High mobility trailer: Diverse team surmounts design problems to produce a trailer capable of living up to its name - Army Equipment Modernization - United States Tank Automotive and Armaments Command

Program Manager, Nov-Dec, 2001 by Nancy A. Moulton, Eric R. Noyes

As the model identifies unacceptable stresses, it can be altered in terms of design or material specifications to measure whether the changes improve the item's performance. Once the FEA predicts an acceptable design, the Computer Aided Design software produces the engineering specifications needed to translate the model into the physical item for manufacturing. SAIC's engineers followed such a process to analyze the surge brake.

Concurrent with development of the surge brake computer model, PM-LTV organized a test at APG to precisely measure the forces exerted on an HMT surge brake and drawbar during fully loaded cross-country travel at required speeds. An HMT surge brake and drawbar were instrumented with strain gages and accelerometers; a towing HMMWV was equipped with data recorders to record 48 channels of data simultaneously 400 times per second for up to 15 minutes; and a video camera provided a visual record of the surge brake throughout the tests. The instrumented HMT was towed several times on the Perryman No. 3 cross-country test course at APG in the fall of 1999.

Once the IPT analyzed the test data from APG to learn the maximum forces being applied to the surge brake, they learned that the heavy HMT surge brake was subjected to peak loads of over 32,000 lbs. along the longitudinal axis of the drawbar, and upward loads of over 8,000 lbs. during the fully loaded cross-country tests. These were loads the surge brake was not designed to withstand.

PM-LTV also analyzed the measured loads for frequency of occurrence and duration, and developed nominal analysis loads to be inputs to the FEA. The HMT Surge Brake Finite Element Analysis is a graphical prediction of the amount of strain each portion of the surge brake might experience in the real world. Different colors highlight the areas where strain occurs at or above levels that are of interest to the designers.

Growing Outside Pressure

While the IPT worked to develop a solution to the HMT's design deficiencies, outside pressure grew to find a solution. In October 1999, the U.S. General Accounting Office issued a report to the U.S. Senate (GAO/NSAID-00- 15), titled "Defense Acquisitions - Army Purchased Truck Trailers That Cannot Be Used as Planned." Prepared at the request of Iowa Senator Tom Harkin, the report detailed the programmatic and technical problems in the program's history and recommended that the Army, before procuring additional trailers, demonstrate that the HMT design will perform, as required, without causing damage to the HMMWV.

Release of the report and Senator Harkin's subsequent press conference on the results focused national news media attention on the HMT. On Oct. 27, 1999, ABC World News Tonight broadcast a report on the HMT in its regular news segment, "It's Your Money." This is a recurring report in which ABC News highlights ways the Federal Government spends or does not spend the taxpayers money The HMT broadcast was quite critical of the HMT program.

Determining a Course of Action