Abstract:
A shock absorber that uses polyurethane discs for aircraft landing gear. The discs are maintained under compression. When the aircraft lands or taxis, loads further compress the discs. Unlike bungee cords, however, the discs do not release their energy immediately. Rather, they release the energy slowly, which produces a smoother reaction to loads that eliminates any bounce back of the aircraft.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     Not Applicable 
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH AND DEVELOPMENT 
     Not Applicable 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to suspension systems for small aircraft landing gear and particularly to suspension systems for small aircraft landing gear that use polyurethane cylinders or disks as shock absorbing and suspension elements. 
     2. Description of the Prior Art 
     Small aircraft that have fixed landing gear must have some type of suspension system to handle the impacts of taxiing and landing. When a small plane lands and its wheels touch the ground, there must be some means for allowing the landing gear struts to deflect and then return to a normal loaded position. One system in use today uses a strut that has an automotive shock absorber type structure as part of the strut. This type of suspension is shown in FIG. 1, labeled as “prior art”. The shock absorber  100  uses a pair of elastic “bungee” cords on “shock rings”. These cords stretch under load, such as landing, allowing the landing gear to spread under the load. The problem with these bungee cords is that when the aircraft has landed and the load recovers, the bungee cords then pull back and contract. This can have the effect of a slingshot that can actually propel the airplane back into the air. This can cause control difficulties and possibly even a crash. 
     BRIEF DESCRIPTION OF THE INVENTION 
     The instant invention solves this problem. It is a shock absorber that uses polyurethane cylinders, discs or a combination of disks and cylinders. The cylinder is maintained under compression. When the aircraft lands or taxis, loads further compress the discs. Unlike bungee cords, however, the discs do not release their energy immediately. Rather, they release the energy slowly, which produces a smoother reaction to loads that eliminates any bounce back of the aircraft. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a front view of a landing gear strut system as prior art. 
     FIG. 2 is a front view of a landing gear strut system showing the instant invention. 
     FIG. 3 is a side view of the assembled invention in cut-away form. 
     FIG. 3 a  is a view of the outer body of the invention. 
     FIG. 3 b  is a detail side view of the assembled outer body. 
     FIG. 3 c  is an exploded view of the inner components of the invention. 
     FIG. 4 a  is a side view of an attachment fitting. 
     FIG. 4 b  is an end view of the attachment fitting. 
     FIG. 4 c  is a front view of a reaction bumper. 
     FIG. 4 d  is a side view of the reaction bumper. 
     FIG. 5 a  is a side view of a weld base. 
     FIG. 5 b  is a top view of the weld base. 
     FIG. 5 c  is a bottom view of the weld base. 
     FIG. 6 a  is a side view of a suspension tube body. 
     FIG. 6 b  is a right end view of the suspension tube body. 
     FIG. 7 a  is a side view of a reinforcing ring. 
     FIG. 7 b  is a cross-section view of the reinforcing ring. 
     FIG. 8 is a side view of a retainer bolt. 
     FIG. 9 a  is a side view of an upper retainer washer. 
     FIG. 9 b  is a front view of the upper retainer washer. 
     FIG. 10 a  is a side view of an upper guide. 
     FIG. 10 b  is a bottom view of the upper guide. 
     FIG. 10 c  is a top view of the upper guide. 
     FIG. 11 a  is a side view of a spring roll pin shown in enlarged size. 
     FIG. 11 b  is an end view of the spring roll pin shown in enlarged size. 
     FIG. 12 a  is a side view of a dynamic suspension rod. 
     FIG. 12 b  is a left end view of the dynamic suspension rod. 
     FIG. 13 a  is a side view of a POLYSORB reaction damper. 
     FIG. 13 b  is an end view of the POLYSORB reaction damper. 
     FIG. 14 a  is a front view of a lower guide. 
     FIG. 14 b  is a side view of the lower guide. 
     FIG. 15 is a side view of a lower-guide retaining bolt, shown in an enlarged size. 
     FIG. 16 is a side view of a POLYSORB reaction damper shown being formed of disks, combined into a cylinder. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring now to FIGS. 3,  3   a    3   b  and  3   c , the assembled suspension assembly  1  is shown in FIG.  3 . FIG. 3 a  is an exploded view of the outer housing components. FIG. 3 b  is a detail view showing these components assembled. 
     FIG. 3 c  is an exploded view of the inner assembly. FIGS. 4 a - 15  are detail views of the various components shown in this view. As shown in FIG. 2, the device is suspended between the V-cabane struts  101 , using attachment points on both ends of the assembly  1 , as discussed below. 
     At the first end of the assembly  1 , is an attachment fitting  10 . This fitting is used to attach one end of the assembly to the airplane V-cabane strut  101 , as discussed above. The attachment fitting  10  has a mounting hole  11  drilled perpendicular to its longitudinal axis. This hole  11  is used to bolt one end of the assembled device to one of the v-cabanes. One end of the attachment fitting  10  is welded to a weld base  15 . As shown in FIG. 3 b , one end the attachment fitting  10  passes through the weld base until it is flush with the inner edge of the weld base. The fitting is first press fit and then welded to the weld base. The weld base  15  is secured inside an outer body tube  18  by welding it into the outer body tube  18 . See FIGS. 6 a  and  6   b.  The outer body tube  18  is hollow and is open at both ends. After the weld base  15  is welded on one end of the outer body tube  18 , the combination forms an outer housing, having a closed end and an open end. As shown in FIGS. 3 a  and  3   b,  the weld base is welded inside of the tube. At the other end of the tube, A tube body reinforcement piece  20  (shown in FIGS. 7 a  and  7   b ) is attached to the other end of the tube body  18 . The reinforcement piece  20  is placed over the outside of the tube. Note that the holes are typically drilled through both the reinforcement ring and the tube body at the same time, to ensure proper alignment. This assembly, shown in FIG. 3 b  forms the outer housing for the device. 
     The inner shock assembly, shown in exploded form in FIG. 3 c , is installed inside the outer housing. First, a reaction bumper  22  (FIGS. 4 c  and  4   d ) is installed in the outer housing. This bumper sits against the weld base to prevent metal-to-metal contact. The reaction bumper  22  can be made of rubber, but in the preferred embodiment, it is made of a heavier grade polyurethane material as the POLYSORB element (discussed below). 
     Next, the inner shock assembly is made up before inserting it into the outer housing. This assembly has a retaining bolt  25  that passes through a retainer washer  27  and a guide  29 . A dynamic suspension rod  30  is threaded onto the bolt as shown. This rod is drilled and tapped on one end to accept the retaining bolt  25 . A spring roll pin  32  is placed through the dynamic suspension rod  30  to secure the retainer bolt in place. This assembly acts as a piston within the outer housing. Next, a length polyurethane shock absorber and suspension element  35  is placed in the tube around the dynamic suspension rod  30 . This polyurethane shock absorber can be a cylinder as shown, or a series of disks that when stacked, form a cylinder. This assembly is then placed into the outer housing. Finally, a lower guide  40  is placed in the end of the device and aligned with the holes in the body tube reinforcing ring. The lower guide is held in place with three bolts  45  that pass through the outer reinforcing ring and the body tube and then screw into tapped holes within the lower guide. A length of stainless steel safety wire  48  is then run between the bolts  45 . The wire passes through holes  46  that are drilled in the tops of the bolts  45  as shown in FIG.  15 . 
     As shown in FIG. 3, the dynamic suspension rod  30  passes through a hole in the center of the lower guide. The dynamic suspension rod  30  has a hole  50  in the protruding end that is used to secure the other end of the assembly to the airplane landing strut system. 
     Referring now to FIGS. 4 a - 15 , details of these components are provided. 
     FIG. 4 a  is a side view of the attachment fitting  10 . FIG. 4 b  is an end view of the attachment fitting  10 . The attachment fitting  10  is designed to connect the assembly  1  to the airplane “V” cabane strut. As shown in the figures, it has a hole  11  drilled through one end. The hole  11  is used to make the connection to the strut, as described below. The body of the fitting  10  is such that it extends out from the body at a sufficient distance to allow for an easy connection, but not so far as to weaken the assembly. 
     The attachment fitting  10  is pressed into the weld base  15 , which is shown in FIGS. 5 a ,  5   b  and  5   c . As shown in FIG. 5, the weld base  15  is also center drilled to receive the retaining bolt  25 . One end of the weld base  15  is chamfered as shown. On the same end, the through hole  12  is also counter bored at  13  to accept attachment fitting. FIG. 5 b  is a top view of the weld base. FIG. 5 c  is a bottom view of the weld base. 
     FIG. 6 a  is a side view of the suspension tube body  18 . FIG. 6 b  is a right end view of the suspension tube body. As shown in the figures, this body  18  is a cylindrical tube that has three holes  19  drilled into one end  18   b . At the other end  18   a  of the tube body, the weld base is installed with the attachment fitting. The weld base is welded into this end of the tube. The weld base reinforces this end of the tube as well as forming the attachment connection for the assembly. 
     The holes  19  are used to secure the body retainer and lower guide. The reinforcing ring  20  is used to strengthen the end of the thin wall tube body opposite to the end that is strengthened by the weld base  15 . As shown in the figures, the reinforcing piece  20  has three holes  21  that correspond to the holes  19  in the body tube. In the preferred embodiment, the reinforcing ring has a slightly larger diameter than the body tube. That allows the ring to be placed on the outside of the body tube (see FIG. 3 a ). The reinforcing piece  20  is welded to the outside of the body tube, which secures it permanently in place. At the attachment fitting end (also the upper end), a bumper is placed within the tube body to eliminate the metal to metal contact between the weld body and the components attached to the dynamic suspension rod  30 . In the preferred embodiment, this bumper is made of a similar material to the shock and suspension element. 
     Referring now to FIG. 8 a side view of a retainer bolt  25  is shown. This bolt is placed into the dynamic suspension rod  30 . This is discussed in detail below. 
     After the retainer bolt is placed in the dynamic suspension rod  30 , two other components are then added. FIGS. 9 a  and  9   b  show views of the upper retainer washer  27 . This is placed over the dynamic suspension rod  30  until it rests against the retainer bolt. The second component is the upper guide  29 , which is shown in FIGS. 10 a ,  10   b  and  10   c . Note that both of these components have drilled centers and countersunk surfaces to accept the retainer bolt  25 . As shown in FIG. 3 b , these components are placed inside the body tube and are stacked against the bumper, as shown. 
     Turning now to FIGS. 12 a  and  12   b , the dynamic suspension rod  30  is shown. The dynamic suspension rod  30  is designed to be longer that the length of the tube body so that one end  31  extends out past the end of the tube body (see FIG. 3 a ). The other end of the dynamic suspension rod  30  is drilled and tapped to receive the retainer bolt  25 . Once in place, the retainer bolt holds the dynamic suspension rod  30  in position within the tube body. To secure the retainer bolt in place within the dynamic suspension rod  30 , the spring roll pin  32  is placed through the dynamic suspension rod  30  as shown. This pin is shown in FIGS. 11 a  and  11   b  in enlarged size. 
     The key to the assembly is a piece of POLYSORB reaction damper  35 , which is shown in FIGS. 13 a  and  13   b . The POLYSORB material is a polyurethane material that has the ability to compress under load and then return to its original form once the load is removed. Another important characteristic of this material is that it restores its original form over a relative long period. This allows the material to provide a shock dampening effect. The elastic used in the prior art bungee systems has the opposite effect; when it contracts, it releases its energy quickly, producing a “bounce back” effect. Thus, using the POLYSORB material eliminates the dangers caused by the old systems. This material can be purchased from polyurethane suppliers. One such supplier is Polyurethane Products Corporation, 100 Interstate Rd, Addison Ill. 60101. For purposes of this device, it can be purchased in disks or in cylinders. In the preferred embodiment, the cylinders are preferred because they make manufacture easier. In the preferred embodiment, the material is considered “medium hard” and has a 15 percent maximum deflection. In the preferred embodiment, a 4000-pound load produces a deflection in the material of approximately 2.5 inches. Another characteristic of this material is durability. It has the ability to contract and expand thousands of times with each expansion and contraction occurring in short periods. This ability to handle many rapid compression-expansion cycles without losing the resilience of the material is key to the operation of this suspension system. Although the solid cylinder is preferred, the “cylinder” may also be made up of a number of disk segments, shown in FIG.  16 . 
     As shown in FIG. 13 b , the end view of the POLYSORB reaction damper shows that it has a hollow core, through which the dynamic suspension rod  30  passes. The POLYSORB reaction damper  35  is placed inside of the body tube as shown in FIGS. 3 a  and  3   b . Note that in the preferred embodiment, the POLYSORB reaction damper  35  is slightly longer that the space provided for it in the body tube. This is done to force the POLYSORB reaction damper  35  into compression in its normal at rest mode. This pre-compression is needed to supply the necessary preload on the POLYSORB element to allow the suspension to hold the static weight of the aircraft. 
     Once the POLYSORB reaction damper  35  has been installed in the tube, the lower guide  40  is installed. FIG. 14 a  is a front view of a lower guide. 
     FIG. 14 b  is a side view of the lower guide. As shown, the lower guide has three holes and has its center drilled. This fits over the dynamic suspension rod  30  and aligns with the holes  19  in the body tube. Once the lower guide is in place, the three bolts  45  pass through holes in the reinforcing ring  20 , which is on the outside of the tube, holes  19  in the body tube, and then into the lower guide  40 . The bolts  45  secure the lower guide into the housing. The bolts  45  are shown in FIG.  15 . Each of the bolts has a small hole  46  through which a piece of stainless steel safety wire is passed. The wire is secured to all three bolts to prevent loss of the bolts. 
     That describes the entire assembly  1 . As shown in FIG. 3 a , the dynamic suspension rod  30  extends out of the end of the body tube. It has a hole  50  at end  31  that is used to secure that end of the assembly to the aircraft landing gear struts. To attach the assembly to the landing gear, the following procedure is used. 
     Referring now to FIG. 1 for details of these first steps, raise the complete aircraft or either main landing gear, one at a time, and support it approximately 2″ off the floor or ground. Remove any covers from the old HYDROSORB and bungee suspension/shock absorber unit(s)  100 . If installed, remove approved F. Atlee Dodge Main Landing Gear Safety Cables (not shown) from the upper end at the “V” cabane using appropriate sized wrenches. Remove the HYDROSORB/bungee unit  100  from the “V” cabane and the upper end of the lower shock strut  101 . 
     Inspect the “V” cabane  102  and lower shock strut assemblies  101  for continued airworthiness condition. Reuse or replace as necessary. 
     Referring now to FIG. 2, install the new replacement BAR-18 suspension/shock absorbing unit  1  in place of the original hydrosorb unit. These units are a direct replacement for the old unit and can be installed in only one way. There is no right or left-hand unit; they work on either side of the landing gear struts. The unit is installed by attaching the attachment fitting  10  to the “V” cabane  102  and the dynamic suspension rod  30  to the lower shock strut  101 . These components are bolted to the V cabane  102  and lower struts using common fasteners suitable for the purpose. Finally, if previously installed, reinstall the main landing gear safety cables removed in step no. 2. 
     The present disclosure should not be construed in any limited sense other than that limited by the scope of the claims having regard to the teachings herein and the prior art being apparent with the preferred form of the invention disclosed herein and which reveals details of structure of a preferred form necessary for a better understanding of the invention and may be subject to change by skilled persons within the scope of the invention without departing from the concept thereof.