DC-10 and TriStar existed because the rules at the time would not let a twin-engine aircraft further than 60min from the nearest diversion airport. This puts you very far north in the Atlantic and forces routing to be within that distance, and gives little or no leeway around poor weather. The rules changed in the 80s with ETOPS.
“ Andrew - We are talking about when the acceleration on the aircraft (and occupants) are equal to gravity, I.E., zero-g, not unaccelerated steady-state flight. (1-G)
Although your statement is true, you’ve missed the critical bit of context that makes it relevant to the conversation. ”
Zero g can exist in any number of situations. If you fly the right profile or if you’re falling as in tne situation after a stall. That’s all I’m saying.
As for the stall, I think the best definition in laymen terms is simply that you’ve lost lift and the control surfaces no longer operate as they should.
Although your statement is true, you’ve missed the critical bit of context that makes it relevant to the conversation. ”
Zero g can exist in any number of situations. If you fly the right profile or if you’re falling as in tne situation after a stall. That’s all I’m saying.
As for the stall, I think the best definition in laymen terms is simply that you’ve lost lift and the control surfaces no longer operate as they should.
You are not falling (EDIT: better said “not free-falling” as in zero-g ) if the wing is stalled. The Wing has exceeded critical AOA -- it hasn't dematerialized and disappeared from the aircraft. There are still forces being applied to it.
Should have stopped here.
No. The control surfaces have to (and do) operate properly after the wing stalls, because if they didn't, you couldn't recover...
Last edited:
Cite a specific example. It is not wise nor helpful to talk simultaneously in both generalities and extreme cases.
To recover from any stall, the airflow needs to be reattached to the top of the wing. The most direct way of doing that, as well as what the airplane will do if you don’t touch anything, (yes, really...) is to lower the nose. That could be considered a “dive.”
To recover from any stall, the airflow needs to be reattached to the top of the wing. The most direct way of doing that, as well as what the airplane will do if you don’t touch anything, (yes, really...) is to lower the nose. That could be considered a “dive.”
That’s why I said the control surfaces do not operate as they should. You can move them round, but there’s not enough or no airflow over them or the wings to effect any control of the aircraft. A a dive is the right thing, but even that’s not guaranteed initially since the plane has to fall fast enough to get the airflow up to speed.
Is the aircraft flying normally in a stalled condition? No. Do the control surfaces work? Yes. Are they working at 100%? No, but your note about airflow is not entirely wrong. Are they operating “as they should”? YES THEY ARE because again, if the controls did nothing, recovery from a stall is impossible.
A wing can be stalled at any speed. Yes, they usually happen at lower speeds but the only requirement necessary to stall a wing is exceed the critical AOA.
A wing can be stalled at any speed. Yes, they usually happen at lower speeds but the only requirement necessary to stall a wing is exceed the critical AOA.
But the critical AOA does depend on airspeed, doesn't it?
The higher the airspeed, the lower the critical AOA?
At a given AOA, does delamination occur earlier with higher airspeed, or inverse?
So, at a given AOA, increasing airspeed gets you closer to a stall?
Jan
The higher the airspeed, the lower the critical AOA?
At a given AOA, does delamination occur earlier with higher airspeed, or inverse?
So, at a given AOA, increasing airspeed gets you closer to a stall?
Jan
No. Critical AOA is essentially constant. Particularly in subsonic flow. As you get local flow into higher Mach the critical AOA decreases a bit, but that’s not relevant to this conversation.
You are confusing pitch with AOA. (at least a little) If you were to speed up and hold pitch constant, you would lower AOA, if you were to speed up and hold AOA constant, you’d have to increase pitch up.
Remember that AOA is the angle between the geometric “cord line” of the wing and the flow of the air opposite to movement of the center of mass of the aircraft. (The “relative wind”)
You are confusing pitch with AOA. (at least a little) If you were to speed up and hold pitch constant, you would lower AOA, if you were to speed up and hold AOA constant, you’d have to increase pitch up.
Remember that AOA is the angle between the geometric “cord line” of the wing and the flow of the air opposite to movement of the center of mass of the aircraft. (The “relative wind”)
Last edited:
Hmmm. Not sure the following is realistic, but for my understanding:
If I am flying at a certain pitch and speed, that comes with a certain AOA.
Now I increase speed, keeping the same pitch.
Does the AOA change?
Jan
If I am flying at a certain pitch and speed, that comes with a certain AOA.
Now I increase speed, keeping the same pitch.
Does the AOA change?
Jan
The short answer is yes, you’ll climb, but that’s not because of the change in AOA but rather the increase in thrust and the change in the equilibrium from whatever steady state you were in previously.
How can stalling a plane where the airflow over the wing and control surfaces is severely compromised be termed 'operating as they should'. The plane has clearly gone outside its normal operational envelope and although a good pilot might recover, often they don't.
The wings and control surfaces will only start to work properly again (i.e. provide lift and control) when the airflow is correctly attached and that wont happen unless the AOA is within operational bounds and the airplane is moving forward fast enough.
The controls do work fairly normal because you can recover. The wing loses lift at different points usually forward of the control surfaces by design. Stall and spin recovery usually involve aileron and rudder input before pitch. I could be wrong though.
- Status
- Not open for further replies.