Tg 747-300
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Compressor Stall During Taxi?

Mon Jan 16, 2006 6:00 am

Is it possible to get a compressor stall while on the ground?
I have been reading briefly about stalls and surges, and to me it doesn't seem very likely to occur on the ground.

The reason I'm asking is that back in 2004 when still with the airforce, A F-16 was said to have experienced a compressor stall while taxing out for depature. I remember it taxi out, then a loud "pop" and it returned to the hangar.

tg 747-300
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fr8mech
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RE: Compressor Stall During Taxi?

Mon Jan 16, 2006 6:40 am

Absolutely. A compressor stall or surge can occur anytime the airflow across the compressor is disturbed to point point of becoming too turbulent to pass through the engine.

The JT9 is famous, amongst maintenance circles, for stalling on the proverbial dime. During high power operations any crosswind presents the opportunity for stall. We are warned and cautioned in the AMM to always point the aircraft into the wind in order to reduce, not prevent, the occurance of a stall.
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Matt72033
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RE: Compressor Stall During Taxi?

Mon Jan 16, 2006 6:51 am

arent they more likely to happen on the ground?
during times of quick acceleration and deceleration of the engine? i.e. during start, and on selecting take off power?
 
greasespot
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RE: Compressor Stall During Taxi?

Mon Jan 16, 2006 6:58 am

The number 2 engine on a B727 is also notorious for compressor stalls in a cross wind during taxi.

GS
Sometimes all you can do is look them in the eye and ask " how much did your mom drink when she was pregnant with you?"
 
Grbld
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RE: Compressor Stall During Taxi?

Mon Jan 16, 2006 7:14 pm

Quoting Matt72033 (Reply 2):
arent they more likely to happen on the ground?
during times of quick acceleration and deceleration of the engine? i.e. during start, and on selecting take off power?

Compressor stalls on modern jet engines are most likely to happen at (1) quick acceleration and (2) high powersettings.

This means that during taxiing, you'll probably never encounter it (on modern aircraft) except if there is damage to the engine, perhaps by a bird strike, or even a big plastic bag or a trench coat that's been sucked in the engine.

A stall simply means that the pressure in the forward part of the compressor section (there may be around 10 compressor discs or so) is insufficient to achieve the higher pressure in the aft part of the compressor section. If a compressor section has a compression ratio of 10:1, this means that the air going into the section at 10 psi is compressed to 100 psi (fictitious figures). Now if for some reason, the airflow is disturbed and entry pressure goes down to, say, 3 psi (ie. there's not enough air going in), then the 100 psi on the other end may expand in a forward direction, which causes the surge (because the engine's not made for that).

As you can imagine, the two most critical times are indeed upon acceleration where you need a continually increasing amount of pressure, and at high power settings, where you also need lots of air pressure in the inlet to maintain the high power setting.

Hope that explains it a bit!


Grbld
 
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HAWK21M
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RE: Compressor Stall During Taxi?

Tue Jan 17, 2006 4:25 pm

Quoting Greasespot (Reply 3):



The number 2 engine on a B727 is also notorious for compressor stalls in a cross wind during taxi.

Why #2 Is it becaue of the Ducting.
regds
MEL
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Starlionblue
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RE: Compressor Stall During Taxi?

Tue Jan 17, 2006 10:13 pm

Quoting HAWK21M (Reply 5):
Quoting Greasespot (Reply 3):



The number 2 engine on a B727 is also notorious for compressor stalls in a cross wind during taxi.

Why #2 Is it becaue of the Ducting.

Yes. In fact on the very first 727 test flight the #2 engine surged on rotation. Boeing went so far as to tuft (attach strings in lots of places) the whole duct to figure it out. While the situation improved with redesign, occasional surges still occur.
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
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HAWK21M
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RE: Compressor Stall During Taxi?

Wed Jan 18, 2006 12:46 am


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MEL
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Tristarsteve
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RE: Compressor Stall During Taxi?

Wed Jan 18, 2006 3:01 am

The Tristar with RB211-524 engines is restricted to about 90% power at standstill due to limited airflow through the intake duct. It will surge if you open the throttle any more. It means you can never do take off power checks on the ground run bay!
With RB211-22B you can get up to 100% power, but must be turned into wind. Any cross wind and it starts surging.

With a large fan engine like Trent on B777, even at idle you can hear it burbling at idle in strong cross winds as it tries to suck in the air.
 
greasespot
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RE: Compressor Stall During Taxi?

Wed Jan 18, 2006 11:42 am

Plus the number two engine attaches to the duct via a flexiable connection that can be dammaged real easy.....A lot of the compresser surges can be attributed to this being bent when the engine is installed and therefore disturbing the airflow...

I believe the UPS #2 intake is unique to the R.R Tay re-engineing that they did.....The -100 has a oval duct while a -200 has a round...

GS
Sometimes all you can do is look them in the eye and ask " how much did your mom drink when she was pregnant with you?"
 
exPratt
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RE: Compressor Stall During Taxi?

Wed Jan 18, 2006 11:57 am

A gas turbine engine can stall or surge whenever it is running. It is more likely to stall at high power or on a quick accel, but it can do it at all power ranges. At low power, it could be a minor chug whereas at high power it could the loud bang complete with flames out the inlet and tailpipe.
 
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HAWK21M
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RE: Compressor Stall During Taxi?

Wed Jan 18, 2006 2:51 pm

Quoting Greasespot (Reply 9):
believe the UPS #2 intake is unique to the R.R Tay re-engineing that they did.....The -100 has a oval duct while a -200 has a round...

Any details/link.
regds
MEL
I may not win often, but I damn well never lose!!! ;)

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