FEATURE


SPRINGS & SHOCK ABSORBERS


WDS’ self-compensating shock absorber was the most flexible option for the ULDs


Needing a shock


absorber to ensure the safety of its Unit Load Devices (ULD),


designed to transport


luggage and freight on aircraft, a materials


handling OEM turned to WDS Components for a solution


transporting luggage and freight safely


U


sed by the aviation industry across the world, Unit Load Devices – ULDs – are essential for transporting luggage and


freight. Constructed in aluminium to ensure they are robust yet lightweight, both cargo and passenger baggage can be placed into the ULD containers, which are then loaded on and off the aeroplane. Loading items in this way, instead of in bulk or individually, means faster baggage handling while, at the same time, enabling accurate planning of loads and weight distribution. The ULDs typically feature ball transfer


units set into the floor to ease the loading and unloading of cargo and baggage and, once loaded onto the aeroplane, are secured to ensure they remain in the same position during the flight.


softening the impact


One UK materials handling equipment manufacturer, however, decided to improve the safety of its ULD design by softening the impact of the side barriers that are deployed when loading and unloading. Each side of the ULD features a barrier that


is lowered to maintain stability on the bed during side loading. After loading, the barriers are returned to their raised position. The barriers are manually operated and are lowered by releasing a latch via a foot-operated pedal. There is the possibility, however, that these barriers could suddenly drop. Not only could this cause injury to the operator, but it could also damage the loading environment’s bed and the ULD itself. To overcome this issue, the OEM got in touch with WDS to specify a shock absorber design that could decelerate


8


and reduce the impact of the barrier. Not only did the solution have to be able to


provide variable shock absorption, but it had to be cost effective as the company had a requirement for high volume production. WDS was able to provide the optimum engineering outcome by specifying a self-compensating shock absorber.


shock absorber specification


In order to specify a shock absorber capable of sufficient deceleration, WDS had to consider the barrier’s velocity, mass, propelling force and frequency of cycles. The speed of the descending barrier could vary, depending on its starting position, meaning adjustable shock absorbers that are set where the factors of impact remain constant would not be suitable. WDS therefore developed a solution involving a self-compensating shock absorber, greatly improving the performance. With the self-compensating shock absorber


design, in the event of a sudden drop or differing forces, the device would still be able to manage the impact and provide sufficient deceleration. While self-compensating shock absorbers are initially selected for high, medium or low speed applications, they function within a range of effective mass, and no other adjustment is required, whether for variations in velocity or propelling force. For the unpredictable loads that can occur on a ULD, WDS’ self-compensating shock absorber was the most flexible option. To specify the device, the customer’s average


load cycle was assessed, and the appropriate shock absorber was selected by the WDS technical team according to the application’s speed. For installation, the shock absorbers were


2 DESIGN SOLUTIONS DECEMBER/JANUARY 2022


Cargo and baggage


are placed in the ULD containers


screwed directly onto the barrier. During the barrier’s descent, they immediately catch the load and support lowering, decelerating the barrier to a safe speed and force. Irrespective of load or speed, the self- compensating shock absorber manages the impact. Rubber caps also remove the potential of damage or marking to the loading/unloading environment. Constructed from


steel, the WDS range of self-compensating shock absorbers provide robust, long-term use, and can variously handle a maximum effective mass of up to 1,200kg, a maximum energy per cycle of 98Nm, and a velocity of up to 4m/s. The material


handling OEM is now trialling the shock absorbers across other applications.


WDS Components www.wdscomponents.com/en-gb


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