lehpron
Posts: 6846
Joined: Tue Jul 10, 2001 3:42 am

A346: Engine Vertical Alignment?

Tue Sep 03, 2002 7:53 am

Look at this pix:

http://www.airliners.net/open.file/257294/M/

To me it looks as if 1) the fuselage is tipped forward, 2) the inboard engines are tipped downward and 3) the outboard engines are tipped upward. Is this right?

Even when the plane flies straight the engines are not thrusting straight. does the moment of all engines cancel-out or is there apparent wing twist-stress to deal with?
The meaning of life is curiosity; we were put on this planet to explore opportunities.
 
Guest

RE: A346: Engine Vertical Alignment?

Tue Sep 03, 2002 8:54 am

Its a forced perspective thing. If the picture were at a straigth angle things would look different, also using my vast knowledge (not) the wings looked tilted upwards, there by helping the illusion.
 
OPNLguy
Posts: 11191
Joined: Tue Jun 15, 1999 11:29 am

RE: A346: Engine Vertical Alignment?

Tue Sep 03, 2002 8:59 am

Looks to me like an optical illusion, caused by the sloping terrain in the foreground, and the top of the #2 engine cowl against the background of the deployed leading edge device.
ALL views, opinions expressed are mine ONLY and are NOT representative of those shared by Southwest Airlines Co.
 
lehpron
Posts: 6846
Joined: Tue Jul 10, 2001 3:42 am

RE: A346: Engine Vertical Alignment?

Tue Sep 03, 2002 9:38 am

I don't think the tilted wings upward would do anything, although it is a good point I did not take into consideration.

Optical illision, yes; and my butt. Slats or no-slats, the engines look off aligned; ( I am concentrating on a line from the center of intake to turbine cone) where the inboard engines appear to blow into the flaps and the outboard's blow into the ground.

Can someone find another pix of this exact plane in another view to help this guy?
The meaning of life is curiosity; we were put on this planet to explore opportunities.
 
AJ
Posts: 2295
Joined: Wed Nov 03, 1999 3:54 pm

RE: A346: Engine Vertical Alignment?

Tue Sep 03, 2002 9:47 am

They might well be rigged to reduce wing bending moment, allowing lighter materials to be used. By toeing the outboard engines down they will produce a downwards force on the wing, balancing the upwards lift bending moment. Most jets with wing mounted engines toe the engines in to reduce the outward pulling effect, so I can understand why they'd apply the same to the upward movement.
 
XFSUgimpLB41X
Posts: 3961
Joined: Fri Aug 25, 2000 1:18 am

RE: A346: Engine Vertical Alignment?

Tue Sep 03, 2002 2:42 pm

Also.. remember the airplane is sitting on the ground so all the load is off the wings.. so the wings arent flexed up like they would be in normal flight.
Chicks dig winglets.
 
AJ
Posts: 2295
Joined: Wed Nov 03, 1999 3:54 pm

RE: A346: Engine Vertical Alignment?

Tue Sep 03, 2002 4:53 pm

They look pretty even in this photo: http://www.airbus.com/multimediaelements/188.jpg
 
User avatar
PW100
Posts: 2748
Joined: Mon Jan 28, 2002 9:17 pm

RE: A346: Engine Vertical Alignment?

Wed Sep 04, 2002 3:14 am

Lehpron
To me it looks as if 1) the fuselage is tipped forward, 2) the inboard engines are tipped downward and 3) the outboard engines are tipped upward. Is this right?

Your observations look pretty correct to me.
Before going into detail, please be reminded that this is a [ultra] long range aircraft. Aircraft configuration is fully optimized for long range cruise flight.
Furthermore be reminded that "tipped forward", "tipped downward", "tipped upward" are all relative terms. When the aircraft is in cruise, most likely the fuselage will have a couple of degrees incidence [typically 2-5 for commercial airliners] where the fuselage will generate a small amount of lift as well.

Usually the landing gear of an aircraft will be set up in such a way to position the fuselage a little nose down when the aircraft is on the ground. This reduces the angle of attack of the wing during take-off roll, thus reducing drag as speed increases upto the point of rotation, thereby reducing the length of the take-off roll. Drag is a byproduct of lift. So during the take-off roll you really want to reduce lift and thus drag.

Generally the engine nacelles [at least the inlet portion of them] will be angled to allow the airflow to enter the inlet in a straight line along the axis of the fan, to optimize inlet airflow. Now it's important to bear in mind that the inboard section of the wing generates more lift than the outboard part of the wing. As a result of the generation of lift, the air approching the wing will experiance an up-wash. That upwash is greater at the inner engine pair than at the outer engine pair. To cope with this upwash [in cruise flight] and have the air enter the inlet in a nice straight and level manner, the inner engine pair is "tilted downward". The upwash in front of the outer engine pair is much smaller, therefore they are angled differently in relation to the inner pair ["tipped upward"].
This also applies to lateral offset of the inner engines. If you would look at a top view, you'll notice that engines [especially those close to the fuselage, like 767/777] are a little towed in, to cope with the air that is beign forced sideways outboard by the fuselage. On rear fuselage engines you'll see that the engines ar towed out, since the fuselage shape curves the airstream back to the fuselage centreline due to the narrowing of the fuselage at the rear of the aircraft.

This "tipping" has nothing to do with wing bending moment. Only the weight of the engine [and fuel load off course among others] will significantly affect wing bending moment. Imagine that you tilt the engine downward in order to reduce wing bending moment. Now when the engine is thrusting downward, it will eat up part of the lift that is being generated by the wing. Therefore the wing now needs to generate even more lift to balance out the 'negative lift' being produced by the downward thrusting engines!! This doesn't make sense at all in terms off alleviating wing bending moment.

Wing tilting when loaded is an interesting concept. Although I doubt that a wing will tilt sufficiently to align the inner and outer engine pair.

PW100
Immigration officer: "What's the purpose of your visit to the USA?" Spotter: "Shooting airliners with my Canon!"

Who is online

Users browsing this forum: Eyad89, SCAT15F and 13 guests