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Boeing 737 Landing Gear Doors?  
User currently offlinePropilot83 From United States of America, joined Jan 2001, 596 posts, RR: 0
Posted (5 years 2 months 3 weeks 5 days 6 hours ago) and read 19129 times:

Does anyone know why Boeing designed the 737 without any landing gear doors for the main landing gear? Its kind of cool seeing the landing gear in its up position from the ground sometimes, and also doesnt it pose some type of safety hazard without having landing gear doors for the main gear on the 737? Doesnt the cold freezing atmosphere conditions at 25,000+ feet have any type of hazards for the main gear?

11 replies: All unread, jump to last
 
User currently offlineKleinsim From Qatar, joined Jan 2007, 154 posts, RR: 0
Reply 1, posted (5 years 2 months 3 weeks 5 days 6 hours ago) and read 19138 times:



Quoting Propilot83 (Thread starter):
Does anyone know why Boeing designed the 737 without any landing gear doors for the main landing gear?

a. Complexity issues and weight savings associated with the doors.

Quoting Propilot83 (Thread starter):
doesnt it pose some type of safety hazard without having landing gear doors for the main gear on the 737? Doesnt the cold freezing atmosphere conditions at 25,000+ feet have any type of hazards for the main gear?

b. Even if there were landing gear doors, the space where the wheels are is not heated. Hence on a four hour cruise the temperature inside the wheel well is the same as not having the door open. Hence there is no problem. I'm sure somewhat would have noticed one in 40+ years of service.  Smile



Kleinsim


User currently offlineSpeedracer1407 From United States of America, joined Dec 2004, 333 posts, RR: 0
Reply 2, posted (5 years 2 months 3 weeks 5 days 5 hours ago) and read 19127 times:



Quoting Propilot83 (Thread starter):

Kleinsim has it right. MLG doors add complexity and weight. And they don't shield the tires from cold cruising temperatures anyway.

The 737 was designed in the 60s, and was initially intended for relatively short flights. At the time, whatever aerodynamic penalties for a door-less MLG were outweighed by the weight and added complexity MLG doors added to the overall design. Over the years, Boeing has had the opportunity to add MLG doors. But because even the relatively long-range newest 737s haven't incorporated this added complexity, it's safe to say that it doesn't buy operators enough efficiency to be worth while in cost, maintenance, or efficiency.



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User currently onlineRoseflyer From United States of America, joined Feb 2004, 9497 posts, RR: 52
Reply 3, posted (5 years 2 months 3 weeks 4 days 20 hours ago) and read 19051 times:



Quoting Propilot83 (Thread starter):
Doesnt the cold freezing atmosphere conditions at 25,000+ feet have any type of hazards for the main gear?

It is less a problem for the tires as it is for all the components in the wheel well. On a 737, real estate is tight, so most of the hydraulic and flight control systems components are in the wheel well. It is a very harsh environment for those components. Temperatures get as low as -65C. Air pressure obviously is only a few PSI. Worst of all, tire spray from runway deicing fluids and any other contamination on a runway gets kicked up in the wheel well which causes corrosion. It is very difficult on valves, pumps and other components. Tires, wheels, and landing gear are more structural components that don't have the tight tolerances and moving parts that make them as susceptible to those conditions.

Quoting Propilot83 (Thread starter):
Does anyone know why Boeing designed the 737 without any landing gear doors for the main landing gear?

Saves weight and reduces complexity. With the aerodynamic hub cap, there isn't that much of a drag penalty.

Quoting Speedracer1407 (Reply 2):

The 737 was designed in the 60s, and was initially intended for relatively short flights. At the time, whatever aerodynamic penalties for a door-less MLG were outweighed by the weight and added complexity MLG doors added to the overall design.

There have been options studied to reduce drag like partial wheel covers, but finding a way for them to fold out of the way when the gear is down is quite complex on a plane as low to the ground. The weight penalty is also a big hit that is hard to justify with drag reductions.



If you have never designed an airplane part before, let the real designers do the work!
User currently offlinePropilot83 From United States of America, joined Jan 2001, 596 posts, RR: 0
Reply 4, posted (5 years 2 months 3 weeks 4 days 14 hours ago) and read 18958 times:

Thanks for the info guys, WOW! I didnt think adding main landing gear doors would cause so much more weight and drag for the plane in flight. Yea, it also makes sense that the plane is real low to the ground to have landing gear doors for the main gear!

User currently offlineMusang From United Kingdom, joined Apr 2001, 861 posts, RR: 7
Reply 5, posted (5 years 2 months 3 weeks 4 days 14 hours ago) and read 18951 times:

The 737 originally had an inflating seal which filled the gap around the outer mainwheel tyre in the stowed position. This proved maintenance-hungry and didn't make much difference to the drag, so was replaced by the multi-petal rubber flap system which seals the gap ever since.

The Cessna 210 originally had main gear doors, but later models didn't for the same reasons as on the 737.

Regards - musang


User currently offlineHAWK21M From India, joined Jan 2001, 31667 posts, RR: 56
Reply 6, posted (5 years 2 months 3 weeks 4 days 13 hours ago) and read 18928 times:

Actually each MLG on the B737 has a Outboard ,mid & Inner Landing gear door,mechanically attached to the gear & operated by it.
True there is no door covering the exposed wheel & a hub cap is provided for aerodynamic reasons.
Considering the weight saved & non use of sequence valves and added components,this MLG construction has served well for the B737.
regds
MEL.



Think of the brighter side!
User currently offlineRandWKOP From Ireland, joined May 2012, 43 posts, RR: 0
Reply 7, posted (11 months 1 week 14 hours ago) and read 6278 times:

If a manufacturer tried to certify the same system, on a new design aircraft, would the FAA / EASA pass it?

User currently onlineStarlionblue From Greenland, joined Feb 2004, 16998 posts, RR: 67
Reply 8, posted (11 months 1 week 14 hours ago) and read 6256 times:

Quoting RandWKOP (Reply 7):
If a manufacturer tried to certify the same system, on a new design aircraft, would the FAA / EASA pass it?

They have and the will. There's nothing inherently unsafe about having the gear exposed.

Case in point, the Cessna Citation X, one of the fastest civilian jets around. Exposed mains.

http://home.iwichita.com/rh1/hold/av/avhist/csn/cx_dayr.jpg



"There are no stupid questions, but there are a lot of inquisitive idiots."
User currently offlineViscount724 From Switzerland, joined Oct 2006, 24837 posts, RR: 22
Reply 9, posted (11 months 1 week 14 hours ago) and read 6237 times:

Another low-slung aircraft, the CRJ (and Challenger business jet predecessor), also lacks landing gear doors.


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User currently offlineyeelep From United States of America, joined Apr 2011, 649 posts, RR: 0
Reply 10, posted (11 months 1 week 10 hours ago) and read 6131 times:

Quoting HAWK21M (Reply 6):
Actually each MLG on the B737 has a Outboard ,mid & Inner Landing gear door,mechanically attached to the gear & operated by it.

To be really picky, the outer gear door is attached to the wing and connected to the gear by a operator rod.


User currently offlineHAWK21M From India, joined Jan 2001, 31667 posts, RR: 56
Reply 11, posted (11 months 2 days 15 hours ago) and read 5228 times:

This is one oldie........

No sequencing valve needed  



Think of the brighter side!
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