Lifting Body Aircraft

Abstract

Take-off and landing distances of a lifting body are significantly reduced by providing a downwardly deflectable inboard control surface at the trailing edge to control lift, and upwardly deflectable control surfaces, outboard in relation to the inboard control surface, to control pitching moment, and thereby adjust angle of attack. A control system not only allows a preliminary "trim" adjustment of all three surfaces but permits the outboard surfaces to be adjusted by the pilot to control the aircraft in flight.

Description

BACKGROUND OF THE INVENTION

This invention relates to aircraft and particularly to a lifting body, that is an aircraft having a substantially continuous airfoil surface from one end of its span to the other and lacking a well-defined transition between wing and fuselage. A typical lifting body is described in U.S. Pat. No. 3,486,719 issued Dec. 30, 1969 to John R. Fitzpatrick and Juergen K. Bock. The lifting body described in that patent is characterized by a substantially triangular or delta-shaped planform, a nose at one corner of the triangle and a trailing edge opposite the nose and extending between a pair of lateral extremities, each at one of the remaining corners of the triangle. The sides of the triangle which meet at the nose form portions of the leading edge, and vertical, longitudinal sections of the lifting body are thick airfoil sections which may be either cambered or uncambered. The lifting body preferably comprises an enclosed hull substantially symmetrical about a central vertical plane extending from its nose to a mid-point at the wide end opposite the nose. The transverse cross-sections throughout substantially all of the length of the lifting body are substantially elliptical on either side of the central vertical plane. From the nose to the point of maximum vertical dimension in the central vertical plane, the elliptical cross-sections become progressively higher and progressively wider, with width increasing more rapidly than height. From the point of maximum vertical dimension toward the trailing edge, however, the elliptical cross-sections continue to increase progressively in width, but decrease progressively in height.

Various deviations from the above-described relationships may exist in a lifting body, for example, with respect to the configuration of the nose and lateral extremities.

Such lifting bodies are designed for longitudinal static stability, possess favorable stall characteristics, and are capable of relatively high cruising speeds and relatively low landing speeds. They can be made to carry a large payload efficiently, and may be operated heavier-than-air, or, with helium, either lighter-than-air or slightly heavier-than-air.

It is well-recognized that a positive (nose-up) pitching moment is required to maintain a positive angle of attack in a longitudinally statically stable aircraft. In a lifting body having a low aspect ratio, the generation of a positive pitching moment by upward deflection of a horizontal control surface located on the trailing edge would ordinarily give rise to a large, downwardly directed lift because of the basic lift distribution, produced by such a deflection, acting on the large airfoil surface forward of the control surface. Conversely, the downward deflection of such a horizontal control surface in order to increase lift would produce a negative pitching moment tending to reduce the angle of attack. These conditions result in relatively high landing and take-off speeds and distances.

In accordance with this invention, the impairment of lift which would result from the upward deflection of control surfaces is minimized by providing at least one additional downwardly deflectable horizontal control surface at the trailing edge in a central location, and by locating the upwardly deflectable control surfaces at an "outboard location" laterally remote from the central axis of the lifting body, or at some other location which insures a reduced airfoil surface area forward of the upwardly deflectable control surfaces, thereby reducing the resultant downward lift, and also increasing the effectiveness of the upwardly deflectable surfaces or of the upwardly deflectable surfaces together with their associated forward surfaces in producing a positive pitching moment and thereby maintaining a positive angle of attack.

The downward deflection of the centrally-located control surface produces a pressure differential between the upper and lower surfaces of the large airfoil surface area ahead of the central control surface that is nearly uniform in the streamwise direction. This pressure distribution produces a resultant lift force acting very nearly at the mid point of the chord line connecting the nose and the trailing edge of the airfoil surface in the region of the central control surface. Since for a stable delta-shaped aircraft, the center of gravity must also lie near this mid-chord point the resultant lift force produced by the downwash deflection of the central control surface will produce very little pitching moment about the center of gravity of the aircraft. Thus, the downwardly deflectable centrally-located control surface produces lift with relatively little tendency to counteract the effect of the upwardly deflected surfaces, i.e., with relatively little tendency to reduce the positive pitching moment and consequent ability of the aircraft to maintain a positive angle of attack.

A control system is provided which permits a trimming adjustment to be made whereby, assuming a neutral stick, the centrally located control surface is deflected downwardly to a desired extent, and the outboard control surfaces are deflected upwardly to an extent depending on the downward deflection of the centrally located surface. While downward deflection of the centrally located surface produces an increased lift, it will also produce a negative pitching moment unless the center of gravity is located sufficiently aft to prevent it. The control system deflects the outboard control surfaces to the extent necessary to compensate for the downward pitching moment, and to produce a constantly increasing pitching moment as the control lever is moved away from its neutral position.

While the control system alone determines the position of the centrally located control surface, the outboard control surfaces can be moved about their preliminary settings as determined by the preliminary trimming adjustment, by the pilot's "stick" for the usual control of banking and elevation.

The outboard control surfaces may be positioned either on the trailing edge of the lifting body, or on auxiliary surfaces, or they may take other forms; for example, pivotable fin-like tips.

The outboard surfaces may be permanently in an upwardly deflected condition. The surfaces may be adjustable only on the ground, but are preferably adjustable in flight by means of a control system which simultaneously controls the inboard and outboard surfaces.

The principal object of the invention is to reduce the take-off and landing speeds of a lifting body. Further objects which include the improvement of control flexibility of the aircraft in flight, will be apparent from the following description.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a lifting body equipped with a set of control surfaces in accordance with the invention;

FIG. 2 is a perspective view of a lifting body showing an alternative arrangement of control surfaces in accordance with the invention; and

FIG. 3 is a perspective view showing apparatus for controlling the deflection of the various control surfaces in FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 1 shows a delta-shaped lifting body 4 comprising an enclosed hull 6, having a nose 8 and a trailing edge 10. Vertical stabilizers 12 and 14 are provided at the lateral extremities of the lifting body at either end of the trailing edge, and rudders mounted in the stabilizers, are indicated at 16 and 18. Propulsion means (not shown) may be in the form of a rear propeller or jet motor.

Surfaces 20 and 22, located at either end of the trailing edge, carry substantially horizontal outboard pitch control surfaces 24 and 26 respectively. These are the surfaces which are normally deflected upwardly to produce a positive pitching moment and thereby maintain a positive angle of attack. They are located aft of the center of lift. It will be noted that the airfoil surface area forward of these control surfaces is relatively small. The drooping configuration of surfaces 20 and 22 is provided to compensate for excessive rolling moment due to sideslip. It is described in the co-pending application, Ser. No. 76,696, filed Sept. 30, 1970, of John P. Kukon and William F. Putman. The axes of rotation of control surfaces 24 and 26 may be somewhat sloped with respect to the horizontal, but the surfaces are nevertheless substantially horizontal in that they perform the function of horizontal control surfaces.

A centrally located substantially horizontal control surface 28 is shown in a downwardly deflected condition.

The center of gravity of the lifting body is located sufficiently forward that downward deflection of surface 28, acting by itself, would produce a net negative pitching moment.

The same surfaces as shown in FIG. 1 are seen in FIG. 3 which illustrates how they are adjusted to the condition shown in FIG. 1 by a trim control lever 30.

Lever 30, which is preferably located within reach of the pilot, is capable of effecting continuous variation of the deflection of surface 28 and simultaneous variation of the deflection of surfaces 24 and 26 dependent on the deflection of surface 28.

Lever 30 is arranged to control simultaneously the positions of three pulleys 32, 34 and 36, fastened together and mounted on shaft 38. These are aircraft pulleys having conventional means (not shown) for fastening the control cables at their peripheries in order to avoid slippage.

Wrapped around the central pulley 34 is a control cable 40, the upper section of which is connected to control horn 42 on the upper side of control surface 28, and the lower section of which is connected to a similar control horn on the underside of control surface 28. It will be apparent that a rearward movement of lever 30 will produce a downward deflection of control surface 28.

Control cable 44 is similarly wrapped around pulley 32, and led by guide sheaves 46, 48, 50 and 52 to another conventional aircraft pulley 54 rotatable on a fixed pivot 56 near the rear of the aircraft.

Link 58 is pivotally fastened to pulley 54 at position 60, which is radially spaced from pivot 56 so that rotation of pulley 54 produces a movement of link 58. The other end of link 58 is pivotally fastened to an intermediate point 62 of link 64. A link 66 is slidable lengthwise in constraint 67 and is pivotally connected to one end of link 64. It is connected at its other end to bellcrank 68 of control surface 24. The lower end of link 64 is pivotally connected at 70 to a link 72. Link 72 is movable by the pilot's stick through control cable 74 and pulley 76 to which link 72 is connected at a pivot 77 radially remote from the axis of rotation.

Control surface 26 is controlled in the same manner as surface 24. A pulley 78 is interconnected through control cable 80 with pulley 36. The pilot's stick controls pulley 82 through control cable 84. Pulleys 78 and 82 respectively control the positions of links 86 and 88 which are respectively connected to intermediate point 90 and end point 92 of link 94. Link 96 is slidable in constraint 97 and is pivotally connected at 98 to the upper end of link 94. It interconnects the upper end of link 94 with bellcrank 100 on control surface 26.

It will be apparent that the position of the control lever 30 determines positions of pivots 62 and 90. Since links 58 and 72 both determine the setting of control surface 24, and since the positions of links 86 and 88 determine the setting of control surface 26, assuming a neutral stick, (i.e., assuming the stick to be in the intermediate position it would be in with all control surfaces in the neutral condition) the adjustment of control lever 30 will move both control surfaces 24 and 26 upwardly to effect a preliminary trimming adjustment or setting depending on the setting of the control lever. Surfaces 24 and 26 are provided with conventional trim tabs 91 and 93 which adjust automatically to prevent aerodynamic forces on the control surfaces from being transmitted back to the control stick or to lever 30. Thus, when lever 30 is pulled back, control surfaces 24 and 26 deflect upwardly without transmitting a large forward pressure to the pilot's stick, and when lever 30 is pushed forward, surfaces 24 and 26 deflect downwardly without transmitting a large backward pressure to the stick.

Central surface 28 is preferably provided with a similar trim tab 95 for preventing large forces on surface 28 from being transmitted back to lever 30. With the pilot's stick in a neutral condition, surfaces 24 and 26 will be deflected upwardly from neutral when lever 30 is pulled rearwardly, although this may not be the case when the stick is forward and lever 30 is pulled back.

Rearward adjustment of lever 30 also effects a downwardly deflected setting of central control surface 28. About this setting of the control surfaces, the pilot's stick can be used to vary the positions of surfaces 24 and 26 to control elevation and banking of the aircraft in flight. The stick 85 is mounted in a frame 87 pivoted at 89 and 99. Control cables 74 and 84 are interconnected to form a continuous cable which passes around pulleys 101 and 103 which are above the pivot axis of frame 87 and pulleys 105 and 107 which are below the pivot axis. Thus, with a backward pull on the stick, the outboard control surfaces 24 and 26 can be simultaneously moved further upwardly to increase the positive pitching moment and thereby increase positively the angle of attack. The outboard surfaces can be moved simultaneously downwardly by forward movement of the stick. The stick is also pivoted at 109 for movement from side to side. Interconnections are made between the stick and the cable at 111 and 113, and banking can be accomplished by movement of the stick from side to side to produce differential movement of surfaces 24 and 26.

All of the stick adjustments are made about variable control surface setting determined by the condition of lever 30. Thus, surface 28 can be used to produce greatly increased lift when deflected downwardly, and the positions of the outboard control surfaces are automatically adjusted upwardly to maintain a suitable deflection angle to compensate for the downward pitching moment created by the downward deflection of surface 28.

FIG. 2 shows a modified lifting body 102 in accordance with the invention having a central control surface 104 and outboard control surfaces 106 and 108, all located between the lateral extremities of the lifting body on the trailing edge. These surfaces are controlled by a control system similar to that shown in FIG. 3, and it will be apparent that similar results are produced when it is noted that control surfaces 106 and 108 are located at least partially behind the respective swept-back portions of the leading edge. Control surfaces 106 and 108 are therefore preceded by considerably less airfoil surface than precedes the central control surface 104, and the configuration is such that the basic lift which is produced as a result of upward deflection of control surfaces 104 and 106 contributes to the production of a positive pitching moment.

In the embodiments of both FIGS. 1 and 2, the airfoil surface forward of the outboard control surfaces is smaller than that behind the central control surface, and located toward the stern of the aircraft. Upward deflection of the outboard control surfaces produces a downward lift because of the basic lift distribution produced by the deflection acting on the airfoil surfaces forward of the outboard control surfaces. This downward lift acts well behind the aircraft center of lift and contributes to the generation of a positive pitching moment. The downward lift is smaller in magnitude than the basic lift produced as a result of the action of the central control surface 28 or 104. Thus, there is produced a net increase in lift as a result of a rearward pull on control lever 30.

Pilot actuation of lever 30 before during and after a typical flight is typically as described below with reference to FIGS. 1 and 3.

Prior to take-off, the pilot adjusts lever 30 to such a position that the central control surface 28 is deflected downwardly approximately one-half its total travel. This deflection increases the aircraft's lifting capacity and hence decreases its take-off speed, thus allowing use of a shorter runway length. Once in the air and approaching the cruise condition the low speed advantage is no longer necessary, and lever 30 may be returned to a neutral condition. Prior to landing the lever 30 is adjusted by the pilot to provide nearly full downward deflection of control surface 28 thereby either reducing his landing speed by providing additional lift or at a fixed landing speed lowering the nose of the aircraft thereby affording better visibility and pilot attitude. In all conditions described the pitching moment generated by surface 28 is small and is at least partially trimmed out by the proportionate upward deflection of surfaces 24 and 26. The use of different amounts of deflection of surface 28 in landing and take-off is due to the desire for a higher drag configuration (hence more deflection) in landing than in take-off.

In addition to the advantages of allowing shortened landing and take-off distances, use of the centrally-located control surface 28 for aircraft flight path control increases the pilot's ability to control the aircraft's rate of sink. In principle, the centrally-located control surface provides direct lift control; that is, the aircraft's aerodynamic lift is controlled and modulated directly without first producing an angular acceleration and consequent angle of attack change to produce a lift change. Operation of lever 30 in flight therefore produces a more rapid response in terms of altitude change than would be produced by a system of control surfaces operating in the conventional manner.

In operation, the pilot actuates the control lever 30 in such a manner as to deflect the trailing edge of the centrally-located control surface 28 downwardly when he desires to increase the aircraft's upward rate of climb, and correspondingly, deflects it upwardly when he desires a downward rate of sink. As previously explained, because of the central location of surface 28, the deflections described will produce principally lift force changes and little pitching moment changes. Any residual pitching moment produced by the centrally-located surface is cancelled by the outboard control surfaces 24 and 26 through the previously-described interconnecting system.

So far, the apparatus has been described as useful for controlling lift while avoiding pitching moment changes usually associated with control of lift. Conversely, the apparatus may be used to adjust the angle of attack of the aircraft without affecting the net lift. In order to increase the angle of attack, the pilot adjusts the stick to deflect surfaces 24 and 26 upwardly, and simultaneously pulls lever 30 back to produce an upward lift sufficient to cancel the downward lift which accompanies the upward deflection of surfaces 24 and 26. In a similar manner, the increase in upward lift accompanying a downward deflection of surfaces 24 and 26 by the stick can be cancelled by pushing lever 30 forward.

In summary, this invention provides, in a lifting body, a means for generating pitching moment for adjusting and controlling the angle of attack which does not adversely affect lift. Viewed in another way, the invention is capable of producing a net increase in lift without producing a substantial change in the pitching moment of the lifting body.

Claims

I claim:

1. A lifting body having a trailing edge, elevation control means, means providing a first substantially horizontal control surface forming part of said trailing edge and adapted to be deflected downwardly to impart a basic lift to the lifting body in flight, a pair of upwardly deflectable substantially horizontal control surfaces located aft of the center of lift, means adjustable to maintain said first control surface in a downwardly deflected condition and to effect a preliminary trim setting whereby, at least with the elevation control means in a neutral condition said upwardly deflectable control surfaces are held in an upwardly deflected condition, said upwardly deflectable control surfaces being positioned so that their upward deflection resulting from adjustment of said maintaining means gives rise to a positive component of pitching moment, and to a downward lift smaller in magnitude than the basic lift imparted to the lifting body as a result of downward deflection of the first control surface, said adjustable means including control means for effecting continuous downward variation of the deflection of said first control surface and simultaneous and dependent upward variation of the deflection of the upwardly deflectable control surfaces.

2. A lifting body according to claim 1 in which the elevation control means comprises a pilot-operable control and means interconnecting said control with the upwardly deflectable control surfaces to effect movement of said upwardly deflectable control surfaces even when the means adjustable to effect a preliminary trim setting is held at a particular adjustment.

3. A lifting body according to claim 1 in which the elevation control means comprises a pilot-operable control and means interconnecting said control with the upwardly deflectable control surfaces to effect movement of the upwardly deflectable control surfaces to control elevation and banking of the lifting body even when the means adjustable to effect a preliminary trim setting is held at a particular adjustment.

4. A lifting body according to claim 1 having a pair of swept-back leading edge portions wherein said upwardly deflectable control surfaces are located on the trailing edge of the lifting body each at least partially behind one of said swept-back leading edge portions.

5. A lifting body according to claim 1 in which the center of gravity is located sufficiently forward that downward deflection of the first control surface produces a negative pitching moment.

6. A lifting body according to claim 5 in which the elevation control means comprises a pilot-operable control and means interconnecting said control with the upwardly deflectable control surfaces to effect movement of said upwardly deflectable control surfaces even when the means adjustable to effect a preliminary trim setting is held at a particular adjustment.

7. A lifting body according to claim 5 in which the elevation control means comprises a pilot-operable control and means interconnecting said control with the upwardly deflectable control surfaces to effect movement of the upwardly deflectable control surfaces to control elevation and banking of the lifting body even when the means adjustable to effect a preliminary trim setting is held at a particular adjustment.

8. A lifting body according to claim 5 having a pair of swept-back leading edge portions wherein said upwardly deflectable control surfaces are located on the trailing edge of the lifting body each at least partially behind one of said swept-back leading edge portions.