CoP movement near the stall as slats deploy

[Boeingdriver999]

Hi all,

Imagine a scenario when you are approaching the stall in clean configuration at 10,000ft (any swept wing airliner type). At the first sign of stall - stall warning, stick shaker, rumbling etc you pitch forward firmly to reduce AoA and on some types you select the first stage of flap. Usually this mean the slats deploy. What does the centre of pressure do in this case? You haven’t stalled and you’ve reduced AoA so by now it should be moving aft.

Thoughts?

BD

[70 Mustang]

You answered the question yourself.
Perhaps depends upon the rate of rotation of the wing around the lateral axis, the resultant change of relative wind vs the rate of respective flap and slat extensions and resultant change of effective camber of wing/flap/slat combined profile.

[vilas]

Hi all,

Imagine a scenario when you are approaching the stall in clean configuration at 10,000ft (any swept wing airliner type). At the first sign of stall - stall warning, stick shaker, rumbling etc you pitch forward firmly to reduce AoA and on some types you select the first stage of flap. Usually this mean the slats deploy. What does the centre of pressure do in this case? You haven’t stalled and you’ve reduced AoA so by now it should be moving aft.

Thoughts?

BD
Slat extension is not a part of stall recovery but it is part of flight pathe recovery. So you extend slat only when out of stall. It decreases VLS and increases stall margin during recovery.

[stilton]

Slat extension is not a part of stall recovery but it is part of flight pathe recovery. So you extend slat only when out of stall. It decreases VLS and increases stall margin during recovery.


Never seen this before, in all jet transports I’ve flown stall recovery was accomplished with no configuration change, that included the after recovery phase

[FullWings]

Never seen this before, in all jet transports I’ve flown stall recovery was accomplished with no configuration change, that included the after recovery phase
B777: “Do not change gear or flap configuration, except: During liftoff, if flaps are up, call for flaps 1”. Rather remote scenario but I suppose the lawyers made them include it...

[70 Mustang]

I simply replied to the question.

which was not “what is the correct stall recovery procedure.”

it would also depend upon the situation.

If memory serves, there was a sentence allowing the addition of Flaps 1 in the stall or windshear section in the 737 QRH or FCTM if close to terrain and the flaps were up. Not able to find it immediately, but will continue looking. Perhaps it has been removed.

if I owned my own 737 or 320, I would take it up and play with it to see why the “no configuration change” was so important and see what would happen.

like I said, he asked the question which included a configuration change.

[Locked door]

A320 memory actions contain the words “if clean and below 20k ft, flap 1 select”. As mentioned above, it comes after “flight path, recover smoothly” so is not there to unstall the wing, but to aid manoeuvring after the wing is unstalled.

[Boeingdriver999]

Thank you Mustang for reading the question :8

During stall training we recover from the stall and then select flaps 1 which gives us the slats. My question is not about that.

My question is what happens to the center of pressure when you select flaps 1/slats out? Not stalled, nose down, wings level, airspeed increasing. Assume pitch is constant to the wing is not rotating around it’s lateral axis.

[vilas]

Never seen this before, in all jet transports I’ve flown stall recovery was accomplished with no configuration change, that included the after recovery phase

Obviously you haven't read something that's recommended for atleast a decade. Time to read now A320 FCTM below:

"When stall indications have stopped, and when the aircraft has recovered sufficient energy, the flight crew can smoothly recover the initial flight path. If in clean configuration and below FL 200, during flight path recovery, the flight crew must select FLAPS 1 in order to increase the margin to AOAstall."
The word used for selection of flap1 is "must".

[vilas]

Thank you Mustang for reading the question :8

During stall training we recover from the stall and then select flaps 1 which gives us the slats. My question is not about that.

My question is what happens to the center of pressure when you select flaps 1/slats out? Not stalled, nose down, wings level, airspeed increasing. Assume pitch is constant to the wing is not rotating around it’s lateral axis.
At the first sign of stall - stall warning, stick shaker, rumbling etc you pitch forward firmly to reduce AoA and on some types you select the first stage of flap. That is what you said and that appears to incorrectly make slat part of stall recovery which is not true.

[BraceBrace]

B777: “Do not change gear or flap configuration, except: During liftoff, if flaps are up, call for flaps 1”. Rather remote scenario but I suppose the lawyers made them include it...

It's a Boeing phrase used for many types and the FCTM always refers to "inadvertent up selection for takeoff".

Even though flaps up takeoff is indeed very remote, myself I have missed the flaps 1 slot completely during acceleration (sim session) and went flaps up from 5. And I have seen one of my FO's do the same thing. As the aircraft is accelerating not that much of a deal you could say. During initial training long time ago I was warned for big brain farts with stories where stressed people apparently overloaded so much they went flaps up when requested gear up as well.

[Boeingdriver999]

I’m not being specific to type vilas. You are being specific to the A320. I said “any swept wing airliner type”.

Anyway this is pedantic because I’m not asking anything about the stall or it’s recovery. I’m asking about the movement of center of pressure. I don’t know how I can make this any clearer? :ugh:

[FullWings]

It's a Boeing phrase used for many types and the FCTM always refers to "inadvertent up selection for takeoff".

Even though flaps up takeoff is indeed very remote, myself I have missed the flaps 1 slot completely during acceleration (sim session) and went flaps up from 5. And I have seen one of my FO's do the same thing. As the aircraft is accelerating not that much of a deal you could say. During initial training long time ago I was warned for big brain farts with stories where stressed people apparently overloaded so much they went flaps up when requested gear up as well.
Interesting. I had assumed “liftoff” to mean as the wheels left the ground, so it was there to cater for the unlikely (but possible) event where you had managed to defeat every checklist and warning system and had attempted a flapless takeoff, getting a stall warning in the process. The old gear/flap mix up seems likely too.

[FullWings]

Anyway this is pedantic because I’m not asking anything about the stall or it’s recovery. I’m asking about the movement of center of pressure. I don’t know how I can make this any clearer? :ugh:
Yes, well, the last time I put the slats out, I was wearing an onion on my belt, as that was the style at the time. They didn’t have white ones because of the Pandemic, so I had to use those big yellow ones... Anyhoo, I would have thought that as it’s increasing the camber of the wing and promoting boundary layer reattachment, dynamically the overall effect would be to move the CofP aft, but what do I know? Where are the aerodynamicists when you need them?

[Obama57]

DC 10 slats would deploy automatically if the stick shaker was activated. This might occur on a heavy weight T/O with turbulence. Additionally, one could expect the moniker, “Slats”, for the rest of the trip.

Re the A320, at my airline, clean stall is trained
1. lower the nose(reduce AOA), wings level, as you call for flaps 1, then check speed brake retracted.
Slats lowers stall speed by approximately 15 kts.

[Boeingdriver999]

That’s settled then :8

[hans brinker]

Just an average punter, but extending the slats creates wing surface ahead of the clean MAC, so I would suggest all else being equal, it would move forward...

[70 Mustang]

Do a Google search:

Aerodynamics for Naval Aviators pdf

It will take you to the FAA website and a pdf document you can download.

If after reading it carefully, you cannot find the answer to your question in that book,

You don't need to know it! 😀

[vilas]

DC 10 slats would deploy automatically if the stick shaker was activated. This might occur on a heavy weight T/O with turbulence. Additionally, one could expect the moniker, “Slats”, for the rest of the trip.

Re the A320, at my airline, clean stall is trained
1. lower the nose(reduce AOA), wings level, as you call for flaps 1, then check speed brake retracted.
Slats lowers stall speed by approximately 15 kts.
Lower nose, wings level, once stall warning has stopped add thrust as required and check speed brake in then flap1 last.