a-v-8er
Well-known member
- Joined
- Oct 10, 2002
- Posts
- 143
Had a student ask why the gyroscopic instruments work by suction and air being directed against the rotor vanes instead of blowing air onto the vanes under positive pressure with a compressor (or pump) installed before the air enters the casing?
I honestly don't know, so here are some elaborate thoughts, but if someone knows feel free to correct me.
*With the pump located past the instruments there less chance that debris or a malfunctioning pump would damage the instruments.
*Seems to me that the suction system is more simple with ambient air being directed in to each instrument and an overpressure relief valve in case the pump would provide too much suction.
*Since the pump is an engine accessory, the engine speed determines the suction and if a pump was installed prior to the instruments maybe the positive pressure entering the instruments wouldn't have anywhere to go if rapidly increasing engine speed, "over pressurizing" the casing. The vacuum pump can operate more efficiently to yield reliable gyro speeds at several different engine speeds.
Anyone, care to give this a more thorough explanation? I feel like I'm just guessing here...
I honestly don't know, so here are some elaborate thoughts, but if someone knows feel free to correct me.
*With the pump located past the instruments there less chance that debris or a malfunctioning pump would damage the instruments.
*Seems to me that the suction system is more simple with ambient air being directed in to each instrument and an overpressure relief valve in case the pump would provide too much suction.
*Since the pump is an engine accessory, the engine speed determines the suction and if a pump was installed prior to the instruments maybe the positive pressure entering the instruments wouldn't have anywhere to go if rapidly increasing engine speed, "over pressurizing" the casing. The vacuum pump can operate more efficiently to yield reliable gyro speeds at several different engine speeds.
Anyone, care to give this a more thorough explanation? I feel like I'm just guessing here...