Lexy From United States of America, joined Jun 2006, 2362 posts, RR: 9 Posted (4 years 10 months 1 week 5 days 2 hours ago) and read 5367 times:
I have seen some shots here on ANet of the nose wheel on the DC10/MD10/MD11 bending backwards with the weight of the aircraft when they are taxing and turning. But while I was out at the airport this morning here in Nashville I saw something I had never EVER seen before from a FedEx MD11. Check this picture out and tell me what's happening with the nose wheel.
It outlines why MD-11 landing gear legs are tilted back. If you imagine the geometry carefully, you can also picture why one of the wheels lifts during extreme nose wheel steering angle situations. The best way to do this, is imagine the extreme situation where the nose-leg is parallel to the ground. The phenomenon in the photo is due to the nose landing gear geometry only, and not due to flexing from weight.
Dl757md From United States of America, joined May 2004, 1555 posts, RR: 18 Reply 2, posted (4 years 10 months 1 week 4 days 22 hours ago) and read 5306 times:
All Douglas civilian jets (not sure about the DC-8) do this and is as Jetmech said it's due to the geometry or angle of the the nose gear strut. It's actually helpful to mtc as you can change a nosewheel without a jack. Simply turn the nose wheel tiller in the direction opposite of the wheel you want to change and turn off hydraulics. The nose gear will remain turned and the wheel needing changing will remain off the ground.
CosmicCruiser From United States of America, joined Feb 2005, 2212 posts, RR: 16 Reply 3, posted (4 years 10 months 1 week 4 days 18 hours ago) and read 5245 times:
Quoting Lexy (Thread starter): have seen some shots here on ANet of the nose wheel on the DC10/MD10/MD11 bending backwards with the weight of the aircraft when they are taxing and turning.
I don't think the MD-11 nose gear strut bends backwards. It better not. The tilt you illustrate with this pic is normal and well explained already.
JetMech From Australia, joined Mar 2006, 2587 posts, RR: 53 Reply 4, posted (4 years 10 months 1 week 4 days 17 hours ago) and read 5237 times:
Quoting CosmicCruiser (Reply 3): I don't think the MD-11 nose gear strut bends backwards. It better not.
If you want to see a nose gear bending, try to observe an A340 or A330 that gets turned onto bay with any sort of vigour. The amount of bend is simply amazing.
Regards, JetMech
JetMech split the back of his pants. He can feel the wind in his hair.
Lexy From United States of America, joined Jun 2006, 2362 posts, RR: 9 Reply 5, posted (4 years 10 months 1 week 4 days 16 hours ago) and read 5196 times:
Many thanks to those that have explained this to me. When I saw this, I thought it was something unique. Thanks again everyone!!!
JetMech From Australia, joined Mar 2006, 2587 posts, RR: 53 Reply 6, posted (4 years 10 months 1 week 4 days ago) and read 5027 times:
Quoting Dl757md (Reply 2): Simply turn the nose wheel tiller in the direction opposite of the wheel you want to change and turn off hydraulics. The nose gear will remain turned and the wheel needing changing will remain off the ground.
What is the exact mechanism that keeps the nose gear in the displaced position as you change tyres? Is the geometry stable enough by itself, or does it rely on some sort of hydraulic lock being formed?
Regards, JetMech
JetMech split the back of his pants. He can feel the wind in his hair.
HAWK21M From India, joined Jan 2001, 31201 posts, RR: 58 Reply 7, posted (4 years 10 months 1 week 3 days 23 hours ago) and read 5020 times:
Quoting JetMech (Reply 6): What is the exact mechanism that keeps the nose gear in the displaced position as you change tyres? Is the geometry stable enough by itself, or does it rely on some sort of hydraulic lock being formed?
Exactly what I was thinking.What stops the NLG from moving while using the Torque wrench.
regds
MEL
Dl757md From United States of America, joined May 2004, 1555 posts, RR: 18 Reply 8, posted (4 years 10 months 1 week 3 days 22 hours ago) and read 5005 times:
Quoting JetMech (Reply 6): What is the exact mechanism that keeps the nose gear in the displaced position as you change tyres? Is the geometry stable enough by itself, or does it rely on some sort of hydraulic lock being formed?
Quoting HAWK21M (Reply 7): What stops the NLG from moving while using the Torque wrench.
It doesn't hydraulic lock but it doesn't return to center by itself either. You can easily turn the nose gear with a towbar for leverage with hydraulics off but your talking about a large lever arm created by the towbar and hence a lot of torque moving around the center axis of the nose strut. Changing a nose wheel doesn't require much torque (50ft-lbs initial torque on an MD-88) and most of that is in line with the center axis of the nose strut rather than around it so you're not going to turn the nose gear by simply changing a wheel assembly.
113312 From United States of America, joined Apr 2005, 537 posts, RR: 1 Reply 9, posted (4 years 10 months 1 week 3 days 18 hours ago) and read 4973 times:
Every Douglas jet has been designed that way. There is less tire scrub in maximum effort turns.
I see. Thanks for the info! I presume that the geometry of the MD-11 nose-leg is mild enough, that even if the axle did turn with a nose-wheel off, it wouldn't make contact with the ground?
Quoting 113312 (Reply 9): There is less tire scrub in maximum effort turns.
Yep, I imagine that this would be another benefit of canting the nose-leg. I suppose the idea behind it is similar to the significant camber you see on the front wheels of some racing cars?
Regards, JetMech
[Edited 2008-07-16 07:06:13]
JetMech split the back of his pants. He can feel the wind in his hair.
Viscount724 From Switzerland, joined Oct 2006, 21465 posts, RR: 24 Reply 11, posted (4 years 10 months 1 week 3 days 10 hours ago) and read 4880 times:
Somewhat related question I've always been curious about -- why are the nosegear wheels on the Lockheed Constellation not parallel to each other? There is a larger gap between the top of the tires than the bottom. It's noticeable in the following photos when you enlarge them.
Dl757md From United States of America, joined May 2004, 1555 posts, RR: 18 Reply 12, posted (4 years 10 months 1 week 3 days 9 hours ago) and read 4863 times:
Quoting JetMech (Reply 10): I presume that the geometry of the MD-11 nose-leg is mild enough, that even if the axle did turn with a nose-wheel off, it wouldn't make contact with the ground?
474218 From United States of America, joined Oct 2005, 6340 posts, RR: 10 Reply 13, posted (4 years 10 months 1 week 3 days 7 hours ago) and read 4840 times:
Quoting Lexy (Thread starter): I have seen some shots here on ANet of the nose wheel on the DC10/MD10/MD11 bending backwards with the weight of the aircraft when they are taxing and turning.
Quoting CosmicCruiser (Reply 3): I don't think the MD-11 nose gear strut bends backwards.
Quoting JetMech (Reply 4): If you want to see a nose gear bending,
The DC-10/MD-10/MD-11 nose landing gear does not bend backwards and it does not bend under the weight of the airframe. When their nose landing gear is fully down and lock it does no reach a full 90 degrees like most aircraft. This picture clearly shows the down and locked position in the air with no weight on the gear.
CosmicCruiser From United States of America, joined Feb 2005, 2212 posts, RR: 16 Reply 14, posted (4 years 10 months 1 week 3 days 7 hours ago) and read 4835 times:
Quoting 474218 (Reply 13): When their nose landing gear is fully down and lock it does no reach a full 90 degrees like most aircraft.
I'm going to have to call you on this one. I just checked my MD-11 CFM and it doesn't really say but I can bet it is more than 90 deg. I may call maint and see what they say but it "ain't" less than 90.
Wingscrubber From UK - England, joined Sep 2001, 834 posts, RR: 0 Reply 15, posted (4 years 10 months 1 week 3 days 5 hours ago) and read 4796 times:
That angle also helps reduce nosewheel shimmy, if it was angled the other way it would be inclined to caster like a shopping cart, usually this is only used on small GA aircraft which steer with differential braking alone.
Dl757md From United States of America, joined May 2004, 1555 posts, RR: 18 Reply 16, posted (4 years 10 months 1 week 3 days 5 hours ago) and read 4795 times:
Quoting CosmicCruiser (Reply 14): I may call maint and see what they say but it "ain't" less than 90.
I think what 474218 meant is that the gear extends less than 90 deg from the longitudinal axis of the airplane. On the DC-10/MD-11 the nose gear strut extends down and back and never reaches full vertical. It may extend 90 deg from the stowed angle but again as 474218 implied it is not 90 deg from the longitudinal axis of the aircraft. The Connie nose strut on the other hand extends forward past vertical and therefor extends more than 90 deg.
HAWK21M From India, joined Jan 2001, 31201 posts, RR: 58 Reply 17, posted (4 years 10 months 1 week 3 days 3 hours ago) and read 4772 times:
Quoting Dl757md (Reply 8): It doesn't hydraulic lock but it doesn't return to center by itself either. You can easily turn the nose gear with a towbar for leverage with hydraulics off but your talking about a large lever arm created by the towbar and hence a lot of torque moving around the center axis of the nose strut.
Thanks.But is the Wheel change without the Jack a company approved procedure on this type....or just an alternative.
regds
MEL
Dl757md From United States of America, joined May 2004, 1555 posts, RR: 18 Reply 18, posted (4 years 10 months 1 week 3 days 1 hour ago) and read 4745 times:
Quoting HAWK21M (Reply 17): But is the Wheel change without the Jack a company approved procedure on this type....or just an alternative.
regds
C'mon Hawk you don't think I'd use an unapproved mtc. method do ya?
It is listed in the MD-88 and MD-90 AMM as an alternative method of lifting each nose wheel for wheel assy change.
CosmicCruiser From United States of America, joined Feb 2005, 2212 posts, RR: 16 Reply 20, posted (4 years 10 months 1 week 2 days 18 hours ago) and read 4693 times:
Quoting Dl757md (Reply 16): think what 474218 meant is that the gear extends less than 90 deg from the longitudinal axis of the airplane
Yeah, I realized that after I hit the "post" button; he got me thinking wrong using the Connie as the example. I was about to post a correction.
Ex52tech From United States of America, joined Dec 2006, 559 posts, RR: 1 Reply 21, posted (4 years 10 months 1 week 10 hours ago) and read 4514 times:
Quoting Dl757md (Reply 8): It doesn't hydraulic lock but it doesn't return to center by itself either. You can easily turn the nose gear with a towbar for leverage with hydraulics off but your talking about a large lever arm created by the towbar and hence a lot of torque moving around the center axis of the nose strut.
I never trusted the steering bypass enough to leave the tow bar attached, not to mention the DC-10 MD-11 tow bar is one heavy tow bar, I don't think I could pick one of them up to swing the nose wheel.
I always wrapped the seat belt around the tiller with the hydraulics on to keep it in place.
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