Citation X's and ASE

[Diesel]

APU.

We took off with the APU everytime.

 

[X-rated]

I was there the other day. What was the tail number? If it was one of XOJET's X's it wasn't the APU. It should have been off before takeoff... Would make sense that it could have been the APU.

Cherry,

APU Shutdown is at the Captains discretion at XO. That's why the before Takeoff checklist says "as required", and APU also appears on the after takeoff checklist. When it is hot, I often leave it on for better cabin cooling, and for better engine performance out of places like ASE. I don't know if it was one of ours, but I'm pretty sure Dangerboy was hearing APU compressor stalls.

 

[CRJFlyer]

I may be wrong but I'm pretty sure the APU does very little to help in cooling or performance, especially during T/O...(obviously on the ground, engines off it does everything)

Cabin air at high power settings is taken of LP air from the 8th stage.. Remember the HP/LP select valve closes when TL's are above 60degrees. Even on the ramp with engines started the air coming in is from the engines and HP 14th stage air...In max cool it may have a greater effect than turning the packs to HIGH, but right now I can't remeber if there is an increase in airflow or not.

APU has nothing to do with performance..

On the other hand, I think it's a great idea to have the APU on for T/O just for the sake of having a 3rd electrical back-up...just my .02

 

[X-rated]

I may be wrong but I'm pretty sure the APU does very little to help in cooling or performance, especially during T/O...(obviously on the ground, engines off it does everything)

Cabin air at high power settings is taken of LP air from the 8th stage.. Remember the HP/LP select valve closes when TL's are above 60degrees. Even on the ramp with engines started the air coming in is from the engines and HP 14th stage air...In max cool it may have a greater effect than turning the packs to HIGH, but right now I can't remeber if there is an increase in airflow or not.

APU has nothing to do with performance..

On the other hand, I think it's a great idea to have the APU on for T/O just for the sake of having a 3rd electrical back-up...just my .02

I agree TOPI limits pressurization to 8th stage LP air for pressurization and therefore performance degradation is minimal, but every little bit helps. Also, the main reason I leave it on on hot days is for cabin cooling. The APU provides more flow to the pacs, and therefore cools the cabin better.

 

[t-bone]

I agree TOPI limits pressurization to 8th stage LP air for pressurization and therefore performance degradation is minimal, but every little bit helps.

Sounds like someone just went to recurrent!!!

 

[scangadah]

The popping you hear is the two pilots a$$ cheeks sucking up the seat cushions when trying to go all the way to KHPN/KBOS on a hot summer day.