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NASA CASE NO.

PRINT FIG. 1

NOTICE

The invention disclosed in this document resulted from research in aeronautical and

space activities performed under programs of the National Aeronautics and Space

Administration. The invention is owned by NASA and is, therefore, available for

licensing in accordance with the NASA Patent Licensing Regulation (14 Code of

Federal Regulations 1245.2).

To encourage commercial utilization of NASA-owned inventions, it is NASA policy to

grant licenses to commercial concerns. Although NASA encourages nonexclusive

licensing to promote competition and achieve the widest possible utilization, NASA

will provide the necessary incentive to the licensee to achieve early practical

application of the invention.

Address inquiries and all applications for license for this invention to NASA Patent

Counsel, Langley Research Center, Code 143, Hampton, Virginia 23681-0001.

,/

LAR 14221-1

Serial No." 08/000,064

01-04-93 LaRC

(NASA-Case-LAR-14Z21-1) STALL

DEPARTURE RESISTANCE ENHANCER

Patent Application (NASA) 10 p

N93-19023

Unclas

G3/06 0149922
NASA Case No. LAR 14221-1 

STALL DEPARTURE RESISTANCE ENHANCER 

AWARDS ABSTRACT 

A stall departure resistance enhancer ("SDRE") for private, military or 

commercial aircraft, or for non-aerospace utility such as in flow defusers for turbines 

and other fluid flow apparatus. The device is used to induce vortical flow for delaying 

stall at or near the stall angle of attack. 

The present invention employs a flat triangular plate mounted to and extending 

from a leading edge of a wing of an aircraft. The flat triangular plate may be hingedly 

mounted on the leading edge of the wing, and a stop provided to prevent the plate 

from pivoting once the stall angle is approached. 

The SDRE of the present invention reduces drag forces associated with 

conventional apparatus since the device is a flat triangular plate mounted to a leading 

edge of a wing or other lift producing body. If the plate is hingedly secured to the 

leading edge, and a stop is provided for preventing hinged movement once the stall 

angle is approached, the drag is further reduced with no penalty in cruise or climb 

performance. 

Inventors: Holly M. Ross Joseph L. Johnson, Jr. 

Address: 1 16 Grays Landing 11 I Central Parkway 

Hampton, VA 23666 Newport News, VA 23606 

Employer: 

ss: 

LESC 

- ss: 

Retired NASA 

- 

Long P. Yip H. Paul Stough, Ill 

1324 Lake James Drive 107 Chuckatuck Turn 

Virginia Beach, VA 23464 Yorktown, VA 23693 

ss: - ss: 111' 

NASA LaRC NASA LaRC 

Initial Evaluator: J. Chambers 

Serial No.: 081000,064 

Filed: 01 -04-93 
LAR 14221-1 -1- PATENT APPLICATION

STALL DEPARTURERESISTANCEENHANCER

Origin of the Invention

5

10

The invention described herein was jointly made by employees of the

United States Government and a contract employee in the performance of

work under a NASA Contract and is subject to the provisions of Section 305

of the National Aeronautics and Space Act of 1958, as amended, Public Law

85-568 (72 Stat. 435; 42 USC 2457).

Background of the Invention

The present invention is directed to a stall departure resistance

enhancer ("SDRE") for aircraft for delaying or controlling air flow separation

15 by inducing vortical flow over a surface of the aircraft's wing.

Conventional apparatus of this type (generally referred to as "vortex

flow generators") consist of small wedges mounted on, and vertical to, the

upper surface of the wing. The vortical flow produced by the wedges delays

flow separation as the aircraft approaches the stall angle of attack.

20 In the above described conventional device, since the wedges are

affixed to the upper surface of the wing and extend vertically therefrom, they

produce drag forces which reduce airspeed and fuel efficiency. These drag

forces are always present since the wedges are fixed in place on the upper

surface of the wing, i.e., they cannot be removed from the flow when

25 desired.

Summary of the Invention

3O

The object of the present invention is to provide a stall departure

resistance enhancer or vortex flow generator with superior characteristics for
5

10

LAR 14221-1 -2- PATENT APPLICATION

preventing stalls, but which does not create significant drag.

The above object has been obtained by employing a flat triangular plate

mounted to the leading edge of the wing, which plate is rigid and has a sharp

tip and thin, sharp edges. The tip is pointed forwardly, and the centerline of

the plate extends through the tip in alignment with the freestream direction.

Since the plate is thin and is mounted on the leading edge of the wing, the

drag is reduced without sacrificing stall resistance characteristics.

In another embodiment, the plate is hingedly mounted to the leading

edge of the wing, and a stop is provided which prevents pivotal movement

of the plate at the predetermined stall angle. This embodiment is particularly

well suited for reducing drag.

Brief Description of the Drawings

15 FIG. 1 is a perspective view of an aircraft wing illustrating an

aerodynamic concept of the present invention;

FIG. 2 is an overhead view of a stall departure resistance enhancer

according to a first embodiment of the present invention;

FIG. 3 is an enlarged overhead view of the stall departure resistance

20 enhancer shown in FIG. 2;

FIG. 4 is a sectional view of the stall departure resistance enhancer and

wing shown in FIGS. 2 and 3, taken along sectional line A-A;

FIG. 5 is an overhead view of an aircraft wing employing the stall

departure resistance enhancer according to the first embodiment of the

25 present invention, including other leading edge modifications;

FIG. 6 is a graph showing lift characteristics for various angles of

attack for the wing shown in FIG. 5;

FIG. 7 is an overhead view of a stall departure resistance enhancer

according to a second embodiment of the present invention;

30 FIG. 8 is an enlarged overhead view of the stall departure resistance
5

10

LAR 14221-1 -3- PATENT APPLICATION

enhancer shown in FIG. 7;

FIG. 9 is a sectional view of the stall departure resistance enhancer

shown in FIGS. 7 and 8, taken along sectional line A-A;

FIG. 10 is another enlarged overhead view of the stall departure

resistance enhancer shown in FIGS. 7-9;

FIG. 11 is an enlarged front view of the stall departure resistance

enhancer shown in FIGS. 7-10; and

FIG. 12 is an enlarged side view of the stall departure resistance

enhancer shown in FIGS. 7-11.

Detailed Description of the Embodiments

The stall departure resistance enhancer or "SDRE" of the present

invention (Fig. 1) induces vortical flow over the upper surface of a wing 1.

15 The vortical flow adds energy into the boundary layer by mixing some of the

high energy fluid from the external flow into the low energy shear layer near

the wing's upper surface and also acts as an aerodynamic fence which

prevents separated flow from spreading to the outboard wing. Thus, the

wing 1 has flow that remains attached at higher angles of attack and

20 improves the aircraft's stall departure resistance.

In the first embodiment (Figs. 2-4), the SDRE (shown within circle "A"

in Figs. 2 and 3) is simply a flat triangular plate pointing forwardly from a

leading edge of the aircraft wing 1. The triangular plate is shown with a 60 °

sweep as measured between left and right leading edges 2, 3 (Fig. 3),

25 although it is possible to employ different sweep angles for the triangular

plate. The tip 4 is sharp, and the left and right leading edges 2, 3 are thin

and sharp in order to induce vortical flow. The thickness of the plate is

minimal (Fig. 4), but it is sufficient to keep the device rigid at all angles of

attack. When mounted to an aircraft wing 1, the device's centerline should

30 be aligned with the freestream direction, so that on a straight wing (Fig. 2),
LAR 14221-1 -4- PATENT APPLICATION

the centerline is perpendicular to the leading edge of the wing 1, and for

tapered or swept wings, the centerline is at a predetermined angle to the

leading edge of the wing 1.

The inventors have conducted wind tunnel tests on the SDRE of the

5 present invention which show the device to work very well on a wing with

a leading edge sweep angle of 26 ° (Fig. 5). Two SDRE's were used on the

inboard section on each side of the wing 1 in combination with other leading

edge modifications 5, 6. Flow visualization using small yarn tufts showed

that the SDRE's worked to produce vortices which kept the flow organized

10 even at high attack angles. Testing performed using a free-to-roll apparatus

showed that the SDRE's were necessary in order to provide stable roll

damping for the configuration that they were tested on. Static force test

results showed that, with the leading edge modifications 5, 6 shown in Fig.

5, resistance to autorotative moments was gained as shown by the flat top

15 lift curve (modified wing curve with square boxes) in Fig. 6.

In the second embodiment of the SDRE of the present invention (Figs.

7-12), the triangular plate (shown within circle "A" in Figs. 7 and 8) is

modified so that it may be hingedly attached (Fig. 10) to the leading edge of

the wing 1. A stop (not shown) is incorporated so that, as the stall angle of

20 attack is approached, the plate is prevented from pivoting and begins to

induce vortical flow. The advantage of this type of device as compared to

the SDRE of the first embodiment is that, due to the hinged action, no drag

penalty in cruise or climb performance is incurred prior to the employment of

the SDRE for preventing stalls.

25 Figs. 8 and 9 are overhead views of the SDRE of the second

embodiment, similar to the overhead views shown in Figs. 2-4 with respect

to the first embodiment, while Figs. 10-12 are enlarged top, front and side

views, respectively, of the SDRE of the second embodiment. The same

reference numerals are used for the first and second embodiments to identify

30 similar features.
LAR 14221-1 -5- PATENT APPLICATION

Fig. 10 shows a mounting rod 7 having a boss portion 8 secured at an

end thereof. The rod 7 is secured at a base end to the leading edge of the

wing 1, and the triangular plate has a slit cut along the plate's centerline with

a pin 9 bridging the slit near the tip end 4 of the triangular plate. The pin 9

5 is inserted into the boss portion 8 so that the triangular plate is hingedly

mounted to the mounting rod 7. As noted above, a stop (not shown) is used

to limit the hinged movement of the plate.

The SDRE of the present invention has been shown to increase the lift

by up to 30% at angles of attack that would otherwise be in the post stall

10 region. In other words, the device is excellent for delaying stalls. It prevents

the wing lift from suddenly dropping, after near what would be the stall

angle, and keeps the lift at around its maximum value. Also, the SDRE

improves the flight handling characteristics near the stall angle of attack.

The SDRE of the present invention is clearly suitable for use in civilian,

15 military and commercial aircraft. In fact, there is great potential for improved

maneuverability and flight handling characteristics for fighter aircraft in the socalled "post-stall" regime, which is of great interest at this time.

The SDRE of the present invention also has other non-aerospace

applications such as for controlling flow separation in flow defusers to be

20 used in combustion power generators and hydro-electric turbines. For these

applications, the SDRE might lay flat on the surface until needed, and then

deflect into the flow to produce vortical flow for delaying or suppressing stall.

There may also be other applications that will occur to engineers involved in

fluid machinery design, fluid flows in processing plants, etc., and the above

25 description is thus not intended to limit the many potential applications of the

invention.
LAR 14221-1 PATENT APPLICATION

STALL DEPARTURE RESISTANCE ENHANCER

Astract of the Disclosure

A stall departure resistance enhancer for an aircraft for controlling flow

separation by inducing vortical flow over the upper surface of the wing. A

flat triangular plate is secured to a leading edge of the wing to reduce drag,

and the tip of the triangular plate is sharp and the edges are thin and sharp

10 to induce good vortical flow. The thickness of the plate is minimal, but it is

sufficient so that the plate remains rigid for all angles of attack. A tip of the

triangular plate protrudes forward from the leading edge of the wing, and the

centerline of the triangular plate extending through the tip is aligned in the

freestream direction. In a second embodiment, the triangular plate is hingedly

15 secured to the leading edge of the wing, and a stop is provided to limit the

hinged movement of the plate at or near the stall angle of attack.
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