WO2017136622A1

WO2017136622A1 - Air cargo handling unit

Info

Publication number: WO2017136622A1
Application number: PCT/US2017/016341
Authority: WO
Inventors: John A. DIESER; Glenn PHILEN
Original assignee: The Carbon Freight Company
Priority date: 2016-02-03
Filing date: 2017-02-03
Publication date: 2017-08-10

Abstract

An air cargo handling unit includes a polygonal base panel having a plurality of edges, a plurality of frame members each defining a channel to engage an edge of the plurality of edges of the base panel, and a plurality of corner members connecting adjacent frame members with locking fasteners. The frame members, when connected by the corner members, secure the base member in the respective channels of the frame member.

Description

AIR CARGO HANDLING UNIT

CROSS-REFERENCE TO RELATED APPLICATIONS

(00011 This application claims the benefit of U.S. provisional application No. 62/290,617, entitled "Easy to Repair Lightweight Air Cargo Pallet" and filed Febmary 3, 2016, the disclosure of which is hereby incorporated by reference in its entirety.

BACKGROUND OF THE INVENTION

Field of the Invention

[0002] The present invention relates generally to the field of cargo handling units. Particularly, the invention relates to cargo handling units used in aircraft, and desirably lightweight and easily repairable air cargo handling units.

Description of Related Art

[0003] Air cargo is typically loaded and transported on standardized shipping pallets and containers, commonly referred to as unit load devices (hereinafter "ULDs"), to ensure safe and efficient transport of the cargo. The advantages of transporting cargo on ULDs are numerous. Cargo may be easily tracked and organized by keeping a recordation log of each ULD's contents. Further, shipping cargo on ULDs allows for rapid loading and unloading of an aircraft. Still further, ULDs allow large and bulky objects to be easily transported inside the aircraft that would otherwise be difficult to secure, and ULDs help protect the cargo from inflight turbulence and damage from cargo handlers and loading equipment.

[0004] However, the practice of shipping cargo in standardized ULDs has a significant disadvantage of adding otherwise unnecessary weight to an aircraft, resulting in increased fuel consumption. In all aircraft, the gross weight of the airplane is a substantial factor in operational costs and capacity because of both the cost of fuel and physical limitations of the propulsion system. Thus, ULDs are ideally manufactured to be particularly light, but capable of carrying heavy loads and being easily repairable when damaged. However, the construction of ULDs is heavily influenced by various airline industry regulations. These regulations include, for example, strict strength requirements which have so far forced manufacturers to produce ULDs that are bulky and suboptimal in terms of weight and repairability. [0005] Due to their nature of use and industry regulations, design of ULDs must balance load capacity and durability against weight and cost. Additionally, ULDs are damaged from time to time due to repeated loading and unloading, and the labor involved in the repair is a significant cost over the lifetime of the ULD.

[0006] Conventional ULDs in use today are typically made of an aluminum base panel attached via rivets to a hollow frame structure composed of extruded aluminum side rails and metal corners. The corners may be pressed or fit into the extruded aluminum side rails, which then interface with cargo systems on board an aircraft in which the ULD is placed in service.

[0007] In addition to strength requirements, manufacturing tolerances of air cargo containers are regulated by the FAA. SAE specification AS 36100 Rev A, Air Cargo Unit Load Devices - Performance Requirements and Test Parameters, which is referenced by the FAA regulation TSO C90d and the EASA regulation ETSO-C90d, governs the minimum load bearing capacity of air cargo pallets and containers used on commercial aircraft. The permitted manufacturing tolerances across an entire ULD have been tightened from previous requirements specified in NAS 3610 by FAA regulation TSO C90c and EASA regulation ETSO-C90c. For instance, in AS 36100 Rev A, new manufacturers are required to hold 0.100 inches of variance across a 125 inch edge of an M4 base configuration, which is half of the previously allowed variance in NAS 3610 for the equivalent base size. This presents significant design challenges as these tolerances can be difficult to achieve in aluminum extrusions and assemblies.

[0008J In conventional ULDs, the total manufacturing tolerance is a summation of the tolerances of the side rails, corner pieces, and base panel. In order to hold the industry-required total tolerance, matched holes for the rivets must be used in the rigid connection between the base panel and side rails, adding significant cost to the manufacture of ULDs.

[0009] Aluminum ULDs have various other disadvantages, including their high weight and their limited stiffness/weight ratio, which often necessitates the use of additional weight distributing planks when carrying an unevenly distributed load such as an automobile. Additionally, while the riveted joint between the panel and the side rail is easy to implement, riveting imposes restrictions on the design of ULDs because the base panel must remain flush with the bottom of the side rails to satisfactorily bear the weight of the cargo. jOOlO] Further, riveted construction imposes restrictions on the materials suitable for use in the various components of the ULDs. In particular, the use of rivets to join the base panel to the side rails limits the choice of material to one with a sufficiently high pin pullout strength and resistance to creep so that the riveted joint does not prematurely fail. Often this consideration alone dictates the use of a metal such as aluminum, because it can be difficult to securely fasten rivets to lighter materials, such as fiber reinforced polymer composites. Additionally, because the use of rivets rigidly secures the base panel against the side rails, the base panel and side rails cannot be made from dissimilar materials having different rates of thermal expansion. If a dissimilar material, such as a fiberglass composite, is used for the base panel, changes in temperature cause the base panel to expand and contract faster than the surrounding side rails, thus causing the base panel to unsatisfactorily distort in the center.

{0011 j Still further, riveted construction makes repair of a damaged ULD both expensive and time consuming. It is common for operators of ULDs, in the process of retrieving a ULD for use, to lift the corner of the ULD with a forklift. Repeated loading in this manner will eventually cause the corner pieces to break. It is also common for the side rails to become damaged during regular use; either becoming bent along their length or accumulating damage to the seat track attachments on the top of the rail. Damage to either a corner piece or side rail can render the ULD unsuitable tor installation in an aircraft and, as such, a damaged ULD must be temporarily taken out of service for repair. Replacement of either a corner piece or side rail is a cumbersome process involving the removal of one entire side rail and replacement of all of the associated rivets.

[0012] To replace a damaged corner piece, all of the rivets of one side rail must have their heads cut off, and the remaining body of the rivet must be punched out of the hole through, the side rail and the base panel. The side rail may then be removed. A new corner piece may then be installed in place of the damaged corner piece, and new rivets must be installed and bucked to secure the side rail to the base panel. To replace a damaged side rail, the same process for replacing a corner piece may be employed, except that a number of matched rivet holes must be drilled by hand into the new side rail to align with the corresponding holes in the base panel.

[0013] The base panel of a conventional ULD is also susceptible to damage from repeated use and therefore requires periodic repair. In particular, aluminum base panels often fatigue and crack after many cycles of being loaded with cargo, transported on aircraft, and lifted by a forklift. As explained above, the use of rivets limits the base panel material to be the same as the side rail. Therefore, a composite material, which may exhibit preferable loading characteristics, may not be substituted for the conventional aluminum base panel. The repair of fatigue cracks in aluminum is difficult and time consuming. First, the crack and some surrounding area must be completely cut out of the base panel. Second, a patch of aluminum two (2) inches or greater in every dimension than the cut-out section must be prepared. Lastly, the patch is joined to the aluminum sheet by preparing a series of matched holes and then joining the patch to the existing base panel by installing stainless steel rivets in each of the holes. This process is time consuming, requires substantial use of skilled labor, and is not always effective in substantially extending the life of the ULD.

[0014] As described above, the processes for repair of the various components of a conventional U LD are time-consuming and often require skilled labor and, as a result, may result in a ULD being removed from service for a substantial length of time. In addition, performing a repair to one component of the ULD may risk damage to other components of the ULD. In view of these considerations, an excess inventory of ULDs must be maintained to ensure that there are enough ULDs on hand to complete all scheduled shipments on the aircraft.

SUMMARY OF THE INVENTION

[0015] In view of the disadvantages of existing ULDs, it is an objective of the present disclosure to provide an air cargo handling unit that meets the strength required by industry regulation, while minimizing the weight of the cargo handl ing unit.

|0016] It is a further object of the present disclosure to provide an air cargo handling unit that may be readi ly disassembled for maintenance, repair, and replacement of the various components thereof.

[0017] It is a further object of the present disclosure to provide an air cargo handling unit that may utilize a wider array of structural materials, including composite materials, in place of the aluminum used in conventional ULDs.

[0018] Accordingly, an air cargo handling unit is provided herein which includes a polygonal base panel having a plurality of edges, a plurality of frame members each defining a channel to engage an edge of the plurality of edges of the base panel, and a plurality of corner members connecting adjacent frame members with locking fasteners. The frame members, when connected by the corner members, secure the base member in the respective channels of the frame members.

[0019] In a non-limiting example, the base panel is secured in the respective channels of the frame members without fasteners.

[0020] In a non-limiting example, the base panel inward from the plurality of edges is curved to form a bottom section to be placed in contact with a support surface.

[0021] In a non-limiting example, the frame members comprise a bottom surface planar with the bottom section of the base panel, such that the bottom surface of the frame members also engages the support surface.

[0022] In a non-limiting example, the frame members are hollow tubular members.

[0023] n a non-limiting example, the corner members comprise at least one flange insertable into the hollow tubular members.

[0024] In a non-limiting example, the hollow tubular members define an interior cavity having an internal ridge to mate with a corresponding external ridge on the corner members to guide engagement of the corner members with the hollow tubular members.

[0025J In a non-limiting example, the frame members are made of stainless steel, carbon steel, or aluminum.

[0026J In a non-limiting example, the frame members are made of continuous glass fiber and polypropylene composite.

[0027J In a non-limiting example, the frame members are manufactured by pultrusion.

[0028] In a non-limiting example, the frame members are manufactured by extrusion.

[0029J In a non-limiting example, the base panel is made of aluminum or a composite material.

[0030] In a non-limiting example, the base panel is rectangular.

[0031] In a non-limiting example, the edges of the base panel define a gap with interior end walls of the respective channels of the frame members to accommodate thermal expansion of the base panel.

[0032] Also provided in the present disclosure is an air cargo handling unit which includes at least one of a base panel and a plurality of side panels, each of the panels having a plurality of edges. The air cargo handling unit further includes a plurality of frame members each defining a channel to engage an edge of the plurality of edges of the panels and a plurality of corner members connecting adjacent frame members with locking fasteners. The frame members, when connected by the corner members, secure the panels in the respective channels of the frame members.

(0033 j In a non-limiting example, the at least one of the panels are secured in the respective channels of the frame members without fasteners.

[0034] In a non-limiting example, the frame members are hollow tubular members.

[0035] In a non-limiting example, the corner members comprise at least one flange insertable into the hollow tubular members.

[0036] In a non-limiting example, the hollow tubular members define an interior cavity having an internal ridge to mate with a corresponding external ridge on the corner members to guide engagement of the corner members with the hollow tubular members.

[0037] In a non-limiting example, the base panel is rectangular.

[0038] Various other aspects of the present disclosure are recited in one or more of the following clauses:

[0039] Clause 1 : An air cargo handling unit, comprising:

a polygonal base panel having a plurality of edges;

a plurality of frame members each defining a channel to engage an edge of the plurality of edges of the base panel ; and

a plurality of corner members connecting adjacent frame members with locking fasteners;

wherein the frame members when connected by the corner members secure the base member in the respective channels of the frame members.

[0040] Clause 2: The air cargo handling unit of clause 1 , wherein the base panel is secured in the respective channels of the frame members without fasteners.

[0041] Clause 3: The air cargo handling unit of any of clauses 1 -2, wherein the base panel inward from the plurality of edges is curved to form a bottom section to be placed in contact with a support surface. [0042] Clause 4: The air cargo handling unit of clause 3, wherein the frame members comprise a bottom surface planar with the bottom section of the base panel, such that the bottom surface of the frame members also engage the support surface.

(00431 Clause 5: The air cargo handling unit of any of clauses 1 -4, wherein the frame members are hollow tubular members.

(0044] Clause 6: The air cargo handling unit of clause 5, wherein the corner members comprise at least one flange insertable into the hollow tubular members.

(0045] Clause 7: The air cargo handling unit of any of clauses 5-6, wherein the hollow tubular members define an interior cavity having an intemal ridge to mate with a corresponding external ridge on the comer members to guide engagement of the corner members with the hollow tubular members.

(0046] Clause 8: The air cargo handling unit of any of clauses 1 -7, wherein the frame members are made of stainless steel, carbon steel, or aluminum.

[0047] Clause 9: The air cargo handling unit of any of clauses 1 -8, wherein the frame members are made of continuous glass fiber and polypropylene composite.

[0048] Clause 10: The air cargo handling unit of any of clauses 1 -7 or 9, wherein the frame members are manufactured by pultrusion.

[0049] Clause 1 1 : The air cargo handling unit of any of clauses 1-8, wherein the frame members are manufactured by extrusion.

[0050] Clause 12: The air cargo handl ing unit of any of clauses 1 -1 1 , wherein the base panel is made of aluminum or a composite material.

[0051 ] Clause 13: The air cargo handling unit of any of clauses 1 -12, wherein the base panel is rectangular.

[0052] Clause 14: The air cargo handling unit of any of clauses 1 -13, wherein the edges of the base panel define a gap with interior end walls of the respective channels of the frame members to accommodate thermal expansion of the base panel.

(0053] Clause 15: An air cargo handling unit comprising at least one of a base panel and a plurality of side panels, each of the panels having a plurality of edges, the air cargo handling unit further comprising: a plurality of frame members each defining a channel to engage an edge of the plurality of edges of the panels; and

wherein the frame members, when connected by the corner members, secure the panels in the respective channels of the frame members.

[0054] Clause 16: The air cargo handling unit of clause 15, wherein at least one of the panels are secured in the respective channels of the frame members without fasteners.

[0055] Clause 17: The air cargo handling unit of any of clauses 15-16, wherein the frame members are hollow tubular members.

[0056] Clause 18: The air cargo handling unit of clause 17, wherein the corner members comprise at least one flange insertable into the hollow tubular members.

[0057] Clause 19: The air cargo handling unit of any of clauses 17-18, wherein the hollow tubular members define an interior cavity having an internal ridge to mate with a corresponding external ridge on the corner members to guide engagement of the corner members with the hollow tubular members.

[0058] Clause 20: The air cargo handling unit of any of clauses 15-19, wherein the base panel is rectangular.

[0059] These and other features and characteristics of the air cargo handling unit will become more apparent upon consideration of the following description and the appended claims with reference to the accompanying drawings, all of which form a part of this specification, wherein like reference numerals designate corresponding parts in the various figures. It is to be expressly understood, however, that the drawings are for the purpose of illustration and description only, and are not intended as a definition of the limits of the invention.

BRIEF DESCRIPTION OF THE DRAW INGS

[0060] FIG. 1 is a perspective view of an air cargo handling unit according to one example of the present invention;

[0061] FIG. 2 is a top view of the air cargo handling unit of FIG. 1;

[0062] FIG. 3 is an exploded perspective view of a corner of the air cargo handling unit of FIG. 1;

[0063] FIG. 4A is a cross section view of a frame member and base panel of the air cargo handling unit of FIG. 1;

[0064] FIG. 4B is the cross section view of FIG. 4A showing an example of loads applied to the frame member and base panel;

[0065J FIG. 5 is a top perspective view of a corner member of the air cargo handling unit of FIG. 1;

[0066J FIG. 6 is a side perspective view of the comer member of FIG. 5;

[0067] FIG. 7 is a perspective view of an air cargo handling unit according to another example of the present invention;

[0068J FIG. 8 is a perspective view of an air cargo handling unit according to another example of the present invention; and

[0069J FIG. 9 is a cross section view of one example of the base panel of FIG. 1, FIG. 7, or FIG. 8.

DETAILED DESCRIPTION

[0070] For the purposes of the description hereinafter, the terms "upper", "lower", "right", "left", "vertical", "horizontal", "top", "bottom", "side", "base" and derivatives thereof, shall relate to the invention as it is oriented in the drawing figures. However, it is to be understood that the invention may assume various alternative variations and step sequences, except where expressly specified to the contrary. It is also to be understood that the specific devices and processes illustrated in the attached drawings, and described in the following specification, are simply exemplary examples of the invention. Hence, specific dimensions and other physical characteristics related to the examples disclosed herein are not to be considered as limiting. Referring to the drawings, like reference characters refer to like parts throughout the several views thereof.

[0071] Referring now to FIGs. 1-2, an air cargo handling unit 100 includes a polygonal base panel 101 constrained by a plurality of frame members 102a-102d that engage a plurality of edges of the base panel 101. The plurality of frame members 102a-102d are connected to a plurality of corner members 105a-105d via locking fasteners 103a-103p to define a generally rectilinear frame, in the illustrated example. The plurality of frame members 102a-102d may define a track 125 to which a cargo net or cargo straps may be attached to secure cargo to the air cargo handling unit 100 in a known fashion. The air cargo handling unit 100 is desirably sized for transport in an aircraft according to industry regulations relating to the size of air cargo shipping containers.

[0072] Referring further to FIG. 3, each of the plurality of corner members 105a-105d is connected to at least two of the plurality of frame members 102a-102d. A corner member 105b may include at least two flanges 115 insertable into respective ends of two adjacent frame members 102b-102c. The flanges 115 are connected to the plurality of frame members 102a- 102d with the locking fasteners 103a-103p. For example, the locking fasteners 103a-103p may be bolts inserted through the frame members 102a-102d and flanges 115 and secured with locknuts designed to prevent the bolts from loosening over time or due to vibration. The locknuts may include either a nylon insert or a distorted thread in order to increase holding force and resist loosening. Alternatively, the locking fasteners 103a-103p may be another suitable device capable of maintaining holding force when subjected to long-term vibration, such as lockbolts or bolts/nuts with an anaerobic locking compound applied to the threads. The plurality of frame members 102a-102d may include respective slots 106a-106d which facilitate access to the locking fasteners 103a-103d with a socket wrench.

(0073] Referring now to FIGs. 4A-B, one of the plurality of frame members 102a is shown in cross section engaged with the base panel 101. The frame member 102a includes a longitudinal channel 140 defined by channel flanges 141a-141b and an interior end wall 142. The edge of the base panel 101 is disposed in the channel 140 between the channel flanges 141a-141b. A gap 144 is maintained between the interior end wall 142 of the channel 140 and the edge of the base panel 101, and between the base panel 101 and the channel flanges 141a-141b, to allow for machine tolerances of the various components and to accommodate thermal expansion of the base panel 101 relative to the frame member 102a. The size of the gap 144 shown in FIGs. 4A- B is exaggerated for clarity.

(0074] The air cargo handling unit 100 may be assembled according to the following method. The frame member 102a is attached to the flanges 115 of adjacent corner members 105a and 105d with corresponding locking fasteners 103a-103b and 103o-103p. Similarly, the opposite frame member 102c is attached to the flanges 115 of adjacent corner members 105b and 105c with corresponding locking fasteners 103g-103h and 103i-103j. The remaining frame members 102b and 102d are then engaged with the base panel 101 by inserting opposite edges of the base panel 101 into the respective channels 140 of the frame members 102b and 102d. The frame members 102a and 102c, already attached to their adjacent comer members 105a-105d, may then be engaged with the base panel 101 and the frame members 102b and 102d. In particular, the channels 140 of the frame members 102a and 102c are engaged with corresponding opposite edges of the base panel 101. At the same time, the flanges 115 of the corner pieces 105a-105d are engaged with the corresponding ends of their adjacent frame members 102b and 102d. Finally, the corner pieces 105a-105d are attached to the frame members 102b-102d with the remaining locking fasteners 103c-103f and 103k-1031.

|0075] The channel 140 may be designed such that no fasteners or adhesives are required to constrain the base panel 101 in place once the plurality of frame members 102a-102d and the plurality of comer members 105a-105d are assembled around the plurality of edges of the base panel 101. The lack of fasteners or adhesives connecting the base panel 101 to the frame members 102a-102d permits a wide range of materials to be used for both the base panel 101 and the frame members 102a-102d. As noted above, conventional ULDs are assembled with rivets attaching the various components, limiting the useable materials to those which exhibit high pin pullout strength and resistance to creep. Composite materials are often poor choices for this type of concentrated loading. Further, the riveted joints used in conventional ULDs cause unsatisfactory distortion if used to join materials having dissimilar rates of thermal expansion, such as metals and composites. Because rivets or like fasteners are not used for connecting the base panel 101 to the frame members 102a-102d of the claimed air cargo handling unit 100, pin pullot strength, creep resistance, and rate of thermal expansion are not restrictive to the types of materials that may be used for either the base panel 101 or the frame members 102a-102d. Therefore, a wider array of suitable materials, and combinations of dissimilar materials, may be utilized for the base panel 101 and the frame members 102a-102d.

(0076] In one example, the base panel 101 may be made from a fiber reinforced polymer composite material, such as continuous glass fiber and polypropylene composite. In another example, the base panel may be made out of a metal sheet, such as aluminum sheet. As illustrated in FIG. 9, the base panel 101 may be a sandwich stmcture including an internal core 130 reinforced by external stiffening skins 131. For example, the internal core 130 may be made of foam, balsa, or a honeycomb-structured material. The stiffening skins 131 may be disposed on the top and bottom surfaces of the internal core 130 and may be made from, for example, aluminum or a composite material.

[0077] Similarly, the frame members 102a-102d may be made from a multitude of materials, including metals and composites. In one example, the frame members 102a-102d may be made of a high-strength, lightweight, extruded aluminum alloy. In another example, the frame members 102a-102d may be made of a high-strength, lightweight fiber reinforced polymer formed by pultrusion of fibers and a polymer matrix through an appropriate aperture. The fiber may be glass fiber with a polyurethane composite, carbon fiber, aramid fiber, or other suitable composite material.

[0078] Various combinations of the above-described material choices for the base panel 101 and the frame members 102a-102d may be combined. In one example, the air cargo handling unit 100 may be constructed using a base panel 101 made of a composite core reinforced by composite stiffening skins and frame members 102a-102d made of extruded aluminum. It may be appreciated that the specific materials and manufacturing methods described herein are exemplary and do not limit the present invention, and many other suitable materials and combinations of materials would also be evident to one having ordinary skill in the art.

|0079] The lack of fasteners or adhesives connecting the base panel 101 to the frame member 102a-102d also reduces the total manufacturing tolerances across the air cargo handling unit 100. As described previously, the total manufacturing tolerance of a conventional ULD is a summation of the individual tolerances of all the major components. In comparison, the total manufacturing tolerance of the air cargo handling unit 100 is governed by only the frame members 102a-102d and the corner pieces 105a-105d, since the manufacturing tolerances of the base panel 101 may be absorbed by the gap 144 between the interior end wall 142 of the channel 140 and the base panel 101. No precisely matched holes are required as in the riveted joints of conventional ULDs, and the design limitations with regard to tolerances are dictated only by the capability of the manufacturers of the frame members 102a-102d and the corner pieces 105a- 105d.

[0080] The lack of fasteners or adhesives connecting the base panel 101 to the frame member 102a-102d also reduces the time and labor required to assemble or repair the air cargo handling unit 100. As noted above, repair of conventional ULDs is costly, time-consuming, and often involves skilled labor. In comparison, the design of the air cargo handling unit 100 facilitates simple repair or replacement of any component of the air cargo handling unit 100.

[0081] Referring again to FIGs. 1-3, a comer member 105a may be replaced by removing the locking fasteners 103a-103d attaching the corner member 105a to the frame members 102a- 102b, and removing the locking fasteners 103g-103h holding an adjacent corner member 105b to a nonadjacent frame member 102c. The adjacent corner members 105a-105b and the adjacent frame member 102b may then be detached from the base panel 101. To reassemble the air cargo handling unit 100, the comer member 105a may be replaced, and the removed frame members 102a-102b and locking fasteners 103a-103d and 103g-103h may be reattached in the reverse order of disassembly.

[0082] A frame member 102a may be replaced by removing the locking fasteners, 103a-103d and 103m-103p, such that the frame member 102a and the corner members 105a and 105d adjacent to the frame member 102a may be detached from the base panel 101. The frame member 102a may then be repaired or replaced as necessary, and the removed components may be reattached in the reverse order of disassembly.

[0083] The replacement of any of the comer members 105a-105d or the frame members 102a- 102d is therefore fast, straightforward, and carries little risk of damage to other components of the air cargo handling unit 100. Further, no holes need to be drilled, and no rivets need cut or punched out. Still further, the repair requires no special skills or tools and is therefore easily accomplished by a layman. |0084] Repair or replacement of the base panel 101 is likewise simplified in comparison to a conventional ULD. Replacement of the entire base panel 101 may be performed by removing all of the locking fasteners 103a-103p and separating the frame members 102a-102d and corner pieces 105a-105d of the existing base panel 101. The frame members 102a-102d and corner pieces 105a-105d are then assembled onto a new base panel 101. The existing locking fasteners 103a-103p are then re-installed, or new locking fasteners 103a-103p are installed. If a composite material is used for the base panel 101, repair of a crack or puncture is also simplified in comparison to an aluminum base such as that used in a conventional ULD. While composite materials do not suffer from fatigue cracks in the same way that aluminum sheets do, a composite used for the base panel 101 may nevertheless crack due to unforeseen or excessive loading. To repair a small section of the base panel 101 , the damaged area may be cleaned of contaminants, a suitable composite patch prepared, and the patch joined to the base panel 101 by wetting both the base panel 101 and patch with an appropriate solvent or solvent adhesive, for example Dichloromethane or Diethyl Ether, to perform a solvent weld between the base panel 101 and patch. A weight, for example sandbags, are then placed on top of the repaired area of the base panel 1 1 until the base panel 101 and patch are suitably joined together.

[0085] Referring again to FIG. 4B, in one example, the channel 140 may be designed such that, under any reasonable load that the air cargo handling unit 100 is likely to experience, the base panel 101 is retained in the channel 140 purely by friction. The inventors have determined that the base panel 101 will be held in place by friction when under a vertical load if the channel 140 is designed in accordance with the following equation:

(00861 Equation 1 : < i_{; w}here

h_g is the distance between the inner faces of the channel flanges,

hp is the thickness of the base panel,

L is the length of the channel flanges, and

μ_¾ is the coefficient of friction between the base panel and flanges,

subject to the condition ^{hg hp} < 0.2.

[0087] For example, the gap 144, representing the distance between the inner faces of the channel flanges 141a-141b less the thickness of the base panel 101, may be 0.010 inches due to manufacturing tolerances. A worst case coefficient of friction may be 0.03, for example if the channel 140 and the base panel 101 were coated with oil. In this case, the minimum length of the channel flanges 141a-141b would be 0.333 inches according to Equation I . The inclusion of additional channel length is necessary when properly considering for the deflection of the channel 140 and base panel 101 under load and the wearing down of the surfaces of the channel 140 and base panel 101 during use. In practice, a lengthening factor of two (2) has been determined to be sufficient to account for the deflection and wearing down of the channel 140 and base panel 101 under a worst case scenario. Applying the lengthening factor, the minimum flange length is increased from 0.333 inches to 0.667 inches.

[0088] In another example, the minimum thickness of the lower channel flange 141b is determined based on the expected distributed load applied to the lower channel flange 141b. First, the bending stress on the outermost fiber of the lower channel flange 141b is determined by the following equation:

[0089] Equation 2: a_AL = ^{9L X F}^^{+t x Ft}, where

GAI. is the bending stress in the outermost fiber of the root of the channel flange,

L is the length of the channel flange,

Fi is the downward load on the channel,

F_t is the lateral force on the channel flange, and

t is the thickness of the channel flange.

[0090] Once the bending stress on the lower channel flange 141b is determined, the required thickness of the lower channel flange 141b may be ascertained using basic engineering principles based on the yield stress of the material of the lower channel flange 141b. In one example, the thickness of the lower channel flange 141b may be chosen according to the maximum load that the base panel 101 can withstand. For example, the base panel 101 may begin to plastically deform under a load of 8000 pounds-force when the air cargo handling unit 100 is supported from underneath only at its perimeter. This corresponds to an average downward load of 24 pounds-per-inch on the lower channel flange 141b. However, the downward load, which is applied approximately at point 143 on the lower channel flange 141b, varies along the longitudinal direction of the channel 140, reaching a maximum of 48 pounds- per-inch at the longitudinal midpoint of the channel 140. Using the maximum load of 48 pounds-per-inch, the previously determined channel flange 141a-141b length of 0.667 inches from Equation 1, and a stress concentration factor of 2.5 where the base of the lower channel flange 141b meets the frame member 102a, the minimum thickness of the lower channel flange 141b is 0.1 13 inches for aluminum having an ultimate strength of 53,000 pounds-per-square- i ch.

(0091 j However, this calculation assumes minimal deflection of the lower channel flange 141b under load. In practice, the lower channel flange 141b may substantially deflect when subjected to the applied load. In order to counteract this deflection and maintain the distance between the inner faces of the channel flanges 141 a-141 b, the thickness of the lower channel flange 141b may be increased above this minimum required value. In the exemplary calculation above, actual deflection of the lower channel flange 141 b, calculated using conventional engineering formulae, is approximately 0.0036 inches, increasing the gap 144 between the channel flanges 141a-141b and the base panel 101 by 36% over the original distance of 0.010 inches. Therefore, the thickness of the lower channel flange 141b may be increased, for example to 0.125 inches, to mitigate at least some of the deflection. Alternatively or in conjunction with thickening the lower channel flange 141b, the channel flanges 14 la-141b may be further lengthened to account for the increased gap 144 due to deflection.

|0092] In another example, the gap 144 is designed to account for dissimilar thermal expansion rates between the plurality of frame members 102a-102d and the base panel 101. For example, one example of the air cargo handling unit 100 may use a base panel 101 made of a composite material, such as glass fiber reinforced polypropylene, and frame members 102a-102d made from aluminum. The relative change in length between the base panel 101 and the frame members 102a-102d can be determined according to the following equation:

|0093] Equation 3: ALength = Lo x α ^χ (Ti - To); where

ALength is the relative change in length between two members,

Lo is the initial length of the members,

a is the difference between the thermal expansion coefficients of the members,

Tj is the final temperature, and

To is the initial temperature. [0094J The longest internal side of a standard-sized ULD side rail, which undergoes the greatest thermal expansion and contraction, is approximately 120.6 inches. The temperature service range of the air cargo handling unit 100 is from -55°F to + 160°F, with manufacturing of the components occurring at approximately 68°F. The coefficients of thermal expansion for glass fiber reinforced polypropylene and aluminum are 18 x lO^{~6 o}F^~1 and 12.6 x 10^{"6 o}F^"1 , respectively. Inserting these values into Equation 3, the aluminum framing members 102a-102d decrease in length by approximately 0.080 inches relative to the glass fiber reinforced polypropylene base panel 101 at -55°F. As a result, the gap 144 is necessary to permit the thermal contraction of the frame members 102a-102d relative to the base panel 101. The gap 144 in the frame member 102a must accommodate half of that relative change in length, or 0.040 inches, while the gap 144 on the opposite frame member 102c accommodates the other half, or 0.040 inches, of the relative change in length.

[0095] Similarly, using the same glass fiber reinforced polypropylene base panel 101 and aluminum frame members 102a-102d at 160°F, Equation 3 may be used to determine that the frame members 102a-102d increase in length relative to the base panel 101 by approximately 0.060 inches. As a result, the edge of the base panel 101 retracts away from the interior end wall 142 of the frame member 102a. Therefore, once the length of the channel flanges 141a-141b sufficient to retain the base panel 101 is determined, an additional 0.030 inches should be added to the length of the channel flanges 141a-141b such that the required engagement between the base panel 101 and the frame members 102a-102d is maintained despite the relative change in length due to thermal expansion.

[0096] Referring again to FIG. 4A, the base panel 101 may include a curve or stepped section 104 located inward of the plurality of edges to form a bottom section 121 of the base panel 101 coplanar with the bottom surface 146 of the frame member 102a. The curve 104 may be formed either during the initial manufacturing of the base panel 101 or in a secondary forming process. The bottom section 121 of the base panel 101 contacts a support surface, such as the ground or a floor, so that the vertical load of any cargo contained within the air cargo handling unit 100 is carried by the base panel 101 rather than the plurality of frame members 102a-102d. In particular, the vertical load is taken off of the channel flanges 141a-141b. Alternatively, the bottom section 121 of the base panel 101 may extend below the bottom surface 146 of the frame member 102a, for example by a few thousandths of an inch, such that the channel flanges 141a- 141b receive less impact from contact with rollers of an air cargo restraint system of an aircraft.

[0097] The plurality of frame members 102a-102d may be hollow tubular members, with each of the frame members 102a-102d defining an hollow interior cavity 145 extending longitudinally through its entire length. The interior cavity 145 may define an internal ridge 150 which extends into the internal cavity 145 away from a bottom wall of the frame member 102a. The internal ridge 150 of the interior cavity 145 corresponds to an external ridge 119 on each of the corner members 105a-105d. The internal ridge 150 of the frame members 102a-102d and the external ridge 119 of the corner members 105a-105d mate to guide the corner members 105a-105d into engagement with the interior cavity 145 of the frame members 102a-102d.

[0098] Additionally, the internal ridge 150 of the interior cavity 145 of the frame member 102a may serve as a countersinking surface for the locking fasteners 103a-103p. Bolts may be countersunk into the internal ridge 150 such that the bolt heads are flush with and do not protrude from the bottom surface 146 of the frame member 102a.

[0099] Referring now to FIGs. 5-6, each of the plurality of corner members 105a-105d may include at least one flange 115 insertable into a corresponding end of one of the framing members 102a-102d. Each of the flanges 115 may terminate at a shoulder 118 which limits the insertion depth of the corner members 105a-105d into the frame members 102a-102d. Each of the flanges 115 may include at least one throughbore 117 for receiving one or more of the locking fasteners 103a-103p. Each throughbore 117 is axially aligned with corresponding holes in the frame member 102a-102d in which the flange 115 is inserted.

[00100] As described above, each flange 115 on the corner member 105a may define an external ridge 119 which mates with an internal ridge 150 in the corresponding frame member 102a-102d to guide engagement of the corner members 105a-105d with the corresponding frame member 102a-102d.

[00101] Each corner member 105a-105d can withstand much larger forces than the corner joints in conventional ULDs. In conventional ULDs, torsional resistance is predominantly provided by the base since the corner joints are not rigidly connected to the other components. In comparison, the rigid connection between the corner members 105a-105d, the frame members 102a-102d, and the locking fasteners 103a-103p reallocates the torsional resistance from the base panel 101 to the corner members 105a-105d of the air cargo handling unit 100. The profile of the corner members 105a-105b is much better suited to withstand torsion than the base panel 101, resulting in reduced likelihood of damage and longer component life.

(00102] The corner members 105a-105b may be manufactured using a variety of methods from a variety of different materials. For example, the corner members 105a-105b may be made from a casting or forging process of a metal, such as aluminum, carbon steel, or stainless steel. Alternatively, the corner members 105a-105b may be machined from a block of a suitable material.

[00103] Referring now to FIG. 7, another example of the air cargo handling unit 100 may include a plurality of side panels 210 and a top panel 220. The plurality of side panels 210 and the top panel 220 define an upper structure suitable for protecting and transporting cargo. The plurality of side panels 210 may be attached to the plurality of frame members 102a-102d in a plurality of vertical channels 170a-170d. The side panels 210 may slide into the vertical channels 170a-170b similar to the manner in which the base panel 101 engages the longitudinal channel 140 of the frame members 102a-102d. The side panels 210 may be rigidly connected to the vertical channels 170a-170d with any suitable fastening means, such as rivets or fasteners such as additional locking fasteners 103a-103p. The plurality of side panels 210 may be connected to the top panel 220 using conventional methods of ULD construction, such as rivets and gusset plates.

[00104] Referring now to FIG. 8, according to another example of the air cargo handing unit 100, at least one of the top panel 220 and plurality of side panels 210 is constrained by additional frame members 102e-102n similar to the manner in which the base panel 101 is constramed by the frame members 102a-102d. in particular, at least one of the top panel 220 and plurality of side panels 210 includes a plurality of edges, each of which engages a channel of an adjacent frame member 102a-102o. Similar to the example shown in FIG. 1, the plurality of frame members 102a-102o are connected to a plurality of corner members 105a-105j. Each of the plurality or corner members 105a-105j includes a number of flanges 115 equal to the number of adjacent frame members 102a-102o. For example, the corner member 105b may include a total of three flanges 115 adapted for insertion into adjacent frame members 102b, 102c, and 102n. The corner member 105b may be secured to adjacent frame members 102b, 102c and 102n by fastening means such as locking fasteners 103a-103p.

[00105] A multitude of arrangements of the frame members 102a-102o, side panels 210, and top panel 220 is possible depending on the intended design of the air cargo handling unit 100. For example, the top panel 220 may not engage a channel 140 of the adjacent frame members 102e- 102h, but may instead be connected to adjacent frame members 102e-102h with rivets. Similarly, any number of the side panels 210 may not be adapted for engagement with a channel 140 of adjacent frame members 102a-102o, but may instead be connected to adjacent frame members 102a-102o with rivets. Further, within each side panel 210 or top panel 220, some of the edges may engage a channel 140 of the adjacent frame member 102a-102o, while other edges of the same side panel 210 or top panel 220 do not.

[00106] Any number of the sides panels 210 or top panel 220 may be assembled with the frame members 102a-102o and the corner members 105a-105j in the same manner as the base panel 101 is assembled to the frame members 102a-102d and the corner members 105a-105d. In particular, the frame members 102a-102o may be secured to the top panel 220 and side panels 210 without fasteners such that a rigid connection is not established between the frame members 102a-102o and top panel 220 and side panels 210, similar to the manner in which the base panel 101 is secured to the frame members 102a-102d. As a result, the side panels 210 and top panel 220 may be designed to take advantage of the lack of a rigid connection as discussed above in regard to the base panel 101. For example, the lack of a rigid connection between the frame members 102a-102o and side panels 210 and top panel 220 permits the side panels 210 and top panel 220 to be made from composite materials as described in the previous examples, resulting in substantial weight savings over a comparable aluminum ULD.

|00107] While several examples of air cargo handling units are shown in the accompanying figures and described hereinabove in detail, other examples will be apparent to, and readily made by, those skilled in the art without departing from the scope and spirit of the invention. For example, it is to be understood that this invention contemplates that, to the extent possible, one or more features of any example can be combined with one or more features of any other example. Accordingly, the foregoing description is intended to be illustrative rather than restrictive.

Claims

THE INVENTION CLAIMED IS:

1. An air cargo handling unit, comprising:

a polygonal base panel having a plurality of edges;

a plurality of frame members each defining a channel to engage an edge of the plurality of edges of the base panel; and

wherein the frame members, when connected by the comer members, secure the base member in the respective channels of the frame members.

2. The air cargo handling unit of claim 1, wherein the base panel is secured in the respective channels of the frame members without fasteners.

3. The air cargo handling unit of claim 1, wherein the base panel inward from the plurality of edges is curved to form a bottom section to be placed in contact with a support surface.

4. The air cargo handling unit of claim 1 , wherein the frame members comprise a bottom surface planar with the bottom section of the base panel, such that the bottom surface of the frame members also engages the support surface.

5. The air cargo handling unit of claim 1 , wherein the frame members are hollow tubular members.

6. The air cargo handling unit of claim 5, wherein the corner members comprise at least one flange insertable into the hollow tubular members.

7. The air cargo handling unit of claim 5, wherein the hollow tubular members define an interior cavity having an internal ridge to mate with a corresponding external ridge on the corner members to guide engagement of the corner members with the hollow tubular members.

8. The air cargo handling unit of claim 1 , wherein the frame members are made of stainless steel, carbon steel, or aluminum.

9. The air cargo handling unit of claim 1 , wherein the frame members are made of continuous glass fiber and polypropylene composite.

10. The air cargo handling unit of claim 1 , wherein the frame members are manufactured by pultrusion.

1 1. The air cargo handling unit of claim 1 , wherein the frame members are manufactured by extrusion

12. The air cargo handling unit of claim 1 , wherein the base panel is made of aluminum or a composite material.

13. The air cargo handling unit of claim 1, wherein the base panel is rectangular.

14. The air cargo handling unit of claim 1 , wherein the edges of the base panel define a gap with interior end walls of the respective channels of the frame members to accommodate thermal expansion of the base panel.

15. An air cargo handling unit comprising at least one of a base panel and a plurality of side panels, each of the panels having a plurality of edges, the air cargo handling unit further comprising:

a plurality of frame members each defining a channel to engage an edge of the plurality of edges of the panels; and

16. The air cargo handling unit of claim 15, wherein at least one of the panels is secured in the respective channels of the frame members without fasteners.

17. The air cargo handling unit of claim 15, wherein the frame members are hollow tubular members.

18. The air cargo handling unit of claim 17, wherein the corner members comprise at least one flange insertable into the hollow tubular members.

19. The air cargo handling unit of claim 17, wherein the hollow tubular members define an interior cavity having an internal ridge to mate with a corresponding external ridge on the corner members to guide engagement of the corner members with the hollow tubular members.

20. The air cargo handling unit of claim 15, wherein the base panel is rectangular.