248 replies to this topic

[MD-11 Vrt pilot]

GOOGLE has it wrong APU's do not provide thrust!

[kenair744]

MD-11 Vrt pilot, on Jan 18 2009, 06:04 PM, said:

GOOGLE has it wrong APU's do not provide thrust!

my link to Google did NOT say that APU provides thrust...

Quote

APU stands for Auxilary Power Unit and is used mainly in commercial jets to produce electricity whilst parked at a gate with the engines turned off. An APU is a small engine, situated at the base of the tail of a plane (in most cases) that can be turned on if ground support is not offered. The APU is also used to start the engines of the plane as this required a great, sudden burst of power which in some cases, the standard battery alone cannot supply.

Where does it SAY that APU provides thrust???

[Independence76]

I would never expect a topic like this to emerge into a flame war about the APU...

[Flightsimulatorpilot]

SunCountry737, on Jan 18 2009, 04:50 PM, said:

89-LX, on Jan 18 2009, 05:17 PM, said:

APU can be left on to provide extra thrust on the engines for takeoff also, or in the event of an engine failure to provide extra thrust to the remaining engine.

Are you kiddng me!? Where did you get that idea!? The APU is there to provide electrical power and bleed air for the packs/starting engines.

Bleed air causes engines to lose a little bit of thrust and increases EGT. Leaving the APU on means the APU provides the bleed air needed for the air conditioning, etc., so the engines don't have to provide bleed air, which means they'll have a little bit more thrust. It doesn't provide extra thrust, but it allows the engines to produce more thrust. I'm pretty sure that's what he was talking about. It's not that big of a difference, but I guess it can make a difference in certain situations.

Edited by Flightsimulatorpilot, 18 January 2009 - 05:36 PM.

[THBatMan8]

Flightsimulatorpilot, on Jan 18 2009, 05:35 PM, said:

SunCountry737, on Jan 18 2009, 04:50 PM, said:

89-LX, on Jan 18 2009, 05:17 PM, said:

APU can be left on to provide extra thrust on the engines for takeoff also, or in the event of an engine failure to provide extra thrust to the remaining engine.

Are you kiddng me!? Where did you get that idea!? The APU is there to provide electrical power and bleed air for the packs/starting engines.

Bleed air causes engines to lose a little bit of thrust and increases EGT. Leaving the APU on means the APU provides the bleed air needed for the air conditioning, etc., so the engines don't have to provide bleed air, which means they'll have a little bit more thrust. It doesn't provide extra thrust, but it allows the engines to produce more thrust. I'm pretty sure that's what he was talking about. It's not that big of a difference, but I guess it can make a difference in certain situations.

Correct, it's sometimes done that way to clear obstacles or the packs are shut off completely.

Edited by THBatMan8, 18 January 2009 - 06:18 PM.

[THBatMan8]

Independence76, on Jan 18 2009, 05:26 PM, said:

I would never expect a topic like this to emerge into a flame war about the APU...

1st a flame war about the ditching switch. Then the cabin pressurization. Then the APU.  

I wonder what the next system on the Airbus will be covered? At least this is turning into a very informative thread.  

Edited by THBatMan8, 18 January 2009 - 06:29 PM.

[kenair744]

Update:

http://www.nytimes.c...ml?ref=nyregion

Quote

The cockpit voice recording from the plane that landed in the Hudson River on Thursday captured both the sound of an impact on the US Airways jet, presumably by birds, and the efforts of a crew that was going through what a senior investigator called a “very calm, collected exercise," even though they were gliding lower and had no way to reach a runway.

The plane lost thrust in both engines soon after takeoff, and never reached an altitude above 3,200 feet, officials of the National Transportation Safety Board said on Sunday.

“About 90 seconds after takeoff, the captain remarks about birds," said Kathryn O. Higgins, a member of the agency who was assigned to the scene, characterizing what could be heard on the cockpit voice recording. The recording was played in the board's laboratory in Washington on Sunday and described to her. “One second later, the cockpit voice recorder recorded the sound of thumps and a rapid decrease in engine sounds," she said.

[THBatMan8]

kenair744, on Jan 18 2009, 09:08 PM, said:

“About 90 seconds after takeoff, the captain remarks about birds,"

I wonder what those remarks were

"Stupid birds!!!!!!!!"

Edited by THBatMan8, 18 January 2009 - 09:14 PM.

[kenair744]

I bet they were remarking how close the birds were...

[Cactus]

"LOOK, BIRDS! You followin' camera guy?"

[kenair744]

Duke, on Jan 18 2009, 10:56 PM, said:

"LOOK, BIRDS! You followin' camera guy?"

^  

[THBatMan8]

kenair744, on Jan 18 2009, 10:04 PM, said:

Duke, on Jan 18 2009, 10:56 PM, said:

"LOOK, BIRDS! You followin' camera guy?"

^  

:hilarious:

[MD-11 Vrt pilot]

kenair744, on Jan 18 2009, 10:04 PM, said:

Duke, on Jan 18 2009, 10:56 PM, said:

"LOOK, BIRDS! You followin' camera guy?"

^  

[89-LX]

NWilkinson, on Jan 18 2009, 04:31 PM, said:

89-LX, on Jan 18 2009, 03:17 PM, said:

APU can be left on to provide extra thrust on the engines for takeoff also, or in the event of an engine failure to provide extra thrust to the remaining engine.

You're joking..  right?  

APU's don't provide thrust.  Yes, they do blow out hot air, and that's probably enough thrust to get a 1500 pound plane moving..  but not a 169,000 pound airliner...   that's like blowing air out of your mouth to propel your bicycle.

SunCountry737, on Jan 18 2009, 04:50 PM, said:

89-LX, on Jan 18 2009, 05:17 PM, said:

APU can be left on to provide extra thrust on the engines for takeoff also, or in the event of an engine failure to provide extra thrust to the remaining engine.

Are you kiddng me!? Where did you get that idea!? The APU is there to provide electrical power and bleed air for the packs/starting engines.

You should know, its striaght from my CRJ-200 CBT, which is straight from Bombardier. Apu will increase thrust on engine by a few thosand lbs. I don't have it in front of me, but I will grab all of it when I go home Tuesday. As stated, I believe it used in the manner of reducing the bleed load on the running engine, which in turn allows for a higher RPM and more thrust.

Edited by 89-LX, 18 January 2009 - 11:13 PM.

[Cactus]

89-LX, on Jan 18 2009, 11:09 PM, said:

As stated, I believe it used in the manner of reducing the bleed load on the running engine, which in turn allows for a higher RPM and more thrust.

See above

[89-LX]

Duke, on Jan 18 2009, 11:22 PM, said:

89-LX, on Jan 18 2009, 11:09 PM, said:

As stated, I believe it used in the manner of reducing the bleed load on the running engine, which in turn allows for a higher RPM and more thrust.

See above

ya, I know. I was just trying to clarify thats what I meant. Only working on a few hours of sleep, so I am dead. Came home to my parents for the weekend to help my brother clear snow and make some money. Snowfall dumped around 7" on us last night.

[_NW_]

89-LX, on Jan 18 2009, 10:09 PM, said:

You should know, its striaght from my CRJ-200 CBT, which is straight from Bombardier. Apu will increase thrust on engine by a few thosand lbs. I don't have it in front of me, but I will grab all of it when I go home Tuesday. As stated, I believe it used in the manner of reducing the bleed load on the running engine, which in turn allows for a higher RPM and more thrust.

Ah yes and the Honeywell APU from a CRJ200 is the same as the APU in the A320  

It does not 'increase' thrust.  It takes workload off the engines.

Since your logic is dumb, I'll learnt you something.

APU's take about 30 seconds to a few minutes to start, depending on model and aircraft.  Since APU's are always turned off prior to take off under normal conditions, upon having a low altitude emergency or abnormality won't result in an instinct of "Oh hey Jimmy lets get that APU crackin!"   The A320 stayed in the air for 3 and a half minutes until it crashed, and they didn't even finish the total engine failure checklist (which is why the ditch button was never pushed.

[89-LX]

NWilkinson, on Jan 19 2009, 12:10 AM, said:

89-LX, on Jan 18 2009, 10:09 PM, said:

You should know, its striaght from my CRJ-200 CBT, which is straight from Bombardier. Apu will increase thrust on engine by a few thosand lbs. I don't have it in front of me, but I will grab all of it when I go home Tuesday. As stated, I believe it used in the manner of reducing the bleed load on the running engine, which in turn allows for a higher RPM and more thrust.

Ah yes and the Honeywell APU from a CRJ200 is the same as the APU in the A320  

It does not 'increase' thrust.  It takes workload off the engines.

Since your logic is dumb, I'll learnt you something.

APU's take about 30 seconds to a few minutes to start, depending on model and aircraft.  Since APU's are always turned off prior to take off under normal conditions, upon having a low altitude emergency or abnormality won't result in an instinct of "Oh hey Jimmy lets get that APU crackin!"   The A320 stayed in the air for 3 and a half minutes until it crashed, and they didn't even finish the total engine failure checklist (which is why the ditch button was never pushed.

Once again, I worded it wrong, but another member knew what I meant and corrected me. Sorry all hail king of never being wrong. Oh wait....

I will show my sources when I get home for you. Since you never seem to read and you always assume, I never once stated that was a procedure or useage for the APU. General APU discussion was brought up, and I provided some other insight with the APU. Once again nick, stop assuming.

[_NW_]

I don't assume, it's not my fault if you misuse words or fail to include certain details.

[AA752]

More info on the pilot. He graduated from the USAF Academy in 1973 and went on to fly F-4's. While he was a cadet, he was a soaring instructor pilot and was voted the top soaring IP by his peers.