Lift enhancing tabs for airfoils

I 1 1 1 1 1 1 l l 1 1 1 1 1 1 1 1 I 1 1 1 1 1 1 1 1 1 1 1 1 l l 1 1 1 1 1 1 1 1 l l 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 l l l l 1 1 1 1 1 1 1 1 l l 1 1 1 1 US005294080A

5,294,080

United States Patent 1191 [ i i ] Patent Number:

1451 Date of Patent: Mar. 15, 1994

Ross

4,702,441 10/1987 Wang .................................. 244/213

[54] LIm ENHANCING TABS FOR AIRFOILS

4,796,840 1/1989 Heynatz .............................. 244/213

[75] Inventor: James C. R o s s , Oakland, Calif.

FOREIGN PATENT DOCUMENTS [73] Assignee: The United States of America as 0230061 7/1987 EuropeanPat.0ff. .

represented by the Administrator of

2253877 6/1973 Fed. Rep. o f Germany ...... 244/213

National Aeronautics and Space

51663 3/1943 France ................................ 244/216

Administrn tion, Washington, D.C.

11205 of 1911 U n i t e d Kingdom .

496522 1 2 , 4 9 3 8 United Kingdom ................ 244/216

[21] Appl. NO.: 14,581 Primary Examiner-Galen L. Barefoot 1221 Filed: Feb. 8,1993 Artorney, Agent, or Finn-Darrell G. Brekke; Guy

Int. (3.5 ................................................ B64C 9/16

[51] Miller; John R. Manning

U.S. c1. ..................................... 244/215; 244/216

[52] 1571 ABsTRAcr Field of Sear& ................................ 244/213-216, [58] 244/201,204 A tab deployable from the trailing edge of a main airfoil 1561 References Cited element forces flow onto a following airfoil element, such as a flap, to keep the flow attached and thus en- U.S. PATENT DOCUMENTS hance lift. For aircraft wings with high lift systems that

3,126,173 3/1964 Alvarez-Calderon .............. 244/216

include leading edge slats, the slats may also be pro-

3,371,888 3/1968 Alverez-Calderon .............. 244/213

vided with tabs to turn the flow onto the following main

3,767,140 10/1973 Johnson .............................. 244/213

element.

4,039,161 8/1977 Bauer .................................. 244/213

4,117,996 10/1978 Sherman .

4,542,868 9/1985 Boyd . 13 Claims, 4 Drawing Sheets

Mar. 15, 1994 Sheet 1 of 4 5,294,080

U,S, Patent

I- I

I F C

I

k A C

FIG. 2

U.S. Patent Mar. 15, 1994 Sheet 2 of 4 5,294,080

FIG. 3

3 . 5

0.01~ tab, 0 . 0 1 ~ from

cove trailing edge \ A

. ( e g . f i g u r e 1 )

C I

2.5

\

Baseline airfoil

d .

1 I

I .5

-5 -I 3 I I 1 5

ANGLE OF ATTACK D E L

FIG. 4

0 . 0 1 ~ tab a t 0 . 0 1 ~ ahead

o f cove trailing edge \

IO

I I I

5 2 2.5 3 .5

U.S. Patent Mar. 15,1994 Sheet 3 of 4 5,294,080

FIG. 5

28 30

FIG. 6

FIG. 7 FIG. 8

FIG. 9

Sheet 4 of 4 5,294,080

US, Patent Mar. 15,1994

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1 2

aircraft in great jeopardy and is typically not an accept- able risk for civilian aircraft. LIFT ENHANCING TABS FOR AIRFOILS Vortex generators have also been used to increase flap effectiveness for high lift. The most successful ap- ORIGIN O F THE INVENTION 5 proach has been to place small vortex generators on the The invention described herein was made by upper surface of the flap element. The vortices energize ees Of the United States Government and may be manu- the boundary layer on the upper surface of the flap, and used by Or for the Government for govern- thereby causing the flow on the flap to remain attached Purposes without the p a p e n t Of at larger flap deflections than is the without the thereon or therefor.

10 vortex generators.

The aforementioned vortex generator concept has BACKGROUND O F THE INVENTION merit in that it is passive. Vortex generators produce The present invention relates generally to the field of drag, however, so whenever the flaps are deployed the aerodynamics and, more specifi&dly, to a lift enhancing vortex generators increase the drag of the aircraft. This tab capable of increasing the maximum lift capability 15 is not significant when extremely high l i f t is desired, and reducing drag at high-lift conditions for airfoils such as for landing, but for moderate lift conditions, as employing multielement flap systems. The tab i s placed during take-off and climb out, this additional drag can near the trailing edge of the cove of a multielement be significant. Making the vortex generators deployable airfoil and is nominally perpendicular to the lower sur- on the flap surface adds significant complexity and . face of the airfoil, and forces the airtlow leaving the 20 makes them much less attractive.

trailing edge to t u r n toward the following wing ele- Gurney flaps have also been used to enhance airfoil ment.

performance. Generally, a Gurney flap is a small tab, typically 1% to 2% of the airfoil chord, located on the TECHNICAL FIELD O F THE INVENTION lower surface (pressure side) at the trailing edge of the Flaps are control surfaces that are mounted at the 25 wing or airfoil. They are usually always placed only on trailing edge of the wing. Lowering the trailing edge the aft-most element of the a i r f o i l , and normally perpen- flaps adds to the effective area and camber of the wing dicular to the airfoil surface.

so that it develops more lift at low speeds. The small The most common use of a Gurney flap is in automo- bile racing. Wings are placed on many types of racing airflow through the gap formed between the flap and 30 cars in order to produce a large downward force so that the wing allows the wing/flap combination to generate the tires do not lose traction around high-speed comers.

a large amount of lift by delaying flow separation. Lead- The drag was found to increase significantly if the flap ing edge flaps or slotted slat elements are often used to was larger than about 1.5% of the airfoil chord. Func- increase the effective wing camber even further.

tionally, the Gurney flap modifies the exit angle of the For frxed wing aircraft, numerous flap deployment 35 flow at the wing trailing edge. Increasing the down- structures have been developed to generate high lift ward exit angle relative to the wing mean chord line during take-off and landing, for example. Currently, the increases the lift.

slotted trailing-edge flap, employing single or multiple The gurney flap is effective in increasing lift when slots, is the most common high lift device found on used on the trailing edge of a single element airfoil and airplanes. It is not uncommon for leading-edge slotted 40 on the trailing edge of the last flap element of a multi- slat elements or leading edge flaps to be used in con- element wing. It has limitations in that it is located at the junction with slotted trailing-edge flaps. Proper place- trailing edge which is generally very thin. This location ment and shaping of the different leading- and trailing- does not lend itself to a deployable device since the edge flap and/or slat elements can produce a wing with required hinge and actuation mechanisms would dictate a high-lift system that can generate large maximum lift 45 a thicker trailing edge than is desirable. An aircraft high and acceptably low drag.

lift system must be stowed or retracted when not Various means have been considered for increasing T h i s is important since the high lift system is needed.

or enhancing the lift capability of an airfoil. Several used only during take-off and landing and not during employ boundary layer control to maintain attached the majority of a typical flight.

flow on the trailing-edge flaps. Both jet blowing and Currently used flap systems have strong sensitivity to 50 moving surface boundary layer control techniques have Reynolds number and hence to the details of the ar- been employed effectively. For example, see J. A.

rangement of the various elements, particularly the gaps Chochrane et al., “Selected Results From the Quiet between the elements. A great deal of experimental Short-Haul Research Aircraft Flight Research Pro- validation of the performance of a system is neceSSary gram”, Journal o f Aircrafi, Vol. 19, no. 12, December 55 before it is incorporated into a new airplane. Since high 1982, pp. 1076-1082.

is difficult to perform and Reynolds number testing The aforementioned boundary layer control tech- very expensive, the many hours of high lift testing per- niques have the disadvantage of not k i n g passive, in formed on new aircraft configurations is generally done that they rely upon some source of power to maintain with small models and low Reynolds numbers rather attached flow on the flaps. T h i s reliance on external 60 than at actual flight conditions. As a result, high lift power leads to complex power delivery systems, partic- systems often do not perform as expected on the actual ularly for moving surface systems (generally a rotating aircraft because small differences in Reynolds number cylinder at the flap hinge). Moreover, the blowing type often makes a large difference in the performance of a of boundary layer control is not as mechanically com- particular high lift system.

plex as the moving surface type but suffers from the In order to generate large lift coefficients, aircraft 65 common inability to maintain high lift capability in the designers often use multiple slotted flaps and significant event of loss of power. Degradation in the performance amounts of Fowler action on the flaps. Fowler action is of a high lift system in the event of power loss places the a large aft translation of a flap element as it is deployed.

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This action adds some effective area to the wing plan- FIGS. 3 and 4 are graphs showing the effectiveness of a lift-enhancing tab placed 1% of the airfoil chord AC form during high lift operations, thus increasing lift.

ahead of the trailing edge of the cove; The mechanical systems required to perform this func- FIG. 5 is a schematic side elevational view of a wing tion are complex and are generally placed inside large 5 employing the device for enhancing lift according to fairings on the lower surface of the wing. These fairings another embodiment of the present invention; cause a significant increase in the drag incurred during FIG. 6 is a schematic side elevational view of a wing cruise flight. The fairings become larger as more flap employing the device for enhancing lift according to elements are added to the high lift system. Design, man- another embodiment of the present invention; ufacturing, and maintenance of complex flap systems FIGS. 7-9 are schematic side elevational views of 10 increases both the initial cost of an aircraft and the different embodiments of lift enhancing tabs according maintenance costs.

to the present invention; and Thus, a continuing need exists for devices which FIG. 10 is a side elevational view of a tab actuator increase the maximum lift capability and reduce the according to the present invention.

drag at high lift conditions for airfoils employing multi- element flap system.

DETAILED DESCRIPTION O F THE INVENTION SUMMARY OF THE INVENTION Referring initially to FIGS. l ( a ) , l ( b ) and 2, a device An object of the present invention is to provide a for enhancing lift of an aircraft wing 10 is shown sche- device for enhancing l i t of an aircraft wing which is 20 matically. The wing 10 is of the type having a high lift relatively simple in construction and compact.

system, and includes a fmed main element 12 which Another object of the present invention is to provide includes a leading edge 14 and a trailing edge 16. A a device for enhancing lift of an aircraft wing which movable element 18 also has an leading edge 20 and a renders the high lift system of the wing less sensitive to trailing edge 22, and is deployable from a cove 2 4 Reynolds number.

25 formed in the trailing edge portion of the fued main Still another object of the present invention is to element 12.

provide a device for enhancing lift of an aircraft wing A tab 26 is deployable from the fixed main element 12 which is more passive than prior techniques, thus pro- from the cove 24 near the trailing edge 16. The tab 26, viding easier operation and control.

when deployed as shown in FIGS. l(b) and 2, forces These and other objects of the invention are met by 30 airflow leaving the trailing edge 16 of the fmed main providing a device for enhancing lift of an aircraft wing element 12 to turn towards the movable element 18, having a fixed main element which includes a leading thereby maintaining attached flow and enhancing lift of edge and a trailing edge, and at least one movable ele- the wing 10. The movable element 18 in the illustrated ment deployable from one or both of the leading edge embodiment is a single-slotted flap. The height “h” of 35 the tab 26 is typically on the order of 1% of the chord and the trailing edge of the fmed main element and length (“AC” for the main element 12 and “FC” for the having a leading edge and a trailing edge, the device movable element 18) of the airfoil element on which it comprising means, deployable from one of the fued is installed, although this dimension can be varied to suit main element and the movable element, for forcing particular applications. Generally, the height h is se- airflow leaving the trailing edge of one of the fued main 40 lected to be sufficient to provide adequate turning of the element and the movable element to turn towards the airflow onto the following airfoil element to keep the other of the fmed main element and the movable ele- airflow attached. By including lift enhancing tabs into a ment, thereby maintaining attached flow and enhancing high-lift system design, the flap deflection angle may be lift of the wing.

increased over what is possible without the tab 26.

Another aspect of the present invention is to provide Typically, tabs 26 are provided for each movable an aircraft wing having a high lift system of the type element 12 of a wing, and each tab preferably extends described above and employing the forcing means also for the length of the corresponding movable element.

described above. In either case, the forcing means is Any suitable attachment means may be provided, such preferably a tab having a height typically on the order as a hinge, for pivotally or otherwise movably mount- of 1% of the chord length of the airfoil element on 50 ing the tab 26 on the movable element 18. Moreover, which it is installed.

any suitable actuators may be provided for moving the Other objects, advantages and salient features of the tab 26 from a stowed position recessed within the cove invention will become apparent from the following 2 4 to an operable position in which the tab 26 is nomi- detailed description, which, taken in conjunction with nally perpendicular to the underside surface of the cove the annexed drawings, discloses preferred embodiments 55 2 4 .

of the invention.

A test was conducted using a model wing having a hinged flap which had a chord length (FC) equal to BRIEF DESCRIPTION O F THE DRAWINGS 30% of the overall airfoil chord (“c”), as seen in FIG. 1.

FIG. l ( u ) is a schematic side elevational view of a The first configuration tested had the flap 18 (the mov- wing employing the device for enhancing lift according 60 able element) set so as to create a flap gap (“g”) to flap to a preferred embodiment of the present invention, and 0.052 and a flap overlap (“fo”) to chord chord ratio of showing a trailing edge flap in the non-deployed posi- ratio of 0.035. The flap was deflected downwardly at tion; 42.5” from its retracted orientation. Both the height h FIG. l ( b ) is a schematic side elevational view of the and the location of the tab could be adjusted for the test.

wing of FIG. 1 , with the flap in the deployed position; 65 Typical variations in the height were from 0.5% to 1% FIG. 2 is an enlarged view of the cove between the of the airfoil chord AC. The position (“p”--corre- trailing edge of the wing element and the flap element sponding to the distance of the tab from the trailing illustrated in FIGS. l ( u ) and l ( b ) ; edge of the flap) of the tab was varied from the trailing 5,294,080

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edge of the main element to a location that is 1.5% of Fowler flap track systems used on most commercial the airfoil chord ahead of the trailing edge. transport aircraft.

Preliminary results showing the effectiveness of a A lift enhancing tab 76 is pivotally connected to the liftenhancing tab placed 1% of the airfoil chord c wing element near a trailiig edge 78 and is normally ahead of the trailing edge of the cove are shown in 5 retracted into the lower surface of the wing 74. Any FIGS. 3 and 4. The tab significantly increases the lift at suitable pivotal connecting means, including a piano a given angle Of attack. The lift increment is equivalent hinge, could be used to connect the tab 76 to the wing t0 a 3.5’ Shift in the lift versus angle of attack curve. The element 74. The tab 76 extends for a length and height liftCnhanChg tab increases the maximum lift coefficient sufficient to effect the desired aerodynamic effect. “mi.

of the airfoil by more than 8% as well. 10 cally, the length (measured in the direction of the wing an even greater effect on element) corresponds substantially to the length of the The liftenhancing tab had the lift-to-drag ratio (LDh as seen i n FIG. 4. The tab flap element 72, although greater and lesser lengths can increased the maximum L/D by aPPro-atelY 40%. be employed depending on the type of aircraft.

The reduced drag is due to an increase in the amount of ~ ~ i c a l l ~ , the A rotary actuator 80 is rotatable in attached flow on the upper surface of the flap. The 15 either of two directions, as indicated by the arcuate Presence of the liftenhancing tab in the cove delayed directional m o w , by any suitable motor m a . A s t e l waration On the flap to about 20% Of the flap cable 82 retracts the tab when the flap is retracted. The Fc compared with 5% without the tab- The delayed rotary actuator 80 takes up and lets Out cable as n m - separation also increased the lift carried by the flap.

sary. The initial position of the tab 76 be &her FIG. 5 illustrates another embodiment in which the 20 forwardextending or rmardcxtenhg.

wing has a main having a leading edge 32 formations can be provided in the wing element 74 to and a trailing edge 34, a forward movable daXh%t 36, provide a flush or recessed position of the tab 76 when also known as a “slat”, having a leading edge 38 and a not deployed, trailing edge 40, and a rearward movable element 42 or During deployment the tab 76 is into position “flap” having a leading edge 44 and a trailing edge 46’ 25 by the air flowing though the slot and the cable acts to A lift-enhancing tab 48 located in the cove Of the main hold the tab 76 in the desired @tion. Due to the action element 30 is deployable into the operative position for Of the air a =lid linkage is not illustrated in FIG. 5, Similarly, a liftenhancing tab 50 is ment. Other actuator systems employing solid linkages deployable into the operative position from a cove be used’ formed in the slat 36. With the three element configura- 30 While advantageous embodiments have been chosen tion of FIG. 5, the slat can be deflected to a more nose- to illustrate the invention, it will be understood by those down position. hi^ allows the thee element airfoil to skilled in the art that various changes and modifications a higher lift coefficient than would be the caSe can be made therein without departing from the scope without the tab on the slat.

defied in the appended According to the present invention, the liftenhanc- 35 of the invention I ing tabs can be provided on either or both of the mov- 1 . A device for enhancing lift of an aircraft wing able elements. When the aircraft is in cruise flight and having a fixed main element which includes a leading the high-lift system is the tab 48 is simply re- tracted to make room for the flap 42 to nest in the cove. edge, a trailing edge, and a cove formed under the trail- Activation of the tab is easily accomplished since it can 40 ing edge, and a flap deployable from the trailing edge, of the trailing edge where hinge the trailing edges of the main element being positionally be located fixed with respect to the remainder of the main element, and actuation hardware do not affect the trailing edge geometry, particularly if the tab retracts i n the forward the device a tab, deployable from the trailing edge of the fued direction.

main element; and Other variations of the present invention are illus- 45 ~ ~ ~ a n s for actuating the tab to move from a non- trated in FIGS. 6-10. FIG. 6 illustrates an application of deployed position to a deployed position in which the cove tab 52 to the main element 54 of a wing 56 also the tab extends into the cove and towards a leading having a flap or movable element 58. In this embodi- edge of the flap, whereby the tab forces airflow ment, the main element 54 has no distinctive cove into .

leaving the trailing edge of the fixed main element which the flap 58 is retracted. Thus, the presence of a 50 to turn towards the flap.

cove is not necessary for operation of the present inven- 2. A device according the claim 1, wherein the flap tion. FIG. 7 illustrates a tab 60 near the trailing edge of the main element 62 in a preferred perpendicular orien- tab has a height between 0.5 and 1.0% of a chord length tation. FIG. 8 illustrates a tab 64 angled acutely aft of the main element.

55 3. A device according to claim 1, wherein the flap tab relative to a lower surface of the main element 66. FIG.

9 illustrates a tab 68 spaced inwardly of the trailing edge is nominally perpendicular to a lower surface of the of the main element 70 and having a range of pivotal main element when deployed.

movement indicated by the arcuate dkctional arrow. 4. A device according to claim 1, wherein the flap tab In the various embodiments of FIGS. 7-9, the tabs is positioned from the trailing edge of the main element illustrated could have been provided on the movable 60 a distance corresponding to about 1.0 to 2.0% of a elements of a wing structure employing a high lift sys- chord length of the main element.

5. A device according to claim 1, wherein the aircraft tem.

FIG. 10 illustrates a typical flap element 72 movably wing further comprises a slat element deployable from connected to an airfoil or wing element 74 through an the leading edge of the main element, and the lift en- external hinge 73. A linear actuator 75, such as a hy- 65 hancing device further comprises a slat tab deployable draulic cylinder with an extensible arm, moves the flap from the slat element near a trailing edge thereof and element 72 into and out of deployment. Other deploy- being deployable to an operable position when the slat ment systems could be used, such as the conventional element is deployed.

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6. A device according to claim 5, wherein the flap tab a tab deployable from the trailing edge of the fixed and the slat tab having a height between 0.5 and 1.0% of mah element; and a chord length of the main element and the slat element, III- for actuating the tab to move from a deployed position to a deployed position in which respectively.

the tab extends into the cove and towards the lead-

, . A device for enhancing lift of an

wing 5 ing edge of the flap, whereby the tab forces airflow having a fued main element which includes a leading leaving the trailing edge of the fued main element edge and a trailing edge, and a flap deployable from the to turn towards the flap.

bailing edge, the edge of the main element 9. A fmed aircraft Wing according to claim 8, wherein being positionally fued with respect to the nmainder of 10 the flap tab has a height between 0.5 and 1.0% of a the main element and defining a cove i n conjunction chord length ofthe main element.

with the flap, the device comprising: 10. A fixed aircraft Wing according to claim 8, a tab integrally formed on the trailing edge of the wherein the flap tab is nominally perpendicular to a m a i n element and being substantially perpendicular lower surface of the main element when deployed.

toalowersurfaceofthemainelement,andextend- 15 11. A fixed aircraft wing according to claim 8, ing into the cove and towards a leading edge of the wherein the flap tab i s positioned from the trailing edge forces dow leaving the O f the main element a distance COlXSpondhlg to about flap, whereby the trailing edge of the fixed main element to turn 1.0 to 2.0% of a chord length of the main element.

12. A fixed wing aircraft according to claim 8, further towards the flap.

20 comprising a slat element deployable from the leading 8. A f u e d aircraft wing comprising: edge of the main element, and a slat tab deployable from a main having a leading edge, a trailing the slat element near a trailing &ge thereof and being and a cove formed under the trailing edge* deployable to an operable position when the slat ele- the trailing edge of the main element being posi- ment is deployed.

tionally fued with respect to the remainder of the 25 13. A fued aircraft wing according to claim 12, main element; wherein the flap tab and the slat tab have a height be- a flap deployable from the trailing edge of the fued tween 0.5 and 1.0% of a chord length of the main ele- ment and the slat element, respectively. main element, the flap having a leading edge and a

trailing edge; and * * * * +