SteelChair
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737 main gear doors fuel inefficiency

Sat Oct 13, 2018 4:11 am

When the 737 was introduced, it was a short range airplane. The argument against main gear doors was that the fuel savings wqs negligible on short routes. Now, more than 50 years later, 3 major variants later, and with 3-4 hour legs routine, it still has no gear doors. It doesnt seem like such a great idea now.

I have no idea what the fuel penalty associated with no gear doors may be. I am guessing it is very small. But according to wiki, 10,240 737s have been delivered. So the cumulative effect could be large. Huge in fact.

Let's say that a 737 flies 2,800 hours a year, the average fuel burn is 6, 200 lbs/hr, and the average airplane flies 60,000 hours in its lifetime. If we assume that the burn penalty is 0.0025%, (1/4 of 1%), many millions of gallons of fuel have been wasted.

6,200x0.0025=15.5
15.5x2,800x10240=444,416,000
444,416,000÷6.7=66,430,716

Not having gear doors on the 737 has caused over 66 million gallons of extra fuel to be burned. Lets say my numbers are way off, 50% high for example. That's still over 30 million gallons gone forever. And my number could be low instead of high. More petroleum gone forever.

Just one more example of how endlessly upgrading this ancient airframe has been costly.
 
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LAX772LR
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Re: 737 main gear doors fuel inefficiency

Sat Oct 13, 2018 4:27 am

Way too simplistic of an assessment.

It neglects the costs of:
  • man-hrs for designing new doors
  • certification process for new doors
  • modifying production, delivery, and assembly of new doors
  • retrofitting aircraft for doors
  • ...and most importantly, WEIGHT of said doors

Quite frankly, if the benefits outweighed the drawbacks, then the airlines would've demanded it and Boeing would've long-since done it.
I myself, suspect a more prosaic motive... ~Thranduil
 
MeCe
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Re: 737 main gear doors fuel inefficiency

Sat Oct 13, 2018 4:35 am

LAX772LR wrote:
Way too simplistic of an assessment.

It neglects the costs of:
  • man-hrs for designing new doors
  • certification process for new doors
  • modifying production, delivery, and assembly of new doors
  • retrofitting aircraft for doors
  • ...and most importantly, WEIGHT of said doors

Quite frankly, if the benefits outweighed the drawbacks, then the airlines would've demanded it and Boeing would've long-since done it.


Is there any official data available somewhere to make this calculation as an airline or just a educated guess ?
 
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seabosdca
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Re: 737 main gear doors fuel inefficiency

Sat Oct 13, 2018 4:36 am

The 737NG had a completely new wingbox. If Boeing could have created a significant financial advantage by redesigning the gear to be fully enclosed, it would have done so for the NG. Instead, it consciously retained the old arrangement. Boeing did create, and then redesigned for the NG, plastic wheel caps that help make the surface of the exposed gear as smooth as possible.
 
MCIRNO
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Re: 737 main gear doors fuel inefficiency

Sat Oct 13, 2018 4:45 am

MeCe wrote:
LAX772LR wrote:
Way too simplistic of an assessment.

It neglects the costs of:
  • man-hrs for designing new doors
  • certification process for new doors
  • modifying production, delivery, and assembly of new doors
  • retrofitting aircraft for doors
  • ...and most importantly, WEIGHT of said doors

Quite frankly, if the benefits outweighed the drawbacks, then the airlines would've demanded it and Boeing would've long-since done it.


Is there any official data available somewhere to make this calculation as an airline or just a educated guess ?

I think it's not a huge, logical leap to be confident that a multi-billion dollar company has done plenty of calculations based on literally hundreds of factors and if they thought there savings was so needed, they would have given the 737 wheel doors...

I'd also like to point out that the 738 still had better range than A320, so there's really no more wasted fuel, at least it's less than an aircraft with a gear door... We're coming up on winter in the USA, also known as "Transcona A320 fuel stop" weather...
 
Pacific
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Re: 737 main gear doors fuel inefficiency

Sat Oct 13, 2018 5:08 am

The Airbus A220 has exposed gears and it's a clean-sheet design. I'm guessing the weight penalty as a percentage of gross aircraft weight is larger for smaller aircraft.

Remember, it's not only the doors, but there's also the associated hydraulics and machinery to open/close them.
 
barney captain
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Re: 737 main gear doors fuel inefficiency

Sat Oct 13, 2018 6:54 am

Now, more than 50 years later, 3 major variants later, and with 3-4 hour legs routine, it still has no gear doors.



The 737 has MLG doors - three in fact. Inner, center and outer.

Image

http://www.b737.org.uk/images/main_gear_ng_labelled.jpg
Southeast Of Disorder
 
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VirginFlyer
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Re: 737 main gear doors fuel inefficiency

Sat Oct 13, 2018 11:10 am

SteelChair wrote:
Just one more example of how endlessly upgrading this ancient airframe has been costly.

Just because something is older doesn’t necessarily make it worse in all regards. Another example: the old Airliners.net forum software had a suggest delete option specifically for “flamebait”, whereas the new software doesn’t.

V/F
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SteelChair
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Re: 737 main gear doors fuel inefficiency

Sat Oct 13, 2018 12:36 pm

Its interesting that the DC9/MD80/90 series, DC8, DC10/MD11, 727, 757, 767, 777, 787, A300, 310, 320, 330, 340, and 380 all have fully enclosed gear. Surely they can't all be wrong? The CS/A220 is the only large airliner I can think of that doesn't have fully enclosed MLG.

I was hoping someone would have a more educated guess than my 0.0025% but it appears that we don't have any aerodynamics engineers on the board.
 
sixtyseven
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Re: 737 main gear doors fuel inefficiency

Sat Oct 13, 2018 1:54 pm

SteelChair wrote:
Its interesting that the DC9/MD80/90 series, DC8, DC10/MD11, 727, 757, 767, 777, 787, A300, 310, 320, 330, 340, and 380 all have fully enclosed gear. Surely they can't all be wrong? The CS/A220 is the only large airliner I can think of that doesn't have fully enclosed MLG.

I was hoping someone would have a more educated guess than my 0.0025% but it appears that we don't have any aerodynamics engineers on the board.


Where did you come up with your math? Or was it just a guess.

Maybe you could provide a guess on what the extra weight of the doors would be plus the associated maintenance costs over the life of the aircraft. Actually don’t. It’d be just a guess and you’ll get bombed on here.

The numbers over the life of an airframe can be pretty big but they carry assumptions. I remember my airline during the lean years after 9/11 and then when fuel was through the roof, they were scouring the airplanes to remove out dated magazines. They removed the ladders in the E/E bays. All for minute fuel savings caused by uwwanted weight.

In the end you might be right. You might be wrong. But if it was that obvious it would have been changed over the years. Probably a strong business case not to enclose the wheels.
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SAAFNAV
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Re: 737 main gear doors fuel inefficiency

Sat Oct 13, 2018 2:15 pm

SteelChair wrote:
When the 737 was introduced, it was a short range airplane. The argument against main gear doors was that the fuel savings wqs negligible on short routes. Now, more than 50 years later, 3 major variants later, and with 3-4 hour legs routine, it still has no gear doors. It doesnt seem like such a great idea now.

I have no idea what the fuel penalty associated with no gear doors may be. I am guessing it is very small. But according to wiki, 10,240 737s have been delivered. So the cumulative effect could be large. Huge in fact.

Let's say that a 737 flies 2,800 hours a year, the average fuel burn is 6, 200 lbs/hr, and the average airplane flies 60,000 hours in its lifetime. If we assume that the burn penalty is 0.0025%, (1/4 of 1%), many millions of gallons of fuel have been wasted.

6,200x0.0025=15.5
15.5x2,800x10240=444,416,000
444,416,000÷6.7=66,430,716

Not having gear doors on the 737 has caused over 66 million gallons of extra fuel to be burned. Lets say my numbers are way off, 50% high for example. That's still over 30 million gallons gone forever. And my number could be low instead of high. More petroleum gone forever.

Just one more example of how endlessly upgrading this ancient airframe has been costly.


1/4 of 1% is 0.25% in my part of the woods.
L-382 Loadmaster; ex C-130B Navigator
 
VetteDude
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Re: 737 main gear doors fuel inefficiency

Sat Oct 13, 2018 2:35 pm

I don't really like coming on this website anymore, at least partially because every week there is a "the 737 is old so it automatically must suck" thread. It's a good plane, get over it.
 
frmrCapCadet
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Re: 737 main gear doors fuel inefficiency

Sat Oct 13, 2018 2:35 pm

I was curious about this issue for a long time, glad to see a thread on it, and that picture of the 3 (three!) doors. Question answered.
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barney captain
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Re: 737 main gear doors fuel inefficiency

Sat Oct 13, 2018 4:26 pm

One of the fastest bizjets ever produced -

Image

The drag penalty must not be that bad -

Image

Somehow I bet the engineers at Boeing have penciled this out.
Southeast Of Disorder
 
jetmatt777
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Re: 737 main gear doors fuel inefficiency

Sat Oct 13, 2018 4:54 pm

At higher altitudes and faster speed there’s probably even less drag due to the lower air density (fewer air molecules even touching the wheels) and the airstream itself flowing around the fuselage.

At lower speeds and altitudes, the aircraft is less fuel efficient anyway so it doesn’t matter.
Lighten up while you still can, don't even try to understand, just find a place to make your stand and take it easy
 
SteelChair
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Re: 737 main gear doors fuel inefficiency

Sat Oct 13, 2018 7:36 pm

SAAFNAV wrote:
SteelChair wrote:
When the 737 was introduced, it was a short range airplane. The argument against main gear doors was that the fuel savings wqs negligible on short routes. Now, more than 50 years later, 3 major variants later, and with 3-4 hour legs routine, it still has no gear doors. It doesnt seem like such a great idea now.

I have no idea what the fuel penalty associated with no gear doors may be. I am guessing it is very small. But according to wiki, 10,240 737s have been delivered. So the cumulative effect could be large. Huge in fact.

Let's say that a 737 flies 2,800 hours a year, the average fuel burn is 6, 200 lbs/hr, and the average airplane flies 60,000 hours in its lifetime. If we assume that the burn penalty is 0.0025%, (1/4 of 1%), many millions of gallons of fuel have been wasted.

6,200x0.0025=15.5
15.5x2,800x10240=444,416,000
444,416,000÷6.7=66,430,716

Not having gear doors on the 737 has caused over 66 million gallons of extra fuel to be burned. Lets say my numbers are way off, 50% high for example. That's still over 30 million gallons gone forever. And my number could be low instead of high. More petroleum gone forever.

Just one more example of how endlessly upgrading this ancient airframe has been costly.


1/4 of 1% is 0.25% in my part of the woods.


Yes my bad. 0.25%=0.0025.
 
SteelChair
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Re: 737 main gear doors fuel inefficiency

Sat Oct 13, 2018 7:39 pm

sixtyseven wrote:
SteelChair wrote:
Its interesting that the DC9/MD80/90 series, DC8, DC10/MD11, 727, 757, 767, 777, 787, A300, 310, 320, 330, 340, and 380 all have fully enclosed gear. Surely they can't all be wrong? The CS/A220 is the only large airliner I can think of that doesn't have fully enclosed MLG.

I was hoping someone would have a more educated guess than my 0.0025% but it appears that we don't have any aerodynamics engineers on the board.


Where did you come up with your math? Or was it just a guess.

Maybe you could provide a guess on what the extra weight of the doors would be plus the associated maintenance costs over the life of the aircraft. Actually don’t. It’d be just a guess and you’ll get bombed on here.

The numbers over the life of an airframe can be pretty big but they carry assumptions. I remember my airline during the lean years after 9/11 and then when fuel was through the roof, they were scouring the airplanes to remove out dated magazines. They removed the ladders in the E/E bays. All for minute fuel savings caused by uwwanted weight.

In the end you might be right. You might be wrong. But if it was that obvious it would have been changed over the years. Probably a strong business case not to enclose the wheels.


It was a total WAG.

My guess is that the business case is good to have enclosed wheels for longer ranged airliners since almost every other airliner has enclosed wheels.
 
SteelChair
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Re: 737 main gear doors fuel inefficiency

Sat Oct 13, 2018 7:51 pm

MCIRNO wrote:
MeCe wrote:
LAX772LR wrote:
Way too simplistic of an assessment.

It neglects the costs of:
  • man-hrs for designing new doors
  • certification process for new doors
  • modifying production, delivery, and assembly of new doors
  • retrofitting aircraft for doors
  • ...and most importantly, WEIGHT of said doors

Quite frankly, if the benefits outweighed the drawbacks, then the airlines would've demanded it and Boeing would've long-since done it.


Is there any official data available somewhere to make this calculation as an airline or just a educated guess ?

I think it's not a huge, logical leap to be confident that a multi-billion dollar company has done plenty of calculations based on literally hundreds of factors and if they thought there savings was so needed, they would have given the 737 wheel doors...

I'd also like to point out that the 738 still had better range than A320, so there's really no more wasted fuel, at least it's less than an aircraft with a gear door... We're coming up on winter in the USA, also known as "Transcona A320 fuel stop" weather...


The fact that Boeing is a multi billion dollar company has nothing to do with this issue. Are multubillion dollar companies infallible? Every other airliner they have built has enclosed gear. If they had to do a cleansheet narrowoidy to replace the MAX, it would almost certainly have enclosed gear. They are stuck with the 1967 design.

Likewise, optimisation of one design has little to do with whether or not another design is optimised. The A320 is a different airplane, its fuselage is wider, its gear are taller (heavier) and it holds 4,500 less lbs of fuel. Heavier, bigger, less fuel capacity, basically the same engines =less range but proves nothing about whether or not the 737 is optimised.
 
SteelChair
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Re: 737 main gear doors fuel inefficiency

Sat Oct 13, 2018 7:54 pm

seabosdca wrote:
The 737NG had a completely new wingbox. If Boeing could have created a significant financial advantage by redesigning the gear to be fully enclosed, it would have done so for the NG. Instead, it consciously retained the old arrangement. Boeing did create, and then redesigned for the NG, plastic wheel caps that help make the surface of the exposed gear as smooth as possible.


I remember 737-200s having the hubcaps.
 
GalaxyFlyer
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Re: 737 main gear doors fuel inefficiency

Sat Oct 13, 2018 8:36 pm

If they had to do a cleansheet narrowoidy to replace the MAX, it would almost certainly have enclosed gear.


Do you know that for a fact or just speculating? The CS/A220 didn’t use gear doors over the wheels, either. Maybe, there just isn’t much drag and isn’t worth the money. Every design feature has a cost vs. benefit analysis aka business case for its incorporation into the final design.

Despite its range, most B737 sectors are under two hours, just not much cruise time.

GF
 
barney captain
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Re: 737 main gear doors fuel inefficiency

Sat Oct 13, 2018 8:40 pm

This has been asked and answered many, many times.

viewtopic.php?t=760901

viewtopic.php?t=768095

viewtopic.php?t=767861

viewtopic.php?t=742447

viewtopic.php?t=722011

It has probably crossed the minds of the engineers at Boeing at least as many times. If it made sense, they would have done it.

Maybe give those folks a little credit, and not assume it is some sort of oversight?
Southeast Of Disorder
 
sixtyseven
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Re: 737 main gear doors fuel inefficiency

Sat Oct 13, 2018 8:42 pm

GalaxyFlyer wrote:
If they had to do a cleansheet narrowoidy to replace the MAX, it would almost certainly have enclosed gear.


Do you know that for a fact or just speculating? The CS/A220 didn’t use gear doors over the wheels, either. Maybe, there just isn’t much drag and isn’t worth the money. Every design feature has a cost vs. benefit analysis aka business case for its incorporation into the final design.

Despite its range, most B737 sectors are under two hours, just not much cruise time.

GF


Your drag/money comment is valid. Who knows what the airflow is around there.

Did a case study on a 767 cockpit window sliding open during takeoff. They didn’t get it closed til about 1000 feet. You figure it’d be like a hurricane. Spoke to the crew. He said hardly any wind. Noisy as hell though.

707 pilot I know took a bird on rotation. Piece of the bird stuck just above the base of the front windshield. For six hours. Some of the feathers didn’t even flutter.

Until you see it in a wind tunnel or something like the above who knows.
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JayinKitsap
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Re: 737 main gear doors fuel inefficiency

Sun Oct 14, 2018 7:23 pm

To put doors over the wheel it would take at least 2", more likely 4" of extra depth in the area of the wheel. That amount of frontal area added probably killed any increase the doors provided.
 
FlyHappy
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Re: 737 main gear doors fuel inefficiency

Mon Oct 15, 2018 1:21 am

SteelChair wrote:

Not having gear doors on the 737 has caused over 66 million gallons of extra fuel to be burned. Lets say my numbers are way off, 50% high for example. That's still over 30 million gallons gone forever. And my number could be low instead of high. More petroleum gone forever.

Just one more example of how endlessly upgrading this ancient airframe has been costly.


The breadth of your assumptions coupled with your certainty is startling.

how many millions of gallons of fuel have been needlessly burned by putting satellite radome humps on top of..... virtually every airframe with 10+ years left of service life?
time to scrap the ancient A350's and B787's flying ULH routes, needlessly providing pax with aerodymically inefficient internet service. its an outrage.

You have informed Airbus of this fatal design flaw on the A220 , right? Good thing their losses can be limited to the $1 they acquired the program for. Wouldn't want them to suffer 50 years of inefficiency.

OTOH, considering that the B737 has delivered exceptional CASM/trip cost (and thus profit) for its operators over 50 years and 4 generations, I'd say that you are simply wrong. Wildly wrong.
 
spacecadet
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Re: 737 main gear doors fuel inefficiency

Mon Oct 15, 2018 7:01 am

SteelChair wrote:
I was hoping someone would have a more educated guess than my 0.0025% but it appears that we don't have any aerodynamics engineers on the board.


What you seem to want is not someone who knows about aerodynamics, but someone who knows about aerodynamics and also works for Boeing on the design of the 737 and is not afraid to break their NDA. And I'm sorry, but you're not going to get that here or anywhere.

Aerodynamically, it is easily possible to design a wingbox that has very little airflow directly under the wheel wells, in the same way it's easy to design a pickup truck that has very little airflow over the exposed truck bed. The question you're asking is whether Boeing has actually done that. And nobody's going to be able to tell you that other than Boeing, who has all the data on this. No doubt, they have giant spreadsheets full of data just on this. All proprietary, all confidential.

People here can tell you (and have told you) all the reasons why it sure *looks* like that's what they've done, but that doesn't seem good enough for you. So, all anyone can say at this point is ¯\_(ツ)_/¯
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Grizzly410
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Re: 737 main gear doors fuel inefficiency

Mon Oct 15, 2018 1:33 pm

It’s not apple to apple but just to show sometimes the benefit is enough to develop a total closure of main landing gear bay, Airbus is currently doing it on the C-295 platform for the Canadian FWSAR fleet. The goal is to reduce drag contributors and permit longer “time on station” (ie. range).

I well understand 737 and C-295 FWSAR doesn’t have the same size nor operational mode but Airbus found the costly solution of removing the drag generated by the open LG bay to be best solution to increase aircraft range rather than doing some cheap aero tweeks.

737 doesn’t have problem to sell its 737 but if it needed range as badly as C-295 needed to get the FWSAR contract, wouldn’t it be a good solution too ?
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7BOEING7
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Re: 737 main gear doors fuel inefficiency

Mon Oct 15, 2018 2:48 pm

Grizzly410 wrote:
It’s not apple to apple but just to show sometimes the benefit is enough to develop a total closure of main landing gear bay, Airbus is currently doing it on the C-295 platform for the Canadian FWSAR fleet. The goal is to reduce drag contributors and permit longer “time on station” (ie. range).

I well understand 737 and C-295 FWSAR doesn’t have the same size nor operational mode but Airbus found the costly solution of removing the drag generated by the open LG bay to be best solution to increase aircraft range rather than doing some cheap aero tweeks.

737 doesn’t have problem to sell its 737 but if it needed range as badly as C-295 needed to get the FWSAR contract, wouldn’t it be a good solution too ?


The C-295 has much more "hanging out" than the 737. Between the recessed gear, the hubcaps and the rubber flanges there's nothing extending below the bottom of the 737 and the gear bay is fairly well sealed. On the C-295 the gear although retracted are protruding below the landing gear bay and the bay itself doesn't appeared to be sealed creating much more drag than the 737.

Relative to a previous comment, having flown a couple of approaches with the window open, the 777 like the 767 mentioned above has little if any airflow into the cockpit but if you don't have a Dave Clark headset on you won't be able to talk to anybody.
 
RandallStephens
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Re: 737 main gear doors fuel inefficiency

Mon Oct 15, 2018 10:40 pm

barney captain wrote:
Now, more than 50 years later, 3 major variants later, and with 3-4 hour legs routine, it still has no gear doors.



The 737 has MLG doors - three in fact. Inner, center and outer.

Image

http://www.b737.org.uk/images/main_gear_ng_labelled.jpg

The outer door is technically called the trunnion door.

I believe the rumors had doors over the wheels as a 500lb of airplane equivalent weight in drag reduction. Unfortunately with all the new systems, doors, and alternate extend changes, the doors didn't buy their way onto the NG.
 
FrmrKSEngr
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Re: 737 main gear doors fuel inefficiency

Sat Oct 20, 2018 3:37 am

seabosdca wrote:
The 737NG had a completely new wingbox. If Boeing could have created a significant financial advantage by redesigning the gear to be fully enclosed, it would have done so for the NG. Instead, it consciously retained the old arrangement. Boeing did create, and then redesigned for the NG, plastic wheel caps that help make the surface of the exposed gear as smooth as possible.


While the 737NG wing box was a redesign from the 737 Classic the design was mostly to do with changing the manufacturing approach, but did not cause drastic changes in the wheel well geometry. The spars in the Classic wing box were built-up assemblies. Webs and stiffeners. On the NG these went to monolithic machined parts (turn a 2,000 lb aluminum billet into a 150 lb part and 1,850 lbs of chips). Structurally more efficient, and dimensionaly more stable for the next higher assembly. The general approach for the 737NG fuselage was a minimal change from the 737 classic, with an anticipation for high re-use of 737 classic parts. However with the change in manufacturing approach from fully tooled to coordinated pilot holes and reduced tooling, most of the classic parts were redrawn with different tolerancing schemes and/or gage changes and new 737NG P/N series. I can't remember any 65B structural parts on the 737NG.
 
MHG
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Re: 737 main gear doors fuel inefficiency

Sat Oct 20, 2018 4:50 am

What are we all talking about here ?????
First of all when Boeing designed the 737 gear wells they knew for sure about the drag issue and certainly did not ignore possible penalties.
But in the case of the 737 only the wheels are not covered.
Boeing designed it in a way that the gap between wheel and gear well is as small as possible reducing turbulences to a minimum.
I have seen such arangements on a few aircraft types and some have sort of a brush-like edge sealing off at least 80% the gap (not sure if the 737 has something similar).
Next to this it might be that the wing design "just so" creates a relatively low airflow exactly in the area of the wheel well or the airflow almost "jumps" over the area creating a negible drag penalty that´s waaay lower than a comparable weight penalty by adding wheel covers (just think of all required parts - not just the cap itself).
Flying is not inherently dangerous but it is very unforgiving in case of carelessness, incapacity or neglect.
 
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7BOEING7
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Re: 737 main gear doors fuel inefficiency

Sat Oct 20, 2018 5:18 am

MHG wrote:
I have seen such arangements on a few aircraft types and some have sort of a brush-like edge sealing off at least 80% the gap (not sure if the 737 has something similar).
.


Rubber flaps on the 737.
 
LH707330
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Re: 737 main gear doors fuel inefficiency

Sat Oct 20, 2018 4:07 pm

7BOEING7 wrote:
MHG wrote:
I have seen such arangements on a few aircraft types and some have sort of a brush-like edge sealing off at least 80% the gap (not sure if the 737 has something similar).
.


Rubber flaps on the 737.

The CRJs have brushes, not sure about the jungle jets, but it's a similar design.
 
stratclub
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Re: 737 main gear doors fuel inefficiency

Sat Oct 20, 2018 4:30 pm

7BOEING7 wrote:
MHG wrote:
I have seen such arangements on a few aircraft types and some have sort of a brush-like edge sealing off at least 80% the gap (not sure if the 737 has something similar).
.


Rubber flaps on the 737.

During development I had heard that Boeing did a considerable amount of R&D work on the drag issues and at one point tried some sort of inflatable seal to close the tire to lower body fairing gap. Apparently the rubber flaps you mentioned ended up being the best production approach to the problem. Simple, low maintenance and gets the job done nicely.
 
stratclub
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Re: 737 main gear doors fuel inefficiency

Sat Oct 20, 2018 4:42 pm

FrmrKSEngr wrote:
seabosdca wrote:
The 737NG had a completely new wingbox. If Boeing could have created a significant financial advantage by redesigning the gear to be fully enclosed, it would have done so for the NG. Instead, it consciously retained the old arrangement. Boeing did create, and then redesigned for the NG, plastic wheel caps that help make the surface of the exposed gear as smooth as possible.


While the 737NG wing box was a redesign from the 737 Classic the design was mostly to do with changing the manufacturing approach, but did not cause drastic changes in the wheel well geometry. The spars in the Classic wing box were built-up assemblies. Webs and stiffeners. On the NG these went to monolithic machined parts (turn a 2,000 lb aluminum billet into a 150 lb part and 1,850 lbs of chips). Structurally more efficient, and dimensionaly more stable for the next higher assembly. The general approach for the 737NG fuselage was a minimal change from the 737 classic, with an anticipation for high re-use of 737 classic parts. However with the change in manufacturing approach from fully tooled to coordinated pilot holes and reduced tooling, most of the classic parts were redrawn with different tolerancing schemes and/or gage changes and new 737NG P/N series. I can't remember any 65B structural parts on the 737NG.

I saw a lot of the monolithic machined parts on the 787. Very little waste I'm sure. They just take all the chips and melt them down and re-use them. The next step I think will be 3D printing. No chips to have to recycle. They just have to learn how to get the process materials right.

Do you remember the Omnibus Delete installations? I took a couples of days of research proving to a 747 customer in the 80's that 2 insignificant angles in the cargo hold were in fact the correct P/N. Customers just love to send that type of stuff to contract$ as unresolved.
 
FrmrKSEngr
Posts: 407
Joined: Sun Apr 13, 2014 6:05 am

Re: 737 main gear doors fuel inefficiency

Sun Oct 21, 2018 1:16 am

stratclub wrote:
I saw a lot of the monolithic machined parts on the 787. Very little waste I'm sure. They just take all the chips and melt them down and re-use them. The next step I think will be 3D printing. No chips to have to recycle. They just have to learn how to get the process materials right.

Do you remember the Omnibus Delete installations? I took a couples of days of research proving to a 747 customer in the 80's that 2 insignificant angles in the cargo hold were in fact the correct P/N. Customers just love to send that type of stuff to contract$ as unresolved.


On the Sing box spars, the big problem was chip removal. I worked a Kiazen event around 1999 to improve the machining operation for these parts. Issue one was improving the billet load to eliminate the need for an overhead crane. Issue 2 was the chip removal. Had to stop the machine every few hours and remove the chips with a snow shovel. Issue 3 (my area) was reducing tool changes by standardizing on cutter radii (the design engineers did not thing that every internal radius required a tool change) and trying to remove minor-model variability (too much weight penalty to go to one spar across all minor models -6/7/701/800).

As for omnibus changes, I believe they were on the classic models (737Classic, 747, 757, 767), I only worked 737NG on the commercial side. I remember hearing about them but never was part of one.
 
stratclub
Posts: 439
Joined: Fri Jan 05, 2018 10:38 pm

Re: 737 main gear doors fuel inefficiency

Thu Oct 25, 2018 7:09 pm

Omnibus Delete installations go back to the 707. I suspect they were used so as to offer customers a fair amount of customization options to the basic airframe. What O/D did was took parts out of a tabbed installation and installed other parts per the customers/engineering requirements. It made navigating the drawings a real nightmare sometimes.

Thankfully, O/D went away once Boeing started making airframes in a more standardized manner. Nowadays, the customer more or less picks options from a standardize list of options that Boeing offers.
 
strfyr51
Posts: 3044
Joined: Tue Apr 10, 2012 5:04 pm

Re: 737 main gear doors fuel inefficiency

Thu Oct 25, 2018 11:46 pm

barney captain wrote:
Now, more than 50 years later, 3 major variants later, and with 3-4 hour legs routine, it still has no gear doors.



The 737 has MLG doors - three in fact. Inner, center and outer.

Image

http://www.b737.org.uk/images/main_gear_ng_labelled.jpg

the B737 does not have doors over the wheels and that appears to be the question but that fact means little since the gear is do short.
the airplane could be re-designed to allow a much taller gear but then it wouldn't be a 737. The 737 has about run it's course..
 
GalaxyFlyer
Posts: 1504
Joined: Fri Jan 01, 2016 4:44 am

Re: 737 main gear doors fuel inefficiency

Thu Oct 25, 2018 11:59 pm

After about another 5,000 deliveries and 25 years, yes, it will hav3 run it’s course. Doors over the tires is a total non-issue—it doesn’t matter and doesn’t cost anything.


GF
 
stratclub
Posts: 439
Joined: Fri Jan 05, 2018 10:38 pm

Re: 737 main gear doors fuel inefficiency

Fri Oct 26, 2018 2:02 am

SteelChair wrote:
When the 737 was introduced, it was a short range airplane. The argument against main gear doors was that the fuel savings wqs negligible on short routes. Now, more than 50 years later, 3 major variants later, and with 3-4 hour legs routine, it still has no gear doors. It doesnt seem like such a great idea now.

I have no idea what the fuel penalty associated with no gear doors may be. I am guessing it is very small. But according to wiki, 10,240 737s have been delivered. So the cumulative effect could be large. Huge in fact.

Let's say that a 737 flies 2,800 hours a year, the average fuel burn is 6, 200 lbs/hr, and the average airplane flies 60,000 hours in its lifetime. If we assume that the burn penalty is 0.0025%, (1/4 of 1%), many millions of gallons of fuel have been wasted.

6,200x0.0025=15.5
15.5x2,800x10240=444,416,000
444,416,000÷6.7=66,430,716

Not having gear doors on the 737 has caused over 66 million gallons of extra fuel to be burned. Lets say my numbers are way off, 50% high for example. That's still over 30 million gallons gone forever. And my number could be low instead of high. More petroleum gone forever.

Just one more example of how endlessly upgrading this ancient airframe has been costly.

Kind of an imbecile argument. The people that promote car emissions promote the same nonsense. If we could just reduce NOX emissions to 1/1000 of a gram per car, we could reduce NOX emissions worldwide by many thousands of tons.

If we rewrite the flight manual for the the 737 to were flaps were never used, engines were shut down on approach, landing gear was not extended until 100 feet and only brakes were used to slow the aircraft, then the fuel saving would be way more than the insignificant drag caused by exposed main gear tires.

With 14,000+ 737's delivered and/or on order, apparently Boeing must be doing something right with the 737. I suggest that you find aerodynamic numbers that support your harebrained theory.
 
stratclub
Posts: 439
Joined: Fri Jan 05, 2018 10:38 pm

Re: 737 main gear doors fuel inefficiency

Fri Oct 26, 2018 2:03 am

SteelChair wrote:
When the 737 was introduced, it was a short range airplane. The argument against main gear doors was that the fuel savings wqs negligible on short routes. Now, more than 50 years later, 3 major variants later, and with 3-4 hour legs routine, it still has no gear doors. It doesnt seem like such a great idea now.

I have no idea what the fuel penalty associated with no gear doors may be. I am guessing it is very small. But according to wiki, 10,240 737s have been delivered. So the cumulative effect could be large. Huge in fact.

Let's say that a 737 flies 2,800 hours a year, the average fuel burn is 6, 200 lbs/hr, and the average airplane flies 60,000 hours in its lifetime. If we assume that the burn penalty is 0.0025%, (1/4 of 1%), many millions of gallons of fuel have been wasted.

6,200x0.0025=15.5
15.5x2,800x10240=444,416,000
444,416,000÷6.7=66,430,716

Not having gear doors on the 737 has caused over 66 million gallons of extra fuel to be burned. Lets say my numbers are way off, 50% high for example. That's still over 30 million gallons gone forever. And my number could be low instead of high. More petroleum gone forever.

Just one more example of how endlessly upgrading this ancient airframe has been costly.

Kind of an imbecile argument. The people that promote car emissions promote the same nonsense. If we could just reduce NOX emissions to 1/1000 of a gram per car, we could reduce NOX emissions worldwide by many thousands of tons.

If we rewrite the flight manual for the the 737 to were flaps were never used, engines were shut down on approach, landing gear was not extended until 100 feet and only brakes were used to slow the aircraft, then the fuel saving would be way more than the insignificant drag caused by exposed main gear tires.

With 14,000+ 737's delivered and/or on order, apparently Boeing must be doing something right with the 737. I suggest that you find aerodynamic numbers that support your harebrained theory.
 
stratclub
Posts: 439
Joined: Fri Jan 05, 2018 10:38 pm

Re: 737 main gear doors fuel inefficiency

Fri Oct 26, 2018 2:09 am

SteelChair wrote:
When the 737 was introduced, it was a short range airplane. The argument against main gear doors was that the fuel savings wqs negligible on short routes. Now, more than 50 years later, 3 major variants later, and with 3-4 hour legs routine, it still has no gear doors. It doesnt seem like such a great idea now.

I have no idea what the fuel penalty associated with no gear doors may be. I am guessing it is very small. But according to wiki, 10,240 737s have been delivered. So the cumulative effect could be large. Huge in fact.

Let's say that a 737 flies 2,800 hours a year, the average fuel burn is 6, 200 lbs/hr, and the average airplane flies 60,000 hours in its lifetime. If we assume that the burn penalty is 0.0025%, (1/4 of 1%), many millions of gallons of fuel have been wasted.

6,200x0.0025=15.5
15.5x2,800x10240=444,416,000
444,416,000÷6.7=66,430,716

Not having gear doors on the 737 has caused over 66 million gallons of extra fuel to be burned. Lets say my numbers are way off, 50% high for example. That's still over 30 million gallons gone forever. And my number could be low instead of high. More petroleum gone forever.

Just one more example of how endlessly upgrading this ancient airframe has been costly.

Kind of an imbecile argument. The people that promote car emissions promote the same nonsense. If we could just reduce NOX emissions to 1/1000 of a gram per car, we could reduce NOX emissions worldwide by many thousands of tons.

If we rewrite the flight manual for the the 737 to were flaps were never used, engines were shut down on approach, landing gear was not extended until 100 feet and only brakes were used to slow the aircraft, then the fuel saving would be way more than the insignificant drag caused by exposed main gear tires.

With 14,000+ 737's delivered and/or on order, apparently Boeing must be doing something right with the 737. I suggest that you find aerodynamic numbers that support your harebrained theory. Sure the 737 may be long in the tooth, but it just seems to be a victim of it's own success. Why would you change something that just plain old works?
 
SteelChair
Topic Author
Posts: 487
Joined: Fri Aug 25, 2017 11:37 am

Re: 737 main gear doors fuel inefficiency

Fri Oct 26, 2018 7:58 pm

How ironic to throw around the imbecile label and then triple post!
 
stratclub
Posts: 439
Joined: Fri Jan 05, 2018 10:38 pm

Re: 737 main gear doors fuel inefficiency

Fri Oct 26, 2018 9:17 pm

SteelChair wrote:
How ironic to throw around the imbecile label and then triple post!

Sorry. I never said the label didn't apply to me. I do apologize, it was very disrespectful of me to throw around such a derogatory term here. :white:
 
SteelChair
Topic Author
Posts: 487
Joined: Fri Aug 25, 2017 11:37 am

Re: 737 main gear doors fuel inefficiency

Fri Oct 26, 2018 9:55 pm

stratclub wrote:
SteelChair wrote:
How ironic to throw around the imbecile label and then triple post!

Sorry. I never said the label didn't apply to me. I do apologize, it was very disrespectful of me to throw around such a derogatory term here. :white:


Haha, thanks for that.

Perhaps you have had some a "harebrained" ideas also?
 
Newbiepilot
Posts: 3312
Joined: Tue Aug 30, 2016 10:18 pm

Re: 737 main gear doors fuel inefficiency

Sat Oct 27, 2018 4:28 am

SteelChair wrote:
When the 737 was introduced, it was a short range airplane. The argument against main gear doors was that the fuel savings wqs negligible on short routes. Now, more than 50 years later, 3 major variants later, and with 3-4 hour legs routine, it still has no gear doors. It doesnt seem like such a great idea now.

I have no idea what the fuel penalty associated with no gear doors may be. I am guessing it is very small. But according to wiki, 10,240 737s have been delivered. So the cumulative effect could be large. Huge in fact.

Let's say that a 737 flies 2,800 hours a year, the average fuel burn is 6, 200 lbs/hr, and the average airplane flies 60,000 hours in its lifetime. If we assume that the burn penalty is 0.0025%, (1/4 of 1%), many millions of gallons of fuel have been wasted.

6,200x0.0025=15.5
15.5x2,800x10240=444,416,000
444,416,000÷6.7=66,430,716

Not having gear doors on the 737 has caused over 66 million gallons of extra fuel to be burned. Lets say my numbers are way off, 50% high for example. That's still over 30 million gallons gone forever. And my number could be low instead of high. More petroleum gone forever.

Just one more example of how endlessly upgrading this ancient airframe has been costly.


First off, the 737 has gear doors that cover the strut. Just the wheel and tire are exposed.

Secondly Your incomplete analysis left out weight savings. Not having full size doors saves weight. Not only are there no doors covering the tires, but also no door actuators, rods and linkages. The shock strut doors are slaved to the gear actuators on the 737. 100lbs of weight savings may be enough to offset the drag.
 
SteelChair
Topic Author
Posts: 487
Joined: Fri Aug 25, 2017 11:37 am

Re: 737 main gear doors fuel inefficiency

Sat Oct 27, 2018 2:10 pm

My analysis was incomplete. I said that it was a WAG.

It seems to me that, if this was the best way to do it, many other airliners would also have gear doors designed this way. Instead, a relative few are designed like this.

Fuel burn deltas vary less with short range. When designed, no one envisioned that the 737 would routinely be flying four to six hour missions. It seems to me rather clear, then, that this short-range design feature has now been back fed on to a longer range airplane and there must be some penalty. Of the longer ranged airplanes of today, only the A220 has doors like this.

Thanks for all the input in the thread (minus the ad hominem attacks, cut downs, and name calling).
 
stratclub
Posts: 439
Joined: Fri Jan 05, 2018 10:38 pm

Re: 737 main gear doors fuel inefficiency

Sat Oct 27, 2018 3:22 pm

SteelChair wrote:
stratclub wrote:
SteelChair wrote:
How ironic to throw around the imbecile label and then triple post!

Sorry. I never said the label didn't apply to me. I do apologize, it was very disrespectful of me to throw around such a derogatory term here. :white:


Haha, thanks for that.

Perhaps you have had some a "harebrained" ideas also?

Oh hell ya. Some of my best learning is when I'm wrong.....................
 
Chemist
Posts: 358
Joined: Tue Oct 20, 2015 4:46 am

Re: 737 main gear doors fuel inefficiency

Sun Oct 28, 2018 6:46 am

You can't say "because few other aircraft do it, it must be suboptimal".
Every airframe is different. Every one has different drag characteristics in different places.
With all the efforts to improve efficiencies on all airliners (winglets, scitmars, engine PIPs, tailcones, etc.), the 737 has had many of these improvements yet still hasn't had addition of wheel doors (or lack of). That says that the change overall is not low hanging fruit. It might not even be a benefit at all, on THAT AIRFRAME.
 
stratclub
Posts: 439
Joined: Fri Jan 05, 2018 10:38 pm

Re: 737 main gear doors fuel inefficiency

Sun Oct 28, 2018 12:55 pm

Ever wonder why Boeing stopped production on the 757 and not the 737? The problem with the 737 main gear is that it fails the LAR (Looks About Right) quotient but in reality the design just plain old works well with apparently a very small aerodynamic penalty and some savings on weight. On paper, the 757 is a better aircraft so it just seems reasonable it would have replaced the 737, but it didn't.
 
mmo
Posts: 1637
Joined: Thu Apr 18, 2013 3:04 pm

Re: 737 main gear doors fuel inefficiency

Mon Oct 29, 2018 1:10 pm

stratclub wrote:
Ever wonder why Boeing stopped production on the 757 and not the 737? The problem with the 737 main gear is that it fails the LAR (Looks About Right) quotient but in reality the design just plain old works well with apparently a very small aerodynamic penalty and some savings on weight. On paper, the 757 is a better aircraft so it just seems reasonable it would have replaced the 737, but it didn't.



But the 757 was designed to be a 727 replacement.
If we weren't all crazy we'd all go insane!

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