Stalling a 747

[ZKTOM]

Can you recover from a vertical stall in a 747. Is this possible?

[benwynn]

Yes, You can- But there are many problems- You must be at a very high altitude- Atleast 10000 feet Id think or your screwed because- The engines in a 747 take a long time to spool up to max thrust, so Its different to the average C152

[Kelburn]

I'd say you can but depending on whats happening to the aircraft at the time.
E.g. If you have the autopilot on:
As the speed decreases the autopilot increases the pitch of the nose to try and maintain the set climb rate. Once the 747 gets to 0 KIAS, if the autopilot isn't off your screwed if it is its still almost impossible because the elevator has no control due to the fact that there is no air going over it (this is all at 0 KIAS) also you'd be falling very fast making it incredibly hard to recover.
E.g. your plane would be at an angle of 75 or so degrees. Think about it. Your plane will fall like a pin and there's almost nothing you can do about it. Also like benwynn said, a 747's engines take along time to spool up. Again cause you're pointing up, the engines are gonna do nothing.

[ZK-Brock]

Read this thread from pprune.

[G-HEVN]

You also need to make sure you're nowhere near coffin corner (where stall speed and Vne or Mmo are within a few knots of each other).

[Jimmy]

  You also need to make sure you're nowhere near coffin corner (where stall speed and Vne or Mmo are within a few knots of each other).

Thats usualy up near the ceiling isn't it? Thats where major turbulance can cause serios concern ae?

and Tom, just why do we wan't to know if you can recouver from a 74 stalling?

James

[towerguy]

I should imagine that a B744 would act just like any other aircraft. After it stalls it will drop and it will depend on the configuration and control surface deflections and any atmospheric variables ie turbulence etc as to how it will fall. Due to its inherent form being similar in shape to other aircraft I would expect it to eventually go nose down. From this point on it is standard recovery. The aircraft can be recovered to an attitude at which it is flyable while any engine power considerations are dealt with.

The major factor would be how high you were when you started the manoeuvre and how far the aircraft fell before the recovery was able to be initiated. As long as you had enough height the spool up factor/relight isn't a factor. see the incidents with the B767 at Gimli and the B744 over Indonesia that lost all 4 engines due volcanic ash ingestion, also the B744 that lost nearly all engine power due bird ingestion at NZAA. For the ultimate in recovery without power just wait and watch the next shuttle re-entry. It starts in the ultimate stall - NO airflow over the wings at all!

[A185F]

Of course you can stall/recover a 747. All pilots have to know what the aircraft they fly are like in the stall situation including 747 so they go through them over and over in the sim. same recpvery for all aircraft, reduce angle of attack. Of course though there are systems in place to help prevent it happening in the first place.

As the speed decreases the autopilot increases the pitch of the nose to try and maintain the set climb rate. Once the 747 gets to 0 KIAS, if the autopilot isn't off your screwed if it is its still almost impossible because the elevator has no control due to the fact that there is no air going over it (this is all at 0 KIAS) also you'd be falling very fast making it incredibly hard to recover.

dunno about that, I dont think you would see a 747 get to 0kts, problems happen alot before then unless there are like 400 people stacked in the back then it might not be your day

your plane would be at an angle of 75 or so degrees

Really ??????

[Kelburn]

thats what the default FS autopilot does. Climb at 2500fpm and reduce the speed, and when the aircraft gets to 0KIAS it will be pointing high.

[towerguy]

the stall occurs when the angle of attack exceeds the critical angle and the airflow over the wing breaks down to the extent that insufficient lift is generated to support the aircraft. This is entirely independant of whether the aircraft is upside down, right side up or even snatched back hard to shock stall it. It still stalls after the critical angle is exceeded. the momentum of the aircraft in pitch may keep the nose climbing momentarily but it will still stall at the critical angle. From memory, in all the PofF lessons I did , the critical angle is ( for the majority ) about 16 degrees. So I don't see a B744 going 75 degrees nose up unless entering from some sort of vertically induced manoeuvre ie pulling too hard into the vertical at the starty of a loop, and if you are trying that in a B744 then you get what you deserve. I don't think that the position of the trim will have any effect on the angle apart from how hard or easy it is to get it there ie a heavy push or pull force.

just my 2C worth and always happy to be corrected if my memory has got rusty.
cheers



edit - 16 not 36 degrees

[scon]

B744 over Indonesia that lost all 4 engines due volcanic ash ingestion,

Wasn't that a BA 742

[ZK-KAG]

thats what the default FS autopilot does. Climb at 2500fpm and reduce the speed, and when the aircraft gets to 0KIAS it will be pointing high.

FS doesn't show the true flight dynamics of the 747 as I highly doubt you can get a 747 to 0KIAS...it would fall out of the sky quite literally and I wouldnt imagine it would be recoverable...

[scon]

yea


remember the stall speed of ANY aircraft is not 0kts the jumbo would be something like 145kts (lower with flap)

[ZKTOM]

and Tom, just why do we wan't to know if you can recouver from a 74 stalling?

I was having and argument with a friend at school who said it was impossible.

[G-HEVN]

To get it vertical, you'd have to be doing aerobatics, as in stall turns, hammerheads, cubans etc. I don't imagine the 747 is certified for that! (which is not to say it couldn't do it). Now, it's known that stalls can become unrecoverable in T-tail aircraft (BAe146, MD80 etc) because the position of the tail plane means there's insufficient elevator authority in the stalled configuration. Maybe there's a similar configuration for the 747 in extremis (although not in regular stalls)...

[A185F]

At the end of the day its very possible and is practiced nearly every day in all aircraft, including 747s. All fixed wing aircraft stall at some point or another.

thats what the default FS autopilot does. Climb at 2500fpm and reduce the speed, and when the aircraft gets to 0KIAS it will be pointing high.

hmm yea well unfortunatly flight sim is a computer game and a boeing 747 is a boeing 747, there is a bit of a difference. Although fs is becoming more and more realistic by the edition, its still just a computer game, otherwise they would train pilots how to fly using fs it would be a bit cheaper

remember the stall speed of ANY aircraft is not 0kts the jumbo would be something like 145kts (lower with flap)

sorta. There is actully no such thing a "stall speed" as such. An aircraft will stall when the angle between the chordline and the ralitive airflow (angle of attack)exceeds a "crititical angle" which is different for different configerations (flaps, slats, power etc) and weights. It is usually on average arround 16 degrees AoA. A "stall speed" is just something people are taught to keep away from (and rightly so) and in most light aircraft is the average speed at the stall in average circumstances. As an example or 2, my little cessna 185 with no one on board (except mwa) will almost hang off the prop with no airspeed indicated but is still flying and not stalled however put 6 people and all their baggage and full gas etc on board then arround 45 odd kts in a normal situation the plane will stall.

Another example would be performing a loop in a basic aerobatic aricraft (like a c152 or something similar), when you get yr speed you pull up gentally (or as appropriate) you basiclly fly up into the loop, and you got through all sorts of angles even 90 (but to the horizon not the relitive air flow) and you are still flying (not stalled) because the relitive airflow basicly "catches up" or stays relitive to the wings. HOWEVER if you get yr speed (say 120kts for e.g) and then pull too hard and fast the relitive air flow won't have time to "catch up" or stay relitive to the wings and you will stall although you are going 120kts !!

Cricky been a while since Ive cranked out the old c-cat stuff, now I remember why I gave it up in the first place

Oh and please excuse the poor spelling, I was away the day they did spelling in school

[ZK-Brock]

One thing that helped me immensely in understanding the stall is the rough definition of the Angle of attack that defines it as "the angle between where you're going and where you're pointed", which I got from the book Stick and Rudder by Wolfgang Langwiezhe . Before this I always thought of the airflow as being horizontal, meaning that bringing the nose 16* above the horizon would stall the aeroplane (even though I'd been told that there's a difference between A of A and attitude), so I didn't understand loops properly either.

The airflow is simply the "relative wind" that the aircraft feels - when you run you feel this "relative wind" rushing past you. Wherever you are going, it feels relative wind opposite to that direction.

The way stalls are taught in lessons confused me further - because we were maintaining height, our relative airflow was horizontal, so out nose would be approx 16* above the horizon at the stall, making it seem like an attitude thing, even though the A of A was brought past the critical angle.

I hope this is all correct because I understand it to be (though I'll probably edit the post if I'm wrong) - but this should shed some light on the stall to add to Ben's post.

'nuff of the nerd stuff, I'm off to bed

[ZKTOM]

I saw somewhere that a stall is when the drag and weight overtake the amount of thrust and lift. Caused by a high AOA. Is this true?

[towerguy]

what is the stall? see my post above.

[FlyingKiwi]

I should imagine that a B744 would act just like any other aircraft. After it stalls it will drop and it will depend on the configuration and control surface deflections and any atmospheric variables ie turbulence etc as to how it will fall. Due to its inherent form being similar in shape to other aircraft I would expect it to eventually go nose down. From this point on it is standard recovery. The aircraft can be recovered to an attitude at which it is flyable while any engine power considerations are dealt with.

I was thinking about this; given that the Boeing 747 has relatively sharply sweptback wings, I actually suspect it may well have a pitch-up tendency at the stall. Any opinions?