SuseJ772
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Are The 737 Wheels On The Outside In This Picture?

Wed Sep 24, 2008 7:21 pm


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When the main wheels on the 737 are retracted are they still exposed to the outside of the plane? I didn't think so, but the above picture sort of looks like it in both the -200 and the -300. If they aren't, what are the black circles under the body?
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KLASM83
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RE: Are The 737 Wheels On The Outside In This Picture?

Wed Sep 24, 2008 7:23 pm

It is a cool pic, is it not?  . As I remember, the 73's do not come with a MLG door, saving on weight, thus making it so that the tires make an aerodynamic seal with the fuselage. Hope that helps!


->Edited for spelling. And Grammar. This post talk gooder now.

[Edited 2008-09-24 12:24:59]
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RE: Are The 737 Wheels On The Outside In This Picture?

Wed Sep 24, 2008 7:24 pm

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KELPkid
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RE: Are The 737 Wheels On The Outside In This Picture?

Wed Sep 24, 2008 7:27 pm



Quoting SuseJ772 (Thread starter):
When the main wheels on the 737 are retracted are they still exposed to the outside of the plane? I didn't think so, but the above picture sort of looks like it in both the -200 and the -300. If they aren't, what are the black circles under the body?

That would be the tires. They lie flush with the fuselage of the aircraft when retracted, and there is an aerodynamic "hubcap" in the middle of the outboard wheel to minimize drag. It saves on weight and landing gear system complexity. IIRC, there is even a piece of rubber trim inside the wheel well to keep the seal tight once the gear are retracted.
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SuseJ772
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RE: Are The 737 Wheels On The Outside In This Picture?

Wed Sep 24, 2008 7:29 pm

I found these pictures too and they all look like the wheels are exposed to the outside.


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Quoting KLASM83 (Reply 1):
thus making it so that the tires make an aerodynamic seal with the fuselage

This would seem to be real prone to problems.

I can't believe I never knew this. I guess you learn something new everyday.
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KELPkid
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RE: Are The 737 Wheels On The Outside In This Picture?

Wed Sep 24, 2008 7:32 pm



Quoting SuseJ772 (Reply 4):
This would seem to be real prone to problems.

I can't believe I never knew this. I guess you learn something new everyday.

Less prone to trouble than an additional hydraulically actuated door that has to be closed when the gear is both retracted and extended  Smile (not to mention the weight of the additional aluminum in the door, additional hydraulic tubing, electronic sequencers, etc. etc.)
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DfwRevolution
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RE: Are The 737 Wheels On The Outside In This Picture?

Wed Sep 24, 2008 7:37 pm



Quoting SuseJ772 (Reply 4):
I can't believe I never knew this. I guess you learn something new everyday.

Same design philosophy is used on the E170/E190 series


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September11
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RE: Are The 737 Wheels On The Outside In This Picture?

Wed Sep 24, 2008 7:48 pm

Even better pictures ...


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Photo © Christian Mueller



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roseflyer
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RE: Are The 737 Wheels On The Outside In This Picture?

Wed Sep 24, 2008 8:04 pm



Quoting KLASM83 (Reply 1):
It is a cool pic, is it not? . As I remember, the 73's do not come with a MLG door, saving on weight, thus making it so that the tires make an aerodynamic seal with the fuselage. Hope that helps!

Just a correction, but there are main landing gear doors. They just don't cover the tire and wheel. The main landing gear doors cover the strut as it moves into the wing/body/wing to body fairing.

Quoting KELPkid (Reply 5):
(not to mention the weight of the additional aluminum in the door, additional hydraulic tubing, electronic sequencers, etc. etc.)

You overestimate the 737. There aren't electronic sequencers. It's manually driven by cables, solenoids and a transfer valve.
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RE: Are The 737 Wheels On The Outside In This Picture?

Wed Sep 24, 2008 8:05 pm



Quoting DfwRevolution (Reply 6):
Same design philosophy is used on the E170/E190 series

Also the CRJ.


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RE: Are The 737 Wheels On The Outside In This Picture?

Wed Sep 24, 2008 8:10 pm



Quoting SuseJ772 (Thread starter):

This topic is well covered and comes up all the time. Along with the B737 there are several other jets that have wheels exposed.
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RE: Are The 737 Wheels On The Outside In This Picture?

Wed Sep 24, 2008 8:22 pm

When the B737 first went into service, it had an inflatable skirt to seal the main gear wells after the gear was retracted. It was later decided that this was too complex and not worth the small drag advantage. From then on, the 737 series has had a simple exposed wheel with a smooth hubcap on the outside wheel.
 
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RE: Are The 737 Wheels On The Outside In This Picture?

Wed Sep 24, 2008 8:31 pm



Quoting KELPkid (Reply 3):
It saves on weight and landing gear system complexity.

Why is it only a few aircraft that do this and not all of them?
 
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RE: Are The 737 Wheels On The Outside In This Picture?

Wed Sep 24, 2008 9:26 pm



Quoting SuseJ772 (Reply 4):
This would seem to be real prone to problems.

What trouble? It's a bit of rubber around the gear well to help smooth out the airflow.

You can see it at the bottom edge of this:


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Quoting SpeedBirdA380 (Reply 12):
Why is it only a few aircraft that do this and not all of them?

A "real" gear door will result in better aerodynamics. But it will be heavier and more complex. For a short range aircraft a small cruise aerodynamic penalty may be outweigh by the extra weight and complexity.

OTOH, given that the range of the 737 has increased rather significantly since the early days, I'd not be at all surprised to see its replacement have "real" gear doors.
 
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United787
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RE: Are The 737 Wheels On The Outside In This Picture?

Wed Sep 24, 2008 9:47 pm



Quoting SuseJ772 (Reply 4):
I can't believe I never knew this. I guess you learn something new everyday.

I saw the same pic and wondered why I never knew that either.

Although the more I look at the picture, the odder it looks...gives another meaning to hanging dirty...too exposed...but some underpants on that thing for pete's sake...
 
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RE: Are The 737 Wheels On The Outside In This Picture?

Wed Sep 24, 2008 10:34 pm



Quoting United787 (Reply 14):

Although the more I look at the picture, the odder it looks...gives another meaning to hanging dirty...too exposed...but some underpants on that thing for pete's sake...

And so being endowed with the rather filthy and yet amusing organ that occupies my skull, I immediately flashed to mental images of various retractable...

...never mind.  angel   duck 
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RE: Are The 737 Wheels On The Outside In This Picture?

Wed Sep 24, 2008 11:38 pm

I honestly can't believe that I've looked at THOUSANDS of pictures of 737's on a.net, let alone worked on every a/c in WN's fleet when I was a FA 6 years ago, and failed to realize those were the tires themselves, not a bay door.

Wow, that's the one thing I've learned today!


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RE: Are The 737 Wheels On The Outside In This Picture?

Thu Sep 25, 2008 12:12 am



Quoting SuseJ772 (Reply 4):
This would seem to be real prone to problems.

Really? So why is the 737 the most popular commercial aircraft in the world?  Silly
 
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RE: Are The 737 Wheels On The Outside In This Picture?

Thu Sep 25, 2008 3:40 am



Quoting AV8orWALK (Reply 16):
let alone worked on every a/c in WN's fleet

Totally thought you were about to say you'd been a WN mechanic and never noticed a lack of doors.
Glad that's not the case!!!!! Lol.

Quoting Pilotboi (Reply 17):
Really? So why is the 737 the most popular commercial aircraft in the world?

Calm down- the most popular aircraft in the world isn't without design flaw (trust me, I work on them). But the gear door thing is really a non-issue.

AND, folks, it makes things WAY more convenient and even SAFE when you're servicing things in the wheel well. On other aircraft, you have to drop the doors to service those systems. I've had coworkers (in the past) been given concussions when they didn't hear the warning that the doors were about to drop open. No exaggeration.
 
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HAWK21M
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RE: Are The 737 Wheels On The Outside In This Picture?

Thu Sep 25, 2008 10:05 am

http://www.b737.org.uk/images/wheelwellboth.jpg
Lower view.
The Hub cap present helps reduce drag by providing a smoother surface.
The b737 has got Three Doors per MLG....Inner/outer & Middle.These doors are attached to the strut directly or via linkage depending on the door & move with it.

regds
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RE: Are The 737 Wheels On The Outside In This Picture?

Thu Sep 25, 2008 3:45 pm

From what I remember the drag-penalty of the gears being exposed was actually less than the weight-penalty of having doors that covered the whole landing gear.


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HAWK21M
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RE: Are The 737 Wheels On The Outside In This Picture?

Thu Sep 25, 2008 4:46 pm



Quoting Blackbird (Reply 20):
From what I remember the drag-penalty of the gears being exposed was actually less than the weight-penalty of having doors that covered the whole landing gear.

Any idea,what caused this......I thought Weight saving & simple mechanism overruled complicative sequencing & added weight.

regds
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G4Doc2004
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RE: Are The 737 Wheels On The Outside In This Picture?

Thu Sep 25, 2008 7:42 pm

The fastest business jet flying right now is the Citation X (Mach .92) and it's wheels are exposed a-la the B-737 as well. When retracted, the edge of the tire sits just below the fairing.
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RE: Are The 737 Wheels On The Outside In This Picture?

Thu Sep 25, 2008 8:05 pm



Quoting HAWK21M (Reply 19):

Great pic, Hawk!

RoseFlyer - look at the photo in Hawk's post. I think you were right on the issue of extending the wheel well on the thread in CivAv on the GTF. While there might be room for a gain of a couple of inches, I don't think it would be enough to overcome the issues faced by a longer LG strut because of the keel structure.

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FlyASAGuy2005
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RE: Are The 737 Wheels On The Outside In This Picture?

Thu Sep 25, 2008 8:50 pm

Didn't hear brush seals mentioned.

I know there is a specific purpose (hence the name brush SEAL) but what exactly? I first noticed it working for a regional on the CRJs. I asked a mech and he gave me a pretty detailed response but this was 2 years ago so I don't really remember Big grin .
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RE: Are The 737 Wheels On The Outside In This Picture?

Thu Sep 25, 2008 10:56 pm



Quoting SpeedBirdA380 (Reply 12):
Why is it only a few aircraft that do this and not all of them?

Bigger aircraft have more space for a door and the related mechanism. Also, widebodies have big bogies, meaning it's not a simple round shape in a round hole. You'd get all sorts of drag between the wheels.
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KELPkid
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RE: Are The 737 Wheels On The Outside In This Picture?

Thu Sep 25, 2008 11:27 pm



Quoting FlyASAGuy2005 (Reply 24):
Didn't hear brush seals mentioned.

Ahem....

Quoting 113312 (Reply 11):
When the B737 first went into service, it had an inflatable skirt to seal the main gear wells after the gear was retracted



Quoting KELPkid (Reply 3):
IIRC, there is even a piece of rubber trim inside the wheel well to keep the seal tight once the gear are retracted.



Quoting Rwessel (Reply 13):
It's a bit of rubber around the gear well to help smooth out the airflow.

 Wink
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pilotpip
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RE: Are The 737 Wheels On The Outside In This Picture?

Fri Sep 26, 2008 3:59 am

The Global Express has exposed mains as well.

BTW, on Embraers the brushes can't be deferred.
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HAWK21M
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RE: Are The 737 Wheels On The Outside In This Picture?

Fri Sep 26, 2008 8:44 am



Quoting Pilotpip (Reply 27):
BTW, on Embraers the brushes can't be deferred.

Whats the reason stated?
On the B737,there is a tolerance to the amount of wear permitted on the rubber seals.
regds
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RE: Are The 737 Wheels On The Outside In This Picture?

Fri Sep 26, 2008 7:42 pm

Some airplanes leave their main gear hanging out in the wind even after they're retracted:


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rwessel
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RE: Are The 737 Wheels On The Outside In This Picture?

Fri Sep 26, 2008 10:02 pm



Quoting 2H4 (Reply 29):
Some airplanes leave their main gear hanging out in the wind even after they're retracted:

True, although I'm almost tempted to make a distinction based on why you move the gear. In those cases it's not for drag reduction in flight, rather it's required to be able to land on water (well, at least if you want to land on water without having to flip the airplane back over and drying it out before using it again).
 
2H4
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RE: Are The 737 Wheels On The Outside In This Picture?

Fri Sep 26, 2008 10:08 pm



Quoting Rwessel (Reply 30):
In those cases it's not for drag reduction in flight, rather it's required to be able to land on water

And to get out of the way of the radar, sure. I was just pointing out some fun and quirky exceptions to the usual objective of retractable landing gear.  Smile

2H4
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jetmech
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RE: Are The 737 Wheels On The Outside In This Picture?

Sat Sep 27, 2008 3:15 am



Quoting Rwessel (Reply 30):
without having to flip the airplane back over and drying it out before using it again).

This is what happens when you do land on water with the wheels extended  Wow! !



Regards, JetMech
JetMech split the back of his pants. He can feel the wind in his hair :shock: .
 
2H4
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RE: Are The 737 Wheels On The Outside In This Picture?

Sat Sep 27, 2008 3:51 am



Quoting JetMech (Reply 32):
This is what happens when you do land on water with the wheels extended!

That guy just needs more practice. Here's what you can do if you've got proper technique:

http://i33.tinypic.com/mvnd60.jpg

http://i38.tinypic.com/d6tue.jpg

http://i37.tinypic.com/x5nsd1.jpg

http://i34.tinypic.com/6ir6e0.jpg

http://i38.tinypic.com/ak9c.jpg


 bigthumbsup 

2H4
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jetmech
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RE: Are The 737 Wheels On The Outside In This Picture?

Sat Sep 27, 2008 3:58 am



Quoting 2H4 (Reply 33):
That guy just needs more practice.

True. I bet the plane was not the only thing hung out to dry after that incident!

Quoting 2H4 (Reply 33):

I remember those pictures! I think there was great debate at the time about whether the situation was genuine or photo-shopped. Do you know what the final consensus was  scratchchin  ?

Regards, JetMech
JetMech split the back of his pants. He can feel the wind in his hair :shock: .
 
2H4
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RE: Are The 737 Wheels On The Outside In This Picture?

Sat Sep 27, 2008 4:04 am



Quoting JetMech (Reply 34):
I think there was great debate at the time about whether the situation was genuine or photo-shopped. Do you know what the final consensus was?

No, I don't even recall that discussion. I know what those airplanes are doing can be done, though, and I can't imagine someone would go to such Photoshopping trouble for such little point.

2H4
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jetmech
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RE: Are The 737 Wheels On The Outside In This Picture?

Sat Sep 27, 2008 4:26 am



Quoting 2H4 (Reply 35):
I know what those airplanes are doing can be done, though, and I can't imagine someone would go to such Photoshopping trouble for such little point.

Fair enough. A little bit of Googling and Youtubing brought up this.



Regards, JetMech
JetMech split the back of his pants. He can feel the wind in his hair :shock: .
 
don81603
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RE: Are The 737 Wheels On The Outside In This Picture?

Sat Sep 27, 2008 4:14 pm



Quoting JetMech (Reply 36):

Holy ***!!! Talk about no room for error! This has to be a pucker factor of at least 250. Thanks for sharing though.
.
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KELPkid
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RE: Are The 737 Wheels On The Outside In This Picture?

Sun Sep 28, 2008 11:49 pm

Here's one for you all to consider (and I ask this innocently, since I'm a single-engine piston GA pilot, and darn near 100% of the time, we'd be able to safely stop on the ground with the remaining field length if it happened to us  Wink ) :

What happens if there's a tire blowout after V1? Do you continue the takeoff and not retract the gear? How does the design of the 737's main gear wheel wells play into this decision (for all the 737 drivers out there...)? Is it more imperative to reduce drag or is there too much of a risk that the remains of a blown tire on the mains will jam up the works?
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HAWK21M
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RE: Are The 737 Wheels On The Outside In This Picture?

Mon Sep 29, 2008 8:15 am



Quoting KELPkid (Reply 38):
How does the design of the 737's main gear wheel wells play into this decision

On the -NGs the "frangible fitting" will avoid that gear to retract.If its a tire burst,to protect the wheel well components.
regds
MEL
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MD11Engineer
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RE: Are The 737 Wheels On The Outside In This Picture?

Mon Sep 29, 2008 9:15 pm



Quoting HAWK21M (Reply 39):
Quoting KELPkid (Reply 38):
How does the design of the 737's main gear wheel wells play into this decision

On the -NGs the "frangible fitting" will avoid that gear to retract.If its a tire burst,to protect the wheel well components.
regds
MEL

To elaborate, it is a thumbsize piece of pipe sticking outfrom the outer edge of each main wheel well, which is close at one end and with the other end fixed to a T-fitting in the landing gear up line. The pipe has a notch about an inch from it's tip.
Should a tyre burst, the remains would be flapping around at high speed and with the landing gear retracting, would smash everything inside the wheel well.
Now the landing gear retracts, the debris will hit this "frangible fitting", which woul break off at the notch and thus bleed the hydraulic pressure from the LDG up line, preventing the gear from retracting. At the same time a hydraulic fuse would close in the up line upstream of the fitting to prevent further loss of hydraulic fluid.

The 737 Jurassic had massive protective screens mounted in the main wheel well.

Jan
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Mender
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RE: Are The 737 Wheels On The Outside In This Picture?

Mon Sep 29, 2008 9:25 pm



Quoting HAWK21M (Reply 39):
On the -NGs the "frangible fitting" will avoid that gear to retract.If its a tire burst,to protect the wheel well components.



Quoting MD11Engineer (Reply 40):
Should a tyre burst, the remains would be flapping around at high speed and with the landing gear retracting, would smash everything inside the wheel well.

When the gear retracts the pressure to the retract actuator applies the brakes. This is known as retract braking. The frangible fitting only prevents gear retraction if a main wheel bursts AND the retract braking fails.

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