Compressor stalls

[Richard]

WRT the sukhoi video Chip posted. I thought I had a good working knowledge of jet engines but if I don't know the answers to such basic questions I guess I don't know as much as I thought.

Q: how is a compressor stall avoided when the pilot intentionally maneuvers the aircraft into a flat spin or other extreme manuever which would result in exceeding critical AoA?

 

[poadeleted20]

Q: how is a compressor stall avoided when the pilot intentionally maneuvers the aircraft into a flat spin or other extreme manuever which would result in exceeding critical AoA?

Really sophisticated variable geometry inlet design, blow-in or other auxiliary air inlet doors, variable geometry blades (i.e., they rotate on their base like constant speed prop blades) in the compressor, and a very smart domputer to manage those moving parts as well as things like nozzle position and fuel control. BTW, you will never, ever have any doubt if a compressor stall does occur -- there's a great BANG and a big fireball blows forward out the intake and past the cockpit.

 

[Arnold]

Really sophisticated variable geometry inlet design, blow-in or other auxiliary air inlet doors, variable geometry blades (i.e., they rotate on their base like constant speed prop blades) in the compressor, and a very smart domputer to manage those moving parts as well as things like nozzle position and fuel control. BTW, you will never, ever have any doubt if a compressor stall does occur -- there's a great BANG and a big fireball blows forward out the intake and past the cockpit.

Ah! The voice of experience.

 

[Richard]

Really sophisticated variable geometry inlet design, blow-in or other auxiliary air inlet doors, variable geometry blades (i.e., they rotate on their base like constant speed prop blades) in the compressor, and a very smart domputer to manage those moving parts as well as things like nozzle position and fuel control. BTW, you will never, ever have any doubt if a compressor stall does occur -- there's a great BANG and a big fireball blows forward out the intake and past the cockpit.

computer controlled variable geometry at the inlet was all I could think of as the answer. When you say nozzle do you mean the aft end? I think you do and if so, wouldn't a change in nozzle 'pitch' effect a change in critical AoA because of a change in thrust vector?

 

[Let'sgoflying!]

Q: how is a compressor stall avoided when the pilot intentionally maneuvers the aircraft into a flat spin or other extreme manuever which would result in exceeding critical AoA?

here's my guess: Pull the throttles back.

 

[poadeleted20]

When you say nozzle do you mean the aft end?

Yes.

wouldn't a change in nozzle 'pitch' effect a change in critical AoA because of a change in thrust vector?

In most cases we're talking axisymmetric nozzles, and all you're doing is changing the nozzle outlet area to balance the engine pressures. In the latest generation, yes, there are vectoring nozzles, but in the compressor stall response, we're just talking about nozzle area management.

 

[Richard]

In the latest generation, yes, there are vectoring nozzles, but in the compressor stall response, we're just talking about nozzle area management.

I had to think about that for awhile before I understood what you were really saying. My conclusion: that's a fine piece of work for whichever aerodynamacist discovered that.

To paraphrase and greatly simplify, they're in the pressure balance business. Yes?

 

[Richard]

here's my guess: Pull the throttles back.

That right there is worthy of it's own thread. Are you talking of when in the stalled condition only? See what I mean?

 

[Tom-D]

here's my guess: Pull the throttles back.

That is what is in the Test cell operators hand book for the J-52.

 

[Richard]

That is what is in the Test cell operators hand book for the J-52.

But the test cell is not in the air coming down.

 

[poadeleted20]

In general, the first response for compressor stall in flight is "Throttle - Idle."

 

[Henning]

But the test cell is not in the air coming down.

Doesn't much matter. The way the engine works is still the same.