Sponsor Message:
Aviation Technical / Operations Forum
My Starred Topics | Profile | New Topic | Forum Index | Help | Search 
Why Do Airbus Aircraft Seem To Be Kneeling?  
User currently offlineMortyman From Norway, joined Aug 2006, 4055 posts, RR: 1
Posted (2 years 5 months 6 days 22 hours ago) and read 9691 times:

Stupid question perhaps, but ...

Why do Airbus aircraft seem to kneel in front ?

Is it because of weight ?



33 replies: All unread, showing first 25:
 
User currently onlineTWA772LR From United States of America, joined Nov 2011, 2331 posts, RR: 1
Reply 1, posted (2 years 5 months 6 days 21 hours ago) and read 9600 times:

Optical illusion? Side-note, it also looks like that on the 764ER.


Go coogs! \n//
User currently offlineKermode From Canada, joined Jun 2012, 36 posts, RR: 0
Reply 2, posted (2 years 5 months 6 days 21 hours ago) and read 9604 times:

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.


User currently offlinempdpilot From United States of America, joined Jul 2006, 998 posts, RR: 0
Reply 3, posted (2 years 5 months 6 days 21 hours ago) and read 9543 times:

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.
User currently offlinecargolex From United States of America, joined Apr 2010, 1277 posts, RR: 8
Reply 4, posted (2 years 5 months 6 days 21 hours ago) and read 9483 times:

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).

User currently offline3DoorsDown From United States of America, joined Oct 2005, 376 posts, RR: 0
Reply 5, posted (2 years 5 months 6 days 21 hours ago) and read 9325 times:

Bowing to Boeing. What else could it be?  

User currently onlineTWA772LR From United States of America, joined Nov 2011, 2331 posts, RR: 1
Reply 6, posted (2 years 5 months 6 days 21 hours ago) and read 9325 times:

Quoting 3DoorsDown (Reply 5):

Best thing I've heard all day!    



Go coogs! \n//
User currently onlineViscount724 From Switzerland, joined Oct 2006, 25859 posts, RR: 22
Reply 7, posted (2 years 5 months 6 days 20 hours ago) and read 9099 times:

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.


User currently offlineSESGDL From United States of America, joined Jan 2001, 3489 posts, RR: 10
Reply 8, posted (2 years 5 months 6 days 20 hours ago) and read 9068 times:

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


User currently offlinegigneil From United States of America, joined Nov 2002, 16347 posts, RR: 85
Reply 9, posted (2 years 5 months 6 days 19 hours ago) and read 8815 times:

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


User currently offlineCZ346 From United States of America, joined Feb 2012, 95 posts, RR: 1
Reply 10, posted (2 years 5 months 6 days 18 hours ago) and read 8717 times:

Quoting TWA772LR (Reply 6):

I was going to say "It's because the suck" but bowing to Boeing is totally acceptable!


User currently offlineMir From United States of America, joined Jan 2004, 21798 posts, RR: 55
Reply 11, posted (2 years 5 months 6 days 18 hours ago) and read 8612 times:

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
User currently offlineMax Q From United States of America, joined May 2001, 4749 posts, RR: 18
Reply 12, posted (2 years 5 months 6 days 18 hours ago) and read 8600 times:

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.
User currently offlinespacecadet From United States of America, joined Sep 2001, 3649 posts, RR: 12
Reply 13, posted (2 years 5 months 6 days 17 hours ago) and read 8483 times:

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!
User currently offlinemaxpower1954 From United States of America, joined Sep 2008, 1142 posts, RR: 7
Reply 14, posted (2 years 5 months 6 days 15 hours ago) and read 7991 times:

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]

User currently offlinemasi1157 From Germany, joined Feb 2011, 124 posts, RR: 0
Reply 15, posted (2 years 5 months 6 days 14 hours ago) and read 7723 times:

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


User currently offlineLH422 From Germany, joined Sep 2010, 422 posts, RR: 0
Reply 16, posted (2 years 5 months 6 days 13 hours ago) and read 7492 times:

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 currently onlineStarlionblue From Greenland, joined Feb 2004, 17113 posts, RR: 66
Reply 17, posted (2 years 5 months 6 days 13 hours ago) and read 7263 times:

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 currently offlinefaro From Egypt, joined Aug 2007, 1584 posts, RR: 0
Reply 18, posted (2 years 5 months 6 days 12 hours ago) and read 7222 times:

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
User currently offlinetdscanuck From Canada, joined Jan 2006, 12709 posts, RR: 80
Reply 19, posted (2 years 5 months 6 days 11 hours ago) and read 7151 times:

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 currently offlineDarksnowynight From United States of America, joined Jan 2012, 1397 posts, RR: 3
Reply 20, posted (2 years 5 months 6 days 6 hours ago) and read 6950 times:

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?



Posting without Knowledge is simply Tolerated Vandalism... We are the Vandals.
User currently offlinetdscanuck From Canada, joined Jan 2006, 12709 posts, RR: 80
Reply 21, posted (2 years 5 months 6 days 5 hours ago) and read 6883 times:

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.


User currently offlineRoseflyer From United States of America, joined Feb 2004, 9697 posts, RR: 52
Reply 22, posted (2 years 5 months 6 days 4 hours ago) and read 6858 times:

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!
User currently offlinetimz From United States of America, joined Sep 1999, 6896 posts, RR: 7
Reply 23, posted (2 years 5 months 5 days 3 hours ago) and read 6438 times:

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?


User currently offlinetdscanuck From Canada, joined Jan 2006, 12709 posts, RR: 80
Reply 24, posted (2 years 5 months 5 days 2 hours ago) and read 6423 times:

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.


25 Viscount724 : 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
26 nomadd22 : 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 getti
27 my235 : Airbuses also seem to be trimmed back more (nose up pitch) when on short final.
28 okees : 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
29 Roseflyer : 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 pavem
30 bikerthai : 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 angl
31 Roseflyer : 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
32 amccann : 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 lan
33 Post contains links speedygonzales : 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/f
Top Of Page
Forum Index

Reply To This Topic Why Do Airbus Aircraft Seem To Be Kneeling?
Username:
No username? Sign up now!
Password: 


Forgot Password? Be reminded.
Remember me on this computer (uses cookies)
  • Tech/Ops related posts only!
  • Not Tech/Ops related? Use the other forums
  • No adverts of any kind. This includes web pages.
  • No hostile language or criticizing of others.
  • Do not post copyright protected material.
  • Use relevant and describing topics.
  • Check if your post already been discussed.
  • Check your spelling!
  • DETAILED RULES
Add Images Add SmiliesPosting Help

Please check your spelling (press "Check Spelling" above)


Similar topics:More similar topics...
Why Do Gate Agents Need To Assign Seats? posted Sun May 6 2012 15:49:40 by AlnessW
Why Are Window Shades Asked To Be Down? posted Sat Oct 29 2011 23:17:06 by wedgetail737
Why Do Airbus Test A380 Unpainted Before Delivery posted Thu Aug 4 2011 15:57:30 by 747400sp
Why Is The 747 Considered To Be "Inflexible"? posted Sun May 30 2010 20:03:00 by b6a322
Why Do Military Aircraft Use UHF And Not VHF? posted Fri Jun 6 2008 11:07:13 by N353SK
Why Do Airbus Tails Have A Bump On The Bottom? posted Sun Apr 29 2007 18:49:29 by Kaitak744
Why Is London ATC Said To Be "among The Best"? posted Wed Dec 17 2003 12:10:11 by Mozart
Why Are Airbus Aircraft Ugly At The Back?! posted Tue Aug 28 2001 14:25:14 by Singapore_Air
Why Do Airbus Elevators+Ailerons Droop Down? posted Sun Jan 7 2001 23:47:20 by Olympic A-340
Why Do Tugs Pull Aircraft To The Gate In The US? posted Fri Aug 19 2011 23:05:51 by Camohe

Sponsor Message:
Printer friendly format