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exploding tyres

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exploding tyres

Old 1st Aug 2000, 15:54
  #1 (permalink)  
keendog
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Exclamation exploding tyres

This is just an idea so if its rubbish or been tried before let me down gently.

What with Concorde etc a lot of focus has been brought to bear on tyre wear and tyre failure.
Presumably, tyres undergo the greatest stress and fatigue in the cycle on landing when they are:-
(i)skidded along the runway for a short while before
(ii)accelerating very quickly to landing speed and
(iii)simultaneously heating up very quickly as they go from being somewhere near freezing to very hot as the rubber deformation caused by their rotation causes large amounts of heat to be generated.

If stress/fatigue factors on landing could be reduced presumably it would contribute to the life span etc. of the tyre/wheel.

Could there not be a practical system for rotating the wheels up to somewhere approaching landing speed before touchdown and/or heating the rubber? This might avoid quite a lot of stress.

A fair amount of energy would be required for such a system and I expect that the weight penalties imposed by electric motors and the associated mechanics would be too great.
What about using bleed air venting on appropriately designed vanes mounted on the undercarriage hubs during approach? Or routing some alternative hydrauic system fluid through an impeller pump. I prefer the former solution as there would be obvious safety advantages in having no mechanical link between the rotating wheels and the rest of the gear.

As I say just an idea. If it works I'll take 10%!
 
Old 1st Aug 2000, 17:23
  #2 (permalink)  
Self Loading Freight
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Unhappy

I'm told by patent officers that this is one of the most common inventions people try and register. Unfortunately, it's not needed (I forget why, but it's something simple).

R
 
Old 1st Aug 2000, 19:29
  #3 (permalink)  
Zeke
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Keendog,

Have a look at http://www.pprune.org/ubb/NonCGI/For...ML/001074.html

Tyres do not have the greatest stress on spin up, it is during the braking cycle and taxi when the aircraft is producing little lift. At spin up little weight (comparatively) is on the wheels.

Many smaller aircraft like citations have gravel kits that include a nose wheel spin up that is operated off the windscreen bleed air. This is designed to minimize stone ingestion into the engines for gravel strip ops, not for tyre life requirements.

Most aircraft tyres are oversized allowing for increased weight on later variants without the need to make the hole to put them away in any bigger later on. In preliminary design a factor of 25% is not unusual.

Aircraft tyres are a complicated design and work well in the environment they are designed for. Certain EU countries have funny ideas of how to connect these tyres to the aircraft which may cause problems. A tribute to this is the EMB series of a/c which have problems with fractures in the gear components …. they have a heavy design influence from certain EU members, but the French do know how to design some things really well.

Regards


Z
 
Old 2nd Aug 2000, 11:04
  #4 (permalink)  
mriya225
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Question

Whooaaaaa...

Can somebody out here help clear this up for me? In my Airframe certification training we learned that the toughest demand on aircraft tires is the rapid heat buildup during lengthy ground operations, and not the impact of landings. The reasoning was put to us as follows: Aircraft tires are designed to flex over twice as much as standard tires. This flexing causes internal stress and friction as the tires roll along the ground, generating an enormous amount of heat, which damages the tires.
We were taught that the best way to extend the service life of tires is to safeguard against heat buidup with: short ground rolls, slow taxi speeds, minimum braking, and proper inflation.

If I'm mistaken, I'd like to know.
Anybody?

[This message has been edited by mriya225 (edited 02 August 2000).]
 
Old 2nd Aug 2000, 21:41
  #5 (permalink)  
Zeke
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Sounds about right "Tyres do not have the greatest stress on spin up, it is during the braking cycle and taxi when the aircraft is producing little lift. ", I cannot vouch for the figures you stated....tyres are evolving all the time as we get to know more about them
 
Old 3rd Aug 2000, 16:43
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BOAC
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Be careful spinning up wheels. It was tried with the Lancaster in WW2 using electric motors. Only trouble was, with those large mainwheels....no-one had thought of precession!
No, I didn't fly it.
 
Old 4th Aug 2000, 14:35
  #7 (permalink)  
MaxDiff
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Cool

Hey, were getting there.
The largest loading a tyre goes through is as previously stated, it's during the taxi out & takeoff roll. No lift & a large dollop of jet A-1 to carry round (upto 160,000+ kgs B744).
 
Old 4th Aug 2000, 16:09
  #8 (permalink)  
mustafagander
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The toughest operating regime for a/c tyres is a long, fast taxi at MTOW. The sidewall flex heats the tyres to very high temps. As evidence, just look at all the failures on t/o ex HNL reef runway (08R). I wonder about some pilots who want to taxi from the 120 gates to 25R at LAX at 30kts on a B744 at 397 tons!!
As has been stated, touchdown is not too tough on tyres because the a/c weight is still largely supported by the wings.
 
Old 4th Aug 2000, 20:53
  #9 (permalink)  
Mechcrit
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Lightbulb

Just another angle a majority of the tyres temperature and tyre bursts come from the heat generated by the brake units hence the american termanology for brakes "Heat packs" a possible cause for the AF conc wheels exploding would have been the fact it was sat at the end of the runway holding on it's brakes whilst using it's re heat
 
Old 5th Aug 2000, 10:57
  #10 (permalink)  
Cunning Artificer
 
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Unhappy

As mustafa says, the toughest time is a long fast taxi at Max weight.

The Air France Concorde was at absolute max weight and was a late departure (hence fast taxi?) Good recipe for an exploding tyre? Perhaps...

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