sfilipowicz
Posts: 290
Joined: Wed Jul 17, 2002 3:59 pm

Skidmarks On Runway.

Tue May 04, 2004 6:41 pm

Hi All,

Last week I went on a flight for a short vacation in Spain and while
lining up on the runway I managed to get a nice shot of the runway.

View Large View Medium
Click here for bigger photo!

Photo © Steven Filipowicz



On the photo you can see that there are lots of skidmarks on the white markings these skidmarks are of aircrafts lining up. But why do the tires leave these marks?? I mean the aicraft isn't going at high speed and breaking will lining up.

Any ideas on this?
 
AUAE
Posts: 292
Joined: Fri Apr 09, 2004 4:41 am

RE: Skidmarks On Runway.

Tue May 04, 2004 7:39 pm

The marks are left because the rear tires do not rotate. That means that any wheel that is on a bogie will scrub the ground when it turns. The weight of the aircraft and the scrubbing leaves a mark.
Air transport is just a glorified bus operation. -Michael O'Leary, Ryanair's chief executive
 
citationjet
Posts: 2259
Joined: Sun Mar 09, 2003 2:26 am

RE: Skidmarks On Runway.

Tue May 04, 2004 10:17 pm

Many people don't realize it, but the ground taxi conditions produce high loads in certain parts of the landing gear. A landing gear is designed for both landing impact loads, and ground loads (taxi, towing, braked roll, turning, etc). These ground handling loads have the highest loads for certain portions of the gear design.
Boeing Flown: 701,702,703;717;720;721,722;731,732,733,734,735,737,738,739;741,742,743,744,747SP;752,753;762,763;772,773.
 
avioniker
Posts: 1099
Joined: Tue Jan 01, 2002 5:38 am

RE: Skidmarks On Runway.

Wed May 05, 2004 12:09 am

A good example of the stresses placed on the gear while taxiing is the Delta 767 that sheared a main strut cylinder in Frankfurt when turning onto the gate a few years ago. Ultimately it was attributed to corrosion caused by washing the oil and grease out of the seals and off the strut but that had to be a heck of a load to cause the fracture.
Gear is good at up and down but side to side is very stressful.
One may educate the ignorance from the unknowing but stupid is forever. Boswell; ca: 1533
 
PW4084
Posts: 287
Joined: Tue Mar 06, 2001 7:31 pm

RE: Skidmarks On Runway.

Wed May 05, 2004 1:48 am

A lot of time you will see heavy black streaks on the lineup portion of the runway from the nosegear. If a pilot advances the throttles for a rolling takeoff before the airplane is reasonably lined up, it can leave some pretty good streaks as the nose gear is dragged to centerline under increasing thrust and sideloads.


PW4084
 
sfilipowicz
Posts: 290
Joined: Wed Jul 17, 2002 3:59 pm

RE: Skidmarks On Runway.

Wed May 05, 2004 6:07 am

Thanks everyone!

I didn't realize that there is so much strain on the gear while taxing, especially in corners.
 
QantasA332
Posts: 1473
Joined: Sat Dec 13, 2003 5:47 pm

RE: Skidmarks On Runway.

Wed May 05, 2004 11:06 am

Yep, with all that weight on the mains, dragging can produce quite a lot of marks on taxiways/runways. Not only do turnable centre gear (like those on the 744) reduce strain for the aircraft, airports must like them because they help reduce those markings!  Laugh out loud

Cheers,
QantasA332
 
IMissPiedmont
Posts: 6200
Joined: Wed May 23, 2001 12:58 pm

RE: Skidmarks On Runway.

Wed May 05, 2004 12:45 pm

"The marks are left because the rear tires do not rotate." I hope you mean they do not pivot, they sure do rotate.

The skid marls you see occur because, even at a little above idle, it takes a lot of braking to hold for takeoff and aircraft brakes are powerful. Especially on slippery surfaces such as paint.
The day you stop learning is the day you should die.
 
greasespot
Posts: 2955
Joined: Sat Apr 24, 2004 10:48 am

RE: Skidmarks On Runway.

Thu May 06, 2004 2:21 am

Actually it takes little Braking.....Chocks will stop a airplane even at power in some cases. Jet engine produce very little torque but lots of thrust.

GS
Sometimes all you can do is look them in the eye and ask " how much did your mom drink when she was pregnant with you?"
 
FutureFlyer
Posts: 37
Joined: Tue Mar 30, 2004 10:35 am

RE: Skidmarks On Runway.

Thu May 06, 2004 5:00 am

I know this doesn't directly relate to the topic at hand but i have one question and it is this:

Once the airplane is lined up on the runway for takeoff, does the pilot lock the nose gear into position (a straight position) so that the nose gear cannot turn left/right during the takeoff roll? I have always wondered this but never had the chance to ask, so i will now. Anyone who has the answer to this question please respond.

Thanks in advance...

FutureFlyer
 
IMissPiedmont
Posts: 6200
Joined: Wed May 23, 2001 12:58 pm

RE: Skidmarks On Runway.

Thu May 06, 2004 12:24 pm

"Actually it takes little Braking....." Ok. But having ridden along with a friend while taxiing a 747 or two (2 engines running at idle) I guess my memory is foggy about his leaning on the brakes to avoid running into the hangar.  Smile/happy/getting dizzy

I'd love to see the results when someone tried to stop a 600,000 lb plus aircraft with a 6 inch block of rubber.
The day you stop learning is the day you should die.
 
TimT
Posts: 168
Joined: Sun Jun 03, 2001 1:38 pm

RE: Skidmarks On Runway.

Thu May 06, 2004 3:10 pm

FutureFlyer--No. The nose wheel is steerable by the pilot until the strut is fully extended. Usually they go to rudder for directional control around 60-80kts IAS.
 
User avatar
Starlionblue
Posts: 17117
Joined: Fri Feb 27, 2004 9:54 pm

RE: Skidmarks On Runway.

Thu May 06, 2004 3:11 pm

FutureFlyer, the tiller is not used during the takeoff run, but the pedals give about 7 degrees of deflection on the nose wheel each way (depending on model), so nosewheel steering works a little bit.

Above a certain speed, though, the nosewheel is ineffective and everything depends on the rudder.

"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
User avatar
Starlionblue
Posts: 17117
Joined: Fri Feb 27, 2004 9:54 pm

RE: Skidmarks On Runway.

Thu May 06, 2004 3:49 pm

Coming out of the shower, I though of an exception (there are probably several).

IIRC, the DC-9 (and the MD-8x?) does not have nose wheel steering with the pedals. So if the F/O is flying the leg, the Captain will steer with the tiller during takeoff up to 80 knots and during landing under 60-80 knots.

One of the reasons for the "80 knot call" on the DC-9 is for the F/O to know that the Captain is letting go of the tiller.
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
Guest

RE: Skidmarks On Runway.

Thu May 06, 2004 6:42 pm

I just wanted to underline what PW4084 said above... I have several times as a passenger felt how the plane more or less slides out on the runway in a skid due to that the thrust was applied a bit too much too early when they got a Clear for Take-Off already before they were lined up.

However my feeling is that this is not so common anymore, I am guessing now but it seems like it was more common back in the DC-9 days etc. Those older engines needed several seconds to spool up where as today's engines are a lot faster. I can easily see that some pilots figured this in and advanced the throttles to begin the take-off roll already on the taxi-way figuring that the thrust would come _just_ right when they were lined up and then sometimes it came faster due to temperature etc...

/Mike
 
FredT
Posts: 2166
Joined: Thu Feb 07, 2002 9:51 pm

RE: Skidmarks On Runway.

Thu May 06, 2004 8:00 pm

I attempted to control the SF34 on the takeoff roll using the tiller in the simulator... made for an interesting track down the runway! Way too sensitive... or I'm too hamfisted for the sensitivity... or both... Big grin

BTW, I do believe the DC-9 has nose wheel steering through the pedals... while the F28 did not. I am hoping for someone with the appropriate type rating to chime in with a definitive answer though.

Cheers,
Fred

[Edited 2004-05-06 13:09:27]

[Edited 2004-05-06 13:09:44]
I thought I was doing good trying to avoid those airport hotels... and look at me now.
 
Mr Spaceman
Posts: 2723
Joined: Thu Mar 15, 2001 5:09 am

RE: Skidmarks On Runway.

Fri May 07, 2004 6:45 am

Hi guys.

Here's some more rubber that's been scrubbed off the tires of airliners while turning onto the active at Zurich and San Francisco.


View Large View Medium
Click here for bigger photo!

Photo © Aeroview Zurich/Worldwide
View Large View Medium
Click here for bigger photo!

Photo © Ben Wang



I'm sure landing an airliner like this also causes extreme stresses on the landing gear struts & tires. Big grin


View Large View Medium
Click here for bigger photo!

Photo © Colin Parker
View Large View Medium
Click here for bigger photo!

Photo © Colin Parker



View Large View Medium
Click here for bigger photo!

Photo © Colin Parker
View Large View Medium
Click here for bigger photo!

Photo © Colin Parker



Just my .02 cents worth of useless info.  Laugh out loud


Chris  Smile
"Just a minute while I re-invent myself"
 
dairbus
Posts: 518
Joined: Mon Nov 17, 2003 10:45 am

RE: Skidmarks On Runway.

Fri May 07, 2004 6:52 am

Having worked on Delta's international 767's, I can add something to this discussion. Delta's 767ER's have a MTGW of 407,000 lbs. However, if they go over 400,000 lbs, the airline's Load Control Center or LCC has to make an adjustment for "lateral imbalance" before the final weight and balance paperwork is generated.

When I asked around to find out this adjustment was for, they told me it had to do with the side loads on the main landing gear during taxi at high gross weights. This ties into what Avioniker said in his post. I assume that the adjustment involves adding up the weights on each side of the aircraft (containers and wing fuel) and ensuring that there is less than a certain % difference between the two in order to prevent excessive side loads during taxi.

For the record, I had several flights that needed this adjustment but apart from the extra time needed by LCC to do their thing, the aircraft departed without changing the load.

Regards
"I love mankind. It's people I can't stand." - Charles Shultz
 
bragi
Posts: 212
Joined: Sun May 27, 2001 5:17 am

RE: Skidmarks On Runway.

Fri May 07, 2004 7:44 am

Many taxiways are actually more strengthened than the runway´s themselves.
Wherever possible, wider turns should be made to lessen the load on the main gear, specially with multi-wheel bogies like most large transport aircraft have.
Muhammad Ali: "Superman don’t need no seat belt." Flight Attendant: "Superman don’t need no airplane, either."

Who is online

Users browsing this forum: thepinkmachine, Tristarsteve and 15 guests