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Faro
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Revving Up The Wheels Before Touchdown

Fri Sep 02, 2011 10:43 am

In order to save on tire wear, how about revving up airliners' wheels before touchdown so that less friction is generated once the wheels hit the tarmac? This may be achieved by a row of weather vane-like cups or paddles fixed around the outside rim of the wheels that present less drag on one face that the other:



Weight would not be a major consideration if you make the paddles from CFRP with a robust attachment point to handle dirt and/or FOD. Conceivably, and given the amount of tire smoke generated during landing, you could prolong tire life considerable with such a contraption...

Faro
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flipdewaf
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RE: Revving Up The Wheels Before Touchdown

Fri Sep 02, 2011 11:01 am

Weight, complexity, another thing to check,another thing to go wrong. Most rubber I believe is scrubbed off when taxiing at high weights.

Fred
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Faro
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RE: Revving Up The Wheels Before Touchdown

Fri Sep 02, 2011 11:23 am

Quoting flipdewaf (Reply 1):
Most rubber I believe is scrubbed off when taxiing at high weights.

Funny then that aprons and taxiways are so clean compared to the touchdown area on runways. I agree thought that high-weight taxiing imposes heavier loads on the tire assemblies than landing, heavier vertical loads that is. When landing you have very significant longitudinal loading on the tires that subsides very quickly as soon as the tires are revved up and stop smoking.

Faro
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hb88
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RE: Revving Up The Wheels Before Touchdown

Fri Sep 02, 2011 11:56 am

The energy absorption via rubber loss and wheel acceleration on touchdown is an important factor in safely slowing the aircraft. Without this, you have increased brake wear and faster speeds on the ground. In short, you don't want to spin up the wheels.

This is one of the most common 'new inventions' relating to aircraft and also one of the most ill-conceived.
 
mandala499
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RE: Revving Up The Wheels Before Touchdown

Fri Sep 02, 2011 12:12 pm

Hmm... I wonder how those "vane cup wheel turners" would do in:
1. Very cold weather landings... on to a short runway, where the temperatures will rise up from minus something to a couple of hundred in less than a minute...
2. Very cold weather maximum energy rejected take off...
3. Hot weather landings... with hot brake temps, followed by a short turn around with brake fans...
4. Same as #3, followed by a maximum energy rejected take off...
5. Hot temp (brake fire) tire burst... these cups can end up becoming dangerous projectiles...
6. Rapid deceleration to stop as the wheels get retracted in take off... either in the well, or as the wheel stops before it gets into the wheel bay.
7. In hot brakes + water spray situation...

The wheels can be replaced easily and is cheaper than the brakes... more brake wear... it'll end up as more expensive...

Mandala499
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tdscanuck
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RE: Revving Up The Wheels Before Touchdown

Fri Sep 02, 2011 1:47 pm

Quoting faro (Reply 2):
Funny then that aprons and taxiways are so clean compared to the touchdown area on runways.

Area. The area of all the aprons and taxiways is at least 2 orders of magnitude larger than the touchdown area so, even if you assumed the same rubber distribution in time you'd see *way* more of it on the touchdown area.

Quoting faro (Reply 2):
When landing you have very significant longitudinal loading on the tires that subsides very quickly as soon as the tires are revved up and stop smoking.

The loading to spin up a tire relates just to the weight of the wheel itself...that's very small (
 
474218
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RE: Revving Up The Wheels Before Touchdown

Fri Sep 02, 2011 1:57 pm

Spinning the tires prior to landing using electric motors was a feature of the Lockheed XR6O-1 Constitution which flew in November of 1946. However the reason was not reduce tire where but to reduce the stress on the main gear struts.
 
flipdewaf
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RE: Revving Up The Wheels Before Touchdown

Fri Sep 02, 2011 2:15 pm

Quoting tdscanuck (Reply 5):
The loading to spin up a tire relates just to the weight of the wheel itself...that's very small (

Sorry to nitpick, its the moment of inertia.   

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DiamondFlyer
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RE: Revving Up The Wheels Before Touchdown

Fri Sep 02, 2011 3:08 pm

Some of the older Cessna Citations have a gravel kit, which one of the parts is a wheel spin up kit. Here's a decent pictures of it. Perhaps someone with more experience with the kit can talk about it.


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mandala499
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RE: Revving Up The Wheels Before Touchdown

Fri Sep 02, 2011 3:59 pm

Quoting diamondflyer (Reply 8):
Some of the older Cessna Citations have a gravel kit, which one of the parts is a wheel spin up kit. Here's a decent pictures of it. Perhaps someone with more experience with the kit can talk about it.

That nice metal cover on the nosewheel is the spin up kit... for nosewheel only... Reduces runway surface bits sticking to the wheels during initial nosewheel contact, which can end up damaging the fuselage or throwing FOD into the engine.

And there are no brakes on the nosewheel...   
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bluejuice
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RE: Revving Up The Wheels Before Touchdown

Sat Sep 03, 2011 12:11 am

On takeoff the wheels would be spinning as well. I'm thinking whatever savings from tire wear on landing will be eaten up by brake wear to slow down the spinning on takeoff. There would also be the extra wear on snubbers inside the wheel well.
 
Fly2HMO
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RE: Revving Up The Wheels Before Touchdown

Sat Sep 03, 2011 1:30 am

At least once a year somebody comes up with this great "new" idea.

In a nutshell (as with all other great new ideas) fuhgeddaboudit.
 
ThirtyEcho
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RE: Revving Up The Wheels Before Touchdown

Sat Sep 03, 2011 4:57 am

Not going to bother looking them up but there must be 500 threads on a.net about this. It is a very bad idea; look it up to see why.
 
fr8mech
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RE: Revving Up The Wheels Before Touchdown

Sat Sep 03, 2011 5:06 am

A couple of issues:
-wheel well clearance (space is at a premium in the wheel well
-weight
-drag on take off
-massive increase in FOD potential
-system inputs (some aircraft use wheel spin-up as an input to other systems)

Look, quite simply, this idea has been around for ages. If the cost/benefit analysis was on the plus side for spinning up the wheels prior to touchdown, it would already be done.
When seconds count...the police are minutes away.
 
bohica
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RE: Revving Up The Wheels Before Touchdown

Sat Sep 03, 2011 3:54 pm

The only thing these so-called wheel spinners would do is cause more drag. More drag means more engine power which means more fuel burned which means money wasted.

On an airplane like a 737 or other aircraft which do not have gear doors, these devices would be sticking out in the airstream causing lots of drag.

Any money saved on tire wear will be lost burning more fuel to compensate for the drag.
 
roseflyer
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RE: Revving Up The Wheels Before Touchdown

Sat Sep 03, 2011 4:25 pm

The thing responsible for tire wear is braking. The tire is designed almost exclusively with the intent to get maximum braking efficiency. Part of the reason why main gear tires only last around 200 cycles between retreads is that the rubber is designed to wear off during the massive heat during braking. Main gear tires are huge because of braking. Nose gear tires also put off smoke on landing, but they do not wear anywhere near as fast as main gear tires (except the rare airplane like the 727s with nose wheel braking). All the energy of the airplane gets turned to heat. The brakes and tires heat up. Brakes are carbon fiber and are designed to perform at high temperatures. Tires are rubber, so they must wear to dissipate heat.

Taxiing at heavy loads puts stress on the tire as a whole, but that does not cause rubber to wear off.
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nomadd22
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RE: Revving Up The Wheels Before Touchdown

Sat Sep 03, 2011 4:27 pm

I'm still waiting for the magnetic brakes that can double as motors for taxing. Sort of like what regenerative hybrids have. Spinning up the wheels for landing would be another function those could handle. They'd even feed a tiny bit of power back to the system when you stopped the wheel spin after takeoff.
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TSS
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RE: Revving Up The Wheels Before Touchdown

Sat Sep 03, 2011 5:11 pm

I suspect that the ability to spin the wheels up to speed before landing will be a feature of the 757 when Boeing restarts that production line.  
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wingscrubber
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RE: Revving Up The Wheels Before Touchdown

Mon Sep 05, 2011 1:31 am

The KERS technology in formula one could be used for this - normally on gear retraction the brakes are applied (or the tyre contacts a skidpad in the wheel well) to reduce the risk of tyre-burst damage. If this energy was captured with a lightweight KERS flywheel or maybe a hydraulic accumulator, the tyres could be spun up prior to touchdown which would increase tyre life and reduce the risk of tyre-burst on landing.

Ultimately, the maintenance savings alone from increased cycle life of the tyres could easily sell this to the airlines, if a small weight trade-off could be justified.
I'm sure engineers at boeing/airbus etc have already made powerpoint slides on their own tyre-spin up concepts.
So, I have to disagree with those who think this is a bad idea - I think it's only a matter of time before it's implemented.
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fr8mech
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RE: Revving Up The Wheels Before Touchdown

Mon Sep 05, 2011 12:12 pm

Quoting Wingscrubber (Reply 18):
Ultimately, the maintenance savings alone from increased cycle life of the tyres could easily sell this to the airlines, if a small weight trade-off could be justified.

Once again, the concept has existed for decades. The trade-off is just not there. Increased weight and cost of maintenance is not adequately accounted for in the potential wear savings on the tire.

Have you ever seen a properly worn tire on an aircraft? They wear just about evenly all the way around, absent an anti-skid issue. That, at least at an anecdotal level, indicates that the majority of wear occurs during taxi, take-off roll and roll-out and not the landing.

Just my observation.
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roseflyer
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RE: Revving Up The Wheels Before Touchdown

Mon Sep 05, 2011 2:42 pm

Quoting Wingscrubber (Reply 18):
The KERS technology in formula one could be used for this - normally on gear retraction the brakes are applied (or the tyre contacts a skidpad in the wheel well) to reduce the risk of tyre-burst damage. If this energy was captured with a lightweight KERS flywheel or maybe a hydraulic accumulator, the tyres could be spun up prior to touchdown which would increase tyre life and reduce the risk of tyre-burst on landing.

The tires are braked so that a loose tread on the tire does not go spinning around in the wheel well after the gear is retracted. A loose piece of rubber moving at over 100 mph will do some considerable damage, and that's not good since the hydraulic systems are located partially in the wheel wells.

Quoting fr8mech (Reply 19):

Have you ever seen a properly worn tire on an aircraft? They wear just about evenly all the way around, absent an anti-skid issue. That, at least at an anecdotal level, indicates that the majority of wear occurs during taxi, take-off roll and roll-out and not the landing.

Flat spots on tires are from skids due to antiskid not working and not tire spin up. And in your list, you forgot landing roll, which is where it occurs as the airplane brakes.

Quoting Wingscrubber (Reply 18):

I'm sure engineers at boeing/airbus etc have already made powerpoint slides on their own tyre-spin up concepts.
So, I have to disagree with those who think this is a bad idea - I think it's only a matter of time before it's implemented.

In general unless it is very advanced technology, if it hasn't shown up on an airplane before, it probably won't. The easy simple ideas have already been implemented.
If you have never designed an airplane part before, let the real designers do the work!
 
cobra27
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RE: Revving Up The Wheels Before Touchdown

Mon Sep 05, 2011 3:52 pm

Somesort of hydraulic device could be used, electrical would also work, but woud probably be heavier. A small turbine you pictured coould also work.
I think than tires wear out at around 150 landings, and can be rebuilt afterwards
 
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longhauler
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RE: Revving Up The Wheels Before Touchdown

Mon Sep 05, 2011 4:54 pm

I recall seeing a study many years ago with the same intent as the OP. However, in this case the actual tire was designed with rubber one-directional vanes on the side wall of the tire. This would spin the tire as soon as it was in the slipstream.

The conclusion was that it did not appreciably reduce tire wear.

As noted above, the majority of tire wear occurs on braking with hot tires.

Quoting RoseFlyer (Reply 15):
main gear tires only last around 200 cycles between retreads

Is this true? I didn't know that!
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fr8mech
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RE: Revving Up The Wheels Before Touchdown

Mon Sep 05, 2011 6:17 pm

Quoting RoseFlyer (Reply 20):
And in your list, you forgot landing roll, which is where it occurs as the airplane brakes.


Semantics, or a bit of ignorance on my part. I use roll-out and landing roll interchangeably.

Quoting RoseFlyer (Reply 20):
Flat spots on tires are from skids due to antiskid not working and not tire spin up.


That is what I was getting at. If the landing was that detrimental to tire wear, you would expect to see a more abnormal tire wear pattern.
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474218
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RE: Revving Up The Wheels Before Touchdown

Mon Sep 05, 2011 7:01 pm

Quoting RoseFlyer (Reply 15):
Part of the reason why main gear tires only last around 200 cycles between retreads is that the rubber is designed to wear off during the massive heat during braking.
Quoting cobra27 (Reply 21):
I think than tires wear out at around 150 landings, and can be rebuilt afterwards
Quoting longhauler (Reply 22):
Is this true? I didn't know that!


We did a survey about 25 years ago requesting the average landing each operator tires were achieving. The 150 to 200 range was what was reported.

Operators with long taxis and many turns were always on the low end. Taxing to takeoff with heavy loads and taxiing to the gate with hot tires from breaking accelerate tire wear. Additionally, when an aircraft turns the inboard tires skid/skip/scrub on the concert in a very tight arc scrubbing off tread.

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