VIGV/VSV
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VIGV/VSV
Can anyone help?
I have a report to do on a fault with a VIGV/VSV actuator to an engine. I have my fault indications.
80 kts, pilot hears a rumbling sound, Tq drops, T6 drops and Nh drops followed by a rapid increase back to normal conditions.
I think I am on the right track with a VIGV/VSV fault causing the compressor to stall followed by surging.
I just cant seem to get the technical part straight in my head, would the guide vanes have to decrease the airflow to cause the stall or merely change the angle at which it entered the compressor,
any help much appreciated.
Ross
I have a report to do on a fault with a VIGV/VSV actuator to an engine. I have my fault indications.
80 kts, pilot hears a rumbling sound, Tq drops, T6 drops and Nh drops followed by a rapid increase back to normal conditions.
I think I am on the right track with a VIGV/VSV fault causing the compressor to stall followed by surging.
I just cant seem to get the technical part straight in my head, would the guide vanes have to decrease the airflow to cause the stall or merely change the angle at which it entered the compressor,
any help much appreciated.
Ross
Join Date: Feb 2005
Location: flyover country USA
Age: 82
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Typically - a compressor stall/surge will result from the VIGV/VSV being too far OPEN for existing compressor parameters (T2 and Nh). This could result from (e.g.) a brief recirculation event - exhaust gas reingestion - which is too quick for the CIT sensor to instantly respond. Thus the stall/Nh rollback/torque drop.
(You didn't specify whether this was a fixed wing or a helo; I think this scenario could apply to either when taking off in a tailwind)
But after a second, the CIT sensor "catches up" with actual inlet temp, the VSVs close to the required position, the stall clears, and things return to normal. Note that the variable vanes are not closing to CHANGE (increase or reduce) airflow, but rather to maintain near-optimum AOA on compressor airfoils.
(You didn't specify whether this was a fixed wing or a helo; I think this scenario could apply to either when taking off in a tailwind)
But after a second, the CIT sensor "catches up" with actual inlet temp, the VSVs close to the required position, the stall clears, and things return to normal. Note that the variable vanes are not closing to CHANGE (increase or reduce) airflow, but rather to maintain near-optimum AOA on compressor airfoils.
