We can tell for sure that it's not 1 g, because the airplane stops climbing and goes into a descent.
This would be after the engines failed though. The plane was initially able to climb for a few seconds, during which, assuming the engines had most of their power, I would consider a stall unlikely.
To perhaps help illustrate my view here is a generic flight envelope:
I removed the top which is not relevant (it mentioned ejection limit) and drew some additional lines. The plane is close to stall on takeoff but as it accelerates into climb (which it should with engines running) it pulls away from the stall limit. Flaps would indeed shift the envelope by some amount (not to scale) but in my estimate the very worst case would still see the plane stay above the stall limit as long as the engines were running.
Also in retrospect I should have moved the TO point more to the right because the plane isn't even taking off at the stall limit and would have some buffer.
The pitch moment is controlled be the elevators, so that's not an issue. The question is not whether they could deploy the flaps to increase the lift with no other effect on the plane, but whether they may have lost lift because of premature retraction of the flaps.
It would be very hard to retract the flaps too early with no loss of lift.
The flaps play a part too when they extend the chord and in doing so move the lift center, or by creating drag and moving the drag center. I bring it up for two reasons. The movement of the flaps could produce a change in attitude of the plane in video and because retracting the flaps could also provide some pitch moment to help orient the plane to the correct AoA.
A lift issue from flaps retraction would require the plane to be in a state very close to stall which I don't foresee if the engines are operating normally. Also keep in mind that the takeoff flap setting is much less aggressive than landing, so the difference between flaps up and down may not even be that great.
You seem to believe that "more lift" means more than 1g, but it's simple more lift than with no flaps, all else being equal. You assume that the wing always can create the same amount of lift at the same speed, as long as you adjust the angle of attack. That's not true. And it's certainly not true for the instant when the flaps are retracted because at that point the AoA has not yet been adjusted and the loss of lift - even if it's just for an instant - is real. You can feel this yourself the next time you go flying. When the flaps are retracted after takeoff you feel lighter for about a second.
If the lift exceeds the weight, by the plane can no longer be flying at 1 g. There is a non zero net force.
I do understand that the flaps expand the flight envelope and there are situations where 1g flight is impossible without flaps and I'm not disputing that, but the plane isn't going to get into that part of the envelope with thrust unless some other major factor is at play, maybe something like running into the wake vortex of a previous takeoff.
In other words, by the time the flaps may have retracted the plane would have sped up to a point where stall was no longer a factor, excluding some other problems.
You're correct that at the moment of flap configuration change the lift may slightly change, though this can be corrected very quickly by the change in moment from the flaps themselves, or from a slight change in the flight path. The worst case would likely be that the plane can no longer climb, but it would be able to fly level.
Not by any law of nature. The airplane systems or the pilot would perhaps try to pitch the nose up in order to generate more lift, but it's not certain that they would do that or that it would be successful. The pilot might be confused about what is happening not realising that the flaps has been retracted. The systems might be limiting the pitch in order to prevent a stall.
The flap moment could pitch the nose as I explained above, but let's say that the nose attitude is fixed. The plane would not have the lift to maintain 1g and would start to descend. This would create a vertical velocity component that would increase the AoA, increasing lift. As long as stall AoA was not hit, you could recover the lift lost. Loss of altitude would also mean more excess thrust as the engines wouldn't spend a tiny bit of their output fighting gravity. So the plane would accelerate and also increase lift.
Or if the airspeed is too slow so that the wing simply can't generate the amount of lift required.
This is really the same as hitting critical AoA though. It means that the lift that the wing provide at maximum AoA is less than the weight of the plane.
You're proposing that the retraction of the flaps caused the wings to be unable to produce enough lift to keep the plane in the air. I'd be surprised if that was the case if the plane was producing thrust because while the flaps retracted, it would accelerate, creating more and more of an AoA buffer.
To takeoff speed, yes. Designed to allow safe climb on one engine. Not designed to allow for premature retraction of the flaps.
It is actually, kind of. You use full power on takeoff to give yourself the maximum amount of energy to expend for an emergency situation. It's built in the procedures. As I'm not a pilot I'll defer to
@Keef and
@Dan_Tes on the piloting side of that and let them correct me if need be, but when the plane is designed you're not going to build it under the assumption that everything is going to be ideal. You have more thrust than you need for takeoff, you have more lift than you need for takeoff, and you have more structural integrity than you need for takeoff.
There's no reason to believe the AoA can't be exceeded at takeoff speed, or slightly above that.
The AoA limit can be exceeded at any point, even at maximum speed. It's not that exceeding the limit is impossible, it's exceedingly unlikely barring other problems.
Not in controlled flight, but only because the pilot aims to achieve a steady climb rate, compensating for the effect of the flaps. That does not mean that it's safe to retract the flaps immediately after takeoff. Don't confuse the goal of 1g with the effect of the flaps.
The pilot isn't compensating for the effect of the flaps, the pilot is
trimming the plane. The flaps are only one tiny part of that process. So in effect if they retracted, the change in flight dynamics should be handled more or less automatically. I'll grant you that an unexpected situation may involve a response time on the part of the pilots, so I can't rule anything out and echo that we must wait on the investigation. But from what information is available, thrust loss is a better root cause of what happened in my perspective.
Assuming that it already has sufficient speed to stay in the air without flaps. Otherwise it would have to accelerate to that speed.
I think that assumption is safe to make.
I do see your side of the argument, and lift would have been lost at some point*. From what I see the loss of lift would have come from the lack of engines though. I may be unaware of some details which could change the situation.
* I don't want to get into the weeds too much, but it is actually possible to fly under the stall speed - the envelope simply becomes sub 1 g, also with an AoA limiter, the plane would have been prevented from exceeding max AoA, making a true stall very unlikely. The plane would not be able to maintain level flight though.
Away from the technical side of things, because my knowledge of aircraft extends to "why is my Airbus barking at me", two bits of info over the weekend:
The plane required the entire length of the runway to take off. That's 3,505m/11,499ft, a third more than the figure I see listed - which strikes me as unusual, and suggests that whatever issues they were having did not begin only in the air. Could it have been overweight in addition to whatever specific flight control problems it experienced?
That could be due to weight or having the flaps set incorrectly the entire time instead of retracted early. I'd wonder how easy of a mistake that is to make, but it's more of a pilot question. Planes do sometimes have WOW (weight on wheels) sensors for functionality like preventing landing gear retraction accidentally on the ground, but I'm not aware of any that actually try to estimate the weight of the plane.
Secondly, a briefing reportedly given by "Indian aviation authorities" (don't know which; the various outlets I quickly notGoogled did not specifically name an authority) revealed the mayday call. I'm not sure if the ellipses indicate pauses or breaks in the transmission, but it has been quoted as: "Thrust not achieved... falling... Mayday! Mayday! Mayday!"
I don't know enough to make much sense out of that in collaboration with the other data.
One puzzle for me is the survivor. Flukes are flukes, but a lot of it isn't sitting right.
This guy's just climbed out of an emergency exit which popped open on a plane that belly-flopped onto this building and - heavy with aviation fuel - burst into a fireball that went higher than the plane ever did, sufficient enough to kill everyone else in front of his eyes (his words)?
View attachment 1458108
I hope it's true.
Yes, the survivor situation is hard to make sense of. Different parts of the plane are more of less safe in a crash. One of my former professors used class time to show some of the work he did with a controled plane crash to study survivability and results changed pretty drastically with location, but the rate of survivable mostly varied with length along the plane. You'd think people sitting near by would have survived too.
That said the crash test was a very hard landing, and not crashing into a building.
en.wikipedia.org
