We have used APSDS to study multiple gear interaction effects for a Boeing 747 using a range of alternative damage models (Wardle and Rodway, 1995b, Rodway, 1995a).
Results from the study show that the successful calibration of simplified design models against the full-scale test data does not create a capability to confidently extrapolate beyond the limits of the full scale test data. The full-scale tests were essentially conducted using single gear assemblies. No tests were carried out to investigate the increased damage due to interaction effects of adjacent gear assemblies.
The study showed that simple damage models give unrealistic predictions for the damage caused by all sixteen wheels when compared to that computed for a single isolated 4-wheel gear. Three different performance models, each of which gave a similar ‘goodness of fit’ to the full-scale test data, gave greatly different predictions of the damage caused by the interactions of the sixteen main wheels. The differences between the alternative predictions increase with increasing depth to subgrade.
Given the above comments a single gear should be used for design analyses. In the case of the B747 the inner and outer gears can be included as separate aircraft types. The damage for the two gears is then calculated separately, with both gears contributing to the total damage.