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Btriple7
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Object On MD-82 Nosewheel

Sat Dec 02, 2006 6:48 pm

Hello everyone,

Can someone please identify and explain the purpose of the black object on the nosewheel of the MD-82 in the photo below.

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Photo © Alex G.-Denicourt - Contrails Aviation Photography



If there has already been a thread about this, just point me in the right direction.

Regards,
Btriple7
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Starlionblue
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RE: Object On MD-82 Nosewheel

Sat Dec 02, 2006 7:07 pm

Hey Btriple7. I assume you mean the horizontal thing hanging off the axle? That's the equivalent of a splash guard on a car wheel. Given the position of the MD-80 engines it keeps crap from getting launched into them by the nose wheel.

You will find a similar but larger device on 737s with the gravel kit (not also the engine devices on this one):

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Photo © Kevin Wachter
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Photo © Aaron Hall

.
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Btriple7
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RE: Object On MD-82 Nosewheel

Sat Dec 02, 2006 7:17 pm

Quoting Starlionblue (Reply 1):

Really, a splash guard?!

I would have thought it would be something a bit more sophisticated than that. You say it is to keep the nose wheel from spewing up junk into the engines, but I can't imagine that the nose wheel would be able to project anything that far, even on a takeoff role.

Regards,
Btriple7
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RE: Object On MD-82 Nosewheel

Sat Dec 02, 2006 8:47 pm

At speeds above 80-100 knots not only water and slush will be thrown against the belly behind the nosewheel leg.Sand,gravel and small stones and other debris will also be deflected by this device.There are similar deflectors on the main wheel legs to prevent objects from damaging the flaps,wing underside and engines.They are not that easy to spot,though.
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zanl188
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RE: Object On MD-82 Nosewheel

Sat Dec 02, 2006 11:45 pm

Quoting Btriple7 (Reply 2):
but I can't imagine that the nose wheel would be able to project anything that far, even on a takeoff role.

The nose wheel only has to chuck it up, the forward motion of the aircraft thru the air brings it into contact with the engine.

Take a look at the picture you referenced at the top of the thread. Below the co-pilots window there is a strake (on the nose!) that helps control airflow into the engine. It is certainly active at take off.
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Starlionblue
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RE: Object On MD-82 Nosewheel

Sat Dec 02, 2006 11:46 pm

Quoting FBU+4EVER%21" class=quote target=_blank>FBU 4EVER! (Reply 3):
deflected

I seem to remember it's called a "gravel deflector" or something like that. And yes, it is indeed a "splash guard".

As FBU 4EVER says, the force of these objects can be considerable. The wheels turn at a prodigious rate and can throw gravel quite a distance.
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zanl188
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RE: Object On MD-82 Nosewheel

Sun Dec 03, 2006 12:04 am

Quoting Starlionblue (Reply 5):
The wheels turn at a prodigious rate and can throw gravel quite a distance.

Er, no. Unlike car wheels aircraft wheels are not under power. A car wheel under power will throw an object. An aircraft wheel will just move it out of the way -- the airflow around the aircraft is what throws it.

BTW: This Boeing 727 nose tire has a "chine" on it. This little chine keeps water and slush from a contaminated runway out of the outboard engine on a 727.


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Photo © Scott Kerhaert



If you're still not convinced there are some fascinating videos of contaminated runway certification tests for various aircraft out on the net. (sorry I can't find them at the moment). I have a video of the 727 tests, both with and without the nose gear chine, and difference the chine makes is huge.

edit: google found this pix of a 727 nose tire chine in action. Without the chine stuff would be getting tossed up high enough to get in the outboard engine.

http://www.airporttech.tc.faa.gov/safety/friction_files/image003.gif

[Edited 2006-12-02 16:11:54]
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SlamClick
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RE: Object On MD-82 Nosewheel

Sun Dec 03, 2006 12:51 am

According to my MD manual the device is properly called a "spray deflector" and is one item on the exterior preflight inspection.

I have the video of the wet runway tests with and without this device. It is quite a difference. The spray is thrown in a much lower arc with the deflector attached and it makes ingestion by the engines much less likely.

Without the deflector the material would not travel much farther, mostly just higher. And if it goes higher it takes longer to arc over the top and fall back to the runway. Longer time = more opportunity for the engines to get there and ingest it.

At 120 knots a plane is traveling just over two hundred feet per second. Let's picture a nosewheel tire with a tread width of ten inches, rolling 200fps through slush lying one-quarter inch deep on the runway. The tire will throw six thousand cubic inches (that is about 26 gallons) of slush per second up, and out to the side. Well, since the engines will arrive where the nosewheel is now in less than one second. The need to keep the spray low becomes pretty obvious when you think of it that way.

Forget gravel and other FOD, I don't think jet engines would be happy being fed 26 gallons of water per second.

When the DC-9-80 entered line service this spray deflector created a small problem. The standard DC-9 towbar was about an inch too narrow of throat to fit over it. A whole new series of towbars was distributed.
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3DPlanes
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RE: Object On MD-82 Nosewheel

Sun Dec 03, 2006 1:00 am

Quoting ZANL188 (Reply 6):
A car wheel under power will throw an object.

[Sarcasm ON]

Funny... I didn't realise that tractor-trailers had started putting power to the trailer wheels... How do they get the power the fifth wheel connection?????

And as the plane rolls on takeoff, just exactly what air flow is rising from the runway at the nosewheel? Those engines are easily 8 to 10 feet of the ground. What's providing the lifting force?

[Sarcasm OFF]

Rubber is sticky, tires have grooves/tread. Simple friction will cause debris or water to stick to the tire for a moment before being ejected upwards.

The "mud flaps" (or chines on 727s) - both on the gear above, and tractor-trailers - are there to deflect that material so it can't make a bee-line for the airframe/engine (or your windshield). Fortunately, they work better on planes...
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2H4
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RE: Object On MD-82 Nosewheel

Sun Dec 03, 2006 1:04 am




Quoting Btriple7 (Reply 2):
I can't imagine that the nose wheel would be able to project anything that far, even on a takeoff role.

Seeing is believing:










 Smile


2H4


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N231YE
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RE: Object On MD-82 Nosewheel

Sun Dec 03, 2006 1:41 am

Quoting Btriple7 (Thread starter):
If there has already been a thread about this, just point me in the right direction.

Indeed it has been: http://www1.airliners.net/discussions/tech_ops/read.main/25633

But no worries, as stated in the previous posts it is a splash guard.
 
zanl188
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RE: Object On MD-82 Nosewheel

Sun Dec 03, 2006 1:43 am

Quoting 3DPlanes (Reply 8):
Funny... I didn't realise that tractor-trailers had started putting power to the trailer wheels... How do they get the power the fifth wheel connection?????

As I think you already know there is no power to the fifth wheel. Those tires are merely pushing (in all directions) debris out of the way.

Quoting 3DPlanes (Reply 8):
And as the plane rolls on takeoff, just exactly what air flow is rising from the runway at the nosewheel? Those engines are easily 8 to 10 feet of the ground. What's providing the lifting force?

I never claimed there was air flow rising from the runway. If you look carefully at 2H4s pictures you will see that the slush is moving in "all" directions. Since the aircraft is moving the aircraft will impact the plume of debris at differnet times based on which direction the debris was thrown. For example: The debris "pushed" forward will appear to have a lesser plume than the debris pushed sideways because the nose of the aircraft impacts that debris much sooner than say the debris pushed sideways which impacts the wings or engine cowl.

As for your comment re: friction. granted there is some truth to that. However that debris would be thrown directly aft impinging the underside of the fuselage.

The majority of this debris is simply getting pushed out of the way much as would occur if you dropped a heavy object in a bucket of water.

Quoting 2H4 (Reply 9):
Seeing is believing:

Thanks 2H4 you always find the awesome, and descriptive, pix.
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Starlionblue
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RE: Object On MD-82 Nosewheel

Sun Dec 03, 2006 2:33 am

Quoting ZANL188 (Reply 6):
Quoting Starlionblue (Reply 5):
The wheels turn at a prodigious rate and can throw gravel quite a distance.

Er, no. Unlike car wheels aircraft wheels are not under power. A car wheel under power will throw an object. An aircraft wheel will just move it out of the way -- the airflow around the aircraft is what throws it.

I know they're not under power. But it's the spinning that "throws", not the power directly.
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zanl188
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RE: Object On MD-82 Nosewheel

Sun Dec 03, 2006 3:06 am

Quoting Starlionblue (Reply 12):
But it's the spinning that "throws", not the power directly.

I think it depends upon the type of debris. A rock run over by the nose gear is probably more likely to get chucked up or thrown, to use your term, out the back and then impact the lower fuselage. Ok maybe the spinning of tire adds some energy to the rock. Whereas on the other hand if the debris is slush or water the spinning of the tire adds much less energy than does the tire simply pushing the debris out of the way.
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SlamClick
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RE: Object On MD-82 Nosewheel

Sun Dec 03, 2006 3:11 am

Quoting Starlionblue (Reply 12):
it's the spinning that "throws",

I disagree.

In the first place NOTHING IS THROWN REARWARD. Can't make that point strongly enough. It is just sprayed up and around and side to side. The engines CATCH UP WITH IT before it falls back to the runway.

The spray deflectors (they are not called splash guards) do not prevent water or other solids from being thrown, they just keep the trajectory down.

In the second place, imagine the passing of a non-powered wheel from the runway's point of view. It is just laying there with a coating of water or slush just laying there on top it. Along comes a torus-shaped object, the nosewheel, rolling through that slush. The wheel, with its share of the airplane weight is going to press itself all the way down to the pavement. To do that it is going to squeeze all the water out from between its surface and the pavement. Okay not ALL the water, the pavement will still be wet, as will the tire, but let's say all but a very thin film of water is going to have to get out of the way.

Now picture an infinitely small plane (the geometry kind) transverse to the direction of travel of the AIRplane. This extends upward from the surface of the pavement to as high as you care, and as far out to either side as you'd like to consider. The water at this plane is going to react to the passing of the wheel.

The first contact, wheel-to-water will come at the surface of the water or slush, and that corresponding point on the tire tread. It is not rolling, it is pressing down. When it presses all the way through the coating of water (because the wheel has rolled forward that far) it is going to press itself to the surface of the pavement then rise up again WITHOUT rotating. That is what rolling wheels do on a surface - they do not rotate against the surface.

So what does the water experience? It gets squeezed - right straight down toward the ground. Since it cannot be compressed it pressurizes and squirts out the gap at the point of least resistance. This is NOT back toward the rear of the plane! It is forward mostly, and to the sides a bit less.

Yes, some of the water will cling to the tread and be thrown by centrifugal force in every direction around the rotation of the tire but the huge majority of the mass and weight of the water or slush will be squirted out FORWARD or TO THE SIDES by the passing of the wheel.

Loose rocks or other solids have different physics and present different results but the spray deflectors on the MD-80 are 99.99% there for water and slush.

The third picture in reply #9 is a good illustration of how one can be deceived by appearances. It looks like the nosewheel is spraying water very far astern but that is an illusion. It is only throwing it up forward, and to the sides. The long stream aft of the nosewheel is us looking BACK IN TIME. The wheel passed that point a second ago and you are seing, if you will, a succession of individual splashes, spaced so close together that they look like a stream from a firehose. But they are not. It is just water droplets arcing up a few feet and falling right back to the ground within a few feet of where they started.


The splash-area gets progressively larger as you go aft because that is what splashes do. They start at the point of initial perturbation and they radiate outward until their energy is spent. These are splashes of water caused by the pressing-down and lifting up of a point on the surface of a tire tread and it makes no difference that the wheel was rotating. If you could press a non-rotating wheel down through the water, lift it up, move it forward a tiny increment, do it again and keep repeating very rapidly the result would look exactly the same. The spray is higher back near the tail only because the water has had time to arc that high. A few feet farther aft, out of this picture it is going to start falling back to the runway.

But it was not sprayed aft. It was sprayed up in just about every direction except aft. Aft just caught up with it.
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Btriple7
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RE: Object On MD-82 Nosewheel

Sun Dec 03, 2006 3:20 am

Thanks for all the replies, guys. I still have one more question though. What other planes have this spray deflector/chine devise. Why doesn't the CRJ family have it as they have rear mounted engines like the MD-80 and the 727?

Quoting 2H4 (Reply 9):
Seeing is believing:

Thanks for those, 2H4. Wow, what those little wheels can do!

Regards,
Btriple7

[Edited 2006-12-02 19:23:09]
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SlamClick
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RE: Object On MD-82 Nosewheel

Sun Dec 03, 2006 5:02 am

As you saw, the 737-200s with the "offroad" kit can have one.

I only recall chined tires on the Cessna Citation but I'm sure there are lots more.
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2H4
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RE: Object On MD-82 Nosewheel

Sun Dec 03, 2006 5:10 am




Quoting SlamClick (Reply 16):
I only recall chined tires on the Cessna Citation but I'm sure there are lots more.

Many (and perhaps most?) Learjet nose tires are chined, as well:





2H4


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Starlionblue
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RE: Object On MD-82 Nosewheel

Sun Dec 03, 2006 6:47 am

Quoting SlamClick (Reply 14):
Quoting Starlionblue (Reply 12):
it's the spinning that "throws",

I disagree.

In the first place NOTHING IS THROWN REARWARD. Can't make that point strongly enough. It is just sprayed up and around and side to side. The engines CATCH UP WITH IT before it falls back to the runway.

The spray deflectors (they are not called splash guards) do not prevent water or other solids from being thrown, they just keep the trajectory down.

Fair point. I stand corrected.
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vc10
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RE: Object On MD-82 Nosewheel

Sun Dec 03, 2006 7:08 am

The good old VC-10 had chined nose wheel tyres to deflect the spray

Concorde also had nose spray deflectors fitted to the nosewheel

Quoting 2H4 (Reply 9):
Seeing is believing:

Great picture and it reminds me of watching a Comet 4 taking off at London one day and it almost disappeared in nose wheel spray , but it's wing root buried engines did not seem to care one bit.
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dl757md
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RE: Object On MD-82 Nosewheel

Sun Dec 03, 2006 8:13 am

The function of the object in question is indeed that of a spray deflector as has been established. I think however that it is a less eloquent solution to the prevention of water ingestion than chined nose tires are. It's heavier - approximately 30 lbs for the the entire assembly. It creates more work when changing a nose tire as the outer support must be removed. And it's prone to mechanical failure. A cracked center spray deflector section caused the recent DEN MD-90 nose gear up landing. The center section failed and one of the outer supports swung outboard and prevented the gear form dropping because it hung up on the frame around the gear doors. The damage to the deflector has been determined to have been caused by normal towing operations utilizing the supertug. Of course none of this would have happened with a chined tire.  Wink

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Starlionblue
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RE: Object On MD-82 Nosewheel

Sun Dec 03, 2006 10:34 am

Quoting Btriple7 (Reply 2):
I would have thought it would be something a bit more sophisticated than that.

Another low tech solution on airliners is the bar above each door. It's basically just a gutter.
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo

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