High-Speed Tyre-Soil Interaction of Aircraft on Soft Runways

Kurzfassung

A fundamental requirement of military transport aircraft is the ability to manoeuvre on soft soil runways whereby the flotation depends on the aircraft/runway strength relationship. One must take into consideration that when operating on substandard airfields take-off distance is increasing and extra propulsive force must be available. Hence predictions for the manoeuvrability, the higher rolling resistance compared to rigid surfaces, not to mention the runway damage should be available. These effects depend essentially on the deformation of soil in contrast to rigid pavements where the rolling resistance is caused mainly by internal hysteresis losses in the tyre. In the design process of concurrent engineering MBS (Multibody System) simulation tools take an important place. In contrast to the CBR (California Bearing Ratio) method, which is until now state-of-the-art in the landing gear design process for soft soil runways, multibody simulation allows to investigate the dynamic behaviour of the vehicle, tyre and soil system. The simulation of tyre-soil interaction by means of multibody tools make use of analytical modelling and specific measureable parameters are used to describe the physical soil behaviour. With analytical approaches for the trye-soil contact area it is possible to reach quite a good approximation for the real contact conditions. The main problems in describing the physical soil behaviour are its non-deterministic properties what gives the simulation results, independent from the modelling approach, in terramechanics always quite a great deviation from measurable results. Other approaches treat the problem of tyre-soil interaction with the method of finite elements (FE). These finite element models are of very fine discretisation and allow a precise simulation of the deformation of either tyre or soil but this modelling approach generally needs a large amount of computation time. From this follows a great advantage of MBS simulation in contrast to FE models that a less detailed model setup is required and MBS models can be calculated on commonly used computer systems in a time range of minutes. For this reason MBS is very interesting for extensive parameter variations. In addition MBS simulation allows the consideration of the dynamic interaction of aircraft undercarriage and soil and the fuselage con be optionally implemented as flexible body.