GAPMAN CONTACT SABER : Electronic feeler gauge

The efficient functioning of an aircraft engine has a direct correlation with controlling the amount of air that passes by the outer fan blades onto the first stage compressor. Capacitec has recently introduced a gap sensor system that measures fan blade tip to engine cowling gaps helping jet engine manufacturers as well as jet engine rebuilders perform a series of inspections to more accurately set this flow of air.

A critical adjustment to this airflow is the setting up of the ideal amount of air gap between the end of the fan blades (intake guide vanes) and the abrasive liner (rub coat) around the circumference of the engine cowling. Too much gap would cause intake turbulence, too little could cause the blades to hit the inside of the shroud.

In the past, engine manufacturers and rebuilders relied on mechanical methods such as step, taper or feeler gauges to make these important measurements. They were not satisfied with the results due to poor accuracy, long measurement time and non-repeatability between operators.

A typical way of setting the air gap begins with the identification of the longest blade among the up to 100 blades in the fan blade assembly. This is done by manually passing each blade over the Capacitec gap measurement wand. Next the wand is placed at several angular locations around the circumference of the engine cowling. The longest blade is then passed over the gap sensor wand at each of these locations to determine the gap. Based on these measurements, the thickness of the liner is adjusted.

This new method has significantly improves measurement time, accuracy and repeatability resulting in reduced needless replacement of the expensive liner (rub coat) and eliminating the requirement to machine the blade to reduce their length.