Birdwatching
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How Can This Nosewheel Not Break Off?

Mon Jul 18, 2005 5:57 am

Hm... keeping in mind that the plane itself might be at a slight angle and not exactly parallel to the photo surface, doesn't it still seem like too much? If the wheel would pull the plane it would be a different thing, but the front wheel is pushed from the back (engines). Is this just an optical illusion?
The caption says "Don't worry about the nosewheel, it is designed to make very sharp turns."
How many degrees do you think the wheel is turned, in relation to the fuselage? I would say at least 80. What do you think?


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flyf15
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RE: How Can This Nosewheel Not Break Off?

Mon Jul 18, 2005 6:01 am

The nosewheel is not the only item used on airplanes to steer them. In this turn, they are most likely using differential braking (braking the left main), and if it were a type with wing mounted engines, applying differential thrust as well (they'd be adding thrust on the right engine). With these factors combined, aircraft can indeed turn very sharply and the nose wheel must be able to turn that sharply aswell.
 
flight152
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RE: How Can This Nosewheel Not Break Off?

Mon Jul 18, 2005 6:01 am

Why would it break off? No additional loads are imposed on the landing gear when making such a hard turn.

..most of the weight is on the main gear.
 
vinceb1117
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RE: How Can This Nosewheel Not Break Off?

Mon Jul 18, 2005 6:22 am

The nose gear of a commercial jetliner is pretty dang sturdy. I think there's a pic of a Qantas 747 landing with it's nose gear off center on a.net, lot's of smoke busted tires but the leg is still there. It's not like the plane's going 100 mph in the posted photo either. Aside from that I'd say 70-80 degrees of tiller would be about right.
 
jetstar
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RE: How Can This Nosewheel Not Break Off?

Mon Jul 18, 2005 6:52 am

There is no load on the nose gear during a turn, the airplane is going in the direction of the nose wheel unless it was taxing at a high speed and the pilot abruptly turns the steering tiller. This will put a strain on the nose gear but most probably the nose wheels would just slide sideways because there is not much of a footprint from the nose tires on the tarmac.

An airliner can almost turn 90 degrees with the airplane pivoting on the inside turn landing gear. Since the main wheels are not locked together, they will rotate at a different speed during a turn.

Tight turns are made using both the steering tiller and if needed differential braking and asymmetrical thrust from the engines, especially if the engines are wing mounted.
 
yhz78
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RE: How Can This Nosewheel Not Break Off?

Mon Jul 18, 2005 8:34 am

The 727 has an amazing nose turn radius. Whenever we have to tow one we disconnect the linkage and can theoretically turn the nose gear 360 degrees if the ramp and tug clearance would allow it. Even with it connected I have been told the turn radius is somewhere around 110 or 120 degrees. Easily within the limits shown in this picture.
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PPVRA
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RE: How Can This Nosewheel Not Break Off?

Mon Jul 18, 2005 8:57 am

Here is another:


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PPVRA
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dl757md
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RE: How Can This Nosewheel Not Break Off?

Mon Jul 18, 2005 9:35 am

Quoting Birdwatching (Thread starter):
How Can This Nosewheel Not Break Off?

Because it's bolted on.  cheeky 
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PPVRA
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RE: How Can This Nosewheel Not Break Off?

Mon Jul 18, 2005 9:40 am

One more!


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242
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RE: How Can This Nosewheel Not Break Off?

Mon Jul 18, 2005 10:56 am

Looks like a normal full left turn, and the tires really take all the abuse. Those red lines on the gear doors are to alert the towing crew the turn limits for the nose gear.
 
roseflyer
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RE: How Can This Nosewheel Not Break Off?

Mon Jul 18, 2005 11:45 am

On a car this would be disastrous because the force of the turn would all be a horizontal moment caused by the friction of the front tires. However on an airplane like previously said, there are at least three ways to turn a plane. First off is the rudder. It is surprising how much force you get by turning a rudder hard over. This does much of the turning in many planes. Next is differential braking from the main landing gear. They are designed to be spaced apart enough for differential braking to cause the plane to do pretty close to a 360 turn with one wheel stopped. Since this is a 727 the last method doesn't work, but often you can give thrust in just one engine to help out a turn and require you to lose less differential braking.

Differential braking is the best way to tightly turn a plane (one wheel or gear locked up with the other rolling on the other side), but it also causes a lot of unecessary wear. It is usually avoided when possible. Using the rudder and turning the nose wheel is less effective, but does not cause any wear on the plane. Finally differential engine thrust helps, but alone won't do a very good job turning a plane. In general all conventional gear planes turn basically the same way (from small Cessnas up to 777s). Planes are much better at turning (at low speeds that is) than a car is.
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twincommander
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RE: How Can This Nosewheel Not Break Off?

Mon Jul 18, 2005 2:43 pm

if you noticed the red line on the door, thats the alignment line for towing... a full 90 degrees of turn is VERY impressive for a turning radius.

gulfstreams are even better as you can do full 360 swings when towing them  Smile
 
LY4XELD
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RE: How Can This Nosewheel Not Break Off?

Mon Jul 18, 2005 10:45 pm

Quoting Jetstar (Reply 4):
There is no load on the nose gear during a turn

I wouldn't go so far to say that...maybe there aren't any additional shear loads on the gear, but there is undoubtedly some additional torsional loads when the nose gear is turned (reaction from the friction of the wheels).
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Shenzhen
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RE: How Can This Nosewheel Not Break Off?

Mon Jul 18, 2005 11:16 pm

Think of the tricycle you had when you were a little kid.

Cheers
 
tinpusher007
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RE: How Can This Nosewheel Not Break Off?

Mon Jul 18, 2005 11:23 pm

That pic of the Varig MD-11 is not uncommon at all for McDD aircraft. I work with MD-88's and when pushing back, if you get close to the turning limit you will frequently notice the outboard nose wheel tire coming off the ground. I almost sh!t a brick the first time I saw it.
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av757
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RE: How Can This Nosewheel Not Break Off?

Mon Jul 18, 2005 11:44 pm

The nose gear normal operating range on the Boeing 727 with the linkage engaged is 0° to 78° degrees on either side using the captains tiller with normal system A hydraulic pressure.

AV757
 
lapper
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RE: How Can This Nosewheel Not Break Off?

Tue Jul 19, 2005 2:10 am

Don't forget as well that the plane would be moving, albeit quite slowly, when the gear changes direction for steering. It's not like in a car where you can turn the wheel and move off, this will have been gradual (sort of) with forward movement. That would counteract any force on the struts.
 
scxmechanic
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RE: How Can This Nosewheel Not Break Off?

Tue Jul 19, 2005 2:14 am

Regarding that MD-11 pic with one nose tire off the ground. While working DC-10's several years ago, I would sometimes use the turned tiller method to change nose tires when a jack wasn't avaliable. Worked pretty slick but you needed two people. One to hold the tiller and one to change the wheel.
 
C133
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RE: How Can This Nosewheel Not Break Off?

Tue Jul 19, 2005 3:01 am

My old 727 operating manual says both the 100 and 200 series airplanes have a 78 degree (maximum) nosewheel turning angle.
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HAWK21M
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RE: How Can This Nosewheel Not Break Off?

Tue Jul 19, 2005 2:52 pm

Why should it.It was designed for turning to Max limitations.Looks like 70-75 deg turn.
Assymetric thrust & Differential braking also assists as stated above.
regds
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wing
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RE: How Can This Nosewheel Not Break Off?

Tue Jul 19, 2005 8:27 pm

Quoting Flyf15 (Reply 1):
The nosewheel is not the only item used on airplanes to steer them. In this turn, they are most likely using differential braking (braking the left main), and if it were a type with wing mounted engines, applying differential thrust as well (they'd be adding thrust on the right engine).

There is no need to use differential braking on airliners,the nose wheel can turn 78 degrees which is more than enough to turn you on a dime.
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Boeing Nut
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RE: How Can This Nosewheel Not Break Off?

Tue Jul 19, 2005 10:51 pm

Here are two very graphic and spectacular examples of how tough nosegears can be....


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SlamClick
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RE: How Can This Nosewheel Not Break Off?

Wed Jul 20, 2005 7:25 am

Here is a personal observation and the lesson I learned from it:

A few years ago, maneuvering a DC-9-15 on a tight GA ramp, I made a sharp turn to the right, then rolled forward a few feet and shut down. I got off and looked at my tire marks on the pavement. The plane had pivoted around the right maingear strut, with the inboard tire rolling forward and the outboard tire rolling backward. (airplane IB & OB #3 and #4 tires not turn IB & OB) They'd scrubbed off some rubber but it was not excessive, no marbles, for example. The nosewheel had scrubbed off a similar amount and the left main wheels hardly left any marks at all.

Looking at the marks it occurred to me that, despite the manufacturer's steering limits there is a practical limit for taxi turns. Think of it this way: If you could plot or map the location of the six wheels (for a DC-9 or B-737) and the struts supporting them, then for a turn to the right, put a compass at the center of the right main gear strut and draw the radius described by the location of the left nosewheel tire. That angle, the tangent of that circle is the sharpest turn you could make while taxiing without dragging the wheels sideways with differential thrust.

It is probably pretty close to the manufacturer's limits.
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HAWK21M
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RE: How Can This Nosewheel Not Break Off?

Wed Jul 20, 2005 1:51 pm


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In the Above pic.The caption says the nose gear was off center.
Look at the Rudder deflection.Is the Nose gear linked to the Rudder on Grd like the B737.
Hows the B747 Rudder pedal steering working like.
regds
MEL
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777wt
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RE: How Can This Nosewheel Not Break Off?

Thu Jul 21, 2005 7:02 am

Quoting SCXmechanic (Reply 17):
Regarding that MD-11 pic with one nose tire off the ground. While working DC-10's several years ago, I would sometimes use the turned tiller method to change nose tires when a jack wasn't avaliable. Worked pretty slick but you needed two people. One to hold the tiller and one to change the wheel.

Is the hyd system online when you do this?
If not doesn't the nose gear stay in position with the hyd system turned off?
 
troubleshooter
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RE: How Can This Nosewheel Not Break Off?

Thu Jul 21, 2005 8:11 am

Quoting C133 (Reply 18):
My old 727 operating manual says both the 100 and 200 series airplanes have a 78 degree (maximum) nosewheel turning angle.

The same as on the 737NG. Max. steering angle 78° to each side.
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Jetlagged
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RE: How Can This Nosewheel Not Break Off?

Tue Jul 26, 2005 4:53 am

Quoting HAWK21M (Reply 23):
Look at the Rudder deflection.Is the Nose gear linked to the Rudder on Grd like the B737.

Yes, pedal steering is also a feature of the 747, as well as many other types. The Emirates 747 nosewheel is deflected because the rudder is, not from tiller input. As the runway is wet the nosewheel would have been aquaplaning, so not under a great deal of side load.
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HAWK21M
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RE: How Can This Nosewheel Not Break Off?

Tue Jul 26, 2005 1:18 pm

Quoting Jetlagged (Reply 26):
As the runway is wet the nosewheel would have been aquaplaning, so not under a great deal of side load.

Is it a delibrite attempt to turn the Nosewheel,or was the Rudder deflection a contributing factor.Seems odd as Rudder control will be approx 10% steering angle compared to that achieved thru Tiller.
Anyone with B747 Experience.
regds
MEL
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APFPilot1985
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RE: How Can This Nosewheel Not Break Off?

Wed Jul 27, 2005 4:31 am

even the little atr's can do it


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