mpdpilot From United States of America, joined Jul 2006, 935 posts, RR: 0 Reply 3, posted (11 months 1 week 5 hours ago) and read 6875 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.
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cargolex From United States of America, joined Apr 2010, 1169 posts, RR: 9 Reply 4, posted (11 months 1 week 5 hours ago) and read 6816 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).
SESGDL From United States of America, joined Jan 2001, 3385 posts, RR: 11 Reply 8, posted (11 months 1 week 4 hours ago) and read 6400 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.
Mir From United States of America, joined Jan 2004, 19719 posts, RR: 56 Reply 11, posted (11 months 1 week 2 hours ago) and read 5945 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
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spacecadet From United States of America, joined Sep 2001, 3255 posts, RR: 14 Reply 13, posted (11 months 1 week 1 hour ago) and read 5816 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.
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maxpower1954 From United States of America, joined Sep 2008, 854 posts, RR: 5 Reply 14, posted (11 months 6 days 23 hours ago) and read 5324 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.
masi1157 From Germany, joined Feb 2011, 73 posts, RR: 0 Reply 15, posted (11 months 6 days 23 hours ago) and read 5056 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:
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.
LH422 From Germany, joined Sep 2010, 278 posts, RR: 0 Reply 16, posted (11 months 6 days 22 hours ago) and read 4825 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.
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.
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faro From Egypt, joined Aug 2007, 1445 posts, RR: 0 Reply 18, posted (11 months 6 days 20 hours ago) and read 4555 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...
tdscanuck From Canada, joined Jan 2006, 12709 posts, RR: 80 Reply 19, posted (11 months 6 days 19 hours ago) and read 4484 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.
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?
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tdscanuck From Canada, joined Jan 2006, 12709 posts, RR: 80 Reply 21, posted (11 months 6 days 13 hours ago) and read 4216 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.
Roseflyer From United States of America, joined Feb 2004, 8754 posts, RR: 52 Reply 22, posted (11 months 6 days 12 hours ago) and read 4191 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!
timz From United States of America, joined Sep 1999, 6468 posts, RR: 8 Reply 23, posted (11 months 5 days 11 hours ago) and read 3771 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?
tdscanuck From Canada, joined Jan 2006, 12709 posts, RR: 80 Reply 24, posted (11 months 5 days 11 hours ago) and read 3756 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?
Viscount724 From Switzerland, joined Oct 2006, 21498 posts, RR: 24 Reply 25, posted (11 months 5 days 9 hours ago) and read 3936 times:
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 From United States of America, joined Feb 2008, 1564 posts, RR: 0 Reply 26, posted (11 months 5 days 7 hours ago) and read 3865 times:
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.
okees From Canada, joined Sep 2005, 424 posts, RR: 6 Reply 28, posted (11 months 2 days 18 hours ago) and read 2936 times:
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.
Roseflyer From United States of America, joined Feb 2004, 8754 posts, RR: 52 Reply 29, posted (11 months 2 days 12 hours ago) and read 2794 times:
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!
bikerthai From United States of America, joined Apr 2010, 1601 posts, RR: 4 Reply 30, posted (11 months 2 days 12 hours ago) and read 2789 times:
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.
Roseflyer From United States of America, joined Feb 2004, 8754 posts, RR: 52 Reply 31, posted (11 months 2 days 9 hours ago) and read 2723 times:
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 From United States of America, joined Mar 2008, 171 posts, RR: 0 Reply 32, posted (11 months 2 days 3 hours ago) and read 2635 times:
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.
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speedygonzales From Norway, joined Sep 2007, 669 posts, RR: 0 Reply 33, posted (11 months 1 day 22 hours ago) and read 2564 times:
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.
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