Tool of the day
01-07-2014, 10:09 PM
#4731
Gets Weekends Off
Joined APC: Jul 2010
Position: window seat
Posts: 12,522
Originally Posted by lolwut
Tool of the day: The pilot that turns it on when the FA asks, knowing the costs, system wear, and that it deviates from your standard procedures.
01-07-2014, 10:37 PM
#4732
Da Hudge
Joined APC: Oct 2006
Position: Poodle Whisperer
Posts: 17,473
Originally Posted by gloopy
You'd be astonished at how many pilots just turn it on to shut them up.
I hate doing a walkaround with the APU on unless absolutely necessary.
01-07-2014, 10:55 PM
#4733
Gets Weekends Off
Joined APC: Sep 2008
Position: Kickin’ Back
Posts: 6,971
Originally Posted by mike734
You're right. For an NG with an Allied Signal 131-9 APU the burn is:
No packs 180 PPH
One Pack 240 PPH
Two Pack 204 PPH
STILL 3000 # for an evening seems a bit high.
No packs 180 PPH
One Pack 240 PPH
Two Pack 204 PPH
STILL 3000 # for an evening seems a bit high.
Denny
01-07-2014, 11:24 PM
#4734
New boss = Old boss
Joined APC: Mar 2005
Position: Ca B737
Posts: 2,762
Originally Posted by Denny Crane
Uhhh, silly me..........just gonna ask, how does a one pack operation use more gas than two pack operation?
Denny
Denny
"A single pack must work harder than two packs to cool the cabin to a given temperature. Hence the APU must supply higher bleed air pressures to assure proper environmental control system operation. This higher pressure requires a greater Inlet Guide Vane (IGV) open position than that required for 2–pack operation. Since there is less airflow required to operate 1–pack than is needed, a significant amount of unused bleed air is exhausted through the Surge Control Valve (SCV). This higher IGV open position and large quantity of unused air translates into higher APU fuel burn and higher EGTs during 1–pack operation. Also, the high airflow levels exhausting through the surge control valve increases the overall APU generated noise by 2dbA. With 2 packs supplying the cabin cooling requirements the pressure requirement is lower, resulting in lower turbine inlet temperatures, EGTs and far less unused air being discharged through the surge valve."
01-07-2014, 11:38 PM
#4735
Gets Weekends Off
Joined APC: Sep 2008
Position: Kickin’ Back
Posts: 6,971
Originally Posted by mike734
I know. Not intuitive but true. Here is the paragraph from the 737 Technical site that explains it.
"A single pack must work harder than two packs to cool the cabin to a given temperature. Hence the APU must supply higher bleed air pressures to assure proper environmental control system operation. This higher pressure requires a greater Inlet Guide Vane (IGV) open position than that required for 2–pack operation. Since there is less airflow required to operate 1–pack than is needed, a significant amount of unused bleed air is exhausted through the Surge Control Valve (SCV). This higher IGV open position and large quantity of unused air translates into higher APU fuel burn and higher EGTs during 1–pack operation. Also, the high airflow levels exhausting through the surge control valve increases the overall APU generated noise by 2dbA. With 2 packs supplying the cabin cooling requirements the pressure requirement is lower, resulting in lower turbine inlet temperatures, EGTs and far less unused air being discharged through the surge valve."
"A single pack must work harder than two packs to cool the cabin to a given temperature. Hence the APU must supply higher bleed air pressures to assure proper environmental control system operation. This higher pressure requires a greater Inlet Guide Vane (IGV) open position than that required for 2–pack operation. Since there is less airflow required to operate 1–pack than is needed, a significant amount of unused bleed air is exhausted through the Surge Control Valve (SCV). This higher IGV open position and large quantity of unused air translates into higher APU fuel burn and higher EGTs during 1–pack operation. Also, the high airflow levels exhausting through the surge control valve increases the overall APU generated noise by 2dbA. With 2 packs supplying the cabin cooling requirements the pressure requirement is lower, resulting in lower turbine inlet temperatures, EGTs and far less unused air being discharged through the surge valve."
Denny
01-07-2014, 11:57 PM
#4736
Da Hudge
Joined APC: Oct 2006
Position: Poodle Whisperer
Posts: 17,473
Originally Posted by mike734
I know. Not intuitive but true. Here is the paragraph from the 737 Technical site that explains it.
"A single pack must work harder than two packs to cool the cabin to a given temperature. Hence the APU must supply higher bleed air pressures to assure proper environmental control system operation. This higher pressure requires a greater Inlet Guide Vane (IGV) open position than that required for 2–pack operation. Since there is less airflow required to operate 1–pack than is needed, a significant amount of unused bleed air is exhausted through the Surge Control Valve (SCV). This higher IGV open position and large quantity of unused air translates into higher APU fuel burn and higher EGTs during 1–pack operation. Also, the high airflow levels exhausting through the surge control valve increases the overall APU generated noise by 2dbA. With 2 packs supplying the cabin cooling requirements the pressure requirement is lower, resulting in lower turbine inlet temperatures, EGTs and far less unused air being discharged through the surge valve."
"A single pack must work harder than two packs to cool the cabin to a given temperature. Hence the APU must supply higher bleed air pressures to assure proper environmental control system operation. This higher pressure requires a greater Inlet Guide Vane (IGV) open position than that required for 2–pack operation. Since there is less airflow required to operate 1–pack than is needed, a significant amount of unused bleed air is exhausted through the Surge Control Valve (SCV). This higher IGV open position and large quantity of unused air translates into higher APU fuel burn and higher EGTs during 1–pack operation. Also, the high airflow levels exhausting through the surge control valve increases the overall APU generated noise by 2dbA. With 2 packs supplying the cabin cooling requirements the pressure requirement is lower, resulting in lower turbine inlet temperatures, EGTs and far less unused air being discharged through the surge valve."
Give me a 757 or 320 any day of the week, please!
01-08-2014, 05:26 AM
#4738
Gets Weekends Off
Joined APC: Apr 2008
Position: 767A
Posts: 791
Originally Posted by lolwut
Tool of the day: The pilot that turns it on when the FA asks, knowing the costs, system wear, and that it deviates from your standard procedures.
01-08-2014, 06:07 AM
#4740
Gets Weekends Off
Joined APC: Jun 2009
Posts: 5,113
Originally Posted by gloopy
You'd be astonished at how many pilots just turn it on to shut them up.
So I do like 80: I lie, and run away. I go walk around in the fresh air. By the time I'm walking back to the front, the Captain has usually caved in.
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