Ever wondered why airliners burn alot of rubber on landings? This is another offtopic, but maybe some of you have an answer! So why is it? Why do the wheels not get spinned up before landing with somekind of system? I'm thinking of radialwindmills fitted on the wheels. Why aircraft manufacturers not incorperate such a feature and save alot of rubber and tires? Is there a practical reason to land with non spinning wheels? Only thing I can think of is heating up the tire to increase the grip-level, but doesn't sound to realistic to me.Any ideas?Claudio

Hmm, makes you wonder. Good question.Bill

Besides the cost of a system as opposed to the cheap cost of tires. Spinning wheels on a flying plane act as gyroscopes and affect the control of the plane. That is why pilots brake and stop the tires spinning after take off.

>Besides the cost of a system as opposed to the cheap cost of>tires. Spinning wheels on a flying plane act as gyroscopes and>affect the control of the plane. That is why pilots brake and>stop the tires spinning after take off. of course, that is why Motor Cycles do not fall over when they are moving :)

Actually some large aircraft of the late 1930's and early 40'sdid have such a feature.If I can recall correctly (which is becoming increasingly difficult)they were Russian designed.When I was a kid my Dad bought me a book about some of theBehemouths of the air,which seemed to be the domain of Germany andRussia at the time. One I do recall reading about was a huge "flying boat", Dornier I believe, which had six engines. It had access tunnelsin the wings to permit inflight maintanence on the engines.As to the rubber use I suppose one could always do what the TurkishAir Force did when I worked with them at Incirlik, just wait untilthree layers of cord was showing and then replace the tires. :-beerchug DN

>Ever wondered why airliners burn alot of rubber on landings?>This is another offtopic, but maybe some of you have an>answer! So why is it? Why do the wheels not get spinned up>before landing with somekind of system? I'm thinking of>radialwindmills fitted on the wheels. Why aircraft>manufacturers not incorperate such a feature and save alot of>rubber and tires? Is there a practical reason to land with non>spinning wheels? >Only thing I can think of is heating up the tire to increase>the grip-level, but doesn't sound to realistic to me.>>Any ideas?>>ClaudioThose windmills would create drag, which is unhappy news, especially when considering impact on engine-out performance. The devices would also keep the wheels spinning fast after takeoff, which increases risk of damage if there's a tire failure or if the tires are loaded up with slush/ice after a cold wx departure. Last thing you want in the wheel well is a tire spinning at 1000 rpm slinging ice and slush into the hydraulic lines and electrical cables...CheersBob ScottATP IMEL Gulfstream II-III-IV-V L-300Washington, DC

>>Besides the cost of a system as opposed to the cheap cost>of>>tires. Spinning wheels on a flying plane act as gyroscopes>and>>affect the control of the plane. That is why pilots brake>and>>stop the tires spinning after take off. >>of course, that is why Motor Cycles do not fall over when they>are moving :)So why do they fall over when moving on ice? Dan

>Besides the cost of a system as opposed to the cheap cost of>tires. Spinning wheels on a flying plane act as gyroscopes and>affect the control of the plane. That is why pilots brake and>stop the tires spinning after take off. First off, airline tires are not cheap! When I was with Boeing, I once read an estimate that the cost of replacement tires for a 747 over it's lifetime can be greater than the original purchase price of the aircraft. They're only good for 200 landings or so before they need to be retreaded, and can only be retreaded a few times. If you're flying a 747 for short haul operations like they do in Japan, you might average 8 cycles per day. So you're looking at a set of 18 tires, 15 times per year.Second, the reason that they apply brakes after takeoff is to stop the wheels from rotating while they are retracted into the wheel wells. It's a pretty tight fit, and the tires actually grow radially at takeoff speeds. It has nothing to do with centripetal acceleration affecting the aircraft's handling.Dan

There are a couple reasons why the wheels are not spun up prior to landing. One is to keep the weight down and to simplify the system. Another reason is the anti skid system. The anti skid system is designed to sense skids and to have the wheels spinning prior to landnig can cause problems with the anti skid system on runways with standing water, snow and ice.The main wheels on modern airliners are automatically braked when retracted. This braking is at a reduced rate and will stop the wheels before they enter the landing gear bay. The pilots are warned not to manually brake the wheels prior to retraction as the sudden stop of the wheel causes excessive gyroscopic forces that can actually break the axles. The nose wheels are usually allowed to spin until they are in the wheel well and snubber pads stop the rotation.JohnBoeing 727/737 & Lockheed C-130/L-100 Mechanichttp://www.precisionmanuals.com/images/forum/ng_driver.jpg

thx for the insights guys! Didn't know that spinning wheels could mess with the antiskid system. System simplicity is always a good thing. But maybe it wouldn't be bad to spin the wheels up to a certain speed, still well under landing speed, which wouldn't mess with the antiskid system but save alot of rubber. I don't know how big the gyroscopic forces can have effect on pitch behavior, but if you spin up the wheels slowly it shouldn't cause much problem. There is most likely a solution to this, but the tire companies may not like it and pay a/c manufactures to let the undercarriage as it is or have somekind of agreement.}( Claudio

With the exception of most nose wheel tires, the main wheeels are allowed to be recapped several times before a new manufactured tire is installed. The basic tire minus tread is called the carcas. When a tire is new and finally worn out, the tread is shaved off the carcas and a new tread is capped on to the carcas. Depending on the aircraft/tire type, this recapping can be unlimited until the carcas is damaged beyond use or the recaps can only be done a finite amount before total scrapping. Thus most tires have several lives before final re'tire'ment. :-lolJohnBoeing 727/737 & Lockheed C-130/L-100 Mechanichttp://www.precisionmanuals.com/images/forum/ng_driver.jpg

I know the following is not really an answer to the question above, but I read in a magazine that a Boeing 747 is burning more rubber on the way to the runway for take off than on landings.The main reason for that is the massive weight of a 747 with filled fuel tanks and the wear during turns on the taxiways.Excuse my short explanation but my english ain't that perfect :-).

Christian

http://img.photobucket.com/albums/v232/chrismo/sigsky.jpgVacation: wasted time between 2 flights!