C 9/00 edge flaps 16 and 18 on the upper surfaces of vortex [52] U.S. Cl. ................................... 244/W R 244/214 stabilized wings 12 and 14, respectively, to shift the [58] Field of Search ............... 244/213, 214, 199, 207, center of lift outboard. A rolling moment is created that 24/90 R, 90 A is used to control roll in flight at high angles of attack. ~561 References Cited The effectiveness of the rolling moment increases lin- early with angle of attack. No adverse yaw effects are U.S. PATENT DOCUMENTS induced. In an alternate mode of operation, both leading 2,070,705 2/1937 Barnhart ............................. 24/214 edge flaps 16 and 18 are deployed together at cruise 2,635,837 4/1953 Grant ................................ 244/90 R speeds to create a very effective airbrake without appre- 2,768,801 10/1956 Bitner et al. ...................... 24/90 R ciable modification in pitching moment. Little trim 3,143,317 8/1964 Walley et al. ....................... 244/214 3,471,107 10/1969 Ornberg .............................. 244/199 change is required. 3,831,885 8/1974 Kasper ................................ 24/214 4,132,375 1/1979 Lamar ............................... 24/90 R 5 Claims, 8 Drawing Figures WING I SPAN US. Patent Dec. 4, 1984 Sheet 1 of 4 4,485,992 0 HIGH ANGLE OF ATTACK FIG. 2 LOW ANGLE OF FIG. 3 ATTACK US. Patent Dec. 4, 1984 Sheet 2 of 4 4,485,992 WING 1 SPAN FIG. 4 .o I CI (ROLLING- MOMENT COEFFICIENT) 0 DVERSE YAW (YAW CnMOMENT COEFFICIENT 1 -.o I .o C, (COEFFICIENT OF LIFT) FIG. 5 US. Patent Dec. 4, 1984 Sheet 3 of 4 4,485,992 0 0 0- 0 4 ! +I +I X 3 E3 z az 0 00 v) >a z aa 0> WJ W ak J a W 3 c c L. J dI L 0 c LL W 0 0 -1 0 c z- wc Iz ow I- 3" y ZL JW JO 00 a v U.S. Patent Dec. 4, 1984 Sheet 4 of 4 4,485,992 ‘01 I -LIFT DRAG CL (COEFFICIENT OF LIFT) FIG. 2 E 0 CL (COEFFICIENT OF LIFT) FIG. 8 4,485,992 1 least effective due to boundary layer flow separation LEADING EDGE FLAP SYSTEM FOR AIRCRAFT close to the leading edge of the wing. CONTROL AUGMENTATION Another object of the invention is to provide a roll control device, unlike traditional aileron controls, that ORIGIN OF THE INVENTION 5 produces favorable yawing moments in flight that are The invention described herein was made in the per- not adverse to coordinated flight control. formance of work under a NASA contract and is sub- A still further object is to provide a device that when ject to the provisions of Section 305 of the National used in combination with conventional elevons pro- Aeronautics and Space Act of 1958, Public Law 85-568 duces a synergistic control effect making simultaneous (72 Stat. 435; USC 2457). lo use of the leading edge flap and elevons more effective This application is a continuation of application Ser. to control roll than a simple addition of their individual No. 301,078, filed 9/10/81 now abandoned. effects would indicate. A final object of the invention is to provide an alter- BACKGROUND OF THE INVENTION nate mode that is a powerful airbraking system by de- This invention generally relates to aircraft roll con- l5 ploying both leading edge flaps simultaneously to cause trol systems. Particular application is to aircraft with rapid and controlled deceleration from high speed flight vortex stabilizing capabilities such as highly swept with neither an increase in pitching moment nor a re- wings or spanwise blowing device. Roll control is quired trim change. achieved with a leading edge flap system and vortex flow manipulation. 20 SUMMARY OF THE INVENTION Leading edge flaps are known to the prior art. One The foregoing and other objects of the invention are such device is the Krueger flap (see e.g., Dommasch D. achieved by using leading edge flaps on subsonic, tran- O.,Airplane Aerodynamics, Pitman Publishing Corpora- sonic, supersonic and hypersonic aircraft to manipulate tion, 4th ed., p. 186). The Kreuger flap pivots about the 25 the vortex flow over a wing so as to generate an aircraft leading edge of the airfoil to augment lift. By rotating rolling moment. Wind tunnel tests have shown that an the leading edge flap downward below the chord line, upper flap affixed to the leading edge of a wing gener- the camber of the wing is increased. This increase in ates an inboard vortex that is energized by the shear camber increments lift. The Krueger flap, however, is layer leaving the unattached edge of the flap. At high not used for roll control. It functions solely by camber 30 angles of attack, the redistribution of lift caused by the modification rather than vortex generation. flap vortices shifts the center of lift on the wing out- The patent to Kasper (US. Pat. No. 3,831,885) dis- board. Accordingly, whenever a leading edge flap is closes another type of leading edge flap. Kasper’s flap raised on one side of an aircraft, the resulting asymme- produces lift on low performance aircraft through vor- try in lift generates an aircraft rolling moment. tex generation. It is designed and structured for low 35 Wind tunnel tests show that the magnitude of the performance aircraft. As a result, the flaps are necessar- rolling moment increases with greater angle of attack. ily highly cambered and thicker than the present inven- As a result, roll control can be maintained with leading tion. Also, the length and width of the Kasper flap edge flaps when ailerons and spoilers are less effective represents a greater percentage of the associated wing’s due to upstream flow separation. Furthermore, results span because its low performance wing application. of 40 indicate that yawing moments remain favorable Kasper’s flaps are not used for roll control. Spanwise lift throughout flap deployment and retraction. The ad- distribution over the wing is not manipulated to create verse yaw problems associated with aileron roll control a rolling moment. The Kasper flap is used solely to systems are avoided. The drag penalty due to the lead- augment lift on low performance tailless aircraft. ing edge flap operation is negligible because vortex- The problem of roll control exists with aircraft. all 45 created thrust on the flap surface counteracts the drag Solutions have been varied and numerous. Generally, due to flap deployment. Tests also show that a synergis- ailerons or spoilers provide the rolling moments needed for aircraft maneuverability about their longitudinal tic effect on roll power is realized at lift coefficients axes. These control surfaces, however, are essentially above 0.6 whenever conventional elevons are used in dependent for efficient operation on attached flow over combination with leading edge flaps. The vortex gener- the wing’s upper surface. As a result, ailerons and spoil- 50 ated by the flap augments the effectiveness of the ele- ers are largely ineffective when flow separation occurs vons so as to create more roll power than would be ahead of them near the leading edges of the wings. The anticipated based on a simple summing Of the individual loss of roll controllability with these prior art devices in roll control contributions from elevons and flaps- high lift conditions, when lateral stability and roll 55 In an alternate mode of operation, both leading edge damping are also reduced, deteriorates tracking ability, flaps can be deployed simultaneously at cruise speeds to handling characteristics, and resistance to departure generate a large drag force. The drag provides a rapid from controlled flight. The present invention avoids and controlled deceleration from high Speed flights. No these adverse effects with the use of independently adverse Pitching moment is induced. AS a result, the opcrated leading edge flaps. 60 trim change associated with conventional high drag It is therefore an object of the invention to disclose a devices, Such as Speed brakes, is not required. The roll control system that uses a leading edge flap device steady flow field associated with the vortex system of to create a vortex that shifts the center of lift on one the leading edge flap assures low levels of buffet and wing panel outboard to produce a controllable rolling wake excitation of the empennage structure unlike tra- moment away from the deployed flap. 65 ditional airbrake devices that generate turbulent wakes. A further object of the invention is to provide a roll A more complete appreciation of the invention can be control device allowing roll moment control at high gained by referring to the following detailed description angles of attack where prior art roll control systems are and associated drawings.

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