Thrust
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Why Is The 737 Only One Without Main Gear Doors?

Thu Aug 25, 2011 7:12 am

Basically what it says...I thought some smaller express jets like those made by Embraer might have this future, i'm not sure. But basically it seems like the 737's practice of no main gear doors and leaving the wheels exposed in the undercarriage bay appears to be unique only to that aircraft. I read somewhere that the practice saves weight and the drag effect was proven to be negligent. So my question is, why wasn't this practice kept up and universalized if they found a way to make it work?
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JRadier
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RE: Why Is The 737 Only One Without Main Gear Doors?

Thu Aug 25, 2011 8:33 am

The Bombardier CRJ series as well as the Embraer ERJ-145 and EMB-170/190 series do not have main gear doors either.
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wn700driver
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RE: Why Is The 737 Only One Without Main Gear Doors?

Thu Aug 25, 2011 11:18 am

Thrust,

It's hard to see until you're right down on the ramp, but the 737's MLG are significantly smaller than what you would find on an A32x a.c (The super80s being the only other a/c in that size category carry over a design that predates the 737; they pretty much had to stick with what they had to keep their common type certificate). That may have a lot to do with it. And the fact that the 737's Main Gear bay is also a smaller, "busier" place than what you see on the 32x, and thus, not a lot of room for door actuators. I also think that being lower to the ground would complicate all that as well, but that's just my theory...
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PapaChuck
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RE: Why Is The 737 Only One Without Main Gear Doors?

Thu Aug 25, 2011 12:34 pm

Just a few that come to mind:


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[Edited 2011-08-25 05:40:55]
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Mir
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RE: Why Is The 737 Only One Without Main Gear Doors?

Thu Aug 25, 2011 1:20 pm

Quoting Thrust (Thread starter):
So my question is, why wasn't this practice kept up and universalized if they found a way to make it work?

It doesn't scale up very well, particularly if you're talking about tandem gear (which rules out everything from the 757 on up).

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dlednicer
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RE: Why Is The 737 Only One Without Main Gear Doors?

Thu Aug 25, 2011 5:19 pm

Two more:

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citationjet
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RE: Why Is The 737 Only One Without Main Gear Doors?

Thu Aug 25, 2011 5:33 pm

Boeing Flown: 701,702,703;717;720;721,722;731,732,733,734,735,737,738,739;741,742,743,744,747SP;752,753;762,763;772,773.
 
PapaChuck
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RE: Why Is The 737 Only One Without Main Gear Doors?

Thu Aug 25, 2011 6:05 pm

And just for fun:


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rwessel
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RE: Why Is The 737 Only One Without Main Gear Doors?

Thu Aug 25, 2011 6:11 pm

The 737 was conceived as a short range aircraft (the -100 had a max loaded range of only 1500nm, although that increased on the -200 to 1900nm). Proper landing gear doors would be better aerodynamically (which increases in importance as the length of your flights increases), but weigh more (which costs on every flight) and are much more complex. So on short flights, a bit of inefficiency is a reasonable tradeoff, especially given the fuel prices in the era in which the 737 was designed. So Boeing went that route, but fiddled the fairings (there's actually a rubber skirt around the bay which helps close the gap between the well and the tire) and added a hubcap, to make up for that a bit.

A nice shot from inside they bay showing the skirt:


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Note that the hubcap is only on the other side of the gear, the one that faces out when retracted. It also shows how busy a place the bay is, and hints at why it would be tough to redesign the gear to use proper doors.
 
474218
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RE: Why Is The 737 Only One Without Main Gear Doors?

Thu Aug 25, 2011 6:46 pm

How could everyone forget:


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HaveBlue
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RE: Why Is The 737 Only One Without Main Gear Doors?

Thu Aug 25, 2011 8:40 pm

I didn't realize and I am quite surprised that the Citation X doesn't have main landing gear doors. I would have thought that an aircraft designed with top speed of utmost importance would have had doors... interesting.
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contrails15
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RE: Why Is The 737 Only One Without Main Gear Doors?

Thu Aug 25, 2011 11:09 pm

Quoting JRadier (Reply 1):
The Bombardier CRJ series as well as the Embraer ERJ-145 and EMB-170/190 series do not have main gear doors either.

I thought the E190 does.
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pilotpip
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RE: Why Is The 737 Only One Without Main Gear Doors?

Thu Aug 25, 2011 11:16 pm

Quoting contrails15 (Reply 11):

I thought the E190 does.

Nope.

I have read a number of articles that indicate that with modern designs it's more efficient to have the wheels enclosed in a fairing than pay the weight penalty for doors. Witness the Citation X if you disagree.
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contrails15
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RE: Why Is The 737 Only One Without Main Gear Doors?

Thu Aug 25, 2011 11:39 pm

Quoting pilotpip (Reply 12):
Nope.

I have read a number of articles that indicate that with modern designs it's more efficient to have the wheels enclosed in a fairing than pay the weight penalty for doors. Witness the Citation X if you disagree.

I load them all the time and always thought they went into a bay. Learn something new everyday.
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Thrust
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RE: Why Is The 737 Only One Without Main Gear Doors?

Fri Aug 26, 2011 7:11 am

Quoting Thrust (Thread starter):

Future = feature. Sorry about that spelling mistake.
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Thrust
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RE: Why Is The 737 Only One Without Main Gear Doors?

Fri Aug 26, 2011 7:15 am

I also forgot to ask...why didn't any other commercial airliner the size of the 737 use this feature. And why don't giant jetliners use this feature?
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rwessel
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RE: Why Is The 737 Only One Without Main Gear Doors?

Fri Aug 26, 2011 7:42 am

Quoting Thrust (Reply 15):
And why don't giant jetliners use this feature?

A multi-axle bogey would make it very difficult to achieve even a partial seal around the wheel(s) as can be done with a single axle. That and larger aircraft are almost always longer range, where the aerodynamic penalty matters more. Also many of the large gears don't have a simple sideways swing for their retraction, which would make the exposed area even worse from a drag perspective.
 
wingscrubber
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RE: Why Is The 737 Only One Without Main Gear Doors?

Fri Aug 26, 2011 3:23 pm

Quoting HaveBlue (Reply 10):
I would have thought that an aircraft designed with top speed of utmost importance would have had doors... interesting.

There are doors/fairing on the gear legs of the X, but the wheels are flush with the belly fairing when retracted. Because of the location of the hinge line and the structure in the wheel well, they can't recess deep enough to justify adding gear doors. This is probably also a carry-over from the Citation 650 which was the design starting point for the X when it was developed.


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bonusonus
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RE: Why Is The 737 Only One Without Main Gear Doors?

Fri Aug 26, 2011 3:32 pm

Is this something that could possibly get changed on the 737RE? I know they are trying to keep redesign limited on that a/c to save resources for the 797 project, but some type of modification to the fairing could yield some benefits for fuel burn.
 
yeelep
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RE: Why Is The 737 Only One Without Main Gear Doors?

Fri Aug 26, 2011 4:34 pm

Quoting pilotpip (Reply 12):
I have read a number of articles that indicate that with modern designs it's more efficient to have the wheels enclosed in a fairing than pay the weight penalty for doors.

The COMAC ajr-21 would support that view as its a update of the DC/MD series.


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dlednicer
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RE: Why Is The 737 Only One Without Main Gear Doors?

Fri Aug 26, 2011 5:08 pm

Two more:
Canadair CL-600 Challenger:

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Bombardier Challenger 300:

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HaveBlue
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RE: Why Is The 737 Only One Without Main Gear Doors?

Sat Aug 27, 2011 3:10 am

Quoting Wingscrubber (Reply 17):
There are doors/fairing on the gear legs of the X, but the wheels are flush with the belly fairing when retracted. Because of the location of the hinge line and the structure in the wheel well, they can't recess deep enough to justify adding gear doors. This is probably also a carry-over from the Citation 650 which was the design starting point for the X when it was developed.

Thanks for the explanation, makes sense.  
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Viscount724
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RE: Why Is The 737 Only One Without Main Gear Doors?

Sat Aug 27, 2011 3:41 am

Another, the Yak-40.


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HAWK21M
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RE: Why Is The 737 Only One Without Main Gear Doors?

Sat Aug 27, 2011 9:17 pm

Reduce weight by less mechanical components & sequencing hurdles.
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