Saab Compressor stalls?

[Flyslow]

Hello all, I have heard Mesaba has had a few compressor stalls this past week on some of the Saabs. I don't fully understand a compressor stall, if someone could elaborate that would be great. Also, what can be done to prevent these. Thanks, I am still in the process of learning so bare with me

 

[grnclvrs]

A compressor stall happens when the air that the compressor takes in the front can't get out the back fast enough (short version). The air flow then typically reverses accross the compressor and when this happens there is a loud bang. The engine has some bleed valves that sense this happening and open to relieve the pressure as compressors can damage an engine, especially that POS CT7. They typically happen when the engine is being started, power applied or power reduced. On start it's because the turbine is not spinning as fast as the compressor, on power application it can be because the power is added too fast, same on power reduction. One night in BOS, I watched as a senior mechanic working on a bleed problem on a 767 retarded the power levers very quickly (part of a test) and the resulting stall a few of the fan blades of the engine.

 

[Seggy]

Slaabs suck

 

[minitour]

A compressor stall happens when the air that the compressor takes in the front can't get out the back fast enough (short version).

What if the air comes in the back and goes out the front?:yup:

-mini

 

[Flyslow]

Thanks grnclvrs for the reply

 

[TallFlyer]

What if the air comes in the back and goes out the front?:yup:

-mini

Heck, thats normal for a PT6.

 

[ajf005]

I was told a good explanation of it once, its like when you're pouring oil into a funnel and you pour too much which makes the funnel overflow. Too much oil and not enough flow

 

[minitour]

Heck, thats normal for a PT6.

That's why I typed my post...

-mini

 

[///AMG]

Can be faulty bleed air valves, faulty bypass doors (for those big high-bypass types), or damaged blades/stators. Saw the latter on a Hornet in tension about to take a cat shot.......he went up to mil power and fire balls started popping out of one of the tailpipes like a roman candle. In my limited experience with turbine aircraft, I have never seen anything quite as dramatic. Correct me if I'm wrong, but it seems like a turboprop aircraft like the Saab would probably not have quite the same issues with jam acceleration related stalling as a normal turbofan/jet would, just due to the inertia of the prop and all.

 

[jynxyjoe]

Slaabs suck

Our new procedure is, I swear to God, dial back the ctot one click and say "I wish I had two pratts". Repeat until power levers take over.

God I miss the Beech

 

[grnclvrs]

That's why I typed my post...

-mini

Back to engine school for you. The front of the engine (lowest station number) is pretty much always at the compressor end. That sound you hear now is 200 pilots googling to find an example where this is not the case, hence I said "pretty much always" not "always".

 

[///AMG]

Back to engine school for you. The front of the engine (lowest station number) is pretty much always at the compressor end. That sound you hear now is 200 pilots googling to find an example where this is not the case, hence I said "pretty much always" not "always".

Hmmm....the airplane I flew with a PT-6 had the intake and compressor section physically behind the hot section and exhaust stacks. Flow came in the front, into the compressor and was reversed back forward into the burners. To add more confusion the exhaust stacks reversed it once more......nice with the canopy open and not wearing an oxygen mask (cough cough cough). Then again, maybe we are arguing two different points here (since you mentioned station number)

 

[minitour]

Back to engine school for you. The front of the engine (lowest station number) is pretty much always at the compressor end. That sound you hear now is 200 pilots googling to find an example where this is not the case, hence I said "pretty much always" not "always".

The PT6 I fly looks mostly like this. The front is the exhaust. Air comes in the back and out the front...just like I said. The compressor section is literally in the back. Obviously, it's the lowest "station number", but it is not up front.

-mini

 

[OldTownPilot]

Outside the world of turbines attached to airplanes, the 'front' of the engine in the intake and first compressor stage. The 'back' of the engine is the last of the turbine stage and the exhaust. Don't confuse the geometry of the installation with how the actual engine works. In a compressor stall you have localized reverse flow 'back to front', and bad things happen.

Check the PT6 install on the Piaggio. The back is the front in the back:crazy:

 

[minitour]

Outside the world of turbines attached to airplanes,

Which is what we're talking about. We aren't talking about engines on trains or mopeds.

Check the PT6 install on the Piaggio. The back is the front in the back:crazy:

The P-180 is an odd bird. Did you know it doesn't really fly? It's just so ugly the Earth repels it.

-mini

 

[OldTownPilot]

Which is what we're talking about. We aren't talking about engines on trains or mopeds.

The P-180 is an odd bird. Did you know it doesn't really fly? It's just so ugly the Earth repels it.

-mini

Yes, but turbine engines for power generation and propulsion of things besides airplane are also subject to compressor stalls. Its a rather unique thing to the PT-6 where its 'normal' geometry is 'reversed'. For most people it is easiest to think of a compressor stall as air flow going backwards. In the PT6's case 'backwards' is in the same direction as forward motion of the thing that it is attached to, yet backwards relative to the engine.

Friggin Canadians.

 

[minitour]

Yes, but turbine engines for power generation and propulsion of things besides airplane are also subject to compressor stalls.

But we aren't discussing those things.

Its a rather unique thing to the PT-6 where its 'normal' geometry is 'reversed'. For most people it is easiest to think of a compressor stall as air flow going backwards. In the PT6's case 'backwards' is in the same direction as forward motion of the thing that it is attached to, yet backwards relative to the engine.

Friggin Canadians.

I don't see what all the fuss is aboot...anic:

-mini

 

[WalterSobchak]

Our new procedure is, I swear to God, dial back the ctot one click and say "I wish I had two pratts". Repeat until power levers take over.

God I miss the Beech

Or push the PL up till they take over and the TQ motor isnt being used and just dial it down.:rawk:

I wish they would teach the newbs more about ballooning so they don't just shove the PL levers to 100% on a standard T/O. It says in the POM within 10-15%.:whatever:

 

[minitour]

Power applications should be made niiiiiiice and smoooooooooooooooooth.

-mini

 

[jynxyjoe]

Or push the PL up till they take over and the TQ motor isnt being used and just dial it down.:rawk:

I wish they would teach the newbs more about ballooning so they don't just shove the PL levers to 100% on a standard T/O. It says in the POM within 10-15%.:whatever:

Yeah, up'ing the power lever is easily my favorite way. But when your full power I'm dialing that sucker back slow like they say.

As far as the ballooning, can someone tell the FO's it's ok if I bring the power levers back when they are in the yellow. It's like a G** **** magic trick that i bring the levers back slightly and the ctot doesn't kick off. *shakes head*