NOTICE

NASA CASE NO. LAR 14682-1

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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 23665-5225.

Serial No.: 07/887,002

Filed: 05-22-92 LaRC

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NASA Case No. LAR 14682-1 

AWARDS ABSTRACT 

CONTROL AND AUGMENTATION OF PASSIVE POROSITY 

THROUGH TRANSPIRATION CONTROL 

Pressure loading of a member is caused by movement of a fluid andlor the 

member relative to one another. Mechanical devices such as strakes and flaps are often 

used on vehicles to effectively alter the exterior surface of the vehicular member to 

achieve a desired reaction to loading. Also various air loading displacement systems are 

used which suck air from a high pressure area andlor forcibly exit air at a low pressure 

area to compensate for load induced pressure gradients. These mechanical devices and 

displacement systems are relatively complicated, have significant energy requirements, 

add weight to the vehicle, consume often critical space, and are often ineffective over a 

wide range of angles of attack and lift conditions. 

A device for controlling pressure loading of a member is provided which consists 

of a porous skin mounted over the solid surface of the member and separated from the 

solid surface by a plenum. Fluid from an area exerting high pressure on the member may 

enter the plenum through the porous surface and exit into an area exerting a lower 

pressure on the member, thus controlling pressure loading of the member. A 

transpirational control device is provided which adds or subtracts pressure or mass to the 

plenum which causes the pressure loading on the forebody to increase or decrease on 

the desired side providing increased control of the forebody. 

INVENTORS: Daniel W. Banks 

Address : 21 1 Collins Drive 

Newport News, VA 23601 

ss: m 

Richard M. Wood 

700 Berklev Court 

Virginia ~e-ach VA 23542 

Steven X.S. Bauer 

ss: - 

21 1 Collins Drive 

N~wDo~~ News, VA 23601 

ss: 

Employer: NASA LaRC 

 valuator: Edgar G. Waggoner 

Serial No.: 071887,002 

Filed: May 22, 1992 
LAR 14682-1 -1- PATENT APPLICATION

CONTROL AND AUGMENTATION OF PASSIVE POROSITY

THROUGH TRANSPIRATION CONTROL

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Ori.qin of the Invention

The invention described herein was made by employees of the United

States Government and may be used by and for the Government for

governmental purposes without the payment of any royalties thereon or

therefor.

Back,qround of the Invention

. Technical Field of the Invention

15 The present invention relates generally to controlling the pressure load

on various members, and more particularly to the active control of pressure

loads using porosity.

20

Discussion of the Related Art

Pressure loading of a member can be caused by movement of the fluid

and/or the member relative to one another. For example, many portions of an

aircraft such as its forebody, canopy, fuselage, wings and tails are subjected

to high air loads during flight. These air loads can vary significantly with model

25 attitude and forward flight speed. Of particular concern for high performance

military aircraft is that, depending on the geometry of the aircraft and its angle

of attack, it may experience a large side force which results in a yawing

moment which may be difficult to control. At low angles of attack the flow field

is usually symmetric. As the angle of attack increases, two counterrotating,

30 stationary vortices form on the leeward side of the forebody of the aircraft. At
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LAR 14682-1 -2- PATENT APPLICATION

higher angles of attack, the vortices become asymmetric creating greater

pressure on one side of the aircraft forebody than the other thus resulting in a

net side force and yawing moment. If not controlled, the resultant force and

moment on the vehicle can be extreme and create an unsafe condition or

significantly reduce the flight envelope of the aircraft.

Likewise, many helicopter components such as the tailboom, helicopter

body, rotor hub and the rotor itself bear high loads. Land based vehicles such

as cars, trucks, vans and especially tractor trailers often encounter huge loads

due to inadequate front, top and rear designs. Also buildings, in particular

roofs, are exposed to loads from wind conditions which can cause undue strain

and even catastrophic failure.

Numerous solutions have been proposed for controlling pressure load

which are usually member specific. Initial design of the exterior of the member

is an important consideration but is unable to adapt to changing loading

conditions. Mechanical devices such as strakes and flaps are often used on

vehicles to effectively alter the exterior surface of the vehicular member to

achieve a desired reaction to loading. Also various air loading displacement

systems are used which suck air from a high pressure area and/or forcibly exit

air at a low pressure area to compensate for load induced pressure gradients.

These mechanical devices and displacement systems are relatively

complicated, have significant energy requirements, add weight to the vehicle,

consume often critical space, and are often ineffective over a wide range of

angles of attack and lift conditions. Most attempts to reduce air loading on

buildings involve initial exterior design as well as flexible internal structure which

yields slightly to wind loads.

It is accordingly an object of the present invention to control pressure

loading on members.

It is another object of the present invention to control pressure loading

over a wide range of member attitude and free stream flow conditions.
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LAR 14682-1 -3- PATENT APPLICATION

It is another object of the present invention to achieve the foregoing

objects with a simple control device using minimal energy.

It is a further object of the present invention to achieve the foregoing

objects with minimal spatial and mass requirements.

It is yet another object of the present invention to accomplish the

foregoing objects in a simple manner.

Additional objects and advantages of the present invention are apparent

from the drawings and specification which follow.

10 Summary of the Invention

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According to the present invention, the foregoing and additional objects

are obtained by providing a pressure equalization device for use on a member

exposed to a fluid load. This device consists of a porous outer skin, a solid

inner surface and a transpirational control device. The porous outer skin is

mounted over the solid inner surface with a plenum created between the two

such that the fluid may pass through the porous material into the plenum and

back through the porous material to equalize the external pressures on the

member. The transpirational control device controls the flow through the

porous outer skin by regulating the conditions in the cavity beneath this outer

skin. Ideally the porous outer skin has a surface porosity of about 10 to 20%

and can be made from a porous material or from a solid material which has

been perforated. If the latter method is used, the perforations should be no

more than about one boundary layer thickness in diameter. The thickness of

the porous outer skin should be no less than the diameter of the perforations.

The plenum may be divided into smaller, separately controlled plenums, which

may be interconnected. The transpirational control device may be a vacuum

pump, stored pressure, stored vacuum, or engine bleed air.

3O
LAR 14682-1

Brief Description of the Drawinqs

-4- PATENT APPLICATION

Fig. 1 is a perspective view showing a porous skin mounted outside of

a solid surface;

5 Fig. 2 is a cross sectional view taken along line I1-11;

Fig. 3a is a side view of a forebody, fig. 3b is a cross-sectional view

taken along II1-111showing the vortices formed on the forebody without a porous

skin; and

Fig. 4a is a side view of a forebody, fig. 4b is a cross-sectional view

10 taken along IV-IV showing the vortices formed on the forebody with a porous

skin.

Detailed Description of the Invention

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Figure 1 shows a forebody 12 of an aircraft. A portion of the forebody

12 is covered with a porous skin 14. The required thickness of the porous skin

14 is a function of the pressure load and the required response time for

pressure equalization, about one boundary layer thickness. The porosity of the

porous skin 14 is optimally between 10 and 20%. The porous skin 14 may be

made from a porous material, such as sintered metal, or from a solid material,

such as steel or fiberglass, which has been perforated, however these

perforations should be no more than about one boundary layer thickness in

diameter in order to minimize the disturbance of the external flow field.

Figure 2 shows the porous skin 14 mounted outside of the solid surface

16 of the aircraft, forming a plenum 18 between the porous skin 14 and the

solid surface 16. The porous skin 14 must be mounted over the plenum 18

such that there is minimal blockage in both the longitudinal and circumferential

directions. Plenum 18 may be divided into subplenums 28 to allow for control

of smaller areas. These subplenums 28 may be interconnected to other
LAR 14682-1 -5- PATENT APPLICATION

subplenums or may be closed off from the other subplenums by engaging door

20 as needed, see figure 2.

At flight conditions where the fluid flow 30 about a forebody becomes

asymmetric (e.g. at high angles of attack) as indicated in figure 3 by the

5 asymmetric vortex formation 32 and 34, the pressure field acting on the

forebody can become distinctly different from one side to the other. This

causes a net side force to act on the forebody and a resultant yawing moment

on the vehicle. When the solid surface 16 is covered with a porous skin 14, as

described above, air from the lower suction side 38 (highest relative pressure)

10 passes through the porous skin 14 into the plenum 18, flows through the

plenum 18, to the higher suction side 40 (lowest relative pressure) thus

equalizing the pressure differential and alleviating the side force and yawing

moment as shown in figure 4. The vortices 36 are symmetric so the pressure

fields acting on either side are equal and the net pressure load is zero. The

15 flowfield becomes the same as that around a forebody at low angles of attack.

This invention may also be used to cause unequal pressure fields to

improve control of the forebody. Pressure or mass is added or subtracted, as

shown by arrows 22 and 24 in figure 1, to modify the cavity condition beneath

the porous surface 14, thus augmenting or inhibiting the effect of the porous

20 surface 14. The transpirational control device 26 regulates the pressure (and/or

mass) inside of the plenum, creating a high or low pressure condition

depending on whether a yaw moment to the left or right is required.

This invention may be used to control pressures on any object in a fluid

flow including but not limited to aircraft, rotorcraft, cars, trucks, ships,

25 submarines, buildings, pipes and ducts.

What is claimed is:
LAR 14682-1 PATENT APPLICATION

CONTROL AND AUGMENTATION OF PASSIVE POROSITY

THROUGH TRANSPIRATION CONTROL

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Abstract of the Disclosure

A device for controlling pressure loading of a member caused by a fluid

moving past the member or the member moving through a fluid. The device

consists of a porous skin mounted over the solid surface of the member and

separated from the solid surface by' a plenum. Fluid from an area exerting high

pressure on the member may enter the plenum through the porous surface and

exit into an area exerting a lower pressure on the member, thus controlling

pressure loading of the member. A transpirational control device controls the

conditions within the plenum thus controlling the side force and yaw moment

on the forebody.
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12

2 22

24

16 20

18

FIGURE 1.
24

22

20

FIGURE 2.

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