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Improved Aircraft Landings

12/03/2009 10:19 AM

When an airplane lands, the wheels have to accelerate from 0 to the landing speed (100mph?). I have always observed a lot of smoke and tire burning at touchdown. Why don't they have a device that brings the speed of the tire up to landing before touchdown. It could be an electric motor or a wind turbine device. The electric motor could also be used to provide braking. Such a device would prolong tire life, especially on aircraft carrier landings.

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Guru

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#1

Re: Aircraft landing

12/03/2009 10:26 AM

I would guess that making the wheels spin would make the plane less maneuverable. This is bad when trying to land.

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#2

Re: Aircraft landing

12/03/2009 10:29 AM

The Cessna Citation business jet actually has a nosewheel spin-up device as an option. This is done not to save the tires but to prevent the spray of gravel up into the engine turbines when landing on gravel airstrips. There are vanes on the rim of the wheel which are spun up by bleeding compressed air from the turbines. It takes about 30 seconds with increased engine speed to spin up the wheel. This wheel is only 18 inches in diameter.

I think you might be underestimating the force necessary to spin up a large aircraft tire. A 747 main wheel is about 50 inches in diameter and probably weighs several hundred pounds. Just little wind vanes wouldn't do the trick. Even for the small Citation wheel it requires compressed air from the engines to get sufficient speed.

Motors to spin up the wheels would be too heavy and expensive. Say a 20 pound motor for each wheel, there are 16 main wheels on a 747 so that is 800 pounds. Each additional pound of weight on an airplane costs about $20 per year for fuel so that's $16,000 per year. Not to speak of the tremendous amount of electrical energy required to spin up several thousand of pounds of wheels shortly before landing.

At first glance, it would seem logical to spin up the tires prior to touchdown to alleviate tire wear and spin-up loads. Several methods have been devised to do this, and some have been tested with various degrees of success. One methods uses an electric motor and antother uses fan-like blades on the wheel or tire. However, the cost/weight/maintainability penalty must be assessed and traded off aginst the advantages gained. First, tire wear at spin-up is minor. Most tire wear is caused by braking and turning. Secondly, spin-up loads do not usually design a great deal of the gear--usually parts of the torque links and piston. Experience has indicated that tire pre-rotation devices are just not worthwhile. For further reading on
this subject, reference should be made to "Prerotation of Landing Gear Wheels," by H.F. Schippel, SAE Journal, Volume 52, No. 10, October 1944.

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#6
In reply to #2

Re: Aircraft landing

12/03/2009 1:40 PM

Wow, you even cited a reference in your answer too. If that doesn't doesn't deserve a GA, I'll eat my hat.

Please, sign up to this blog. The more intelligent and coherent people we can gather here, the better.

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#3

Re: Aircraft landing

12/03/2009 10:30 AM

My guess is that the added complexity, weight and costs make it less attractive than periodic tire replacement.

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#9
In reply to #3

Re: Aircraft landing

12/03/2009 11:17 PM

Challenge question.

What would be the difference between reply #3 and reply #2?

Helloooo ... Echo ... desert wind.

Quantity versus quality.

OK, ok ... I'm off topic.

P.S. Definition of desert wind.

A wind blowing off the desert, which is very dry and usually dusty, hot in summer but cold in winter.

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Guru

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#11
In reply to #9

Re: Aircraft landing

12/03/2009 11:49 PM

Guest, I don't know if your display system matches mine, but mine shows that answers #2 and #3 came in one minute apart. That strongly suggests that they were being composed simultaneously, and that neither responder saw the other's answer prior to submitting their own.

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#17
In reply to #11

Re: Aircraft landing

12/04/2009 8:10 AM

Thanks, but you've just played into the ass h*le's hand by responding to it's bait.

Just ignore it and it will leave.

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#4

Re: Aircraft landing

12/03/2009 10:41 AM

I remember 20+ years ago asking people "in the know" this question. If I recall correctly the spinning would do very little good unless it is at the perfect speed. Perfect is pretty hard to hit. In trying to get it close you would add weight and complexity to the plane. If you are not perfect then the weight might cause efficiency harm and the system might not do much good.

The tire area, especially on retractable gear of a carrier aircraft, is not a nice place to add weight and complexity to.

You also have the problem of something going wrong. This is especially bad if that something going wrong either damages the aircraft that the system is installed on or leaves FOD on the runway for someone else to hit.

The tire spinning may be done someday, it might even be done a little now. But, in a "lawsuit lottery" world it is much easier to add operating expense to the buyer than to add a purchase cost burden and a lawsuit liability burden to the manufacturer/seller.

I read a story a few weeks ago about a pro hockey player from Michigan that bought a limo from an Ohio car dealer. One night when the hockey player was not wearing a seat belt the hired limo driver fell asleep at the wheel and caused an accident. The hockey player was injured and could not play hockey any more. The hockey player sued the car dealer and the financial losses forced the car dealer out of business. If our current legal system allows this kind of nonsense then the legal liability of putting a new fangled tire spinner thing on an airplane is out of the question (especially if hockey players are allowed to buy airplanes).

PS I'm not against hockey. Any game where you can be hit by a speeding puck, smashed by a big stick, cut by sharp blades, squished by a check and hit in the face by other players sounds like a bloody good time.

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#14
In reply to #4

Re: Aircraft landing

12/04/2009 7:07 AM

Hello Guest ...

What does " FOD " stand for ? I guess it's something like " Foreign Object Detritus " ??? I am a pilot and I have never heard of this term. I remember a foreign object on a runway in France resulted in an engine fire that brought down a Concorde which ultimately led to the retirement of the the entire Concorde fleet from service. I wonder if airport operators like the black marks ( mostly rubber ) being deposited on their runways and they have to be cleaned since they might might reduce braking efficiencies. I suppose pilots like using these marks besides the numbers as landing targets ?

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Guru

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#16
In reply to #14

Re: Aircraft landing

12/04/2009 8:05 AM

FOD = Foreign Object Damage. In my experience, most often used with regard to jet engines, which generally don't like to ingest anything thicker than clouds. Think Hudson River Landing, Sully, and Skiles as an example of what FOD can do.

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#19
In reply to #14

Re: Aircraft landing

12/04/2009 1:42 PM

FOD = Foreign Object Damage. An object introduced to the system from outside the system, e.g. safety wire sucked into a running turbine engine.

DOD = Domestic Object damage. An object introduced into the system from within the system, e.g. compressor blade liberates from disk causing downstream damage in the engine flow path

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Guru
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#22
In reply to #14

Re: Aircraft landing

01/13/2010 3:32 PM

OT, I would like to know (assuming you fly out of trenton, and are a military pilot) how an F117 flight characteristics compare to a 'normal' jet with curves... does the 'creased' geometry add or take away any performance ... or where can I find some information? is it a more turbulent-creating design?

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#5

Re: Improved Aircraft Landings

12/03/2009 1:26 PM

There is plenty of information on the web (including various patents). Any commercial design would have to be super reliable and not interfere with plane's aerodynamics or weight distribution. Not very realistic for large planes like the 747, but perhaps for smaller planes. This is also totally ignoring the biggest hurdle - getting such a major design change approved in an industry tighter than even the auto industry.

Try Googling "Aircraft tire wear" for more information.

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Guru

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#7

Re: Improved Aircraft Landings

12/03/2009 9:10 PM

I believe this question was asked before.

In fact I think it may have been to this question what got me my first, or one of my first GAs.

I forget now exactly what I wrote.

It has been now at least two years.

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Guru

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#8
In reply to #7

Re: Improved Aircraft Landings

12/03/2009 11:03 PM

http://cr4.globalspec.com/thread/17808#comment184580 will give you at least one of the previous passes through this topic.

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#10

Re: Improved Aircraft Landings

12/03/2009 11:28 PM

especially on aircraft carrier landings.

Oh yeah that's a priority Just reduce a little ordinance or fuel

tailhooker??

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#12

Re: Improved Aircraft Landings

12/04/2009 1:00 AM

I remember a student asking the teacher,(retired Naval aviator, WW2 through 50's), this question in an aeronautical Engineering class, back in the mid 70's.

His answer was , that it had been tried, but it was preferable to have the tires "bark"on landing , which added a braking effect, small but necessary . Spinning the wheel before contact would increase the roll distance.

But there may have been a similar device on the Cutlass, it had a 13 foot front strut and My fuzzy memory seems to recall it having one to prevent the strut from being damaged?

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Guru

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#13
In reply to #12

Re: Improved Aircraft Landings

12/04/2009 4:19 AM

Spot on packrat. Though Guest has done most of this and I was just going to lurk; from a piloting point of view, you want that deceleration - and that 'bark' is felt. It counts off as the main gear is grounded - and the amount of 'bark/bite' indicates the amount of breaking available (wet, oily, icy, soft etc).

When this pre-rotation thing comes up, as it does regularly, craft fitted rob pilots of those important inputs.

However; when it's too fast and it kicks the gear forward.

Most main gear 'folds forward' (to some degree). Ummmmmmmm?

Your Air speed might be in a narrow band, but ground speed is a function of head or crosswind component. I've landed at virtual VTOL in "brisk" conditions.

It also removes/complicates, the option to 'touch' not quite locked gear on the deck to lock it.

Nose wheel? who cares - but if it 'locks forward' and 13 ft long- 'faster would be an advantage'.

Main gear is a different thing all together. Not all landings are "By the Book". Die or spend fu#k-all % of overall maintenance buying rubber - it's a choice?

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#15
In reply to #13

Re: Improved Aircraft Landings

12/04/2009 7:18 AM

Hi Kyzine,

I concur with what you said , especially the last , even if the rubber is expensive, it's cheap compared to pranging an airframe.

Packy

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#18

Re: Improved Aircraft Landings

12/04/2009 1:36 PM

Thank you for all the good answers. I just wasn't aware that it had been tried and dismissed. At least I know where to go when I want the answer.

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Anonymous Poster
#20

Re: Improved Aircraft Landings

12/05/2009 7:43 AM

Weight is fuel, it is cheaper to replace tires than the fuel weight a spinning device would cost.

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Anonymous Poster
#21

Re: Improved Aircraft Landings

12/06/2009 2:14 PM

This concerned me some years ago and the best explanation that I found is that it is a bit like a dragster warming its tyres before a race, the tyres are designed to grip at temperature and the skid, as they come up to speed, does that nicely. Just watch a race car or bike try to go round corners with cold tyres, and on an aircraft coming down from cruise altitude, the tyres are very cold (I wouldn't want to lick them). I know it seems a waste of rubber, but as one other correspondent noted the added weight of a spin-up device is added cost, complexity and weight - all undesirable.

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