User avatar
Mortyman
Topic Author
Posts: 4078
Joined: Sat Aug 12, 2006 8:26 pm

Why Do Airbus Aircraft Seem To Be Kneeling?

Fri Jun 22, 2012 1:21 am

Stupid question perhaps, but ...

Why do Airbus aircraft seem to kneel in front ?

Is it because of weight ?

 
User avatar
TWA772LR
Posts: 3601
Joined: Thu Nov 17, 2011 6:12 am

RE: Why Do Airbus Aircraft Seem To Be Kneeling?

Fri Jun 22, 2012 1:40 am

Optical illusion? Side-note, it also looks like that on the 764ER.
Not every day we find light winds. What do we do in these situations? Fly.
 
Kermode
Posts: 36
Joined: Wed Jun 20, 2012 8:43 pm

RE: Why Do Airbus Aircraft Seem To Be Kneeling?

Fri Jun 22, 2012 1:42 am

It's funny you should say that. I always see 737's as "kneeling" so to speak.


View Large View Medium
Click here for bigger photo!

Photo © Dejan Milinkovic - Pixstel Photography
View Large View Medium
Click here for bigger photo!

Photo © Mats Salder



Having said that, I would agree with you on A330's, i always saw that about them. Hopefully someone know's more than we do.
 
mpdpilot
Posts: 688
Joined: Fri Jul 28, 2006 6:44 am

RE: Why Do Airbus Aircraft Seem To Be Kneeling?

Fri Jun 22, 2012 1:47 am

i can't speak for the A380 pictured but the A330 does actually lean forward on the ground, it is because of this that with the A330F they had to lengthen the nose gear to level it out for freight pallets, hence the bubble under the nose to accomodate the larger landing gear.

It isn't that un common for aircraft on the ground to kneel as you say. Look at the CRJ700 and CRJ900 they kneel by almost a full 5 degrees.
One mile of highway gets you one mile, one mile of runway gets you anywhere.
 
cargolex
Posts: 1201
Joined: Fri Apr 23, 2010 5:20 pm

RE: Why Do Airbus Aircraft Seem To Be Kneeling?

Fri Jun 22, 2012 1:52 am

I don't know the reason for the A330/A340's nose-down stance, but it is significantly more pronounced than that of the 737, and represents a MAJOR challenge for the A330 freighter conversion program, and is why the production A330-200 freighter has the modified nose (to provide a level main deck).
 
3DoorsDown
Posts: 347
Joined: Tue Oct 18, 2005 3:55 pm

RE: Why Do Airbus Aircraft Seem To Be Kneeling?

Fri Jun 22, 2012 2:16 am

Bowing to Boeing. What else could it be?  
 
User avatar
TWA772LR
Posts: 3601
Joined: Thu Nov 17, 2011 6:12 am

RE: Why Do Airbus Aircraft Seem To Be Kneeling?

Fri Jun 22, 2012 2:17 am

Quoting 3DoorsDown (Reply 5):

Best thing I've heard all day!    
Not every day we find light winds. What do we do in these situations? Fly.
 
Viscount724
Posts: 18822
Joined: Thu Oct 12, 2006 7:32 pm

RE: Why Do Airbus Aircraft Seem To Be Kneeling?

Fri Jun 22, 2012 2:58 am

Quoting Kermode (Reply 2):
It's funny you should say that. I always see 737's as "kneeling" so to speak.

That's only noticeable on the 737NG which, if memory correct, has slightly taller main landing gear struts than earlier 737 models.
 
SESGDL
Posts: 2610
Joined: Sat Jan 13, 2001 6:25 am

RE: Why Do Airbus Aircraft Seem To Be Kneeling?

Fri Jun 22, 2012 3:04 am

Quoting Viscount724 (Reply 7):

That's only noticeable on the 737NG which, if memory correct, has slightly taller main landing gear struts than earlier 737 models.

The 737-200 leans forward as well, as do many other airplane types, such as the MD-80/90.

Jeremy
 
gigneil
Posts: 14133
Joined: Fri Nov 08, 2002 10:25 am

RE: Why Do Airbus Aircraft Seem To Be Kneeling?

Fri Jun 22, 2012 4:16 am

The definitive nose-down aoa does in fact help the aircraft get off the ground at a lower speed, from what i've been told.

NS
 
CZ346
Posts: 95
Joined: Wed Feb 01, 2012 2:57 pm

RE: Why Do Airbus Aircraft Seem To Be Kneeling?

Fri Jun 22, 2012 4:46 am

Quoting TWA772LR (Reply 6):

I was going to say "It's because the suck" but bowing to Boeing is totally acceptable!
 
Mir
Posts: 19092
Joined: Mon Jan 05, 2004 3:55 am

RE: Why Do Airbus Aircraft Seem To Be Kneeling?

Fri Jun 22, 2012 5:06 am

Quoting cargolex (Reply 4):
I don't know the reason for the A330/A340's nose-down stance,

IIRC, it's because they used the same (shorter) nose gear from the A300 but different (higher) main gear, presumably to compensate for larger engines on the 330. Thus, the slightly nose-down pitch on the ground.

It makes sense from an engineering perspective - why would you bother with a longer nose gear (more weight, takes up more space) just to have the cabin perfectly flat?

-Mir
7 billion, one nation, imagination...it's a beautiful day
 
Max Q
Posts: 5628
Joined: Wed May 09, 2001 12:40 pm

RE: Why Do Airbus Aircraft Seem To Be Kneeling?

Fri Jun 22, 2012 5:09 am

Quoting gigneil (Reply 9):


The definitive nose-down aoa does in fact help the aircraft get off the ground at a lower speed, from what i've been tol

Wadrs that does not make any sense.
The best contribution to safety is a competent Pilot.
 
spacecadet
Posts: 2788
Joined: Thu Sep 20, 2001 3:36 am

RE: Why Do Airbus Aircraft Seem To Be Kneeling?

Fri Jun 22, 2012 5:40 am

Gotta have something to do with the relationship between cruise attitude and ground/takeoff/landing attitude. The wing cord is fixed - wings don't move in flight, so the only way to adjust their position into the wind while on the ground is through overall attitude.

Most airplanes are designed to cruise at a 2-3 degree nose-up attitude. My guess is that to design a wing for best efficiency at cruise just required a slight nose-down attitude on the ground.

Would love to hear someone with more technical knowledge than I have, but that'd be my guess.
I'm tired of being a wanna-be league bowler. I wanna be a league bowler!
 
maxpower1954
Posts: 1040
Joined: Thu Sep 25, 2008 1:14 am

RE: Why Do Airbus Aircraft Seem To Be Kneeling?

Fri Jun 22, 2012 7:48 am

You guys - any jet transport from the 707/DC-8 on up has a slight negative attitude on the the ground to improve braking and nose wheel steering action on landing and during a rejected take-off.

[Edited 2012-06-22 00:54:14]
 
masi1157
Posts: 139
Joined: Sun Feb 06, 2011 11:56 am

RE: Why Do Airbus Aircraft Seem To Be Kneeling?

Fri Jun 22, 2012 8:35 am

Quoting Mir (Reply 11):
IIRC, it's because they used the same (shorter) nose gear from the A300 but different (higher) main gear, presumably to compensate for larger engines on the 330. Thus, the slightly nose-down pitch on the ground.

The nose landing gears are definitely not the same. Compare these photos:

A330:

View Large View Medium
Click here for bigger photo!

Photo © Didier JH Goursolas


A300:

View Large View Medium
Click here for bigger photo!

Photo © Jin Kim



I also seem to remember that Airbus did not anticipate this nose down attitude (so it was a kind of design mistake) and that they had a lot of problems with e.g. the water/waste system.


Regards, masi1157
 
LH422
Posts: 384
Joined: Thu Sep 16, 2010 9:21 pm

RE: Why Do Airbus Aircraft Seem To Be Kneeling?

Fri Jun 22, 2012 9:27 am

Quoting mpdpilot (Reply 3):
i can't speak for the A380 pictured but the A330 does actually lean forward on the ground, it is because of this that with the A330F they had to lengthen the nose gear to level it out for freight pallets, hence the bubble under the nose to accomodate the larger landing gear.

Here's a picture of that:


View Large View Medium
Click here for bigger photo!

Photo © Stephan Kruse

 
User avatar
Starlionblue
Posts: 17049
Joined: Fri Feb 27, 2004 9:54 pm

RE: Why Do Airbus Aircraft Seem To Be Kneeling?

Fri Jun 22, 2012 9:56 am

Quoting Mir (Reply 11):


It makes sense from an engineering perspective - why would you bother with a longer nose gear (more weight, takes up more space) just to have the cabin perfectly flat?

IIRC this is correct.

Quoting spacecadet (Reply 13):

Gotta have something to do with the relationship between cruise attitude and ground/takeoff/landing attitude. The wing cord is fixed - wings don't move in flight, so the only way to adjust their position into the wind while on the ground is through overall attitude.

I don't think that's it.
"There are no stupid questions, but there are a lot of inquisitive idiots."
 
User avatar
Faro
Posts: 1491
Joined: Sun Aug 12, 2007 1:08 am

RE: Why Do Airbus Aircraft Seem To Be Kneeling?

Fri Jun 22, 2012 10:49 am

Quoting gigneil (Reply 9):
The definitive nose-down aoa does in fact help the aircraft get off the ground at a lower speed, from what i've been told.


Lower airspeed or shorter takeoff run? I'd like to have that one explained...negative AoA = less (wing and/or fuselage?) drag on acceleration to Vr?...Seems counter-intuitive...


Faro
The chalice not my son
 
tdscanuck
Posts: 8572
Joined: Wed Jan 11, 2006 7:25 am

RE: Why Do Airbus Aircraft Seem To Be Kneeling?

Fri Jun 22, 2012 12:08 pm

Quoting Max Q (Reply 12):
Quoting gigneil (Reply 9):

The definitive nose-down aoa does in fact help the aircraft get off the ground at a lower speed, from what i've been tol

Wadrs that does not make any sense.

Wing incidence angle is fixed by cruise configuration. If you raise the nose in ground attitude you increase the wing AoA during the takeoff roll, which leads to more induced drag. You want minimum drag during the roll so you can get up to speed in the shortest distance, then rotate to start generating lift.

It's not so much about having a negative AoA (that would actually push the airplane down into the ground, which is also bad), it's about reducing the positive AoA during the takeoff roll.

Tim.
 
User avatar
DarkSnowyNight
Posts: 1786
Joined: Sun Jan 01, 2012 7:59 pm

RE: Why Do Airbus Aircraft Seem To Be Kneeling?

Fri Jun 22, 2012 5:02 pm

Quoting maxpower1954 (Reply 14):


You guys - any jet transport from the 707/DC-8 on up has a slight negative attitude on the the ground to improve braking and nose wheel steering action on landing and during a rejected take-off

Not true. The E170 has a very pronounced nose up stance. Less noticeable but still there just the same are the 757, 767-300, Dash 8 100 - 300, & CRJ-200 families. As well, many aircraft in the Tupolev and Illyusion families are oriented this way.

As well, any airbus narrowbody, but especially the 321, can actually go from one to the other depending on loading. It is a matter of routine to observe the NLG struts extend a good six - ten inches as the aircraft is de-barked and unloaded.

Quoting tdscanuck (Reply 19):

Wing incidence angle is fixed by cruise configuration. If you raise the nose in ground attitude you increase the wing AoA during the takeoff roll, which leads to more induced drag. You want minimum drag during the roll so you can get up to speed in the shortest distance, then rotate to start generating lift

That certainly makes sense, but what are the design advantages that support the opposite tendencies in some of the aircraft I've mentioned above? While I can't guess there would be much there aerodynamically speaking, perhaps is it a manufacturing or weight benefit to build them that way at times?
You Sir, are a very funny lady.
 
tdscanuck
Posts: 8572
Joined: Wed Jan 11, 2006 7:25 am

RE: Why Do Airbus Aircraft Seem To Be Kneeling?

Fri Jun 22, 2012 6:22 pm

Quoting Darksnowynight (Reply 20):
That certainly makes sense, but what are the design advantages that support the opposite tendencies in some of the aircraft I've mentioned above?

It all depends on how the wing incidence angle plays out on the ground. If an airplane has a more nose-up design cruise attitude that would drive into a more nose-up ground attitude (for equal takeoff drag). There's also a trade between nose gear size/weight and wing drag that probably changes depending on the intended takeoff performance.

Tom.
 
roseflyer
Posts: 9606
Joined: Fri Feb 13, 2004 9:34 am

RE: Why Do Airbus Aircraft Seem To Be Kneeling?

Fri Jun 22, 2012 7:02 pm

Quoting maxpower1954 (Reply 14):
You guys - any jet transport from the 707/DC-8 on up has a slight negative attitude on the the ground to improve braking and nose wheel steering action on landing and during a rejected take-off.

When loaded, the DC10 had a nose up attitude on the ground. The DC10 also has the nose gear mounted further aft than most airplanes.

Quoting tdscanuck (Reply 19):

Wing incidence angle is fixed by cruise configuration. If you raise the nose in ground attitude you increase the wing AoA during the takeoff roll, which leads to more induced drag. You want minimum drag during the roll so you can get up to speed in the shortest distance, then rotate to start generating lift.

It's not so much about having a negative AoA (that would actually push the airplane down into the ground, which is also bad), it's about reducing the positive AoA during the takeoff roll.

While that is true, I believe the nose down attitude is moreso important for braking distance. Less lift means more weight on wheels, which shortens RTO and brake distances. It presents a problem for the MAX.
If you have never designed an airplane part before, let the real designers do the work!
 
timz
Posts: 6081
Joined: Fri Sep 17, 1999 7:43 am

RE: Why Do Airbus Aircraft Seem To Be Kneeling?

Sat Jun 23, 2012 8:20 pm

It hasn't been settled whether Boeing fuselages are pointed downward on the runway. Can we assume the cabin floor is parallel to the centerline of the fuselage? Can we assume the door sill is level with the floor? Can we assume Boeing floors don't curve upward toward the rear of the aircraft?

If so, then the 767-400 nose is a bit lower than the tail, but the 767-300 nose isn't. So maybe the -400 floor does curve?
 
tdscanuck
Posts: 8572
Joined: Wed Jan 11, 2006 7:25 am

RE: Why Do Airbus Aircraft Seem To Be Kneeling?

Sat Jun 23, 2012 8:36 pm

Quoting timz (Reply 23):
It hasn't been settled whether Boeing fuselages are pointed downward on the runway.

The standard ground attitude is listed in the maintenance manuals for every aircraft. I haven't looked up the widebodies but the 737NG is about 1.5 degrees nose-down if the gear is properly serviced and everything is normal. Exact attitude will vary with weight, CG, strut pressure, and tire pressure.

Quoting timz (Reply 23):
Can we assume the cabin floor is parallel to the centerline of the fuselage?

Yes, it is.

Quoting timz (Reply 23):
Can we assume the door sill is level with the floor?

Yes, it is.

Quoting timz (Reply 23):
Can we assume Boeing floors don't curve upward toward the rear of the aircraft?

Correct, they're flat all the way back.

Tom.
 
Viscount724
Posts: 18822
Joined: Thu Oct 12, 2006 7:32 pm

RE: Why Do Airbus Aircraft Seem To Be Kneeling?

Sat Jun 23, 2012 9:48 pm

Quoting timz (Reply 23):
If so, then the 767-400 nose is a bit lower than the tail, but the 767-300 nose isn't. So maybe the -400 floor does curve?

764 has a completely new main landing gear 18 inches taller than the 763, while the nose gear is basically the same. That's why the 764 sits slightly nose-down. Following excerpt from a document on the Boeing website describing the 764.

The stretched fuselage significantly reduced the rotation attitude of the airplane during takeoff and landing. The reduced body angles resulted in undesirable effects on takeoff field length and approach speeds.

Boeing resolved this situation by incorporating an all-new landing gear that is 18 in (46 cm) taller than the existing gear. The wheels, tires, and brakes are identical to those on the 777. The new gear features 50-in (127-cm) radial tires, compared to 46-in (117-cm) diameter bias ply tires on the 767-300ER. Fitting this larger rolling stock into the existing wheel well caused relocation of most of the hydraulic lines and a shift in the wing-mounted trunnion of 10 in (25 cm) outboard and 4 in (10 cm) downward. The nose landing gear is basically unchanged except for strengthening to accommodate the increased gross weight of the 767-400ER.
 
nomadd22
Posts: 1566
Joined: Fri Feb 22, 2008 7:42 pm

RE: Why Do Airbus Aircraft Seem To Be Kneeling?

Sun Jun 24, 2012 12:26 am

Quoting tdscanuck (Reply 24):

The standard ground attitude is listed in the maintenance manuals for every aircraft. I haven't looked up the widebodies but the 737NG is about 1.5 degrees nose-down if the gear is properly serviced and everything is normal. Exact attitude will vary with weight, CG, strut pressure, and tire pressure.

After about 30 seconds of highly questionable math done in my head after looking at a photo of a 738 and guessing at the distance involved, I'm getting about half that 1.5 degrees disappearing because of the longer nose gear on the Max.
Anon
 
my235
Posts: 94
Joined: Mon Mar 23, 2009 10:21 pm

RE: Why Do Airbus Aircraft Seem To Be Kneeling?

Mon Jun 25, 2012 3:21 pm

Airbuses also seem to be trimmed back more (nose up pitch) when on short final.
 
okees
Posts: 365
Joined: Tue Sep 20, 2005 2:41 pm

RE: Why Do Airbus Aircraft Seem To Be Kneeling?

Tue Jun 26, 2012 1:29 pm

I seem to remember a discussion similar to this on here a few years ago, and someone said it had to do with landing, apparently the slight slant helps "plant" the aircraft firmly on the ground when it lands, something to do with the angle providing sufficient air pressure on top of the wings to push the air frame downwards a bit. I could be way off, but this is what I remember.
mobs jakis
 
roseflyer
Posts: 9606
Joined: Fri Feb 13, 2004 9:34 am

RE: Why Do Airbus Aircraft Seem To Be Kneeling?

Tue Jun 26, 2012 6:52 pm

Quoting okees (Reply 28):
I seem to remember a discussion similar to this on here a few years ago, and someone said it had to do with landing, apparently the slight slant helps "plant" the aircraft firmly on the ground when it lands, something to do with the angle providing sufficient air pressure on top of the wings to push the air frame downwards a bit. I could be way off, but this is what I remember.

That is correct. When all wheels are on the ground a nose down attitude decreases lift from the wing, which increases force of the tires on the pavement and improves braking. Ground spoilers significantly reduce lift, but any addition lift removed from the wing will shorten the braking distance.
If you have never designed an airplane part before, let the real designers do the work!
 
User avatar
bikerthai
Posts: 2152
Joined: Wed Apr 28, 2010 1:45 pm

RE: Why Do Airbus Aircraft Seem To Be Kneeling?

Tue Jun 26, 2012 7:11 pm

Quoting timz (Reply 23):
It hasn't been settled whether Boeing fuselages are pointed downward on the runway.

As Tom pointed out, the 737 NG is nose down. The angle of incident depends on the length of the aircraft. The -500 would have the most nose down angle.

Quoting timz (Reply 23):
Can we assume the cabin floor is parallel to the centerline of the fuselage?

Yes, but I think you really meant fuselage water line.

Quoting okees (Reply 28):
something to do with the angle providing sufficient air pressure on top of the wings to push the air frame downwards a bit.


At the small negative angle involved, the wing still provides lift. Specially if you deploy the flaps at takeoff and landing. You don't really pushes the air downward, rather you remove lift from the wing . . . which is the purpose of the spoilers.

Of all the reason noted above, I see weight is the only logical reason for the length of the nose gear, and cruise efficiency determines the fuselage to wing angle. And the two don't necessary coincide. That is why some plane may nose down on the ground an nose up at cruise.


bt
Intelligent seeks knowledge. Enlightened seeks wisdom.
 
roseflyer
Posts: 9606
Joined: Fri Feb 13, 2004 9:34 am

RE: Why Do Airbus Aircraft Seem To Be Kneeling?

Tue Jun 26, 2012 9:56 pm

Quoting bikerthai (Reply 30):
Of all the reason noted above, I see weight is the only logical reason for the length of the nose gear,

There are more reasons that determine nose and main gear length. Engine clearance height and cargo door loading height are important. One look at the 777-300ER versus 777-300 nose landing gear will show how different the height and design can be based on takeoff weight. Under low loading conditions, the 777-300ER nose gear extends 10 inches, to maintain rear cargo bin height and a level floor.
If you have never designed an airplane part before, let the real designers do the work!
 
amccann
Posts: 121
Joined: Sat Mar 08, 2008 9:14 pm

RE: Why Do Airbus Aircraft Seem To Be Kneeling?

Wed Jun 27, 2012 4:18 am

I'd imagine it is safe to say that Airbus did not change the wing incidence angle for the A330F but did however change the positioning of the nose landing gear. This new nose landing gear position drives the takeoff roll AOA and landing rollout AOA of the A330F (freighter) to values higher than that of the A330 (passenger). I'd love to know how this has effected takeoff and landing distances of the freighter. Of course to answer the question we would have to have some sort of controlled environment including similarly loaded airplanes (weight and cg) and similar operating environments.
What one person receives without working for, another person must work for without receiving. - Ronald Reagan
 
speedygonzales
Posts: 518
Joined: Thu Sep 13, 2007 5:01 pm

RE: Why Do Airbus Aircraft Seem To Be Kneeling?

Wed Jun 27, 2012 8:45 am

Quoting amccann (Reply 32):
This new nose landing gear position drives the takeoff roll AOA and landing rollout AOA of the A330F (freighter) to values higher than that of the A330 (passenger). I'd love to know how this has effected takeoff and landing distances of the freighter.

Airbus shows the same take-off and landing performance for all three A330 variants, so the differences should be quite small.
http://www.airbus.com/fileadmin/medi...h_data/AC/Airbus-AC_A330_Dec11.pdf
Las Malvinas son Argentinas

Who is online

Users browsing this forum: No registered users and 36 guests