B737 Gear, wheels uncovered when retracted

[LambOfGod]

I thought it was only the 100, 200 & 300 series that the wheel hub and part of the tyre were not covered. But after looking at the 800 in cruise, the wheels were there.

Does this keep the cost down more than the increased drag reduces economy? And do the exposted wheels get more fatigued from high airspeed and extreme cold? Just seems a little odd to me... Is the gear bay, on say a B777, pressurised?

And what is the smoke that comes from the tyres and why? I was told once but that was when I was young and did not understand things very well...

Thanks for your answers:ok:

[flyboyike]

By "smoke from tires", do you mean on landing?

[Admiral346]

None of the gearwells are pressurised, on no plane I know of. So the tyres are always subjected to the cold and pressure changes. It is amazing though to see how long the brake temp stays warm, considering how cold it is out there... I have not heard of tyres wearing down faster when not covered and I don't think it makes any difference whatsoever.

But I have no way to prove this to you...

Maybe someone else knows more

Nic

edit:

If you are talking about the smoke upon landing, it is from rubber being burnt when the wheel starts spinning. There is a lot of friction, kind of like a locked brake on a car, just the other way around...
And I have been told by engineers at my flight school, that there were experiments to get a wheel spinup before touchdown to reduce tyrewear, but the speed of the tyre would have to match groundspeed of the aircraft pretty exactly, other wise theere wouldn't be much gain. And as that iis too hard to achive, it seems to be cheaper to just have a little more wear on the tyres instead of flying spinup motors for the wheels around...

Nic

[barit1]

Of course the original 737 was built as a short-medium range ship, and I'm sure Boeing thought the wheel doors wouldn't pay off. I doubt anyone would take issue with their KISS approach in 1966.

Today is 42 years later, with the BBJ flying ETOPS several times the original -200 optimum range, & we might argue with Boeing about this. In fact this thread ran rather lengthy in pprune 2-3 years ago. Right now I can't seem to find it.

But commonality is a virtue, too.

[LambOfGod]

Yeah, I knew that some of the smoke is burning rubber. Thats why there are black marks on the runway:)
But, when I went to an aviation museum there was a nose gear from some sort of airliner... The guide explained that it was not completely burning rubber but gas and that the tyres need to be re-inflated before TO. Just cant remember what the gas was. I'm guessing a hard landing would increase the pressure it the tyres a fair bit so possibly there is some release valve?

And why havn't Boeing put gear doors on the 737NG?, or is there... Even an optional extra:confused:

[Ex Cargo Clown]

But, when I went to an aviation museum there was a nose gear from some sort of airliner... The guide explained that it was not completely burning rubber but gas and that the tyres need to be re-inflated before TO. Just cant remember what the gas was. I'm guessing a hard landing would increase the pressure it the tyres a fair bit so possibly there is some release valve?

I'd hope that the gas isn't burning, it's nitrogen.

If I could make that bloody thing react I'd be a millionaire !!!

[hoover1]

the tires are filled with nitrogen and i don't think you would see it when it came out if it ever did wich it does not unless the tire blows. they are not refilled after every landing only when need be.

the outside of the main gear tires have a cover on them that helps protect them from the wind and weather when flying although the tires fit snuggly int he wheel well and do not produce much drag. the reason there is no gear doors is that is more weight and something to fail. they try to make the plane as reliable as they can. plus it just dosen't need them.

the wheel wells are not presurized becuase everytime you lowered the gear there would be a massive loss of pressure that the outflow valves would not be able to overcome. like opening a big door inflight. sometimes the gear is lowered above 10k feet to get the plane to slow down if needed.

[LambOfGod]

Okay, sweet, nitrogen...:cool:

I don't mean mixed pressure with the cabin, just a secondary section, with its own pressure. I thought maybe the tyre could explode;)

[captjns]

No main gear doors mean fewer sequencing valves and system processes to raise and lower the gear… thus lower maintenance. Easier for manual gear extension versus older Boeings such as the 707 and 727 where one had to crank the gear doors open first before lowering the landing gear.

[BOAC]

Perhaps it is worthwhile also to correct the misleading thread title? The wheels on the 737 do not 'stick out' when retracted. They are flush with the skin, but uncovered. I suspect the drag caused at this point on the airframe where I would suspect any 'laminar' flow has long since given up the ghost is not great? Therefore no 'biggie'. Also one less mechanical bit to go wrong.

[tttoon]

And on the pressurizing of the wheel well, the differential pressure between the cabin (or possible pressurized wheel well) and the outside is about 8psi max, while the wheel is inflated to 160psi. So the pressurization would only reduce the differential by 5% (168psi in cruise vs. 160 at landing and T/O), for a whole lot of weight. Plus the cold at altitude helps too.

[Mad (Flt) Scientist]

Perhaps it is worthwhile also to correct the misleading thread title? The wheels on the 737 do not 'stick out' when retracted. They are flush with the skin, but uncovered. I suspect the drag caused at this point on the airframe where I would suspect any 'laminar' flow has long since given up the ghost is not great? Therefore no 'biggie'. Also one less mechanical bit to go wrong.

Actually, one of the larger potential sources of drag in such a configuration is if the airflow gets inside the wheel well and recirculates; all that wasted energy with airflow inside the wheel well has to come from somewhere, which means drag.

That's why even with exposed wheels you'll still see an attempt to seal the tyres against the edges of the wheel well, with brush seals or similar; the extra mass of the seals is small, and the benefit woirthwhile.

[james ozzie]

Does the low temperature of the tyre have any significant influence on its pressure at touch down? Assuming the wheel is well & truly chilled in the cruise, I assume it could still be very cold at touch down, even if dangled for a few minutes on approach? But I guess there have been many landings on chilled tyres so this is not really an issue?

[LambOfGod]

correct the misleading thread title

Yeah, I changed it to "B737 Gear, Wheels uncovered during cruise" but nothing happened.:ugh:

If you look under the original post you will see the Last edited part.:=

[Mad (Flt) Scientist]

correct the misleading thread title

Yeah, I changed it to "B737 Gear, Wheels uncovered during cruise" but nothing happened.:ugh:

If you look under the original post you will see the Last edited part.:=

It changed the title for your post, but after a few minutes (2?5?) only a site admin or mod can change a thread title on a vBulletin forum. Nothing you can do about it now.

[BigHitDH]

Classic 737's used to have inflatable seals around the MLG doors. It didn't take long for these to be considered too unreliable/expesnsive (bleed air reqs) for them to be dropped in favour of the current rubber seals.

[MyNameIsIs]

The Cessna 210 used to have main gear doors, but they were done away with on later models.

No real need for them because apparently, like BOAC suggested, the airflow is not as 'critical' back there, and as such there was no real benefit of having a smooth surface for the air to flow over.

Also saved a few kilos, less to go wrong.

[showtime777]

There would be a weight penalty too with the addition of doors and the hydraulic system required to operate them.

[Hasselhof]

Cessna 210 used to have main gear doors

No gear doors also allowed for a higher gear extension speed (ie. 165kts on an N model against 140kts on an M). An engineer I spoke to told me that many of the older models had the doors removed as a retrofit as people had a tendency of extending them at too high an airspeed and ripping them off.

[LambOfGod]

But I feel so much safer when the wheels are protected. What will the general public do?:ooh:

[MyNameIsIs]

They probably don't know.

And if they ask about it, just tell 'em that its normal and everything else that covers them up is weird!

Just like telling people who are scared about flying in "small planes" that there's less to go wrong on them than on the airliners! :}

[porch monkey]

The general public will continue to get on 737's, as they have for 40 odd years. They don't know, and don't care.

[HAWK21M]

A simpler, less complicated & no sequence valves needed,as the Doors [fwd/Mid/Aft] are attached to the Strut.
regds
MEL

[barit1]

But I feel so much safer when the wheels are protected.

Protected from WHAT?

Air?

:}

[framer]

Lamb of God,
When the Designers are designing a new plane they are always looking for ways to reduce weight . I don't think there are many things on aircraft that are there "just cause it's nice".
They fill the tyres up with Nitrogen rather than air because it is an inert gas, it expands and contracts less than air and it carries less moisture (think corrosion) .
Framer
(ps my opinions only please correct if I am wrong)

[barit1]

framer, in most respects you are quite right, but there's a bigger issue: Airlines like things that will make them more money, & give them a competitive edge.

Thus IFE systems, & other gee-whiz gadgets that will attract pax or reduce cost. Think A380 with 2 seats in front and 500-600-700 in back. And an airline will accept 100# increase in engine weight if it saves 200# fuel on a long flight.