Abstract:
A suspension lug for releasably suspends loads under aircraft. The suspension lug has a lug eye and a threaded base and a rotation mechanism is inserted into the threaded portion. When the suspension lug is threaded into a compatible well in the load and the load is released from the aircraft, the rotation mechanism causes the suspension lug to rotate by ninety degrees from an initial orientation in which the face of the lug eye is pointed in the direction of flight to a final orientation in which the edge of the lug eye is pointed in the direction of flight. The rotation of the lug eye significantly reduces the drag on the load. Also described are methods of manufacturing and using the suspension lug of the invention.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to the field of aviation. Specifically the invention relates to systems for suspending loads on the underside of an aircraft, which can be released when the aircraft is in flight. 
       BACKGROUND OF THE INVENTION 
       [0002]    Worldwide, the most commonly used system for attaching detachable loads to an aircraft makes use of a pair of suspension lugs attached to the load. On the underside of the aircraft is an assembly comprising hooks that fit through the lug eyes. When it is desired to release the load, the assembly on the aircraft is activated to slide the hooks out of the lug eyes allowing the load with the lugs attached to fall away from the aircraft. 
         [0003]      FIG. 1  shows a typical load  10  with two suspension lugs  12  attached. In  FIG. 2  is shown a standard suspension lug  12 . Suspension lug  12  is made from a solid piece of metal and comprises a threaded base  14  to attach it to the load and a lug eye  16  into which the hook fits to secure the load to the aircraft. In most of the air forces in the Western world, the lugs are standard and, depending on the size of the load, conform to the specification Mil-A-8591, which governs all characteristics of the lug, such as physical dimensions, minimum load carrying ability, etc. 
         [0004]    In normal use, the lugs are stored separately from the loads. Each load has two standard sized threaded wells located on its top side. The wells are spaced apart by a distance that is standard, and conforms to the specification Mil-A-8591 and are located relative to the center of gravity of the load, such that the load will separate from the aircraft properly when released. When the time comes to attach the load to the aircraft, the load and lugs are removed from storage and brought near to the aircraft. The ground crew screws the lugs into the threaded wells on the load. The lugs are screwed in by hand and are turned until the bottom of the lug eye is level with the surface of the load and the lug eyes are perpendicular to the direction of flight as shown in  FIG. 1 . The load is then raised under the aircraft and the hooks on the assembly of the aircraft are slipped through the lug eyes. 
         [0005]    After releasing the load from the aircraft, the lugs remain attached to the load and make a significant contribution to the total aerodynamic drag on the load as it moves through the air. In modern combat situations it is of critical importance to the completion of the mission and, more importantly, to the safety of the aircraft and its crew to increase the stand-off distance for releasing payloads to the maximum. Therefore a great deal of attention has been given to reducing the drag on the load, thereby allowing it to be released further from the target. 
         [0006]    Theoretical calculations, which have been verified by means of measurements combining wind tunnel tests, show that in the typical case of a freefalling payload of the type shown in  FIG. 1  the two lugs of the standard type shown in  FIG. 2  may contribute up to 16% of the parasitic drag on the load. 
         [0007]    The most common technique used in the prior art to reduce the drag caused by the lugs that connect detachable loads to aircraft before release is to modify the load in such a way that the lugs are withdrawn beneath the surface of the load once it is released from the aircraft. Examples of arrangements of this type of varying degree of complexity are disclosed in the following patents U.S. Pat. No. 5,056,408, U.S. Pat. No. 5,961,075, U.S. Pat. No. 3,967,529, and U.S. Pat. No. 4,170,923. 
         [0008]    Taking into account the vast quantity of loads, especially armament of various types, that are stored at any one time in various locations around the world, the comparable numbers of suspension lugs, and especially the desire and necessity of maintaining standardization so that loads can easily be attached to and released from various types of aircraft, it would be desirable to provide an easy method of reducing the drag caused by the suspension lugs, which would allow the continued use of these available stores and further would allow continued production using existing production lines and standards. Such a method should ideally require no changes to the aircraft or load and should involve minimal changes to the work routine of the ground crews that prepare the loads and attach them to the aircraft. 
         [0009]    It is therefore a purpose of the invention to provide a modified suspension lug which will allow loads to be releasably connected to aircraft and will contribute significantly less than standard lugs to the drag on the load after it released. 
         [0010]    It is another purpose of the invention to provide a modified suspension lug in which comprises a mechanism that is simple, reliable, and safe. It is yet another purpose of the invention to provide a modified suspension lug which interfaces to the load and aircraft while complying with the requirements of the widely-accepted standard MIL-A-8591. 
         [0011]    It is yet another purpose of the invention to provide a modified suspension lug which can be attached to or removed from the load easily using only standard equipment or tools. 
         [0012]    Further purposes and advantages of this invention will appear as the description proceeds. 
       SUMMARY OF THE INVENTION 
       [0013]    In a first aspect the invention is a suspension lug for releasably suspending loads under aircraft. The suspension lug comprises a lug eye and a threaded base and is characterized in that a rotation mechanism is inserted into the threaded portion. When the suspension lug is threaded into a compatible well in the load and the load is released from the aircraft, the rotation mechanism causes the suspension lug to rotate by ninety degrees from an initial orientation in which the face of the lug eye is pointed in the direction of flight to a final orientation in which the edge of the lug eye is pointed in the direction of flight. The rotation of the lug eye significantly reduces the drag on the load. 
         [0014]    Embodiments of the rotation mechanism comprise a stopper, which comprises a locking mechanism; a bushing; a return spring; and a retaining screw. 
         [0015]    In embodiments of the suspension lug of the invention, the locking mechanism is a separate brake attached to the stopper by a screw that can be turned from outside of the threaded base of the suspension lug when the suspension lug is threaded into a well in the load. Tightening the screw causes the brake to move radially outwards jamming it against the interior wall of the well thereby locking the stopper preventing it from rotating relative to the load. After the stopper is locked, the other components of the rotation mechanism allow the suspension lug to rotate relative to the load. 
         [0016]    In embodiments of the suspension lug the threaded base of the suspension lug has been modified to allow the suspension lug to be rotated clockwise or counterclockwise within a maximum range of ninety degrees. 
         [0017]    In another aspect the invention is a method of making a suspension lug according to the first aspect of the invention from a standard suspension lug. The method comprising:
       a. removing a section of the bottom of the threaded base of the standard suspension lug to create a hollow space to accommodate the rotation mechanism; and   b. removing at least a part of the face on each side of the lug eye of the standard suspension lug to create a more slender side profile of the lug eye.       
 
         [0020]    In another aspect the invention is method of using one or more suspension lugs according to the first aspect of the invention for reversibly suspending a load comprising one or more compatible wells appropriately located on its top side from the bottom of an aircraft. The method comprises the steps of:
       a. bringing the load and the one or more suspension lugs from storage to a location close to the aircraft;   b. screwing the one or more suspension lugs into the one or more wells as far as possible by hand without the use of tools;   c. unscrewing each of the one or more suspension lugs a partial turn until the edge of the lug eye of each of the suspension lugs is pointed in the direction of flight;   d. inserting a tool through a channel bored through the threaded base of each of the suspension lugs and tightening the screw of the locking mechanism, thereby preventing rotation of the stopper of the rotation mechanism of the suspension lug relative to the load;   e. rotating, using a hand held tool, each of the suspension lugs ninety degrees clockwise so that the face of the lug eye of each of the suspension lugs is pointed in the direction of flight, thereby tensioning the spring of the rotation mechanism of each of the suspension lugs;   f. holding, using the hand held tool, each of the suspension lugs so that the face of the lug eye of each of the suspension lugs is pointed in the direction of flight while raising the load towards the underside of the aircraft and slipping a hook of the suspension apparatus of the aircraft through the lug eye of each of the suspension lugs, thereby suspending the load from the bottom of the aircraft; and   g. slipping the hooks out of the lug eye of each of the suspension lugs, thereby allowing the springs in the rotation mechanisms to return to their untensioned state and causing the suspension lugs to rotate until the edge of the lug eye of each of the suspension lugs is pointed in the direction of flight.       
 
         [0028]    All the above and other characteristics and advantages of the invention will be further understood through the following illustrative and non-limitative description of preferred embodiments thereof with reference to the appended drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0029]      FIG. 1  shows a typical load with two prior art suspension lugs attached; 
           [0030]      FIG. 2  shows a prior art suspension lug; 
           [0031]      FIG. 3  shows the suspension lug of the invention; 
           [0032]      FIG. 4A  is a side view of the prior art suspension lug shown in  FIG. 2 ; 
           [0033]      FIG. 4B  is a side view of a prior art suspension lug whose lug eye has been modified according to the invention; 
           [0034]      FIG. 5  and  FIG. 6  show the modifications that are made to a standard suspension lug in order to convert it to the suspension lug of the invention; 
           [0035]      FIG. 7A ,  FIG. 7B ,  FIG. 8 , and  FIG. 9  show the major components of the rotation mechanism of the invention; 
           [0036]      FIG. 10 ,  FIG. 11 , and  FIG. 12  show the manner in which the major components of the rotation mechanism are assembled into the threaded base of the suspension lug of the invention; 
           [0037]      FIG. 13A  to  FIG. 13G  schematically show the different stages in the installation and operation of the suspension lugs of the invention. 
       
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0038]      FIG. 3  shows a suspension lug  100  according to the present invention. The present invention reduces the drag caused by the suspension lugs by modifying the standard lug shown in  FIG. 2  in two ways. Firstly, the bottom of the threaded base  104  is hollowed out and a mechanism  102  is inserted in the hollowed out space that causes suspension lug  100  to rotate by ninety degrees when the hook is withdrawn from the lug eye  106 , i.e. when the load is released from the aircraft. 
         [0039]    After the suspension lug has rotated by ninety degrees, the edge of the lug eye is facing the direction of flight. If a conventional suspension lug  12 , such as that shown in  FIG. 4A , were used in the invention the profile facing the direction of flight after the rotation would still be relatively large because of the sloped surfaces  18 . Therefore, the second modification made to the standard lug is to reduce the profile of the lug eye  106  in the direction of flight as shown in  FIG. 4B . 
         [0040]    The present invention does not require that the aircraft or the load be modified in any way. The modifications made to the standard lug are such that the interfaces with the aircraft and the load are unchanged. Furthermore, because of over design of the standard suspension lugs, even after the modifications are carried out the suspension lug of the invention fulfills the requirements of MIL-A-8591 and functions exactly as does the standard lug that it replaces. 
         [0041]      FIG. 5  and  FIG. 6  show the modifications that are made to a standard suspension lug  12  ( FIG. 4A ) in order to convert it to the suspension lug  100  of the invention. Firstly the sloped surfaces  18  on the faces of the lug eye  16  are removed to create a lug eye  106  having a more slender side profile, for example as shown in  FIG. 4B . Secondly, the lower section of the threaded base  104  is machined removing material from the interior to create a cylindrical post  116  surrounded by an annular hollow space  108 . Thirdly two sections of the wall surrounding annular hollow space  108  are removed leaving two remaining wall sections  120  whose edges  122  are angularly spaced apart by ninety degrees to allow limited rotation of suspension lug  100 , as will be explained herein below. Finally two holes, which are best seen in  FIG. 6 , which is a cross-sectional view of lug  100  along line A-A in  FIG. 5 , are machined in the upper solid section of threaded base  104 . Well  118  comprises internal threads (not shown in the figures) into which the retaining screw  130  (see  FIG. 10 ) of the rotation mechanism  102  can be threaded. Cylindrical channel  110  is drilled vertically through the upper part of threaded base  104  in order to allow access to the Allen screw  141  (see  FIG. 7 ) that is used to lock the stopper  124  of the rotation mechanism as will be explained herein below. An approximately ninety degree section of the lower part of threaded base  104  is removed to create a clearance space  123  for the head of Allen screw  141  when lug  100  rotates relatively to the locked stopper  124 . The modification process is divided into various steps above merely for convenience. Skilled persons will easily be able to determine the most efficient and cost effective manner to carry out the modifications of the standard lugs required by the invention. 
         [0042]    The major components of the rotation mechanism  102  ( FIG. 3 ) are shown in  FIG. 7A  to  FIG. 9  and the manner in which they are assembled into hollow space  108  created in the threaded base of the suspension lug of the invention is shown in  FIG. 10  to  FIG. 12 . 
         [0043]    In  FIG. 7A  is shown the stopper  124 , which is essentially a cylindrical disk  132  having a diameter that allows it to fit into and rotate freely within annular hollow space  108  in threaded base  104  of suspension lug  100 . The center of the disk  132  has a hole bored through it, which is surrounded on the top side of the disk by an annular shaped wall  134 . The inner diameter of annular wall  134  is determined to allow bushing  126  ( FIG. 8 ) to slide through it. On each of the opposite ends of a diameter of the stopper is located a projection  136  and  136 ′, that is part of the mechanism for locking the suspension lug in the correct starting orientation relative to the load. The diameter of stopper  124  measured at upper end of projections  136  and  136 ′ equals that of the outer diameter of threaded base  104 . Each projection  136 ,  136 ′ fits into one of the sections of the wall of the threaded base  104  has been removed between wall sections  120 . A vertical unthreaded hole, through which Allen screw  141  passes, is drilled through projection  136 ′. 
         [0044]      FIG. 7B  is a magnified view of the area of projection  136 ′ in  FIG. 7A . As can be seen in  FIG. 7B , a trapezoidal shaped section of the lower part of disc  132  and projection  136 ′ is removed. Into this is inserted a matching trapezoidal shaped piece referred to herein as the brake  140 . Brake  140  has a treaded hole in it into which Allen screw  141  can turn. Turning Allen screw  141  clockwise will cause brake  141  to move upwards. As brake  140  moves upwards relative to the bottom of disc  132 , the sloped surfaces on disc  132  and brake  140  push against each other forcing brake  140  outwards, jamming it (and also projection  136 ) against the inside wall of the well in the load, thereby locking the stopper in place in the well of the load. Note that the hole drilled through projection  136 ′ has a wider inside diameter than the diameter of Allen screw  141 , thereby allowing the sidewards movement of brake  140 . Skilled persons will realize that other locking mechanisms can be used to lock stopper  124  in place in the well and prevent rotation of the stopper relative to the load. For example, no brake of cut out portion of disc  132  need be provided and Allen screw  141  could be screwed in the threads of an appropriately located channel through projection  136 ′ until it is firmly screwed against the bottom of the well. Similarly, screw  141  need not be an Allen screw, but can be any type of screw that can be turned from outside of the threaded base of the suspension lug through channel  110 , for example by the use of a thin screw driver. 
         [0045]    In  FIG. 8  is shown bushing  126 . The cylindrical annular upper part  144  of bushing  126  fits inside the annular wall  134  of stopper  124  and the hollow center  146  of bushing  126  slides over cylindrical post  116  (see  FIG. 6 ,  FIG. 7 , and  FIG. 10 ). The disk-like base  142  of bushing  126  fits into a cylindrical recess  148  in the bottom of stopper  124  (see  FIG. 10 ). A retaining screw ( 130  shown in  FIG. 10 ) is passed through the center of bushing  126  and threaded into well  118 , thereby pushing the base of the bushing against the stopper  124  to hold the parts of the rotation mechanism  102  together in place. 
         [0046]    In  FIG. 9  is shown return spring  128 . As will be described hereinbelow, return spring  128  supplies the force needed to cause suspension lug  100  to rotate ninety degrees when the load is released from the aircraft. Spring  128  fits around the outside of annular wall  134  of stopper  124 . One end of return spring  128  is bent at a right angle forming a short tail that fits into a hole  114  (see  FIG. 11 ) in threaded base  104 . The other end of return spring  128  is straight and pushes against a projection (not shown) on the top of stopper  124 . Thus, if force is applied to rotate the lug relative to the stopper in one direction, the spring is compressed. The energy stored in the spring can later be released to cause relative rotation in the opposite direction. 
         [0047]      FIG. 10  is a cross-sectional view of suspension lug  100  with the components of rotation mechanism  102  installed.  FIG. 11  shows suspension lug  100  with part of threaded base  104  removed to reveal some of the components of rotation mechanism  102 . From  FIG. 11  it can be seen how the return spring  128  fits around annular wall  134  on stopper  124  with its bent end inserted into hole  114  in threaded base  104 . From  FIG. 10  and  FIG. 11 , it can be seen how the retaining screw  130  passes through bushing  126 , which in turn passes through stopper  124  thereby holding the return spring  128  in place. Screwing retaining screw  130  into the threaded well  118  in cylindrical post  116  holds the rotation mechanism  102  in position inside threaded base  104 . Note that the dimensions of the components of rotation mechanism  102  are chosen to allow clearance spaces  150  and  152  between the top of annular wall  134  of stopper  124  and the top of annular hollow space  108  in threaded base  104  and between the head of retaining screw  130  and the top of cylindrical post  116  respectively. These clearance spaces, in addition to previously described recess  148  allow room for compression and expansion of spring  128  and free rotation of lug  100  relative to stopper  124 . 
         [0048]    The principle of operation of the invention can be understood by referring to  FIG. 12 . From  FIG. 12  it can clearly be seen how the projection  136 ′, with brake  140  attached to it by Allen screw  141 , fits into the section of wall of threaded base  104  surrounding hollow space  108  that has been removed. This makes it possible to rotate suspension lug  100  relative to stopper  124 , within the limits defined by edges  122 . If, for example, stopper  124  is firmly anchored by means of brake  140  against the interior wall of the well of the load so that it can not move and suspension lug  100  is rotated clockwise as far as it can, i.e. until the side of projection  136 ′ hits the left edge  122 ; then return spring  128  will be tightened. If the suspension lug is then released, the spring will unwind causing the suspension lug  104  to rotate relative to the fixed stopper  124  until the side of projection  136 ′ hits right edge  122  preventing further rotation. According to the invention, the distances between right and left edges  122  are such that the range of rotation in either direction will be limited to exactly ninety degrees. 
         [0049]      FIG. 13A  to  FIG. 13G  schematically show the different stages in the installation and operation of the suspension lugs of the invention. In these figures, a section of the detachable load is represented by reference numeral  160 , the direction of flight of the load once it is released from the airplane is from left to right in each figure, and the direction of rotation of suspension lug  100  when threaded into the well in the load is represented by the curved arrows. 
         [0050]    When it is required to attach the load to the aircraft the procedure followed by the ground crew is essentially the same as that followed in the prior art. The load and two suspension lugs  100  of the invention are brought from storage to a location close to the aircraft. If present, the protective cover of the well in the load is removed and suspension lug  100  is screwed into the well ( FIG. 13A ). Suspension lug  100  is screwed into the well as far as possible by hand without the use of tools. Since the threads of the well and those on the lug are not all created exactly the same, the rotation of the suspension lug  100  will be stopped at the bottom of the well with the lug oriented at some arbitrary angle with respect to the direction of flight ( FIG. 13B ). To properly orientate suspension lug  100 , it is now rotated in the opposite direction (unscrewed) a partial turn until the edge of the lug eye  106  is pointed in the direction of flight  20  ( FIG. 13C ). 
         [0051]    The stopper  124  of rotation mechanism  102  is now locked in place. Referring to  FIG. 13D  and  FIG. 20 , an Allen wrench is inserted into hole  110  and turned screwing Allen screw  141  into brake  140  causing the brake to jam against the threads on the inside of the well locking stopper  124  in place inside the well on the load. 
         [0052]    After stopper  124  has been locked by means of Allen screw  141  ( FIG. 13D ), a tool  162 , for example a crescent or a pipe wrench, is used to rotate suspension lug  100  ninety degrees clockwise, as shown in  FIG. 13E , from the orientation shown in  FIG. 13D , so that the face of the lug eye  106  is pointed in the direction of flight  20 . Since the stopper can not move, when suspension lug  100  is rotated the return spring  128  will be placed in tension. 
         [0053]    With the lug manually held in the position shown in  FIG. 13E , the load is raised under the aircraft and the hook of the suspension apparatus on the aircraft (not shown) is slipped into lug eye  106  of suspension lug  100  of the invention ( FIG. 13F ) preventing lug  100  from rotating and keeping spring  128  in tension. The aircraft takes off and over the target hook  160  is slipped out of lug eye  106 . As the load separates from the aircraft, the return spring  128  is free to return to its untensioned state and when doing so causes suspension lug  100  to rotate ninety degrees in a counter clockwise direction relative to the fixed stopper  124  and load, i.e. lug rotates to the orientation it had in  FIG. 13D . In its downward flight towards the target, the narrow edge of the lug eye  106  of the suspension lug  100  is pointed in the direction of flight ( FIG. 13G ) thereby greatly reducing the drag on the load caused by the suspension lugs when compared to the orientation of the prior art suspension lugs ( FIG. 1 ). 
         [0054]    Theoretical calculations show that replacing standard suspension lugs with those of the invention will reduce the parasitic drag on the released load from 16% to 4%, which will increase the range of a gliding bomb by about 7% and a bomb propelled by a jet engine by about 10%. 
         [0055]    Although embodiments of the invention have been described by way of illustration, it will be understood that the invention may be carried out with many variations, modifications, and adaptations, without exceeding the scope of the claims.