United States Patent [19] [11] Patent Number: 4,739,957 Vess et a1. [45] Date of Patent: Apr. 26, 1988

[54] STRAKE FENCE 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 to augment the low-speed lift of [21] Appl. N01: 860,841 con?gured general 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

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18\' 18w 4,739,957 1 2 gravity to maintain longitudinal trim. An aircraft STRAKE FENCE FLAP has a strake if its extends forward toward ' the , 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 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 . 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. The air?ow over the ing moment of the aircraft while greatly enhancing the strake is not disturbed by the presence of the retracted lift. fence and the wetted area of the aircraft is not altered Another object of the invention is to provide a device since the strake fence ?ap occupies existing surface area to produce drag for deceleration of a canard-con?gured of the strake. The result is no net drag rise due to the aircraft. strake fence ?ap in this position. Another object of the invention is to design a strake In the deceleration or landing mode, where addi fence ?ap which does not require mounting on the tional lift and drag are required, the strake fence ?ap is leading edge of a strake, but may be mounted on the extended. Preferably, strake fence ?aps on both strakes upper surface of a strake. will be extended an equal amount at the same time. The Another object of the invention is to design a strake frontal area of the strake fence flap is projected into the fence ?ap that may be hinged about its lower edge. air?ow above the strake resulting in additional drag. Another object of the invention is to design a strake The geometry and positioning of the strake fence ?ap fence ?ap which is both extendable and retractable. causes the flow to seperate from its upper edge and roll Another object of the invention is to design a strake up into a vortex which trails longitudinally over the fence-flap which is ?ush with the aircraft exterior when strake. Due to the usually large leading edge radius and retracted so as to produce no additional drag. thickness of the strake, a leading edge vortex does not Another object of the invention is to design a flap form naturally at a moderate as it would system with adaptability to the aerodynamic require on a thin wing with the same leading edge sweep. ments and constraints of a particular aircraft. Therefore, the maximum lift attainable on the strake is Still other objects and advantages of the invention solely dependent on the aforementioned airfoil shape will become apparent to those of skill in the art after and the extent of attached ?ow if the strake fence ?ap is reading the following the description of the preferred not deployed. However, when a vortex is created due 25 embodiments. to an extension of the strake fence flap, the intense suc» tion which accompanies the vortex acts directly on the BRIEF DESCRIPTION OF THE DRAWINGS strake upper surface, thereby signi?cantly increasing FIG. 1 is a perspective view of a typical canard-type the lift. aircraft with delta-shaped strake fence flaps in the de The strake fence flap may be positioned on the strake 30 ployed position; so that the resultant of the vortex lift acts at, or close to, FIG. 2 is a perspective view of the strake fence ?ap in the aircraft center of gravity, thus minimizing or totally the deployed position; eliminating any longitudinal pitching moment while FIG. 3 is a perspective view of the strake fence ?ap in greatly enhancing the overall lift of the aircraft. Simi the retracted position and the associated air?ow; and larly, the strake fence ?ap may be positioned to control FIG. 4 is a perspective view of the deployed position the trajectory of the vortex to avoid potential problems of the strake fence ?ap and the associated vortex gener such as propeller vibration due to vortex impingement ation, which is representative of a deceleration or land on its blades. ing mode. The size and geometry of the strake fence ?ap is FIG. 5 is a plan view of a canard-type aircraft having determined for a particular aircraft such that it pro the strake fence ?ap system of the invention. duces a strong, stable vortex which trails close to the FIG. 6 is a view of different shapes the strake fence surface of the strake and persists past the trailing edge ?ap may have. without breakdown. Optimization of this geometry must also include consideration of the frontal area re DESCRIPTION OF THE PREFERRED quirements for the desired drag increment and any 45 EMBODIMENTS other constraints which are dictated by the aircraft on FIG. 1 is a perspective view of a typical canard-type which it will be used. These will usually result in a aircraft with strake fence flaps deployed on the upper strake fence ?ap with a surface area which will be be surface of the strakes. The aircraft includes a forward tween lO to 30 percent of the surface area of the strake wing or canard 1, and rear wings 2. Each rear wing also to which it is af?xed. The preferred angular orientation includes a strake region 3, which is the region where the of the strake fence ?ap (as de?ned by the angle between angle of the leading edge 4 projects forward (changes a line perpendicular to the longitudinal axis of the air sweep) as it nears the fuselage 5. The area of the strakes craft and the lower hinged edge of the ?ap) will be is carefully distributed about the center of gravity of the between 60 and 80 degrees in either a clockwise or aircraft so that when they are loaded internally with counterclockwise direction. However, tests have indi varying amounts of fuel or baggage, the center of grav cated that the vortex generated by the flap acts on a ity is not shifted signi?cantly. greater area of the strake when the ?ap is pointed FIG. 2 is a closeup view of the left strake as illus toward the fuselage, as shown in the drawings (i.e. the trated in FIG. 1. The strake fence ?ap 6 is extended angular orientation is between 60 and 80 degrees of a above the upper surface 7 and behind the leading edge counterclockwise rotation for the left strake, and a 28 of the strake. The flap is depicted with a representa clockwise rotation for the right strake. tive triangular shape having a front face 8, a lower hinged edge 9, a free upper edge 10, and a rear edge 11. OBJECTS OF THE INVENTION In this extended position of the ?ap, the upper edge 10 One object of the invention is to increase the maxi and the rear edge 11 project upward from the strake mum lift attainable of a canard-con?gured aircraft. 65 surface, while the front face 8 becomes exposed to the Another object of the invention is to design a strake oncoming air?ow. fence ?ap system which may be so positioned as to FIG. 3 is a perspective view of the left strake region allow the resultant of the created vortex lift to occur at showing the strake fence ?ap in the retracted or cruise 4,739,957 5 6 position. The air ?ow over the wing is indicated by the not essential that this width continue to increase until it arrow over the wing. The front face of the ?ap 13 is reaches the opposite end of the ?ap. In the double ?ush with strake 14, allowing the air?ow to pass undis gothic shape for example, the width of the ?ap gradu turbed. Since the flap in this position occupies existing ally increases from the ?rst tip 32 closest to the traverse wetted area of the strake, no drag penalty is realized. axis to the midpoint, then decreases towards the second FIG. 4 is a perspective view of the extended position tip 33. of the strake fence ?ap which is representative of a We claim: deceleration or landing mode. The air ?ow over the 1. An aircraft strake-?ap combination comprising: wing is indicated by the arrow over the wing. Since the an aircraft strake having a top side and a bottom side; ?ap is situated at an effective angle of attack with re 10 a front and a rear; spect to the free stream flow direction, the front face 15 a leading edge and a trailing edge; and provides projected frontal area and, hence, produces a strake fence ?ap attached to the top side of the the drag required for quick deceleration. As the ?ow aircraft strake; said flap having a lower edge, said impinges on the ?ap, it shears toward and separates lower edge having a ?rst tip and a second tip; from the unattached edge 16. The formation of a strong, capable of being placed in a ?rst position wherein the stable vortex 17 results and trails back longitudinally flap is ?ush with the top surface of the strake; over the upper surface of the strake. The intense suction capable of being placed in a deployed position such which accompanies the vortex therefore acts upon the that the ?ap extends at an upward angle of de?ec strake, producing a net augmentation in the lift as tion relative to said strake; shown by the upward arrow. The combination of the 20 said ?rst tip being positioned on the strake closer to increased lift and drag produced by the de?ection of the the front of the strake than said second tip; strake fence ?ap allows the canard aircraft to assume a said ?rst tip having an acute angle; said ?rst tip being slower, steeper descent to landing which has not been positioned on the strake closer to the centerline of demonstrated without major complications with con the aircraft than said second tip; and the width of ventional flap systems common to the prior art. 25 the ?ap increasing from the ?rst tip to a maximum FIG. 5 is a plan view of the same canard-con?gured width with the maximum width occurring rear aircraft presented in the previous figures with the strake ward of the ?rst tip. fence ?aps of this invention. This ?gure clari?es the 2. The aircraft strake-?ap combination of claim 1 geometry which is characteristic of canard aircraft with wherein: the aforementioned canard 18, rear wings 19, strakes 20, 30 the ?ap can be moved to any position between the and fuselage 21. Dashed line B indicates the outer ?rst and deployed positions. bound of strakes 20, which are also bounded by the 3. The aircraft strake-?ap combination of claim 1 fuselage 21. Although the strake fence ?aps are in wherein: tended to be deployed together, they are shown in the the angle between a line perpendicular to the longitu retracted 22 and extended 24 modes on the left and right 35 dinal centerline of the aircraft and the lower edge strakes, respectively. Notice on the left strake 20 that of the strake fence ?ap is 60 to 80 degrees. the flap 22 lies ?ush with the strake surface and is posi 4. The aircraft strake-?ap combination of claim 1 tioned behind the leading edge 23. The lower hinged wherein: v edge of the ?ap is positioned at an angle A with respect the strake fence ?ap has a triangular shape. to the traverse axis of the aircraft. Ideally, this angle A 5. The aircraft strake-?ap combination of claim 1 is between 60 and 80 degrees. Howver, this angle may wherein: . also ideally be between 100 and 120 degrees, in which the strake fence ?ap has a cropped delta shape. case the ?ap would “poin ” in the opposite direction, 6. The aircraft strake-?ap combination of claim 1 but still have the same angular orientation with respect wherein: to the air?ow. 45 the strake fence ?ap has a gothic shape. The right strake region shows the strake fence flap 24 7. The aircraft strake-?ap combination of claim 1 in a vertically deployed position with a representative wherein: vortex 25 trailing back as discussed previously. This the strake fence flap has a double gothic shape. illustrates the importance of the ability of this invention 8. A canard-con?gured aircraft comprising: to be positioned as required to obtain the maximum 50 a fuselage; bene?ts while avoiding any detrimental effects. Here, a forward canard wing the spanwise position is determined such that the vortex a main wing located behind the forward canard wing avoids contact with the propeller disk 26. Also note having a strake; that, once the resultant of the vortex lift force is deter said strake having a top side and a bottom side; mined for a particular application, the longitudinal posi 55 a front and a rear; tion of the ?ap must be determined such that it allows a leading edge and a trailing edge; and this force to act close to the aircraft center of gravity 27 a strake fence flap attached to the top side of the so as to avoid any major changes in longitudinal trim. aircraft strake; said ?ap having a lower edge, said The shape of the ?ap may take several forms, in addi lower edge having a ?rst tip and a second tip; tion to the vdelta shape disclosed in the previous draw 60 capable of being placed in a ?rst position wherein the ings. FIG. 6 discloses cropped delta 29, gothic 30 and ?ap is ?ush with the top surface of the strake; double gothic 31 shapes which may also be used. How capable of being placed in a deployed position such ever, regardless of the particular shape employed, it is that the ?ap extends at an upward angle of de?ec essential that the flap be capable of de?ecting air?ow tion relative to said strake; upward and into a vortex. This is accomplished by 65 said ?rst tip being positioned on the strake closer to ensuring that the width of the ?ap increases from the the front of the strake than said second tip; point closest to the traverse axis of the aircraft to a point said ?rst tip having an acute angle; said ?rst tip on the ?ap further from the traverse axis. However, it is being positioned on the strake closer to the cen 4,739,957 7 8 terline of the aircraft than said second tip; and 13. The canard-con?gured aircraft of claim 8 the width of the flap increasing from the ?rst tip wherein: the strake fence ?ap has a gothic shape. to a maximum width with the maximum width 14. The canard-con?gured aircraft of claim 8 occurring rearward of the first tip. wherein: 9. The canard-con?gured aircraft of claim 8 wherein: the strake fence ?ap has a double gothic shape. the ?ap can be moved to any position between the 15. The canard-con?gured aircraft of claim 8 ?rst and deployed positions. wherein: _ 10. The canard-con?gured aircraft of claim 8 the strake fence flap is located forward of the center 10 of gravity of the aircraft. wherein: 16. The canard-con?gured aircraft of claim 8 the angle between a line perpendicular to the longitu wherein: dinal centerline of the aircraft and the lower edge the ?rst tip of the strake fence ?ap is located forward of the strake fence ?ap is 60 to 80 degrees. of the center of gravity of the aircraft and the sec 11. The canard-con?gured aircraft of claim 8 ond tip of the strake fence flap is located aft of the wherein: center of the gravity of the aircraft. the strake fence flap has a triangular shape. 17. The canard-con?gured aircraft of claim 8 wherein: 12. The canard-con?gured aircraft of claim 8 the strake fence flap is located aft of the center of wherein: 20 gravity of the aircraft. the strake fence flap has a cropped delta shape. * * it it *

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