US2930619A - High speed aerial tow target - Google Patents

Description

March 29, 1960 M. H. GREENWOOD HIGH SPEED AERIAL TOW TARGET Filed March 25, 1957 INVENT OR Marvin H Greenwaod ATTORNEYS United States Patent HIGH SPEED AERIAL TOW TARGET Marvin H. Greenwood, Houston, Tex., assignor to Anderson, Greenwood & Company, Houston, Tex., a corporation of Texas Application March 25, 1957, Serial No. 648,269 1 Claim. (Cl. 273-1053) This invention relates to tow targets, and particularly to targets adapted to be towed behind modern high-speed aircraft.

The target comprises a non-rigid streamlined body envelope in the form of a surface of revolution and constructed of air-impervious, fabric-like material with very little stretch so configured as to offer a minimum of drag. The forward end of the body is defined by a rigid aerodynamically refined entrance opening whereby movement through the air causes air to enter the body envelope, and high velocity builds suflicient air pressure in the target body to maintain the same in fully distended condition, whereby it acts essentially as a rigid body. The target further includes a plurality of light weight guiding fins near the tail of the target, which is closed, to render the target highly stable during its high-speed movements. To stabilize the target effectively, it is necessary that the center of pressure of the air on the outer surface of the target, including the fins, be located as far to the rear of the center of gravity as possible, and the invention comprises recognition of the importance of the relative location of center of gravity, center of pressure, and tow point, and novel features for producing the desired rela tionships. The invention also comprises the means of obtaining proper inflation and maintaining this inflation.

It is, therefore, an object of this invention to provide a high-speed aerial tow target of economical construction, reliable in operation, and stable in very high speed flight.

It is another object of this invention to provide a highspeed aerial tow target having a minimum of internal structure and a flexible envelope whereby it can be folded or rolled into a relatively compact package for storage and handling, and which acts as an elongated, substantially rigid body when in operation.

It is still another object of this invention to provide a tow target so designed and proportioned as to be unusually stable in operation, whereby it will at all times properly trail in the direction of flight.

A further object of this invention is to provide a tow target having the above-noted characteristics, and which is yet inexpensive to produce, and thereby expendable.

A still further object of the invention is to provide a non-rigid and collapsible tow target for high-speed operation, and which utilizes ram air for inflation and rigidity.

Still further objects and advantages will become apparent to those skilled in the art as the description proceeds in connection with the accompanying drawings, wherein:

Fig. 1 is a perspective view illustrating a tow target of the present invention in flight;

Fig. 2 is a longitudinal, vertical, sectional view of the target of Fig. 1; and

Fig. 3 is a transverse, sectional view taken substantially along the line 3-3 of Fig. 2.

Referring now to the drawings, the target of the present invention comprises an elongated tear drop body 2 of flexible minimum-stretch material which may be any suit- 2,930,619 Patented Mar. 29, 1960 be the well-known oil cloth of commerce. Preferably,

the air-impervious fabric is arranged to have a smooth exterior surface whereby to offer a minimum drag or resistance to movement through the air. Some leakage of air, corresponding to a reasonable number of bullet holes, can be tolerated. However, it is recognized that unless the fabric is nearly completely impervious it will not retain suflicient pressure to act as a rigid body. This is true because of the low-drag design. g

The target'body 2 is shown as being provided with a rearwardly-tapered, generally conical, closed rear portion" 3 which may be an integral continuation of the body 2, or it may be a separate conical portion if desired.

As its forward end, the open end of the fabric envelope 2 is recessed into and permanently fixed to an annular nose ring 4. The nose ring 4 is preferably of fairly heavy material, such as metal or a dense wood or the like, fora purpose to be described later. The nosepiece 4, however,

is faired or streamlined as at 6 and S, and is provided with a central'axial opening 10 therethrough. A suitable tow line 12 is attached to a bridle 14 comprising a generally V-shaped loop of wire, cable, or the like, fixed at 16 to diametrically opposed portions of the nosepiece, 4. The tow line 12, which may be of any desired length, is suitably attached to a towing aircraft (not shown). "It" will be obvious that the movement of the towing aircraft will cause the air to enter and pass through the central opening 10 of'the nosepiece 4 into the airtight interior of the body envelope 2. At the high speeds contemplated, the ram effect of the air entering opening 10 causes a substantial air pressure to be built up and retained inside the body 2, and thus inflates the body envelope and maintains the same in a substantially rigid condition, whereby, during use, the target responds to pressure on the guide fins and acts as though it were a rigid body having a rigid framework extending therethrough from end to end.

Near its closed rear end, the target is provided with a number of guiding fins 20, 22, 24, and 26, and each may comprise a single board or other flat sheet of light weight material, which may be balsa wood, honeycomb core structure or the like. The guiding fins 20, 22, 24, and 26 are arranged in radial planes, whereby they engage the air through which the target moves to exert their stabilizing or guiding influence. The guiding fins 20, 22, 24, and 26 are secured to the fabric 2, in any suitable or desirable manner, such as by being provided with bases 28 cemented or glued to the fabric 2.

As previously stated, the tow target of the present invention is relatively long and narrow, and is provided with a smooth exterior to minimize drag and thus permit high operational speeds without undue tension in the tow line 12. Such a device tends to become unstable, i.e., tends to oscillate in flight, unless designed in such a manner that stability does not depend on skin friction or drag. The tow target of the present invention is designed for stability by being so arranged that the center of gravity thereof is markedly forwardly of the center of pressure. By center of pressure is meant. that point within the transverse outline of the assembly at which all forces due to air pressure on the sides of the target can be considered to be concentrated as a single force. Thus, if the target were to assume a transverse or partly transverse attitude with relation to its direction of movement during flight, the air pressure on its foremost side surfaces would act thereon as though the forces on all ,3 incremental portions of the Surface area were a single fbfc concentrated at the Center Of pressure. The provision of the guiding tail fins 2t), 22, 24, and 26 has the efiEect of moving the center of pressure rearwardly of the position it would have without'those'fins.

It is well known that any force applied to a free body tends to cause that body to rotate about its center of gravity. Therefore, it is necessary that the center of pressure of the target be located rearwardly of the center of gravity to insure that pressure forces due to a misalignment of the target with the direction of flight tend to return the target to the proper orientation relative to the direction of flight. Toinsure that the center of gravity of the target be forward of the center of pressure, the guiding fins 20, 22, 24, and 26 are made as light Weight as possible. For the same reason the nosepiece 4 is made of rather substantial volume and of relatively heavy material. a s

It is also recognized asimpor't a'nt that the target be towed from a point as near 'to the center of gravity as physically possible so that variation in the-magnitude or direction of the towing force does not cause a turning or yawing of the target about its center of gravity. This is a further reason for a forward center of gravity which has been achieved by spending weight generously in the construction of the nose air entry or weighting the nose air entry and by being as economical of weight as possible in the rest of the structure.

When the target is being towed at high speeds, it is maintained in an inflated and substantially rigid condition as heretofore described, and the entire target thereby has a fixed and determinate center of gravity as indicated in- Fig. 2. By employing substantially non-stretchable material for the envelope 2, the target is assured the chari 4' acteristic of rigidity when inflated in the manner described.

'While' a single specific embodiment of the invention has been shown and described herein, the same is merely illustrative and not limiting. It is intended that the invention embrace all modifications falling fairly within the scope of the appended claim.

I claim:

An aerial tow target for use at high speed comprising; an elongated, non-rigid, streamlined body of flexible, minimurn-s'tretch, substantially air-impervious material; said body consisting of an envelope having an open forward end and a closed rear end, a relatively heavy annular nose ring secured in the open end and arranged to admit air to inflate and maintain the inflation of the body envelope, and individual rigid guiding fins of light weight material individually and separately secured to and extending outwardly from spaced portions of said body adjacent the rear end thereof, said nose ring, body, and guiding fins beingso proportioned and positioned that the centerjof gravity of said target is substantially forward of the center of pressure thereof, the material of the nose ring being relatively heavy and the materials of the body and fins being relatively light so as to position the center of gravity of the target as far forward as possible, and means adjacent the forward end of said target, closely adjacent said center of gravity, for the attachment of a tow line thereto.

References Cited in the file of this patent UNITED STATES PATENTS 1,860,982 Binnie May 31, 1932 2,667,351 McKinney Jan. 26, 1954 2,821,396 Seeley Jan. 28, 1958

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