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A340 Engine Angle During Take-off

Posted: Tue Feb 03, 2009 9:05 am
by varig767
Hello all,

Is it an optical illusion or is engine no.4 of this A340 pointing upwards???


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Photo © Konstantin von Wedelstaedt



Kind regards, Martijn

RE: A340 Engine Angle During Take-off

Posted: Tue Feb 03, 2009 10:37 am
by keta
Well, that's how it's supposed to be on takeoff - but don't worry, it's not thrust vectoring. When the plane rotates, the whole plane 'points' upwards.

I guess you're having an optical illusion making you see the outermost engine like rotated with respect to the wing. I don't see any inconsistence in the picture, the whole plane looks with a correct angle to me.

RE: A340 Engine Angle During Take-off

Posted: Tue Feb 03, 2009 11:06 am
by Starlionblue
Yes, you are correct. They do point upwards a bit.

This is a result of the engines pulling the plane and the plane's inertia resisting the movement. The pylon bends from the forces applied. The pylons are not rigid and this sort of movement is normal. During turbulence you can see the engines on 340s and 747s bobbing up and down quite dramatically.

Quoting Keta (Reply 1):

I guess you're having an optical illusion making you see the outermost engine like rotated with respect to the wing.

It's not an optical illusion. The engine really has rotated with respect to the wing.

RE: A340 Engine Angle During Take-off

Posted: Tue Feb 03, 2009 2:31 pm
by keta


Quoting Starlionblue (Reply 2):
It's not an optical illusion. The engine really has rotated with respect to the wing.

Indeed, the pylon moves and I agree that it can be noticeable. In this picture, though, I don't know to what extent it is rotated or is it an illusion. I for myself don't see it like the engine is that much rotated.

RE: A340 Engine Angle During Take-off

Posted: Tue Feb 03, 2009 5:36 pm
by vikkyvik


Quoting Starlionblue (Reply 2):
It's not an optical illusion. The engine really has rotated with respect to the wing.

That may be true, but I'd venture to say that in the photo, there's not nearly enough visual reference to say with any certainty that you're seeing the engine pointing more upwards than the No.3 engine, based on the angle from which the photo was taken, etc.

RE: A340 Engine Angle During Take-off

Posted: Tue Feb 03, 2009 7:34 pm
by speedracer1407


Quoting Starlionblue (Reply 2):
This is a result of the engines pulling the plane and the plane's inertia resisting the movement. The pylon bends from the forces applied. The pylons are not rigid and this sort of movement is normal. During turbulence you can see the engines on 340s and 747s bobbing up and down quite dramatically.

Seems to me like engines 2 and 3 are mounted at a different angle than the 1 and 4, and the angle seems consistent with the OP's photo.


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Photo © Rotate


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Photo © Helmut Bierbaum


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Photo © Klaus Ecker



I'd guess the outer engines are angled "up" compared to inner engines to align each pair with the local air flow.

RE: A340 Engine Angle During Take-off

Posted: Tue Feb 03, 2009 8:08 pm
by vikkyvik


Quoting Speedracer1407 (Reply 5):
Seems to me like engines 2 and 3 are mounted at a different angle than the 1 and 4, and the angle seems consistent with the OP's photo.

Engine intakes are generally mounted in order to be aligned with the local airflow.

You'll frequently notice that they appear to be canted slightly inwards toward the fuselage, and also may be pitched slightly.

I wouldn't doubt that the airflow closer to the fuselage has more of an upward component to it than the airflow farther out on the wing.

RE: A340 Engine Angle During Take-off

Posted: Tue Feb 10, 2009 5:04 pm
by ex52tech
Think about the stresses on that engine pylon, it can go from having an upward forward pulling load on it, and in a matter of seconds it can have the weight of the engine trying to pull it downward if the throttle were to be retarded to idle. Engine pylons are some very unique pieces of the aircraft structure. They can be a mix of exotic metals Titanium, inconel, hardened steel, magnesium, and aluminum all in one unit. The dissimilar metal corrosion problems abound, along with tortional load stresses, and heat stress.

RE: A340 Engine Angle During Take-off

Posted: Wed Feb 11, 2009 12:48 pm
by jetmech


Quoting Starlionblue (Reply 2):
During turbulence you can see the engines on 340s and 747s bobbing up and down quite dramatically.



Quoting Keta (Reply 3):
Indeed, the pylon moves and I agree that it can be noticeable. In this picture, though, I don't know to what extent it is rotated or is it an illusion.

The 747 outboard engine pylons are designed to flex, so that stresses upon the attachments to the wing are minimised during rapid upward and downward movement of the wing. This is done by using special spring beams in the strut. You can just see them in the following picture where they are labelled as "beam assembly".

Big version: Width: 566 Height: 800 File size: 43kb
747 Outboard and Inboard struts.


Regards, JetMech