The Development and Implementation of a New Surface Erosion Measurement Technique

Abstract

During the System Development and Demonstration (SDD) phase of the F-35B Joint Strike Fighter (JSF) program it is a requirement to prove that the JSF aircraft can operate within existing military environments. Thus it is necessary to prove that the JSF aircraft can operate out of the same airfields, off the same aircraft carriers, and from within similar expeditionary environments that the USAF/USN/USMC and Royal Navy/Royal Air Force currently operate their existing fleet of aircraft. A major element in achieving this requirement is to determine the effect of the JSF STOVL variant's hot JSF core jet efflux on the surfaces from which the aircraft is likely to operate. It is necessary to quantify potential damage to these surfaces (from a maintenance point of view) and establish whether the damage will be hazardous to the aircraft and/or ground crew/equipment. In order to fulfil this requirement a method of testing and accurately measuring surface erosion is needed. The BAE SYSTEMS Hot Gas Laboratory at Warton in the UK has the capability to test samples of various surfaces with a sub scale jet operating at full-scale temperature and pressures. However, until recently surface erosion was entirely characterised by the time to failure. This was assessed by scrutinising video recordings after the event, as quantitative measurements of surface loss have traditionally been considered impractical. Driven by the need to assess the onset of asphalt binder loss (which can occur imperceptibly), a post-test measurement method using a scanning laser has been developed. The new system is capable of measuring depth to an accuracy of 25 microns on the types of surfaces tested and provides a repeatable method of assessing and quantifying surface loss. This paper describes how the determination of the extent of damage caused by surface erosion from the efflux of a jet engine evolved from being a less than precise qualitative test process into a more rigorous science.