US3223418A - Subsonic and supersonic towed aerial target - Google Patents

Description

DeC- 14, 1965 R. NORMAN ETAL 3,223,418

SUBSONIC AND SUPEHSONIC TOWED AERIAL TARGET Filed July 27. 1964 f ma@ I W M f w w 1mi/,M E MN hwt MW mf WQ M Y\\ Gym@ l Wr M m. Qkmm/ w wo* mv SN .qw d r Km mr. N l RN lwMQw Q im lnm n u |w E Q m`1 ml www Q WN vu@ N hlm United States Patent 3,223,418 SUBSONIC AND SUPERSGNKC TWED AERIAL TARGET Robert I. Norman, Birmingham, Ala., and Norman F.

Meullen, Charlotte, N.C., assignors to Hayes International Corporation, a corporation of Delaware Filed July 27, 1964, ser. No. 335,331

4 Claims. (Cl. 273-1053) This application is a continuation-in-part of our copending application Serial No. 119,080, filed lune 23, 1961, Towed Aerial Target, now abandoned.

Our invention relates to towed aerial targets and has for its principal and general object the provision of a target capable of steady flight while being towed at subsonic, transonic or supersonic speeds. I Heretofore in this art some targets have been towed by attaching a cable to the nose of the body through a swivel. In flight such targets have rotated about their longitudinal axes, and in fact this rotation has been purposely brought about. Such spinning targets have not been capable of a wide speed range because the spin rate required for stability could not be held within acceptable limits and consequently such targets have tended to roll, pitch and yaw to a large degree at one end or the other of their speed range. Targets of the general kind involved in this application are equipped with various kinds of devices such as means to provide infrared appearance, radio receivers and the like. The efficiency of such devices in prior targets has been considerably decreased and this is due in large measure to the erratic flight characteristics of such prior targets.

For the exercise or" ground-to-air and air-to-air weapons aerial targets have been a training tool of military services for quite some time. These were intended to simulate the aircraft against which the weapons were designed to be used. To further the simulation of speed and altitude some types of these targets were towed by cables from aircraft having comparable performance. As this required level of performance increased, it became more and more diicnlt to achieve simulation by a tow target system because the same problems of high speed flight beset the target and cable as those which were encountered by the aircraft. In this period free-flight targets gained ascendency, being less encumbered by the problems of older systems. However, free-flight targets required costly propulsion, controls, and supporting equipment that all too often became an irretrievable loss at the end of one flight. This cost finally dictated the return to captive tow targets, but all of the old problems were still there. The targets had frontal areas and stabilizing surfaces with airfoil sections that were incompatible with supersonic speeds. To make them smaller would inhibit their ability to represent the full sized aircraft they were meant to simulate, and even a reduction in size does not guarantee that stable flight characteristics good enough for subsonic speeds would carry over into the supersonic region.

In view of the foregoing, a prime object of our invention is to provide a target capable of being towed throughout the range of speed from subsonic to supersonic and which, at all speeds, is aerodynamically stabilized for straight, non-spinning flight within a very narrow range of angle of attack, thus to improve the towing characteristics and to enhance the efficiency of the instruments and devices carried by the target.

Another object is to provide a target of the character designated in which the point of connection of the tow cable, the center of gravity of the target and the centers of lift and side force, i.e., the location of the resultants of the forces generated by the surface of the target in the vertical and horizontal planes, all are related to each 3,223,418 Patented Dec. 14, 1965 ICC other in such manner as to result in the aforementioned trim throughout a narrow range of angle of attack, at all speeds.

Another object is to provide a stable, all speed aerial target which may be towed from a point along its longitudinal center line near its center of gravity as distinguished from towing the same from the nose, and in which the target is aerodynamically balanced for stable flight.

More specifically, we provide a target which is towed from a position on or near the center of gravity of the vehicle as a whole, and in which trim for stable flight, for all practical purposes, is accomplished by means of fixed horizontal and vertical wings or surfaces, thereby eliminating the necessity of any adjustable trimming devices.

Briefly, we obtain the foregoing objects by providing a target the body of which is symmetrical about its longitudinal axis. The cable from the towing aircraft is attached directly on the longitudinal center line of the target, the cable or end fitting passing through the skin of the fuselage or body of the target. The general configuration of the target is that of a slender body made up of cylindrical and conic sections having small included angles. The fuselage is of high fineness ratio. We provide rearwardly of the center of gravity wings or stabilizing surfaces mutually perpendicular which are highly swept, low aspect ratio and clipped delta in plan form, and have a low thickness ratio airfoil. Specifically, the general configuration of the fuselage is a body of revolution with an overall ineness ratio above seven. The center of gravity is located between fty and sixty percent of the total length of the target aft of the nose. The cable preferably is attached at the center of gravity, but at no time at a point farther than about one body diameter forwardly of the center of gravity or no more than about one-fourth body diameter rearwardly of the center of gravity. The horizontal stabilizing surfaces are provided with positively cambered sections which create a zero lift nose-down torque which is substantially equal and opposite to the nose-up torque resulting from the relative positions of the center of gravity and the center of pressure of the target through which the trimmed lift is negative or downward. A target constructed in accordance with our invention trims under all flight conditions above knots indicated air speed with its principal axis maintained within plus or minus live degrees of the flight path. This is because of the very small variation in aerodynamic characteristics with Mach number. Cross coupling of longitudinal and lateral types of motion which can produce dynamic instability are thus minimized. Further, all aerodynamic components of the target, namely the body and wing surfaces, are selected with regard to minimizing their sensitivity to Mach number elect. This is done by using a high neness ratio for the body and low thickness ratio for the wing surfaces, both of which have nearly constant aerodynamic characteristics.

A target illustrating features of our invention is shown in the accompanying drawings forming a part of this application in which:

FIG. 1 is a somewhat diagrammatic plan view;

FIG. 2 is a somewhat diagrammatic side elevational view;

FIG. 3 is a detail sectional View taken generally along line 3 3 of FIG. 2;

FIG. 4 is a detail fragmental sectional view taken generally along line 4-4 of FIG. l :and showing the location of the tow connection;

FlG. 5 is a sectional View taken on line 5--5 of FIG. 1; and,

FIG. 6 is a force diagram in side elevation.

Referring now to the drawings for a better understanding `of our invention, we show our improved target as embodying a main body portion A and a fore body B. It will be noted that the general Configuration of the target may be defined as being a long slender body. Specifically, the ratio of the length of the body as a whole, namely the fore body B and main body A to the diameter of the body part A is a fineness greater than seven. Actually, in the target shown the neness ratio approaches about seventeen.

At the forward or leading end of the fore body part B, we provide a propeller driven generator indicated by the numeral 10.

The body portion A is equipped with horizontal stabilizing surfaces or wings 13. Also, the body portion A is provided with vertical stabilizing surfaces or wings 14. It will be noted that these sets of surfaces are :arranged in cruciform manner. Further, the vertical surfaces are made up of what is known in the art as a modied diamond airfoil whereas the horizontal surfaces are moditied :half-diamond sections. Both sets of surfaces have thickness to chord ratios less than ve percent. These provisions materially increase the range of air speeds through which aerodynamic characteristics are constant.

The center of gravity of the target as a Whole is indicated :at 17. It will be especially noted that the center of gravity is forward of the leading edges of both the stabilizing surfaces 13 and 14. With respect to the stabilizing surfaces it will be noticed that their leading edges are highly swept, that they have low aspect ratios, and are clipped delta in planform. These provisions all tend to reduce variations in stability over large ranges of air speed.

The `tow cable T is attached to a swivel indicated at 18. The swivel in turn is attached to a bolt, rivet or the like 19, which lies on the longitudinal axis or center line of the target indicated at 21. In connection with the location of the attaching point 19, We prefer to locate the center of gravity 17 relative to this point so that 19 is never any further forward of 17 than one body diameter, and never any further rearward of 17 than one-fourth body diameter. We locate the horizontal surfaces 13 to assure that the lift center of pressure of the entire target is a minimum of one body diameter aft of the center of gravity 17. Likewise, the vertical wings or stabilizing surfaces 14 are placed so that the side force center of pressure of the overall configuration is also a minimum of one body diameter aft of the center of gravity 17 With the foregoing description in mind, and based upon actual experience and actual ight tests of a target constructed in accordance therewith, we find that our target flies with the longitudinal principal axis 21 maintained within plus or minus tive degrees of the flight path under all flight conditions above 150 knots indicated air speed. With the tow cable :attached at the relative point indicated, the effects of weight and atmospheric variations will not materially alter the determination of trim angles of .attack for air speeds above 150 knots, indicated, provided the horizontal wing area and its aft location are such as to keep the trim angle of attack requirement below tive degrees.

As a specific example of a target which has been successfully ilown at Mach 1.7, we cite the following:

The body A was formed of a tube 8 inches in diameter and about 83 inches long; the fore body part B (excluding the forward cylindrical generator shown in FIGS. 1 and 2) was formed of a frustum of a cone equal in diameter to the body part at its :aft end and tapering down through a length of 36 inches to about 4.5 inches in diameter adjacent the base of the wind driven generator. The height of each of the vertical stabilizers from the surface of the body was about 9.9 inches up to the clipped tip, and the chord was :about 27 inches long at the iin-body intersection. Thus, both vertical stabilizers provide a combined exposed area of 296 square inches. The horizontal stabilizing surfaces extended outwardly from the body along the line 22 about 14 inches and extended 39 inches along the surface-body intersection. Thus, both horizontal stabilizers provide a combined exposed area of 593 square inches. The planform of the surfaces 13 is a clipped delta having a leading edge sweep back angle of 70 degrees and an aspect ratio of about 1.4. The taper ratio is one-tenth and they are mounted at zero angle of incidence relative to the longitudinal center line of the body. In section the surfaces 13 are modified half diamond shapes having planar lower surfaces. The maximum depth of the horizontal sections 13 at the root chord was about 1.54 inches characteristic of a 4% thickness ratio constant for the entire surface and the camber is thus a positive 2% and extends as shown in FIG. 5. The lines 16aL and 16h are the points of maximum thickness of the chord, line 162L lying at about 45% of the chord aft of the leading edge 13a and 1Gb lying at about 55% aft of the leading edge. The overall length of the target was about 13() inches. The center of gravity of the target was about 18 inches forwardly of the leading edge 13a of the horizontal surfaces 13. The tow cable attachment point 19 was located substantially coincident with the Center of gravity. A target made in accordance with this specific example has been flown at Mach 1.7, has proven to be aerodynarnically stable and entirely satisfactory in all respects. The camber of the horizontal surfaces 13 was such as to develop a nose-down torque within the range of trimmed angle of attack. This torque rotates the target to produce a negative angle of attack Where the wings generate a downward lift. This creates a nose-up torque suicient to balance the target. We find that by connecting the tow cable to the target through a pivot in the horizontal plane and perpendicular to the center line adjacent the center of gnavity and on the horizontal center line of the target, all rolling turques acting upon the target are resisted by the tension of the cable, thereby preventing target spin. The tow cable was attached to a swivel 18 which in turn was mounted pivotally so as to permit undrestricted rotation of the swivel in .a vertical plane containing the target center line from 45 to 100 degrees to the horizontal, while resisting any rotation in the lateral plane.

In FIG. 6 we show a force diagram which illustrates how our target is trimmed. The negative lift L of the surface 13 is a result of the pitching moment M, which moment is a resultant of the positively cambered airfoil section. The moment M forces the nose down until the wing adopts a sufficiently negative angle of attack to generate the negative lift L. This Ilift acting about the center of gravity 17 through arm b equals the moment M. Cable tension T equals and diametrically opposes the resultant of the drag D and the weight and lift forces F of the target. The angle a is a function of the relationship between D and F. Therefore, when constructed as herein disclosed, our target trims with less drag and a greater angle a than any such vehicle having uncambered surfaces 13.

In view of the foregoing it will be apparent that we have devised an improved towed aerial target, and one which may be towed from a position adjacent the center of gravity thereof and which is aerodynamically trimmed for ight within a very narrow range of angle of attack. It will be understood that the fuselage or body of the target may be tubular and that the target may house any of the desired instrumentalities common to such devices. In the target of our improved design and which has been tested, the same has been equipped with various devices such as infrared sources, radar augmentation, radio receivers and the like. Our target lends itself to launching and recovery from launchers carried by the aircraft.

While we have shown our invention in but one forni, it will be obvious to those skilled in the art that it is not so limited,I but is susceptible of various changesand modications without departing from the spirit thereof, and we desire, therefore, that only such limitations shall be placed thereupon as are specically set forth in the appended claims.

What we claim is:

1. In a target adapted to be towed through the air at the end of a cable by an aerial vehicle at speeds above Mach 1, a tube-like elongated body symmetrical about its longitudinal axis and having an overall iineness ratio greater than seven, a connection for attaching the tow cable to the body intermediate its ends on the longitudinal center line of the body in the form of a horizontal pivot extending transversely of the longitudinal center line of the target and limiting the target to rotational movement in a plane defined by the line of pull of the cable and the longitudinal center line of the target, vertical and horizontal stabilizing surfaces located to create a center of lift pressure at least one body diameter rearwardly of the center of gravity of the target, said horizontal surfaces being cambered to create a nosedown pitching moment which is substantially constant throughout subsonic and supersonic speed ranges of the target, said tow cable connection being located substantially on the center of gravity of the target, thereby to provide a target which flies with its longitudinal axis substantially within plus or minus 5 degrees of any given flight path at all speeds above 150 knots indicated air speed.

2. The target of claim 1 in which the aspect ratio of the horizontal stabilizing surfaces is on the order of 1.4 and the thickness ratio of the airfoil section of said horizontal stabilizing surfaces is on the order of about 4%.

3. The target of claim 1 in which the vertical and horizontal surfaces have thickness to chord ratios less than 5%, the vertical surfaces being of modied diamond airfoil shape.

4. In a target adapted to be towed through the air at the end of a cable by an aerial vehicle, a *long slender tube-like body symmetrical about its longitudinal aXis and having a Iineness ratio greater than seven, a tow cable connection on the longitudinal center line of the body in the form of a horizontal pivot extending transversely of the longitudinal center line of the target and limiting the target to rotational movement in a plane dened by the line of pull of the cable and the longitudinal center line of the target, said two cable connection being located at the center of gravity of the target, and horizontal and vertical stabilizing surfaces located wholly rearwardly of the cable connection and being of highly swept low aspect ratio, clipped delta in planform and being of low thickness ratio airfoil shape, said horizontal surfaces being constructed of modified half-diamond sections cambered to create a nose-down torque substantially equal to the nose-up torque resulting from the relative locations of the center of pressure of the target and the center of gravity of the target.

References Cited by the Examiner UNITED STATES PATENTS 2,551,596 5/1951 Haglund.

2,667,351 1/1954 McKinney et al. 273-1053 2,779,553 1/ 1957 Troxell 244-3 2,821,396 1/1958 Seeley 273-105.3 2,879,999 3/ 1959 Marshall 273-1053 2,930,619 3/1960 Greenwood 273-1053 3,030,111 4/ 1962 Hendershott 273-105 .3 3,135,511 6/1964 Norman et al. 273-1053 DELBERT B. LOWE, Primary Examiner.

Claims (1)

1. IN A TARGET ADAPTED TO BE TOWED THROUGH THE AIR AT THE END OF A CABLE BY AN AERIAL VEHICLE AT SPEEDS ABOVE MACH 1, A TUBE-LIKE ELONGATED BODY SYMMETRICAL ABOUT ITS LONGITUDINAL AXIS AND HAVING AN OVERALL FINENESS RATIO GREATER THAN SEVEN, A CONNECTION FOR ATTACHING THE TOW CABLE TO THE BODY INTERMEDIATE ITS ENDS ON THE LONGITUDINAL CENTER LINE OF THE BODY IN THE FORM OF A HORIZONTAL PIVOT EXTENDING TRANSVERSELY OF THE LONGITUDINAL CENTER LINE OF THE TARGET AND LIMITING THE TARGET TO ROTATIONAL MOVEMENT IN A PLANE DEFINED BY THE LINE OF PULL OF THE CABLE AND THE LONGITUDINAL CENTER LINE OF THE TARGET, VERTICAL AND HORIZONTAL STABILIZING SURFACES LOCATED TO CREATE A CENTER OF LIFT PRESSURE AT LEAST ONE BODY DIAMETER REARWARDLY OF THE CENTER OF GRAVITY OF THE TARGET SAID HORIZONTAL SURFACES BEING CAMBERED TO CREATE A NOSEDOWN PITCHING MOMENT WHICH IS SUBSTANTIALLY CONSTANT THROUGHOUT SUBSONIC AND SUPERSONIC SPEED RANGES OF THE TARGET, SAID TOW CABLE CONNECTION BEING LOCATED SUBSTANTIALLY ON THE CENTER OF GRAVITY OF THE TARGET, THEREBY TO PROVIDE A TARGET WHICH FLIES WITH ITS LONGITUDINAL AXIS SUBSTANTIALLY WITHIN PLUS OR MINUS 5 DEGREES OF ANY GIVEN FLIGHT PATH AT ALL SPEEDS ABOVE 150 KNOTS INDICATED AIR SPEED.

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