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Predicting constraint point loads for a vehicle towed along a fixed path

Braun, Jarrod
Towing a vehicle along a fixed path is useful in automation processes. Understanding the forces involved while towing a vehicle is critical for the design of the towing system. For aircraft in particular, careful measures must be taken to ensure that loads remain within the envelope prescribed by the manufacturer. These loads may be determined via testing. However, this is expensive, and each vehicle or vehicle configuration requires its own test. An analytical method for predicting loads is much quicker, more cost effective, and more easily enables vehicle compatibility with the system. To create such a method, known models for predicting a vehicle's wheel trajectory are combined with a prescribed velocity profile along the trajectory. From these, the vehicle's linear and angular accelerations at every point along the path are derived. The equations of motion for the vehicle may then be solved to determine key unknown forces, such as the overall towing force and lateral wheel friction. A first validation of this approach was performed by comparing the predicted direction of the lateral towing force to the direction recorded while towing a scale aircraft. The experiment was repeated at multiple speeds. The predicted force direction matched the measured direction for over 94% of the path length at all speeds tested. The highest correlation for any test was 99%, while the lowest was 94.3%. The agreement between the predicted and recorded direction suggest that further investigation of this approach is warranted.