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Compressor Stalls

After installation of an engine you should check engine alignment. If the engine alignment is out there may be loads imposed on the output and the main drive shaft. This can cause stress & increased wear on components more power and increase vibration, all destructive. Be sure to check and adjust N1 rigging before the first ground run. Check rigging and adjust N2 to specs. Hooking things up and the engine runs is not sufficient.

After N1 and N2 are rigged correctly check the VIGV ( variable inlet guide vanes ) are rigged correctly if this out of rig it can cause compressor stalls. Check that the bleed band is closing at the right time as this can cause compressor stalls.

These checks are found in the airframe manual and the engine manual.

The engine may have been run on a test stand, but the test stand run criteria is different from the aircraft. These engine can be used in various airframes. If all is in order fly the aircraft and check that upper end of the VIGV range full open falls within the chart. When all is good then perform a topping check.

If these things are not done at the airfield, they may be done unintentionally over forests, lakes, canyons or other bad places. There are basic performance checks that can be done before take off or in the air at the first flight of the day to determine the health of the engine. Dirty filter systems, dirty and eroded compressors can drop the compressor efficiency below the capability of the VIGV’s and bleed band capability.

The VIGV’s and the bleed band are responsible for keeping the air flowing through the compressor efficiently and eliminating compressor stalls. The VIGV’s and bleed band are controlled by the Fuel Control. There are adjustments on the Fuel Control can be made to bring the VIGV and bleed band into the proper ranges. If you are not able to adjust these correctly you may have to replace the Fuel Control.

All these things are mechanical and can fail at any time. If things are maintained and adjusted correctly problems may be found before they become catastrophic. Proper checks prior to releasing the aircraft for return to service will help reduce the possibility of removing the aircraft from service for good and the possible human toll.

Pete Frinchaboy

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