If high-quality equipment for rescue purposes has to be transported to crisis regions, the challenges are all the greater if there is only a small amount of space available for protection. This is the case with a transport aircraft for which SMJ Sondermaschinenbau has developed an ingenious fastening system. The object being transported is a helicopter, which has to be transported like raw eggs inside a cargo plane with the rotor blades removed. The interior dimensions are only a few centimetres more than the external dimensions of the helicopter body.

In order to efficiently protect the overall structure, a landing protection system for attaching the helicopter was developed to series maturity together with the client. This depends on special devices that transfer the occurring loads into the helicopter structure. Extensive calculations were necessary to ensure the load transfer to the individual structural points on the main rotor head and the cabin floor. In addition to secure attachment, the problem of overloading the structure also had to be avoided. Weather-related turbulence, rapid changes of direction and maneuvers during take-offs and landings lead to considerable force effects.

As helicopters are built to save a lot of weight and have a correspondingly fragile design, simply lashing them down with chains and tensioning straps is not enough. This is mainly because the forces acting on the body during flight can correspond to a load multiple of over 4.6 g, i.e. more than four times its own weight. Even without the rotor blades, this amounts to slightly more than three tons. Perfect protection is required to prevent structural damage, which is very difficult to detect during an inspection after air transportation. In this particular case, SMJ Sondermaschinenbau cooperated with ACE shock absorbers.

Customized Tubus safety dampers are part of the damping systems. © ACE

Tube dampers for safe transportation
A precise design was required to determine the exact type of structural damper. This involved determining the necessary energy absorption or force-displacement characteristic. It was taken into account that the helicopter skids allow a certain amount of deflection due to their design and can therefore absorb some of the energy in the event of a hard landing. However, this ability is not sufficient to prevent damage in the event of a rough landing or transportation.

For example, if a load of 10,000 newtons is applied vertically to the helicopter, the skids deform by 30 millimetres. The greater the load, the more serious the deformation. Based on these values, the two selected tube safety dampers had to have a special force-displacement characteristic. Accordingly, the dampers had to adopt a specific design, as they also had to fit into the design of the overall SMJ damping system.

In line with these requirements, ACE manufactured customer-specific special models. Because the individual safety dampers had to be tested before delivery as proof of the characteristic curve, various loads were applied during development. The tube safety dampers specially modified for the application in the course of this process enable the additionally required energy absorption of 124 kilonewtons and thus prevent damage to the helicopter structure in the event of an extreme landing or other shocks during flight.