Abstract:
The bottom surface of an aircraft, such as an Osprey V-22 propeller driven aircraft, has at least four distributed hook attachment points. A load suspension apparatus is attached to the four attachment points with elongated slings. The load suspension apparatus includes an upper rigid frame and a lower rigid frame of lesser dimensions. The lower frame is suspended from the upper frame with V-shaped slings. A cargo load is attached to the lower frame. The load suspension apparatus provides stable attachment of loads to tilt wing and rotary wing aircraft at high aircraft speeds, at transitions between high and low speeds and through aircraft turns.

Description:
STATEMENT OF GOVERNMENT INTEREST 
     The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to aeronautics. More particularly, the invention relates to aircraft structure and load accommodation. The invention also relates to cargo loading or discharging, particularly releasable, externally mounted cargo. 
     2. Discussion of the Related Art 
     Suspension slings are used for suspending a cargo load below an aircraft during flight. Loads are typically attached to a helicopter with a sling suspension attached to structurally strengthened hard points on the under surface of the fuselage. There is substantial benefit when jettisoning load for suspension from a single cable. Dropping or jettisoning cargo is inherently more balanced because it is accomplished by opening a single attachment hook. However, a single cable system produces an undistributed point load on the aircraft resulting in instability problems. At speeds greater than low speeds, a load will twist on a single cable to a position broadside to the direction of flight. Flight with the widest area facing the direction of flight induces yawing of the load. As a result, the pilot must limit aircraft speed to approximately 50 knots to reduce instability in the aircraft. 
     In order to overcome the single cable load yawing, loads have been suspended from two or more cables. It has been found that this reduces aerodynamically induced load yawing at lower speeds but yawing resumes at higher speeds. Two or more suspension cables are used for low speed flight but produce instability at higher speeds of 120 knots or more. Aircraft turns may initiate instability at any aircraft speed, especially at higher speeds. 
     In order to use the capability speed of aircraft, there a need for an attachment apparatus that provides stable suspension of externally mounted cargo loads at higher air speeds. 
     SUMMARY OF THE INVENTION 
     An aircraft is configured with four or more structurally strengthened hard points for engagement of hard point attachment means. Elongated attachment slings attach the cargo suspension apparatus to the hard point attachment means. 
     The cargo suspension apparatus comprises an upper rigid frame and a lower rigid frame. The lower frame is geometrically similar and dimensionally smaller that the upper frame. 
     V-shaped slings connect the upper frame with the lower frame and suspend the lower frame therebelow. The lower frame has load attachment means. A load, such as a cargo receiving holder, is attached to the lower rigid frame. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A more complete appreciation of the invention and many of its attendant advantages will be readily appreciated as it becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawing wherein: 
         FIG. 1  is a side elevated view of an aircraft in flight with a cargo suspension apparatus and suspended cargo according to the invention. 
         FIG. 2  is a partial overhead sectional view as seen from section line  2 - 2  in  FIG. 1 . 
         FIG. 3  is a partial perspective view of the cargo suspension apparatus separated from the aircraft shown in  FIG. 1 . 
         FIG. 4  is a partial view of an attachment arrangement associated with the cargo suspension apparatus shown in  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The invention is described with reference to the drawing wherein numerals in the written description correspond to like-numbered elements in the figures. The drawing discloses a preferred embodiment of the invention and is not intended to limit the generally broad scope of the invention as set forth in the claims. 
     Reference is made to  FIG. 1  in which the horizontal and vertical axes are labeled x and y. This is a side view so the z-axis is not seen in this view as it is seen in  FIG. 3 . An Osprey V-22 tilt rotor aircraft  10  is in transition from vertical flight to horizontal flight. Transition is accomplished by means of aircraft engine  11  which drives propellers  11   a  and is tilted to provide propulsion in a direction indicated by arrow  11   b . Arrow  11   b  includes components along both the horizontal x-axis and the vertical y-axis. Forward is labeled FWD and aft is labeled AFT on aircraft  10 . The forward and aft labeling also extends to the load suspension apparatus  14  and to the load  12 . 
     The reported suspended cargo carrying capacity for the Osprey V-22 is 10,000 to 15,000 pounds. An external cargo load suspended beneath a tilt rotor aircraft or a helicopter is susceptible to aerodynamic instability. This instability can be transmitted through the cargo suspension apparatus to the aircraft. The cargo suspension apparatus of the invention allows for aerodynamic movement of the cargo and compensation for that movement with V-shaped slings. Dynamic moments are opposed and compensated in the suspension apparatus with reduced transmission of dynamic moments to the aircraft. 
     Packaged cargo load  12  is suspended from aircraft  10  by a load suspension apparatus  14  attached to the underside  16  of the aircraft fuselage  18 . Load suspension apparatus  14  is joined to aircraft  10  by means of aircraft attachment slings  32  and  35 . The Osprey V-22 aircraft is exemplary of an aircraft that is sensitive to destabilizing by a suspended cargo load and therefore benefits from use of the cargo suspension frame of the invention. The invention was discovered while investigating stable suspension systems for the Osprey V-22 tilt rotor aircraft and its use with this aircraft is the Best Mode contemplated by the inventors. Because of the enhanced load stability, use with an aircraft such as a helicopter will also enhance load stability. 
     Military aircraft ordinarily have structurally strengthened hard points in the airframe or attached to the airframe for the attachment of external loads and for ground and shipboard tie down. A hard point can be configured to mount a hook for releasable fastening of a cargo cable, cargo net, cargo sling and the like. Helicopters and the V-22 Osprey aircraft have structurally strengthened hard points spaced forward and aft on the underside of the fuselage. The invention requires at least four spaced, structurally strengthened hard points. The V-22 Osprey has tie-down points attached to the airframe on the underside of the fuselage. These tie-down points are structurally strengthened hard points and are useful for attachment of the cargo suspension apparatus of the invention. Helicopters also have similar tie-down points. 
     In  FIG. 2 , load suspension apparatus  14  has an upper rigid frame  20  of rectangular configuration shown horizontally positioned just below the fuselage underside  16 . Also associated with the load suspension apparatus  14  is a lower rigid frame  20   a  of a similar rectangular geometrical configuration but of smaller dimensions. A lower rigid frame  20   a  is shown positioned horizontally below the upper rigid frame  20 . Frame  20  and frame  20   a  share the general forward (FWD) and aft (AFT) orientation of aircraft  10 . The forward end is defined by forward end bar  28  and forward end bar  28   a . The aft end is defined by aft end bar  30  and aft end bar  30   a.    
     Upper rigid frame  20  is formed from a pair of parallel spaced side bars  22  connected by a forward end bar  28  and an aft end bar  30 . The side bars  22  are attached to forward end bar  28  at attachment point  28   x  and at opposing attachment point  28   y . The side bars  22  are attached to aft end bar  30  at attachment point  30   x  and at opposing attachment point  30   y.    
     Lower rigid frame  20   a  is formed from a pair of parallel spaced side bars  22   a  connected by a forward end bar  28   a  and an aft end bar  30   a . The lower side bars  22   a  are attached to forward end bar  28   a  at attachment point  28   ax  and at opposing attachment point  28   ay . The side bars  22   a  are attached to aft end bar  30   a  at attachment point  30   ax  and at opposing attachment point  30   ay.    
     In  FIG. 2  it is clear that frame  20  and frame  20   a  are geometrically similar. Frame  20   a  has smaller dimensions. Smaller dimensions means that side bars  22   a  are shorter than side bars  22 . In the alternative smaller dimensions means that forward end bar  28   a  and aft end bar  30   a  are shorter than forward end bar  28  and aft end bar  30 . In another alternative, smaller dimensions means that each of  22   a ,  28   a  and  30   a  is shorter than the corresponding  22 ,  28  and  30  as shown in  FIG. 2 . The lower frame  22   a  forms the top of a cargo holder within which the load  12  is contained as shown in  FIG. 1 . 
     The V-22 Osprey aircraft external fuselage length is about 57.33 feet and width is about 84.6 feet. Typical dimensions for the load suspension frame of the invention for use with this aircraft are as follows:
         a. Side bar  22  is 18 to 22 feet   b. Side bar  22   a  is 16 feet (for a howitzer or Humvee high mobility multipurpose vehicle)   c. Side bar  22   a  is 20 feet (for a cargo container)   d. Forward end bar  28  is 8 to 10 feet   e. Forward end bar  28   a  is 6 to 8 feet   f. Aft end bar  30  is 8 to 10 feet   g. Aft end bar  30   a  is 6 to 8 feet   h. Preferred ratio of side bar  22 :forward end bar  28  is 2.1:1   i. Preferred ratio of side bar  22 :side bar  22   a  is 1.1:1   j. Preferred ratio of forward end bar  28 :forward end bar  28   a  is 1.1:1   k. Distance between frame  20  and frame  20   a  is 4 to 6 feet   l. Distance between frame  20  and aircraft underside  16  is 2 to 4 feet   m. Distance between forward and aft attachment points on aircraft is 26 to 27 feet   n. Distance between lateral attachment points on aircraft is
           7 to 8 feet (forward)   11 to 12 feet (aft)
 
Dimensions for use with another aircraft are scaled according to the dimensions of the available hard points.
   
               

     A cargo holder may be attached to lower frame  20   a . In the alternative, lower frame  20   a  may be integrally connected with a cargo container. In another alternative, an aerodynamically irregularly shaped load such a vehicle can be attached to lower frame  20   a  with cargo straps. The optimum stability of the cargo suspension frame is achieved by limiting cargo load to dimensions less than the dimensions of the aircraft structurally strengthened hard points. 
     Materials of construction for cargo suspension frames is well known in the industry. Aircraft aluminum or aerospace aluminum usually refers to 7075 aluminum, a zinc and copper alloy. Aircraft aluminum also includes 6061 aluminum 6063 aluminum, 2024 aluminum and 5052 aluminum. Frames are made of aircraft specification aluminum alloy brackets or tubing. The bracket or tubing material is selected to carry the weight lifted with an allowance for safety. 
     In  FIG. 3 , three orthogonal axes are labeled x, y and z. These axes are consistent with the axes shown in  FIG. 1  and consistent with the forward (FWD) and aft (AFT) labeling. In  FIG. 3  and  FIG. 4 , an elongated aircraft attachment sling  32  is mounted on the forward and aft frame end bars  28  and  30 . Elongated aircraft sling  32  has a slot  34  at the upper end for reception of a hook  36  attached to a hard point on the underside  16  of aircraft  10 . Elongated aircraft slings  35  are also mounted on the frame side bars  22 . Each of the elongated aircraft slings  35  has a slot  34  formed in the upper end thereof for reception of a hook  36  on hook attachment bracket  38  connected by a bolt  39  to a hard point on the fuselage underside  16 . Attached to the aircraft frame are four spaced structurally strengthened hard points on the fuselage underside  16 , including hook attachment brackets  38 , respectively attached to the aircraft  10  for suspension of frame  20  from the fuselage underside  16  at four locations established by the elongated aircraft slings  32  and  35 . 
     As described above, the suspension apparatus  14  includes a lower rigid frame  20   a  of a similar rectangular geometrical configuration as the upper frame  20  but of smaller dimension. That is, the corresponding members of the rectangle are shorter. Lower rigid frame  20   a  includes forward end bar  28   a , aft end bar  30   a  and two side bars  22   a . Upper rigid frame  20  includes forward end bar  28 , aft end bar  30  and two side bars  22 . 
     The term V-shaped sling means a sling having three attachment points The three attachment points correspond with the three vertexes of a triangle. Sling material usually comprises only two legs of a triangle. A third leg, as seen in  FIG. 3  need not be present. Although the third leg is not present, the slings may be referred to as triangulated slings. Because of the three attachment points, the visual impression is of a V-shaped or triangulated sling. In the alternative, the V-shaped sling can include the three legs of a triangle. 
     V-shaped slings  40 ,  42 ,  44  and  46  are attached at a forward end to one of two corner attachment points on the upper frame  20  and at an aft end to a diagonal corner attachment point on the upper frame. The V-shaped sling is also attached at an intermediate point to the lower frame at one of two points. One point is on the same end and the opposing side on the lower frame. The other intermediate point on the lower frame is on the opposite end and non-opposing side. 
     The lower frame  22   a  is suspended from the upper frame  20  by a minimum of four flexible V-shaped slings. The V-shaped slings are connected as follows: 
     (a.) V-shaped sling  40  is attached at a forward end to attachment point  28   x , at an intermediate point to attachment point  28   ay  and at an aft end to attachment point  30   y.    
     (b.) V-shaped sling  42  is attached at a forward end to attachment point  28   y , at an intermediate point to attachment point  28   ax  and at an aft end to attachment point  30   x.    
     (c.) V-shaped sling  44  is attached at a forward end to attachment point  28   y , at an intermediate point to attachment point  30   ay  and at an aft end to attachment point  30   x.    
     (d.) V-shaped sling  46  is attached at a forward end to attachment point  28   x , at an intermediate point to attachment point  30   ax  and at an aft end to attachment point  30   y.    
     Each attachment point on the upper frame is connected to its diagonal attachment point on the upper frame with two V-shaped slings. Each of the two V-shaped slings transits the load suspension apparatus  14  differently. One transit by the sling is by diagonal intermediate attachment at the same end to the opposing attachment point on the lower frame end bar. The other transit is by intermediate attachment at the opposite end to the non-opposing attachment point on the lower frame end bar. Both transits form a diagonal from the upper frame to the lower frame. The result is a series of diagonal crossings between the upper frame and the lower frame. The diagonal crossings form triangles. The crossed V-shaped slings dynamically stabilize suspended loads from lateral forces in all lateral directions. Inverted V-shaped slings are functionally equivalent. 
     By virtue of the foregoing described light weight arrangement of the load suspension device  14 , increased restraint and stability is provided for the cargo load  12 . The upper rectangular frame  20  enables use of distributed structurally strengthened hard points for suspension by the aircraft attachment slings  32  and  35  from the fuselage underside  16 , while the attachments of the V-shaped slings  40 ,  42 ,  44  and  46  at the opposite frame ends  24  and  26  provides for enhanced stabilized suspension of the load  12  therebelow. Furthermore, the configuration of the load suspension apparatus  14  allows for normal operation of the aircraft  10  when no load is attached. Also, the sling attachments including hook  36  and attachment bracket  38  on the aircraft underside allow jettisoned release of the suspension slings. 
     Materials of construction of aircraft cargo slings are well known in the industry. Slings are made of nylon and polyester web material in widths of 1 inch to 12 inches, typically 1 inch to 6 inches. The slings have strength in the range of 7500 lb/inch to 9800 lb/inch (MIL-W-4088/MIL-W-27265). Materials are sold under trade names including Nomex®, Vectran®, Cordura®, Kevlar® and Spectra®. In the alternative, aircraft attachment slings  32  and  35  and V-shaped slings  40 ,  42 ,  44  and  46  may be made from conventional aircraft cargo slings, cables or ropes. 
     Means for attaching cargo slings to aluminum frames are well known and commercially available. The structurally strengthened hard points on the aircraft are equipped with releasable cargo hooks for air drop of a load. Hooks are attached to the elongated aircraft attachment slings through a slot in the cargo sling. The slot is reinforced with sewing to form an eyelet. The slot may further be reinforced with metal or plastic inserts. The term hard point attachment means is intended to include hooks and all functional equivalents such as clips, eyelets and the like. 
     The aircraft attachment slings and the V-shaped slings are fabricated by a sewing to form a sewn connection loop. Other connectors including buckles, latches, and swiveling connectors are available for use with cargo slings. 
     According to other embodiments of the invention, the rectangular configuration of the upper and lower frames  20  and  20   a  may be replaced, for example, by circular, elliptical or greater than four-sided polygonal configurations. 
     The foregoing discussion discloses and describes embodiments of the invention by way of example. One skilled in the art will readily recognize from this discussion, that various changes, modifications and variations can be made therein without departing from the spirit and scope of the invention as defined in the following claims.