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Why Is The 737 Only One Without Main Gear Doors?  
User currently offlineThrust From United States of America, joined Sep 2003, 2688 posts, RR: 10
Posted (2 years 11 months 3 days 21 hours ago) and read 6406 times:

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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23 replies: All unread, jump to last
 
User currently offlineJRadier From Netherlands, joined Sep 2004, 4670 posts, RR: 50
Reply 1, posted (2 years 11 months 3 days 20 hours ago) and read 6358 times:

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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User currently offlinewn700driver From , joined Dec 1969, posts, RR:
Reply 2, posted (2 years 11 months 3 days 17 hours ago) and read 6280 times:

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...


User currently offlinePapaChuck From United States of America, joined Aug 2010, 136 posts, RR: 0
Reply 3, posted (2 years 11 months 3 days 16 hours ago) and read 6227 times:

Just a few that come to mind:


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[Edited 2011-08-25 05:40:55]


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User currently onlineMir From United States of America, joined Jan 2004, 21510 posts, RR: 55
Reply 4, posted (2 years 11 months 3 days 15 hours ago) and read 6191 times:

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).

-Mir



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User currently offlinedlednicer From United States of America, joined May 2005, 542 posts, RR: 7
Reply 5, posted (2 years 11 months 3 days 11 hours ago) and read 6074 times:
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Two more:

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User currently offlineCitationJet From United States of America, joined Mar 2003, 2421 posts, RR: 3
Reply 6, posted (2 years 11 months 3 days 11 hours ago) and read 6061 times:

Some previous threads on this topic:
http://www.airliners.net/aviation-fo...chid=144042&s=citationjet#ID144042
http://www.airliners.net/aviation-fo...chid=149478&s=citationjet#ID149478
http://www.airliners.net/aviation-forums/tech_ops/read.main/104356/
http://www.airliners.net/aviation-forums/tech_ops/read.main/3798/
http://www.airliners.net/aviation-forums/tech_ops/read.main/45353/

Quoting PapaChuck (Reply 3):
Just a few that come to mind:

Also the Citation X:

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User currently offlinePapaChuck From United States of America, joined Aug 2010, 136 posts, RR: 0
Reply 7, posted (2 years 11 months 3 days 10 hours ago) and read 6032 times:

And just for fun:


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In-trail spacing is a team effort.
User currently offlinerwessel From United States of America, joined Jan 2007, 2311 posts, RR: 2
Reply 8, posted (2 years 11 months 3 days 10 hours ago) and read 6026 times:
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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.


User currently offline474218 From United States of America, joined Oct 2005, 6340 posts, RR: 9
Reply 9, posted (2 years 11 months 3 days 10 hours ago) and read 5986 times:

How could everyone forget:


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User currently offlineHaveBlue From United States of America, joined Jan 2004, 2098 posts, RR: 1
Reply 10, posted (2 years 11 months 3 days 8 hours ago) and read 5882 times:

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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User currently offlinecontrails15 From United States of America, joined Oct 2008, 1181 posts, RR: 0
Reply 11, posted (2 years 11 months 3 days 5 hours ago) and read 5775 times:

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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User currently offlinepilotpip From United States of America, joined Sep 2003, 3144 posts, RR: 11
Reply 12, posted (2 years 11 months 3 days 5 hours ago) and read 5771 times:

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.



DMI
User currently offlinecontrails15 From United States of America, joined Oct 2008, 1181 posts, RR: 0
Reply 13, posted (2 years 11 months 3 days 5 hours ago) and read 5755 times:

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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User currently offlineThrust From United States of America, joined Sep 2003, 2688 posts, RR: 10
Reply 14, posted (2 years 11 months 2 days 21 hours ago) and read 5575 times:

Quoting Thrust (Thread starter):

Future = feature. Sorry about that spelling mistake.



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User currently offlineThrust From United States of America, joined Sep 2003, 2688 posts, RR: 10
Reply 15, posted (2 years 11 months 2 days 21 hours ago) and read 5569 times:

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?


Fly one thing; Fly it well
User currently offlinerwessel From United States of America, joined Jan 2007, 2311 posts, RR: 2
Reply 16, posted (2 years 11 months 2 days 21 hours ago) and read 5563 times:
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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.


User currently offlineWingscrubber From UK - England, joined Sep 2001, 845 posts, RR: 0
Reply 17, posted (2 years 11 months 2 days 13 hours ago) and read 5415 times:

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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User currently offlinebonusonus From United States of America, joined Nov 2009, 403 posts, RR: 0
Reply 18, posted (2 years 11 months 2 days 13 hours ago) and read 5402 times:

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.

User currently offlineyeelep From United States of America, joined Apr 2011, 649 posts, RR: 0
Reply 19, posted (2 years 11 months 2 days 12 hours ago) and read 5359 times:

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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User currently offlinedlednicer From United States of America, joined May 2005, 542 posts, RR: 7
Reply 20, posted (2 years 11 months 2 days 11 hours ago) and read 5335 times:
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Two more:
Canadair CL-600 Challenger:

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Bombardier Challenger 300:

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User currently offlineHaveBlue From United States of America, joined Jan 2004, 2098 posts, RR: 1
Reply 21, posted (2 years 11 months 2 days 1 hour ago) and read 5110 times:

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.  



Here Here for Severe Clear!
User currently offlineViscount724 From Switzerland, joined Oct 2006, 24803 posts, RR: 22
Reply 22, posted (2 years 11 months 2 days 1 hour ago) and read 5091 times:

Another, the Yak-40.


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User currently offlineHAWK21M From India, joined Jan 2001, 31667 posts, RR: 56
Reply 23, posted (2 years 11 months 1 day 7 hours ago) and read 4888 times:

Reduce weight by less mechanical components & sequencing hurdles.


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