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How Planes Check Their Own Tire Pressure  
User currently offlineThrust From United States of America, joined Sep 2003, 2691 posts, RR: 10
Posted (10 years 2 weeks 6 days 15 hours ago) and read 3615 times:

I just had to ask this question..I'm not very experienced in this field either, so forgive me if this question seems grade school level. How are planes able to check their own tire pressure? Do the pilots measure the pressure from gauges, or do the planes just do it automatically? Thanks.


Fly one thing; Fly it well
21 replies: All unread, jump to last
 
User currently offlineSlamClick From United States of America, joined Nov 2003, 10062 posts, RR: 68
Reply 1, posted (10 years 2 weeks 6 days 15 hours ago) and read 3559 times:

Hey, I've flown planes that did that and I'd like to know too!

Had a main tire go flat over Greenland one day. We talked it over and decided that we wished we didn't even know. We were not going to land for another five hours. And what could we do? Not land? Land with the gear UP?

The one thing we did was to inform the airport of arrival and ask to have the "equipment standing by." They asked if we were declaring an emergency because they could not roll the equipment unless we did. We told them that we did not have an "emergency" but we knew that we had one flat main tire and nearly three hundred souls on board - but they could make the call.

We got the firetrucks.

So I'd like to know how we found out about the flat. I'd assume that the pressure sensor sends the message to the non-rotating parts of the gear electrically through some sort of brush-and-armature arrangement but I just don't know.

Anyone?



Happiness is not seeing another trite Ste. Maarten photo all week long.
User currently offlineMD11Engineer From Germany, joined Oct 2003, 14138 posts, RR: 62
Reply 2, posted (10 years 2 weeks 6 days 14 hours ago) and read 3528 times:

Ok, concerning the MD-11, there is a capacitive pressure transducer fitted to each wheel (a small cylinder attached to a hollow stud on the rim, similar to the fill valve). From there the signal goes through a steel braid protected wire to a transmitting unit inside the axle. Since the transducer rotates with the wheel, the signal has to be transmitted to the wireloom in the fixed axle through this transmitter, which basically consists of two coils, one rotating with the wheel and the other one being fixed in the axle. I will see if I can get some pictures.
From there the signals of all wheels go to the Brake Temperature Tire Pressure Computer in the Center Accessory Compartment. There the signal gets digitized and sent by seriel data bus to the Display Electronics Units (DEUs) and from there to the Display Units (DUs).
As the name of the computer says, it also processes the brake temperature signals from the main wheels.

Jan


User currently offlineSlamClick From United States of America, joined Nov 2003, 10062 posts, RR: 68
Reply 3, posted (10 years 2 weeks 6 days 13 hours ago) and read 3462 times:

Hey MD11Engineer if I am reading you correctly the transmittal from rotating to non-rotating is done without "solid state" connection? That would certainly make more sense than the brush system that I had envisioned - less wear.





Happiness is not seeing another trite Ste. Maarten photo all week long.
User currently offlineMD11Engineer From Germany, joined Oct 2003, 14138 posts, RR: 62
Reply 4, posted (10 years 2 weeks 6 days 12 hours ago) and read 3441 times:

Acc. to the wiring diagram / schematic, the pressure pick up uses a capacitance bridge, so alternating currents would be used anyway. They can easily be coupled using two coils acting like a transformer, so no wearable part like a carbon brush required.

Jan


User currently offlineKaddyuk From Wallis and Futuna, joined Nov 2001, 4126 posts, RR: 25
Reply 5, posted (10 years 2 weeks 6 days 6 hours ago) and read 3361 times:

TPIS... Fantastic System... such a shame we only have 5 aircraft with it installed...


Whoever said "laughter is the best medicine" never had Gonorrhea
User currently offlineKlaus From Germany, joined Jul 2001, 21520 posts, RR: 53
Reply 6, posted (10 years 2 weeks 6 days 5 hours ago) and read 3346 times:

VCRs use the same principle to couple the signals to/from the rotating head drum. It´s by far the best way to deal with this kind of problem.

As far as I know there are some systems for ground cars which use rotating sensors and external transmitters (outside of the hub); But the downside in that case is that you need the wheel to rotate in order to get the signal regularly. And that´s obviously not good enough for airplane landing gear as the above example demonstrates...


User currently offlineJfkaua From United States of America, joined Aug 2004, 1000 posts, RR: 3
Reply 7, posted (10 years 2 weeks 6 days 4 hours ago) and read 3335 times:

hmm just curious.. did you get this from the gmc truck commercial... i was thinking the same thing  Laugh out loud

User currently offlineVidens From Argentina, joined Mar 2004, 133 posts, RR: 0
Reply 8, posted (10 years 2 weeks 6 days 3 hours ago) and read 3321 times:

These systems have existed on trucks for many years... Surprisingly, it's not a widespread thing in the US... I have no clue why though...


Travel? Why would i travel if I can watch it on TV?
User currently offlineCaptoveur From , joined Dec 1969, posts, RR:
Reply 9, posted (10 years 2 weeks 6 days 2 hours ago) and read 3309 times:

"Surprisingly, it's not a widespread thing in the US... I have no clue why though..."

Simple: Cost

Most trucking companies large or small do not want this extra option, which will add to the initial cost of the truck and add little to no value. This will also be one more thing that probably fails pretty often and is not cheap or easy to replace.

If you find a truck driver with half a brain (a hard thing to do) they will typically check their own tire pressures before every trip, because they know that is better than being stuck along side the road with an exploded tire.


User currently offlineVC-10 From United Kingdom, joined Oct 1999, 3708 posts, RR: 34
Reply 10, posted (10 years 2 weeks 5 days 19 hours ago) and read 3246 times:
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TPIS... Fantastic System... such a shame we only have 5 aircraft with it installed...

Kaddyuk you work for VS don't you? I think you better have a closer look at the a/c.


User currently offlineMr Spaceman From Canada, joined Mar 2001, 2787 posts, RR: 9
Reply 11, posted (10 years 2 weeks 5 days 9 hours ago) and read 3124 times:

Hi guys.

>> Captoveur, Hey hey hey. Come on now. Regarding your comment about truck drivers having half a brain ... if that!

Well, I'll have you know that ... "I resemble that remark." hehe (check my profile). BTW, the next time you're driving away from a supermarket or shopping mall, try driving around the back of the store so you can see what's parked against the store's loading docks, or waiting for their turn to ..... so the store is stocked up for the public. That's right, they're called trucks, and they make it there because of truck drivers!

Anyhow, gentlemen, here's a few photos of main landing gear that show these devices that measure an airliner's tire pressures. You can see them attached to the wheel hubs.


View Large View Medium
Click here for bigger photo!

Photo © Paul Barbee
View Large View Medium
Click here for bigger photo!

Photo © Bo Kim



Chris  Smile



"Just a minute while I re-invent myself"
User currently offlineThrust From United States of America, joined Sep 2003, 2691 posts, RR: 10
Reply 12, posted (10 years 2 weeks 5 days 2 hours ago) and read 3074 times:

Appreciate your help greatly, all participants. This system of checking pressure seems 100 years ahead of its time!!! We definitely need more of them Big thumbs up

I would imagine overtime the U.S. is going to be hard-pressed to apply these advanced systems to the majority of their aircraft. All cars and planes should come with them. Not applying them because of cost jeopardizes safety. I believe safety and efficiency are worth the cost no matter what.



Fly one thing; Fly it well
User currently offlineThrust From United States of America, joined Sep 2003, 2691 posts, RR: 10
Reply 13, posted (10 years 2 weeks 5 days 2 hours ago) and read 3071 times:

What other aircraft besides the MD-11 feature these devices which can check the pressure of tires without human assistance?


Fly one thing; Fly it well
User currently offlineThrust From United States of America, joined Sep 2003, 2691 posts, RR: 10
Reply 14, posted (10 years 2 weeks 5 days 2 hours ago) and read 3069 times:

I would imagine most modern jets are equipped with these devices.


Fly one thing; Fly it well
User currently offlineMeister808 From United States of America, joined Jan 2000, 973 posts, RR: 1
Reply 15, posted (10 years 2 weeks 3 days 14 hours ago) and read 2948 times:

Not to further distract this thread, but:

It would seem with the giant number of truck tires laying shredded on the road in the U.S., such a system could be a sensible addition to truck fleets, yes?

-Meister



Twin Cessna 812 Victor, Minneapolis Center, we observe your operation in the immediate vicinity of extreme precipitation
User currently offlineThrust From United States of America, joined Sep 2003, 2691 posts, RR: 10
Reply 16, posted (10 years 2 weeks 2 days 1 hour ago) and read 2869 times:

Tire-pressure checking systems are worth the expense. in the long run what is more important? Money? Or life-saving technology? Personally, I would give up all the money in the world just to be able to live. I would imagine as time goes on, and as technology moves ahead, these devices will become more common everywhere.


Fly one thing; Fly it well
User currently offlineCaptoveur From , joined Dec 1969, posts, RR:
Reply 17, posted (10 years 2 weeks 2 days ago) and read 2872 times:

"It would seem with the giant number of truck tires laying shredded on the road "in the U.S., such a system could be a sensible addition to truck fleets, yes?"


Not really, if you drive 2 hours on the same highway you may see two alligator backs laying along side the road, this is based on my own observations driving between San Antonio and Corpus Christi, TX as well as between Dayton and Cincinnati, OH. Both these stretches of road have many many many trucks passing through there every hour. A roadside call for a truck tire may cost anywhere from $350 to $500, sometimes more including the tire, depending on how bad the shop wants to stick it to you.

I used to work for a trucking company they operated 15 trucks all over most of the US. While these incidents did take place with a tire coming apart they were not by any means a weekly occurence, even more rare if you eliminate times when a tire is flat due to a nail, or the tire is replaced just because it has reached its replacement mileage. Also, tire dealers would be the first to tell you, sometimes tires just come apart regardless of the pressure inside and a new tire is as likely or even more likely than a recap to fail for no particular reason. Some of the engineers on here can figure out how much heat and stress a 22.5in low profile tire goes through running at 70mph all day every day if they are really curious.

The price the company I worked for paid for their International 9800i tractors was around $110,000, they are considered to have a 5 year useful life, at which time they should be fully depreciated and traded in on new equipment.

That price tag was without anything to measure the tire pressure. Say the tire pressure reading equipment cost an additional $500 per wheel initially (very conservative guess).. that is an extra $5000 per tractor, now we are talking $115,000 per unit, we haven't even considered the cost per trailer. Then we consider how often these things are going to break and the hours that it will take to fix them, remember, you have 18 of these thingies per truck moving down the road. When they do break that is time you both have to pay a mechanic and take the lost time from not moving. When you are not moving you are not making money. If these things would actually increase time on the road. great. However, it would have to be a pretty big time savings and I honestly don't see how it could be.

Without getting super nit picky, the economics do not make sense to put them on heavy trucks, especially considering how long some trailers sit without moving on drop lots. Brake lines, steel wheels, tires and other things corrode, deteriorate and have enough problems already without adding another expensive item to break, corrode, or fall off. An item which most companies would probably not bother to repair because the cost to add/fix this would not add any kind of real value to the asset and it would not cause a signifigant increase in revenue or resale value. Also, checking the tires before leaving on a trip, and if smart, at the end of every rest period is going to be just as good as messing with a new gadget that is really only going to tell you information you already know, that your tire is now flat.

When a large truck does have a flat they very rarely go skidding off the road, into the ditch, where they roll over, burst into flames, and possibly kill 300 people. On rare occasions blowouts do cause accidents but once again, that is the exception, not the rule. That is the short version of why Airliners need tire pressure instrumentation but trucks do not.


User currently offlineMinuteman From United States of America, joined Aug 2000, 271 posts, RR: 0
Reply 18, posted (10 years 1 week 5 days ago) and read 2712 times:

I should mention that many cars don't directly measure the pressure in a tire. Instead they compare the rotational speeds, so if one wheel is getting low, it spins faster (sensors may already be there for anti-lock/traction control). The trouble with this is if you're driving on a rough or gravel road, some wheel slip can trick the computer into thinking there's a flat.

User currently offlineN328KF From United States of America, joined May 2004, 6491 posts, RR: 3
Reply 19, posted (10 years 1 week 4 days 16 hours ago) and read 2682 times:

The HMMVW (and civilian derivatives) have this system in place. In fact, it can dynamically alter the pressure as well.


When they call the roll in the Senate, the Senators do not know whether to answer 'Present' or 'Not guilty.' T.Roosevelt
User currently offlineMD11Engineer From Germany, joined Oct 2003, 14138 posts, RR: 62
Reply 20, posted (10 years 1 week 4 days 14 hours ago) and read 2664 times:

Captoveur,

Going to work a few years ago, I was driving on an Autobahn behind a cistern semi truck, when suddenly on of it´s trailer rear tires blew with a loud bang (comparable to the explosion of a grenade).
Pieces of rubber shredded and dented the fender of a BMW that was just passing the wheel. The truck started weaving and snaking all over the road, but the driver got it under control and managed to stop it on the shoulder. I stopped as well to offer assistance and myself as a witness (as did the BMW). The BMW driver was lucky that the explosion just happened beside his rear fender and not the passenger compartment, because parts of the fender and bumper got torn off and the metal heavily dented, they would have certainly penetrated the side windows and injured the driver.

Jan


User currently offlineThrust From United States of America, joined Sep 2003, 2691 posts, RR: 10
Reply 21, posted (10 years 1 week 4 days 4 hours ago) and read 2622 times:

Wow...the Autobahn certainly is not a place for a tire to explode!!! Cars on the Autobahn definitely need these devices to check tire pressure!!!! I'm surprised the driver actually survived...few drivers I've heard are ever lucky enough to walk away unhurt on that highway. Is it true the Autobahn can support the weight of a fully loaded 744 on it?


Fly one thing; Fly it well
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