What are the Characteristics of a Good Performance Parameter?

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Too often today, legacy performance requirements are invoked on new military ground vehicle programs without giving any thought to whether they will result in a suitable capability or not.  It is assumed that by invoking legacy requirements from the M1 or Bradley, that a new vehicle program will enjoy comparable performance.  That is simply not the case.

So, if available legacy performance requirements are insufficient to ensure suitable operational capability, what characteristics need to be considered for updated performance parameters?  There are a few.  

First and foremost, each invoked performance metric should be operationally relevant.  That means that metrics should assess capabilities required to complete an operational mission; not simply testing for testing sake.  One example of this type of outdated metric is the ability to ascend and descend a paved 60% grade.  Paved 60% surfaces occur nowhere except at test facilities.  Paved roads grades are typically capped at no more than 8%, but may have short stretches up to 15% grades; well below the typical legacy test requirement for military vehicles. It is understood that military vehicles should be able to traverse terrain that may not be passable by commercial vehicles.  So, is there a better way to assess a military vehicle’s capability to ascend and descend grades?  The answer is ‘Yes”.  Instead of evaluating a vehicle’s grade climbing ability on a dry solid surface, it would be more operationally relevant to assess that capability on natural soil.  

Another feature of good performance parameters is a metric that assesses multiple vehicle features with a single test.  An example of a multidimensional metric is speed on grade.  This parameter considers such features as torque available at the drive sprocket or wheel hubs, capability of the cooling system to stay within operating temperature limits when under load for an extended time and transmission gear ratios and shift points.

The last key feature of good metrics is those that are unambiguous.  Good metrics identify test conditions such as weight (curb, gross vehicle, or both), (air conditioning on or off), fuel type, air temperature, etc. as well as a detailed test procedure.

The bottom line is there are performance parameters that are much better suited to providing appropriate operational capabilities than those invoked on many legacy vehicle systems.  Requirement developers and testers need to try and avoid simply plagiarizing metrics from previous programs and ask themselves “Is there a better way?’

Guest Blog Written By:
Bill Ross, Sr. Mobility Systems Engineer
Nevada Automotive Test Center