Why are fuel tanks located in wings?












52














Passenger aircraft have fuel tanks in the wings. Why?
What are the advantages and disadvantages of this location ?



examples of disadvantages I would suspect:




  • added weight increases the structural load applied to the wings

  • different gravitational forces and wing-bending between full and empty tanks result in repeating stresses shortening the aircraft life-span

  • higher risk of catastrophic damage to wings in case of in-flight fuel ignition

  • higher risk of fire when lightning strikes a wing


img










share|improve this question




















  • 43




    Keeping fuel in the wings actually helps to maintain their structural integrity, see aviation.stackexchange.com/questions/42613/…
    – DeepSpace
    Dec 10 at 11:46








  • 32




    On the ground, the aircraft rests on the wheels. In flight, it rests on the wings - so weight in the wings reduces structural loading, not increases it.
    – Therac
    Dec 10 at 18:53






  • 1




    @summerrain it doesn’t reduce it per se, it reduces the need for an even high structural (bending) load that would come from storing it in the main body.
    – Notts90
    Dec 11 at 8:01






  • 7




    Where else would you put the fuel??? There's literally nowhere else. I mean, you could turn the passenger compartment in to a fuel tank I guess?
    – Fattie
    Dec 11 at 12:23






  • 1




    @Fattie I'm pretty sure there are some people who would pay to sit on the wings. Wonder if this is a commercially viable concept...
    – Doktor J
    Dec 13 at 4:20
















52














Passenger aircraft have fuel tanks in the wings. Why?
What are the advantages and disadvantages of this location ?



examples of disadvantages I would suspect:




  • added weight increases the structural load applied to the wings

  • different gravitational forces and wing-bending between full and empty tanks result in repeating stresses shortening the aircraft life-span

  • higher risk of catastrophic damage to wings in case of in-flight fuel ignition

  • higher risk of fire when lightning strikes a wing


img










share|improve this question




















  • 43




    Keeping fuel in the wings actually helps to maintain their structural integrity, see aviation.stackexchange.com/questions/42613/…
    – DeepSpace
    Dec 10 at 11:46








  • 32




    On the ground, the aircraft rests on the wheels. In flight, it rests on the wings - so weight in the wings reduces structural loading, not increases it.
    – Therac
    Dec 10 at 18:53






  • 1




    @summerrain it doesn’t reduce it per se, it reduces the need for an even high structural (bending) load that would come from storing it in the main body.
    – Notts90
    Dec 11 at 8:01






  • 7




    Where else would you put the fuel??? There's literally nowhere else. I mean, you could turn the passenger compartment in to a fuel tank I guess?
    – Fattie
    Dec 11 at 12:23






  • 1




    @Fattie I'm pretty sure there are some people who would pay to sit on the wings. Wonder if this is a commercially viable concept...
    – Doktor J
    Dec 13 at 4:20














52












52








52


7





Passenger aircraft have fuel tanks in the wings. Why?
What are the advantages and disadvantages of this location ?



examples of disadvantages I would suspect:




  • added weight increases the structural load applied to the wings

  • different gravitational forces and wing-bending between full and empty tanks result in repeating stresses shortening the aircraft life-span

  • higher risk of catastrophic damage to wings in case of in-flight fuel ignition

  • higher risk of fire when lightning strikes a wing


img










share|improve this question















Passenger aircraft have fuel tanks in the wings. Why?
What are the advantages and disadvantages of this location ?



examples of disadvantages I would suspect:




  • added weight increases the structural load applied to the wings

  • different gravitational forces and wing-bending between full and empty tanks result in repeating stresses shortening the aircraft life-span

  • higher risk of catastrophic damage to wings in case of in-flight fuel ignition

  • higher risk of fire when lightning strikes a wing


img







aircraft-design wing fuel-tanks aircraft-structures fuel-systems






share|improve this question















share|improve this question













share|improve this question




share|improve this question








edited Dec 14 at 16:10

























asked Dec 10 at 9:51









summerrain

1,0781620




1,0781620








  • 43




    Keeping fuel in the wings actually helps to maintain their structural integrity, see aviation.stackexchange.com/questions/42613/…
    – DeepSpace
    Dec 10 at 11:46








  • 32




    On the ground, the aircraft rests on the wheels. In flight, it rests on the wings - so weight in the wings reduces structural loading, not increases it.
    – Therac
    Dec 10 at 18:53






  • 1




    @summerrain it doesn’t reduce it per se, it reduces the need for an even high structural (bending) load that would come from storing it in the main body.
    – Notts90
    Dec 11 at 8:01






  • 7




    Where else would you put the fuel??? There's literally nowhere else. I mean, you could turn the passenger compartment in to a fuel tank I guess?
    – Fattie
    Dec 11 at 12:23






  • 1




    @Fattie I'm pretty sure there are some people who would pay to sit on the wings. Wonder if this is a commercially viable concept...
    – Doktor J
    Dec 13 at 4:20














  • 43




    Keeping fuel in the wings actually helps to maintain their structural integrity, see aviation.stackexchange.com/questions/42613/…
    – DeepSpace
    Dec 10 at 11:46








  • 32




    On the ground, the aircraft rests on the wheels. In flight, it rests on the wings - so weight in the wings reduces structural loading, not increases it.
    – Therac
    Dec 10 at 18:53






  • 1




    @summerrain it doesn’t reduce it per se, it reduces the need for an even high structural (bending) load that would come from storing it in the main body.
    – Notts90
    Dec 11 at 8:01






  • 7




    Where else would you put the fuel??? There's literally nowhere else. I mean, you could turn the passenger compartment in to a fuel tank I guess?
    – Fattie
    Dec 11 at 12:23






  • 1




    @Fattie I'm pretty sure there are some people who would pay to sit on the wings. Wonder if this is a commercially viable concept...
    – Doktor J
    Dec 13 at 4:20








43




43




Keeping fuel in the wings actually helps to maintain their structural integrity, see aviation.stackexchange.com/questions/42613/…
– DeepSpace
Dec 10 at 11:46






Keeping fuel in the wings actually helps to maintain their structural integrity, see aviation.stackexchange.com/questions/42613/…
– DeepSpace
Dec 10 at 11:46






32




32




On the ground, the aircraft rests on the wheels. In flight, it rests on the wings - so weight in the wings reduces structural loading, not increases it.
– Therac
Dec 10 at 18:53




On the ground, the aircraft rests on the wheels. In flight, it rests on the wings - so weight in the wings reduces structural loading, not increases it.
– Therac
Dec 10 at 18:53




1




1




@summerrain it doesn’t reduce it per se, it reduces the need for an even high structural (bending) load that would come from storing it in the main body.
– Notts90
Dec 11 at 8:01




@summerrain it doesn’t reduce it per se, it reduces the need for an even high structural (bending) load that would come from storing it in the main body.
– Notts90
Dec 11 at 8:01




7




7




Where else would you put the fuel??? There's literally nowhere else. I mean, you could turn the passenger compartment in to a fuel tank I guess?
– Fattie
Dec 11 at 12:23




Where else would you put the fuel??? There's literally nowhere else. I mean, you could turn the passenger compartment in to a fuel tank I guess?
– Fattie
Dec 11 at 12:23




1




1




@Fattie I'm pretty sure there are some people who would pay to sit on the wings. Wonder if this is a commercially viable concept...
– Doktor J
Dec 13 at 4:20




@Fattie I'm pretty sure there are some people who would pay to sit on the wings. Wonder if this is a commercially viable concept...
– Doktor J
Dec 13 at 4:20










8 Answers
8






active

oldest

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115














Several advantages:




  1. Wing structures are hollow and voluminous in order to provide structural rigidity against flutter and carry flight loads. This provides the space needed to store fuel.

  2. On a conventional aircraft, placing fuel tanks in the wings places the fuel mass very close to, or on, the center of lift. This dramatically reduces Cg shift during flight and reduces the size and weight of the tailplane to maintain stable flight. It also reduces Cg shifts due to sloshing of the fuel inside the tanks, due to the limited constraints of longitudinal travel for the fuel in the tanks.

  3. In the event of a crash landing, having the fuel in the wings keeps it away from the cabin and the occupants, reducing risks of cabin fires.

  4. The weight of the fuel reduces the loading moment on the wing roots, reducing the weight of the structure needed to support the aircraft during flight.






share|improve this answer



















  • 5




    Possible additional: adding weight to the wings increases their inertia, reducing the influence that turbulent airflow has on them. In simple terms, if the air/wind spends all its time trying to wag the wings up and down and snap them off the plane, making the wings heavier makes them harder to wag, reducing the amount of repeated bending stress the mount points are subject to, and providing for a plane that flies more stably
    – Caius Jard
    Dec 12 at 10:29






  • 11




    Also: increasing fuel capacity in the fuselage would reduce available cargo space; the wings can't be practically used for this, but they can be used very practically for fuel because it's not constrained to a particular container height/size. It's liquid, so they can fit the cell around and between structural parts of the wing and make use of a great deal of it. Conversely, relatively few suitcases could be fit practically along the wing, probably primarily near the root, and trying to design around the necessary volume would be an engineering challenge to keep the wings structurally sound.
    – GalacticCowboy
    Dec 12 at 14:43






  • 3




    @GalacticCowboy not to mention, trying to balance the weight, since same-sized pieces of luggage may weigh differently.
    – Doktor J
    Dec 13 at 4:22



















79














I see what you're saying, but there's something you're overlooking in your logic. You're looking at an airplane sitting on the ground, where the wheels are near the fuselage and most of the wings are dead weight that creates strain on the structure.



Think about one in flight. Now all the lift is coming from the wings, imagine the airplane suspended by a couple dozen (billion) cables spread around the wing surfaces. Now the fuselage is dead weight and the strain in the structure is from carrying the fuselage.



So when you add weight to the wings evenly, it adds practically zero structural load for the wings. What's being lifted is inside the source of the lift. So from a structural load perspective, it's a wash: it doesn't matter.



Whereas if you add more tanks in the fuselage, that's fine on the ground, but it adds huge stresses to the wings in flight, effectively reducing practical cargo capacity.



The strain on wings from sitting on the ground is much less worrisome to designers than the strains in flight.



See also "Zero Fuel Weight".






share|improve this answer



















  • 1




    Exactly what I was thinking, but you said it much better!
    – Michael Hall
    Dec 10 at 22:44










  • +1, for a great explanation.
    – Wossname
    Dec 12 at 11:56






  • 2




    "where the wheels are under the fuselage and the wings are dead weight that creates strain on the structure." One important note here: Most airplanes with tricycle landing gear actually have the main gear mounted to the wings, not the fuselage. Some very large aircraft do have an additional inboard set of main gear under the fuselage, but they usually still have outboard main gear under the wings.
    – reirab
    Dec 14 at 17:47












  • For example Boeing 757, PA-28-140, Airbus A320, Boeing 747
    – reirab
    Dec 14 at 17:53



















27















added weight increases the structural load applied to the wings
different gravitational forces and wing-bending between full and empty tanks result in repeating stresses shortening the aircraft life-span




As a result of the effects of lift (and the deceasing need for it as the plane lightens) the reverse is actually true see here




higher risk of catastrophic damage to wings in case of in-flight fuel ignition




As opposed to higher risk of catastrophic damage to the cabin in the case of in-flight fuel ignition?



Assuming a non-explosive ignition having the fuel in the wings means you can take action to dump the fuel. If you have a fire begin in the main fuselage however you've got a higher chance of the fire incapacitating the crew before they can take steps. Or damage occuring to the avionics, the pressure cabin etc.




maybe higher risk of fire when lightning strikes a wing ?




Wing tips are one of the locations on a plane that is more prone to lightning strikes - and the potential for fuel fires is there but steps are taken to counter this and in the vast majority of cases lightning does very little damage






share|improve this answer





























    14














    Quite simply: there's a lot of empty space in those wings, and there's a lot of empty space needed for fuel.



    Creating space elsewhere for fuel would make the entire aircraft larger and heavier, so makes little sense.



    And it's not just the wings, many aircraft carry fuel in the vertical stabiliser as well.






    share|improve this answer

















    • 58




      In other words: Why are fuel tanks located in the wings? Because the passengers wouldn't fit in there. :)
      – Tanner Swett
      Dec 10 at 13:14






    • 35




      @TannerSwett Don't give them any ideas...
      – pipe
      Dec 10 at 15:33






    • 7




      @pipe en.wikipedia.org/wiki/Junkers_G.38 ?
      – DeepSpace
      Dec 10 at 17:24






    • 4




      @TannerSwett hmm, Ryanair wants to talk with you about that idea.
      – jwenting
      Dec 11 at 5:05



















    13














    Along with the other answers, I'll point out most of the recent the cases where an aircraft fuel tank exploded, the center tank, which is in the fuselage, was implicated. There are two reasons:



    First, a fuselage tank is located lower than the engines and requires pumps to raise the fuel. Electrical pump failures have caused explosions. This also means that a pump failure results in unusable fuel, whereas wing tanks can naturally feed the engines via gravity.



    Second, fuselage tanks are closer to sources of heat. This was a cause of the TWA flight 800 accident, where heat from nearby air conditioning equipment lead to a flammable vapor in the fuel tanks. In contrast, wing tanks are naturally cooled by airflow and are less susceptible to forming such explosive vapors.






    share|improve this answer



















    • 1




      Not sure if you meant "that in all the cases ... it was the center tank which was implicated" (which is apparently true), but if so, you could probably make it more explicit.
      – jcaron
      Dec 11 at 13:27










    • @jcaron Reworded. I'm sure a wing tank has exploded at some time in the history of aviation, but certainly the center tank has been the main cause of accidents recently.
      – user71659
      Dec 12 at 16:31



















    10
















    • added weight increases the structural load applied to the wings




    Only when the plane's on the ground. When it's in the air, it decreases the load on the wings because their lift balances the weight.





    • different gravitational forces and wing-bending between full and empty tanks result in repeating stresses shortening the aircraft life-span




    At the rate of one cycle per flight. And the wings already go through a stress cycle once per flight (flexed down when the plane's on the ground and up when it's in the air).





    • higher risk of catastrophic damage to wings in case of in-flight fuel ignition




    The fuel tanks catching fire in flight is catastrophic wherever you put them.





    • higher risk of fire when lightning strikes a wing




    When did that last happen? Wikipedia's list of plane crashes suggests LANSA flight 508 in 1971. Such incidents are now even rarer, because fuel tanks are fitted with inerting systems. This was originally recommended after the crash of Pan Am flight 214 in 1963 but it took a long time for it to actually happen.






    share|improve this answer



















    • 1




      This answer seems to imply that inerting systems have been used since sometime shortly after 1963, or at least that inerting systems are responsible for the lack of lightning-induced fire since 1971. The link you provided, however, says inerting systems were not installed for 40 years after the crash of Pan Am 214. Here's an article describing the state of the art in 2004: airspacemag.com/how-things-work/safer-fuel-tanks-5883916
      – David K
      Dec 11 at 13:15










    • @DavidK Yes, it looks like I've exaggerated what actually happened. I'll come back and edit when I have time, or you're welcome to propose an edit yourself if you have the time. Thanks for letting me know.
      – David Richerby
      Dec 11 at 14:50












    • @DavidK Edited.
      – David Richerby
      Dec 13 at 23:35






    • 1




      @summerrain Do you have any examples of planes that have made successful emergency landings after fuel tank fires? It feels like your argument is completely hypothetical.
      – David Richerby
      Dec 14 at 16:50






    • 1




      @summerrain I already explained why there aren't fuel tanks under the cockpit. Your question amounts to "In an alternate universe, would..." and we're not in an alternate universe so there's no value in addressing your question. As for an example, you are claiming that putting fuel tanks in different places would give more time for emergency landings. I suggest to you that fuel tank fires are so catastrophic that no emergency landing is going to be possible. A great way for you to argue against that claim would be to say "But it happened on flight XYZ."
      – David Richerby
      Dec 14 at 17:19



















    1














    More weight on the wings is actually good as it makes the aircraft more balance and more resistant to unnecessary swerving during turbulence or wind current, like a person walking on tight rope carrying a horizontal rod(bar) for balancing. Check out radius of Gyration in mechanics.






    share|improve this answer





























      -2














      There is no other reason.
      The engine is attached to the wing and They are trying to design a fuel tank to fuel the engine,
      There is no space on the torso. So they make a hole in the wings.






      share|improve this answer



















      • 1




        welcome to aviation.SE. Please be aware that this is an english-only website. as such, we will have to remove the part of your answer written in Korean. Moreover, please be aware that we like answers that contain a bit of detail, and possibly references.
        – Federico
        Dec 16 at 8:24













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      8 Answers
      8






      active

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      votes








      8 Answers
      8






      active

      oldest

      votes









      active

      oldest

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      active

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      115














      Several advantages:




      1. Wing structures are hollow and voluminous in order to provide structural rigidity against flutter and carry flight loads. This provides the space needed to store fuel.

      2. On a conventional aircraft, placing fuel tanks in the wings places the fuel mass very close to, or on, the center of lift. This dramatically reduces Cg shift during flight and reduces the size and weight of the tailplane to maintain stable flight. It also reduces Cg shifts due to sloshing of the fuel inside the tanks, due to the limited constraints of longitudinal travel for the fuel in the tanks.

      3. In the event of a crash landing, having the fuel in the wings keeps it away from the cabin and the occupants, reducing risks of cabin fires.

      4. The weight of the fuel reduces the loading moment on the wing roots, reducing the weight of the structure needed to support the aircraft during flight.






      share|improve this answer



















      • 5




        Possible additional: adding weight to the wings increases their inertia, reducing the influence that turbulent airflow has on them. In simple terms, if the air/wind spends all its time trying to wag the wings up and down and snap them off the plane, making the wings heavier makes them harder to wag, reducing the amount of repeated bending stress the mount points are subject to, and providing for a plane that flies more stably
        – Caius Jard
        Dec 12 at 10:29






      • 11




        Also: increasing fuel capacity in the fuselage would reduce available cargo space; the wings can't be practically used for this, but they can be used very practically for fuel because it's not constrained to a particular container height/size. It's liquid, so they can fit the cell around and between structural parts of the wing and make use of a great deal of it. Conversely, relatively few suitcases could be fit practically along the wing, probably primarily near the root, and trying to design around the necessary volume would be an engineering challenge to keep the wings structurally sound.
        – GalacticCowboy
        Dec 12 at 14:43






      • 3




        @GalacticCowboy not to mention, trying to balance the weight, since same-sized pieces of luggage may weigh differently.
        – Doktor J
        Dec 13 at 4:22
















      115














      Several advantages:




      1. Wing structures are hollow and voluminous in order to provide structural rigidity against flutter and carry flight loads. This provides the space needed to store fuel.

      2. On a conventional aircraft, placing fuel tanks in the wings places the fuel mass very close to, or on, the center of lift. This dramatically reduces Cg shift during flight and reduces the size and weight of the tailplane to maintain stable flight. It also reduces Cg shifts due to sloshing of the fuel inside the tanks, due to the limited constraints of longitudinal travel for the fuel in the tanks.

      3. In the event of a crash landing, having the fuel in the wings keeps it away from the cabin and the occupants, reducing risks of cabin fires.

      4. The weight of the fuel reduces the loading moment on the wing roots, reducing the weight of the structure needed to support the aircraft during flight.






      share|improve this answer



















      • 5




        Possible additional: adding weight to the wings increases their inertia, reducing the influence that turbulent airflow has on them. In simple terms, if the air/wind spends all its time trying to wag the wings up and down and snap them off the plane, making the wings heavier makes them harder to wag, reducing the amount of repeated bending stress the mount points are subject to, and providing for a plane that flies more stably
        – Caius Jard
        Dec 12 at 10:29






      • 11




        Also: increasing fuel capacity in the fuselage would reduce available cargo space; the wings can't be practically used for this, but they can be used very practically for fuel because it's not constrained to a particular container height/size. It's liquid, so they can fit the cell around and between structural parts of the wing and make use of a great deal of it. Conversely, relatively few suitcases could be fit practically along the wing, probably primarily near the root, and trying to design around the necessary volume would be an engineering challenge to keep the wings structurally sound.
        – GalacticCowboy
        Dec 12 at 14:43






      • 3




        @GalacticCowboy not to mention, trying to balance the weight, since same-sized pieces of luggage may weigh differently.
        – Doktor J
        Dec 13 at 4:22














      115












      115








      115






      Several advantages:




      1. Wing structures are hollow and voluminous in order to provide structural rigidity against flutter and carry flight loads. This provides the space needed to store fuel.

      2. On a conventional aircraft, placing fuel tanks in the wings places the fuel mass very close to, or on, the center of lift. This dramatically reduces Cg shift during flight and reduces the size and weight of the tailplane to maintain stable flight. It also reduces Cg shifts due to sloshing of the fuel inside the tanks, due to the limited constraints of longitudinal travel for the fuel in the tanks.

      3. In the event of a crash landing, having the fuel in the wings keeps it away from the cabin and the occupants, reducing risks of cabin fires.

      4. The weight of the fuel reduces the loading moment on the wing roots, reducing the weight of the structure needed to support the aircraft during flight.






      share|improve this answer














      Several advantages:




      1. Wing structures are hollow and voluminous in order to provide structural rigidity against flutter and carry flight loads. This provides the space needed to store fuel.

      2. On a conventional aircraft, placing fuel tanks in the wings places the fuel mass very close to, or on, the center of lift. This dramatically reduces Cg shift during flight and reduces the size and weight of the tailplane to maintain stable flight. It also reduces Cg shifts due to sloshing of the fuel inside the tanks, due to the limited constraints of longitudinal travel for the fuel in the tanks.

      3. In the event of a crash landing, having the fuel in the wings keeps it away from the cabin and the occupants, reducing risks of cabin fires.

      4. The weight of the fuel reduces the loading moment on the wing roots, reducing the weight of the structure needed to support the aircraft during flight.







      share|improve this answer














      share|improve this answer



      share|improve this answer








      edited Dec 13 at 17:42

























      answered Dec 10 at 14:30









      Carlo Felicione

      40.5k373148




      40.5k373148








      • 5




        Possible additional: adding weight to the wings increases their inertia, reducing the influence that turbulent airflow has on them. In simple terms, if the air/wind spends all its time trying to wag the wings up and down and snap them off the plane, making the wings heavier makes them harder to wag, reducing the amount of repeated bending stress the mount points are subject to, and providing for a plane that flies more stably
        – Caius Jard
        Dec 12 at 10:29






      • 11




        Also: increasing fuel capacity in the fuselage would reduce available cargo space; the wings can't be practically used for this, but they can be used very practically for fuel because it's not constrained to a particular container height/size. It's liquid, so they can fit the cell around and between structural parts of the wing and make use of a great deal of it. Conversely, relatively few suitcases could be fit practically along the wing, probably primarily near the root, and trying to design around the necessary volume would be an engineering challenge to keep the wings structurally sound.
        – GalacticCowboy
        Dec 12 at 14:43






      • 3




        @GalacticCowboy not to mention, trying to balance the weight, since same-sized pieces of luggage may weigh differently.
        – Doktor J
        Dec 13 at 4:22














      • 5




        Possible additional: adding weight to the wings increases their inertia, reducing the influence that turbulent airflow has on them. In simple terms, if the air/wind spends all its time trying to wag the wings up and down and snap them off the plane, making the wings heavier makes them harder to wag, reducing the amount of repeated bending stress the mount points are subject to, and providing for a plane that flies more stably
        – Caius Jard
        Dec 12 at 10:29






      • 11




        Also: increasing fuel capacity in the fuselage would reduce available cargo space; the wings can't be practically used for this, but they can be used very practically for fuel because it's not constrained to a particular container height/size. It's liquid, so they can fit the cell around and between structural parts of the wing and make use of a great deal of it. Conversely, relatively few suitcases could be fit practically along the wing, probably primarily near the root, and trying to design around the necessary volume would be an engineering challenge to keep the wings structurally sound.
        – GalacticCowboy
        Dec 12 at 14:43






      • 3




        @GalacticCowboy not to mention, trying to balance the weight, since same-sized pieces of luggage may weigh differently.
        – Doktor J
        Dec 13 at 4:22








      5




      5




      Possible additional: adding weight to the wings increases their inertia, reducing the influence that turbulent airflow has on them. In simple terms, if the air/wind spends all its time trying to wag the wings up and down and snap them off the plane, making the wings heavier makes them harder to wag, reducing the amount of repeated bending stress the mount points are subject to, and providing for a plane that flies more stably
      – Caius Jard
      Dec 12 at 10:29




      Possible additional: adding weight to the wings increases their inertia, reducing the influence that turbulent airflow has on them. In simple terms, if the air/wind spends all its time trying to wag the wings up and down and snap them off the plane, making the wings heavier makes them harder to wag, reducing the amount of repeated bending stress the mount points are subject to, and providing for a plane that flies more stably
      – Caius Jard
      Dec 12 at 10:29




      11




      11




      Also: increasing fuel capacity in the fuselage would reduce available cargo space; the wings can't be practically used for this, but they can be used very practically for fuel because it's not constrained to a particular container height/size. It's liquid, so they can fit the cell around and between structural parts of the wing and make use of a great deal of it. Conversely, relatively few suitcases could be fit practically along the wing, probably primarily near the root, and trying to design around the necessary volume would be an engineering challenge to keep the wings structurally sound.
      – GalacticCowboy
      Dec 12 at 14:43




      Also: increasing fuel capacity in the fuselage would reduce available cargo space; the wings can't be practically used for this, but they can be used very practically for fuel because it's not constrained to a particular container height/size. It's liquid, so they can fit the cell around and between structural parts of the wing and make use of a great deal of it. Conversely, relatively few suitcases could be fit practically along the wing, probably primarily near the root, and trying to design around the necessary volume would be an engineering challenge to keep the wings structurally sound.
      – GalacticCowboy
      Dec 12 at 14:43




      3




      3




      @GalacticCowboy not to mention, trying to balance the weight, since same-sized pieces of luggage may weigh differently.
      – Doktor J
      Dec 13 at 4:22




      @GalacticCowboy not to mention, trying to balance the weight, since same-sized pieces of luggage may weigh differently.
      – Doktor J
      Dec 13 at 4:22











      79














      I see what you're saying, but there's something you're overlooking in your logic. You're looking at an airplane sitting on the ground, where the wheels are near the fuselage and most of the wings are dead weight that creates strain on the structure.



      Think about one in flight. Now all the lift is coming from the wings, imagine the airplane suspended by a couple dozen (billion) cables spread around the wing surfaces. Now the fuselage is dead weight and the strain in the structure is from carrying the fuselage.



      So when you add weight to the wings evenly, it adds practically zero structural load for the wings. What's being lifted is inside the source of the lift. So from a structural load perspective, it's a wash: it doesn't matter.



      Whereas if you add more tanks in the fuselage, that's fine on the ground, but it adds huge stresses to the wings in flight, effectively reducing practical cargo capacity.



      The strain on wings from sitting on the ground is much less worrisome to designers than the strains in flight.



      See also "Zero Fuel Weight".






      share|improve this answer



















      • 1




        Exactly what I was thinking, but you said it much better!
        – Michael Hall
        Dec 10 at 22:44










      • +1, for a great explanation.
        – Wossname
        Dec 12 at 11:56






      • 2




        "where the wheels are under the fuselage and the wings are dead weight that creates strain on the structure." One important note here: Most airplanes with tricycle landing gear actually have the main gear mounted to the wings, not the fuselage. Some very large aircraft do have an additional inboard set of main gear under the fuselage, but they usually still have outboard main gear under the wings.
        – reirab
        Dec 14 at 17:47












      • For example Boeing 757, PA-28-140, Airbus A320, Boeing 747
        – reirab
        Dec 14 at 17:53
















      79














      I see what you're saying, but there's something you're overlooking in your logic. You're looking at an airplane sitting on the ground, where the wheels are near the fuselage and most of the wings are dead weight that creates strain on the structure.



      Think about one in flight. Now all the lift is coming from the wings, imagine the airplane suspended by a couple dozen (billion) cables spread around the wing surfaces. Now the fuselage is dead weight and the strain in the structure is from carrying the fuselage.



      So when you add weight to the wings evenly, it adds practically zero structural load for the wings. What's being lifted is inside the source of the lift. So from a structural load perspective, it's a wash: it doesn't matter.



      Whereas if you add more tanks in the fuselage, that's fine on the ground, but it adds huge stresses to the wings in flight, effectively reducing practical cargo capacity.



      The strain on wings from sitting on the ground is much less worrisome to designers than the strains in flight.



      See also "Zero Fuel Weight".






      share|improve this answer



















      • 1




        Exactly what I was thinking, but you said it much better!
        – Michael Hall
        Dec 10 at 22:44










      • +1, for a great explanation.
        – Wossname
        Dec 12 at 11:56






      • 2




        "where the wheels are under the fuselage and the wings are dead weight that creates strain on the structure." One important note here: Most airplanes with tricycle landing gear actually have the main gear mounted to the wings, not the fuselage. Some very large aircraft do have an additional inboard set of main gear under the fuselage, but they usually still have outboard main gear under the wings.
        – reirab
        Dec 14 at 17:47












      • For example Boeing 757, PA-28-140, Airbus A320, Boeing 747
        – reirab
        Dec 14 at 17:53














      79












      79








      79






      I see what you're saying, but there's something you're overlooking in your logic. You're looking at an airplane sitting on the ground, where the wheels are near the fuselage and most of the wings are dead weight that creates strain on the structure.



      Think about one in flight. Now all the lift is coming from the wings, imagine the airplane suspended by a couple dozen (billion) cables spread around the wing surfaces. Now the fuselage is dead weight and the strain in the structure is from carrying the fuselage.



      So when you add weight to the wings evenly, it adds practically zero structural load for the wings. What's being lifted is inside the source of the lift. So from a structural load perspective, it's a wash: it doesn't matter.



      Whereas if you add more tanks in the fuselage, that's fine on the ground, but it adds huge stresses to the wings in flight, effectively reducing practical cargo capacity.



      The strain on wings from sitting on the ground is much less worrisome to designers than the strains in flight.



      See also "Zero Fuel Weight".






      share|improve this answer














      I see what you're saying, but there's something you're overlooking in your logic. You're looking at an airplane sitting on the ground, where the wheels are near the fuselage and most of the wings are dead weight that creates strain on the structure.



      Think about one in flight. Now all the lift is coming from the wings, imagine the airplane suspended by a couple dozen (billion) cables spread around the wing surfaces. Now the fuselage is dead weight and the strain in the structure is from carrying the fuselage.



      So when you add weight to the wings evenly, it adds practically zero structural load for the wings. What's being lifted is inside the source of the lift. So from a structural load perspective, it's a wash: it doesn't matter.



      Whereas if you add more tanks in the fuselage, that's fine on the ground, but it adds huge stresses to the wings in flight, effectively reducing practical cargo capacity.



      The strain on wings from sitting on the ground is much less worrisome to designers than the strains in flight.



      See also "Zero Fuel Weight".







      share|improve this answer














      share|improve this answer



      share|improve this answer








      edited Dec 16 at 18:28

























      answered Dec 10 at 18:32









      Harper

      2,735618




      2,735618








      • 1




        Exactly what I was thinking, but you said it much better!
        – Michael Hall
        Dec 10 at 22:44










      • +1, for a great explanation.
        – Wossname
        Dec 12 at 11:56






      • 2




        "where the wheels are under the fuselage and the wings are dead weight that creates strain on the structure." One important note here: Most airplanes with tricycle landing gear actually have the main gear mounted to the wings, not the fuselage. Some very large aircraft do have an additional inboard set of main gear under the fuselage, but they usually still have outboard main gear under the wings.
        – reirab
        Dec 14 at 17:47












      • For example Boeing 757, PA-28-140, Airbus A320, Boeing 747
        – reirab
        Dec 14 at 17:53














      • 1




        Exactly what I was thinking, but you said it much better!
        – Michael Hall
        Dec 10 at 22:44










      • +1, for a great explanation.
        – Wossname
        Dec 12 at 11:56






      • 2




        "where the wheels are under the fuselage and the wings are dead weight that creates strain on the structure." One important note here: Most airplanes with tricycle landing gear actually have the main gear mounted to the wings, not the fuselage. Some very large aircraft do have an additional inboard set of main gear under the fuselage, but they usually still have outboard main gear under the wings.
        – reirab
        Dec 14 at 17:47












      • For example Boeing 757, PA-28-140, Airbus A320, Boeing 747
        – reirab
        Dec 14 at 17:53








      1




      1




      Exactly what I was thinking, but you said it much better!
      – Michael Hall
      Dec 10 at 22:44




      Exactly what I was thinking, but you said it much better!
      – Michael Hall
      Dec 10 at 22:44












      +1, for a great explanation.
      – Wossname
      Dec 12 at 11:56




      +1, for a great explanation.
      – Wossname
      Dec 12 at 11:56




      2




      2




      "where the wheels are under the fuselage and the wings are dead weight that creates strain on the structure." One important note here: Most airplanes with tricycle landing gear actually have the main gear mounted to the wings, not the fuselage. Some very large aircraft do have an additional inboard set of main gear under the fuselage, but they usually still have outboard main gear under the wings.
      – reirab
      Dec 14 at 17:47






      "where the wheels are under the fuselage and the wings are dead weight that creates strain on the structure." One important note here: Most airplanes with tricycle landing gear actually have the main gear mounted to the wings, not the fuselage. Some very large aircraft do have an additional inboard set of main gear under the fuselage, but they usually still have outboard main gear under the wings.
      – reirab
      Dec 14 at 17:47














      For example Boeing 757, PA-28-140, Airbus A320, Boeing 747
      – reirab
      Dec 14 at 17:53




      For example Boeing 757, PA-28-140, Airbus A320, Boeing 747
      – reirab
      Dec 14 at 17:53











      27















      added weight increases the structural load applied to the wings
      different gravitational forces and wing-bending between full and empty tanks result in repeating stresses shortening the aircraft life-span




      As a result of the effects of lift (and the deceasing need for it as the plane lightens) the reverse is actually true see here




      higher risk of catastrophic damage to wings in case of in-flight fuel ignition




      As opposed to higher risk of catastrophic damage to the cabin in the case of in-flight fuel ignition?



      Assuming a non-explosive ignition having the fuel in the wings means you can take action to dump the fuel. If you have a fire begin in the main fuselage however you've got a higher chance of the fire incapacitating the crew before they can take steps. Or damage occuring to the avionics, the pressure cabin etc.




      maybe higher risk of fire when lightning strikes a wing ?




      Wing tips are one of the locations on a plane that is more prone to lightning strikes - and the potential for fuel fires is there but steps are taken to counter this and in the vast majority of cases lightning does very little damage






      share|improve this answer


























        27















        added weight increases the structural load applied to the wings
        different gravitational forces and wing-bending between full and empty tanks result in repeating stresses shortening the aircraft life-span




        As a result of the effects of lift (and the deceasing need for it as the plane lightens) the reverse is actually true see here




        higher risk of catastrophic damage to wings in case of in-flight fuel ignition




        As opposed to higher risk of catastrophic damage to the cabin in the case of in-flight fuel ignition?



        Assuming a non-explosive ignition having the fuel in the wings means you can take action to dump the fuel. If you have a fire begin in the main fuselage however you've got a higher chance of the fire incapacitating the crew before they can take steps. Or damage occuring to the avionics, the pressure cabin etc.




        maybe higher risk of fire when lightning strikes a wing ?




        Wing tips are one of the locations on a plane that is more prone to lightning strikes - and the potential for fuel fires is there but steps are taken to counter this and in the vast majority of cases lightning does very little damage






        share|improve this answer
























          27












          27








          27







          added weight increases the structural load applied to the wings
          different gravitational forces and wing-bending between full and empty tanks result in repeating stresses shortening the aircraft life-span




          As a result of the effects of lift (and the deceasing need for it as the plane lightens) the reverse is actually true see here




          higher risk of catastrophic damage to wings in case of in-flight fuel ignition




          As opposed to higher risk of catastrophic damage to the cabin in the case of in-flight fuel ignition?



          Assuming a non-explosive ignition having the fuel in the wings means you can take action to dump the fuel. If you have a fire begin in the main fuselage however you've got a higher chance of the fire incapacitating the crew before they can take steps. Or damage occuring to the avionics, the pressure cabin etc.




          maybe higher risk of fire when lightning strikes a wing ?




          Wing tips are one of the locations on a plane that is more prone to lightning strikes - and the potential for fuel fires is there but steps are taken to counter this and in the vast majority of cases lightning does very little damage






          share|improve this answer













          added weight increases the structural load applied to the wings
          different gravitational forces and wing-bending between full and empty tanks result in repeating stresses shortening the aircraft life-span




          As a result of the effects of lift (and the deceasing need for it as the plane lightens) the reverse is actually true see here




          higher risk of catastrophic damage to wings in case of in-flight fuel ignition




          As opposed to higher risk of catastrophic damage to the cabin in the case of in-flight fuel ignition?



          Assuming a non-explosive ignition having the fuel in the wings means you can take action to dump the fuel. If you have a fire begin in the main fuselage however you've got a higher chance of the fire incapacitating the crew before they can take steps. Or damage occuring to the avionics, the pressure cabin etc.




          maybe higher risk of fire when lightning strikes a wing ?




          Wing tips are one of the locations on a plane that is more prone to lightning strikes - and the potential for fuel fires is there but steps are taken to counter this and in the vast majority of cases lightning does very little damage







          share|improve this answer












          share|improve this answer



          share|improve this answer










          answered Dec 10 at 12:43









          motosubatsu

          47317




          47317























              14














              Quite simply: there's a lot of empty space in those wings, and there's a lot of empty space needed for fuel.



              Creating space elsewhere for fuel would make the entire aircraft larger and heavier, so makes little sense.



              And it's not just the wings, many aircraft carry fuel in the vertical stabiliser as well.






              share|improve this answer

















              • 58




                In other words: Why are fuel tanks located in the wings? Because the passengers wouldn't fit in there. :)
                – Tanner Swett
                Dec 10 at 13:14






              • 35




                @TannerSwett Don't give them any ideas...
                – pipe
                Dec 10 at 15:33






              • 7




                @pipe en.wikipedia.org/wiki/Junkers_G.38 ?
                – DeepSpace
                Dec 10 at 17:24






              • 4




                @TannerSwett hmm, Ryanair wants to talk with you about that idea.
                – jwenting
                Dec 11 at 5:05
















              14














              Quite simply: there's a lot of empty space in those wings, and there's a lot of empty space needed for fuel.



              Creating space elsewhere for fuel would make the entire aircraft larger and heavier, so makes little sense.



              And it's not just the wings, many aircraft carry fuel in the vertical stabiliser as well.






              share|improve this answer

















              • 58




                In other words: Why are fuel tanks located in the wings? Because the passengers wouldn't fit in there. :)
                – Tanner Swett
                Dec 10 at 13:14






              • 35




                @TannerSwett Don't give them any ideas...
                – pipe
                Dec 10 at 15:33






              • 7




                @pipe en.wikipedia.org/wiki/Junkers_G.38 ?
                – DeepSpace
                Dec 10 at 17:24






              • 4




                @TannerSwett hmm, Ryanair wants to talk with you about that idea.
                – jwenting
                Dec 11 at 5:05














              14












              14








              14






              Quite simply: there's a lot of empty space in those wings, and there's a lot of empty space needed for fuel.



              Creating space elsewhere for fuel would make the entire aircraft larger and heavier, so makes little sense.



              And it's not just the wings, many aircraft carry fuel in the vertical stabiliser as well.






              share|improve this answer












              Quite simply: there's a lot of empty space in those wings, and there's a lot of empty space needed for fuel.



              Creating space elsewhere for fuel would make the entire aircraft larger and heavier, so makes little sense.



              And it's not just the wings, many aircraft carry fuel in the vertical stabiliser as well.







              share|improve this answer












              share|improve this answer



              share|improve this answer










              answered Dec 10 at 10:31









              jwenting

              11k12744




              11k12744








              • 58




                In other words: Why are fuel tanks located in the wings? Because the passengers wouldn't fit in there. :)
                – Tanner Swett
                Dec 10 at 13:14






              • 35




                @TannerSwett Don't give them any ideas...
                – pipe
                Dec 10 at 15:33






              • 7




                @pipe en.wikipedia.org/wiki/Junkers_G.38 ?
                – DeepSpace
                Dec 10 at 17:24






              • 4




                @TannerSwett hmm, Ryanair wants to talk with you about that idea.
                – jwenting
                Dec 11 at 5:05














              • 58




                In other words: Why are fuel tanks located in the wings? Because the passengers wouldn't fit in there. :)
                – Tanner Swett
                Dec 10 at 13:14






              • 35




                @TannerSwett Don't give them any ideas...
                – pipe
                Dec 10 at 15:33






              • 7




                @pipe en.wikipedia.org/wiki/Junkers_G.38 ?
                – DeepSpace
                Dec 10 at 17:24






              • 4




                @TannerSwett hmm, Ryanair wants to talk with you about that idea.
                – jwenting
                Dec 11 at 5:05








              58




              58




              In other words: Why are fuel tanks located in the wings? Because the passengers wouldn't fit in there. :)
              – Tanner Swett
              Dec 10 at 13:14




              In other words: Why are fuel tanks located in the wings? Because the passengers wouldn't fit in there. :)
              – Tanner Swett
              Dec 10 at 13:14




              35




              35




              @TannerSwett Don't give them any ideas...
              – pipe
              Dec 10 at 15:33




              @TannerSwett Don't give them any ideas...
              – pipe
              Dec 10 at 15:33




              7




              7




              @pipe en.wikipedia.org/wiki/Junkers_G.38 ?
              – DeepSpace
              Dec 10 at 17:24




              @pipe en.wikipedia.org/wiki/Junkers_G.38 ?
              – DeepSpace
              Dec 10 at 17:24




              4




              4




              @TannerSwett hmm, Ryanair wants to talk with you about that idea.
              – jwenting
              Dec 11 at 5:05




              @TannerSwett hmm, Ryanair wants to talk with you about that idea.
              – jwenting
              Dec 11 at 5:05











              13














              Along with the other answers, I'll point out most of the recent the cases where an aircraft fuel tank exploded, the center tank, which is in the fuselage, was implicated. There are two reasons:



              First, a fuselage tank is located lower than the engines and requires pumps to raise the fuel. Electrical pump failures have caused explosions. This also means that a pump failure results in unusable fuel, whereas wing tanks can naturally feed the engines via gravity.



              Second, fuselage tanks are closer to sources of heat. This was a cause of the TWA flight 800 accident, where heat from nearby air conditioning equipment lead to a flammable vapor in the fuel tanks. In contrast, wing tanks are naturally cooled by airflow and are less susceptible to forming such explosive vapors.






              share|improve this answer



















              • 1




                Not sure if you meant "that in all the cases ... it was the center tank which was implicated" (which is apparently true), but if so, you could probably make it more explicit.
                – jcaron
                Dec 11 at 13:27










              • @jcaron Reworded. I'm sure a wing tank has exploded at some time in the history of aviation, but certainly the center tank has been the main cause of accidents recently.
                – user71659
                Dec 12 at 16:31
















              13














              Along with the other answers, I'll point out most of the recent the cases where an aircraft fuel tank exploded, the center tank, which is in the fuselage, was implicated. There are two reasons:



              First, a fuselage tank is located lower than the engines and requires pumps to raise the fuel. Electrical pump failures have caused explosions. This also means that a pump failure results in unusable fuel, whereas wing tanks can naturally feed the engines via gravity.



              Second, fuselage tanks are closer to sources of heat. This was a cause of the TWA flight 800 accident, where heat from nearby air conditioning equipment lead to a flammable vapor in the fuel tanks. In contrast, wing tanks are naturally cooled by airflow and are less susceptible to forming such explosive vapors.






              share|improve this answer



















              • 1




                Not sure if you meant "that in all the cases ... it was the center tank which was implicated" (which is apparently true), but if so, you could probably make it more explicit.
                – jcaron
                Dec 11 at 13:27










              • @jcaron Reworded. I'm sure a wing tank has exploded at some time in the history of aviation, but certainly the center tank has been the main cause of accidents recently.
                – user71659
                Dec 12 at 16:31














              13












              13








              13






              Along with the other answers, I'll point out most of the recent the cases where an aircraft fuel tank exploded, the center tank, which is in the fuselage, was implicated. There are two reasons:



              First, a fuselage tank is located lower than the engines and requires pumps to raise the fuel. Electrical pump failures have caused explosions. This also means that a pump failure results in unusable fuel, whereas wing tanks can naturally feed the engines via gravity.



              Second, fuselage tanks are closer to sources of heat. This was a cause of the TWA flight 800 accident, where heat from nearby air conditioning equipment lead to a flammable vapor in the fuel tanks. In contrast, wing tanks are naturally cooled by airflow and are less susceptible to forming such explosive vapors.






              share|improve this answer














              Along with the other answers, I'll point out most of the recent the cases where an aircraft fuel tank exploded, the center tank, which is in the fuselage, was implicated. There are two reasons:



              First, a fuselage tank is located lower than the engines and requires pumps to raise the fuel. Electrical pump failures have caused explosions. This also means that a pump failure results in unusable fuel, whereas wing tanks can naturally feed the engines via gravity.



              Second, fuselage tanks are closer to sources of heat. This was a cause of the TWA flight 800 accident, where heat from nearby air conditioning equipment lead to a flammable vapor in the fuel tanks. In contrast, wing tanks are naturally cooled by airflow and are less susceptible to forming such explosive vapors.







              share|improve this answer














              share|improve this answer



              share|improve this answer








              edited Dec 12 at 16:30

























              answered Dec 10 at 22:57









              user71659

              2,473619




              2,473619








              • 1




                Not sure if you meant "that in all the cases ... it was the center tank which was implicated" (which is apparently true), but if so, you could probably make it more explicit.
                – jcaron
                Dec 11 at 13:27










              • @jcaron Reworded. I'm sure a wing tank has exploded at some time in the history of aviation, but certainly the center tank has been the main cause of accidents recently.
                – user71659
                Dec 12 at 16:31














              • 1




                Not sure if you meant "that in all the cases ... it was the center tank which was implicated" (which is apparently true), but if so, you could probably make it more explicit.
                – jcaron
                Dec 11 at 13:27










              • @jcaron Reworded. I'm sure a wing tank has exploded at some time in the history of aviation, but certainly the center tank has been the main cause of accidents recently.
                – user71659
                Dec 12 at 16:31








              1




              1




              Not sure if you meant "that in all the cases ... it was the center tank which was implicated" (which is apparently true), but if so, you could probably make it more explicit.
              – jcaron
              Dec 11 at 13:27




              Not sure if you meant "that in all the cases ... it was the center tank which was implicated" (which is apparently true), but if so, you could probably make it more explicit.
              – jcaron
              Dec 11 at 13:27












              @jcaron Reworded. I'm sure a wing tank has exploded at some time in the history of aviation, but certainly the center tank has been the main cause of accidents recently.
              – user71659
              Dec 12 at 16:31




              @jcaron Reworded. I'm sure a wing tank has exploded at some time in the history of aviation, but certainly the center tank has been the main cause of accidents recently.
              – user71659
              Dec 12 at 16:31











              10
















              • added weight increases the structural load applied to the wings




              Only when the plane's on the ground. When it's in the air, it decreases the load on the wings because their lift balances the weight.





              • different gravitational forces and wing-bending between full and empty tanks result in repeating stresses shortening the aircraft life-span




              At the rate of one cycle per flight. And the wings already go through a stress cycle once per flight (flexed down when the plane's on the ground and up when it's in the air).





              • higher risk of catastrophic damage to wings in case of in-flight fuel ignition




              The fuel tanks catching fire in flight is catastrophic wherever you put them.





              • higher risk of fire when lightning strikes a wing




              When did that last happen? Wikipedia's list of plane crashes suggests LANSA flight 508 in 1971. Such incidents are now even rarer, because fuel tanks are fitted with inerting systems. This was originally recommended after the crash of Pan Am flight 214 in 1963 but it took a long time for it to actually happen.






              share|improve this answer



















              • 1




                This answer seems to imply that inerting systems have been used since sometime shortly after 1963, or at least that inerting systems are responsible for the lack of lightning-induced fire since 1971. The link you provided, however, says inerting systems were not installed for 40 years after the crash of Pan Am 214. Here's an article describing the state of the art in 2004: airspacemag.com/how-things-work/safer-fuel-tanks-5883916
                – David K
                Dec 11 at 13:15










              • @DavidK Yes, it looks like I've exaggerated what actually happened. I'll come back and edit when I have time, or you're welcome to propose an edit yourself if you have the time. Thanks for letting me know.
                – David Richerby
                Dec 11 at 14:50












              • @DavidK Edited.
                – David Richerby
                Dec 13 at 23:35






              • 1




                @summerrain Do you have any examples of planes that have made successful emergency landings after fuel tank fires? It feels like your argument is completely hypothetical.
                – David Richerby
                Dec 14 at 16:50






              • 1




                @summerrain I already explained why there aren't fuel tanks under the cockpit. Your question amounts to "In an alternate universe, would..." and we're not in an alternate universe so there's no value in addressing your question. As for an example, you are claiming that putting fuel tanks in different places would give more time for emergency landings. I suggest to you that fuel tank fires are so catastrophic that no emergency landing is going to be possible. A great way for you to argue against that claim would be to say "But it happened on flight XYZ."
                – David Richerby
                Dec 14 at 17:19
















              10
















              • added weight increases the structural load applied to the wings




              Only when the plane's on the ground. When it's in the air, it decreases the load on the wings because their lift balances the weight.





              • different gravitational forces and wing-bending between full and empty tanks result in repeating stresses shortening the aircraft life-span




              At the rate of one cycle per flight. And the wings already go through a stress cycle once per flight (flexed down when the plane's on the ground and up when it's in the air).





              • higher risk of catastrophic damage to wings in case of in-flight fuel ignition




              The fuel tanks catching fire in flight is catastrophic wherever you put them.





              • higher risk of fire when lightning strikes a wing




              When did that last happen? Wikipedia's list of plane crashes suggests LANSA flight 508 in 1971. Such incidents are now even rarer, because fuel tanks are fitted with inerting systems. This was originally recommended after the crash of Pan Am flight 214 in 1963 but it took a long time for it to actually happen.






              share|improve this answer



















              • 1




                This answer seems to imply that inerting systems have been used since sometime shortly after 1963, or at least that inerting systems are responsible for the lack of lightning-induced fire since 1971. The link you provided, however, says inerting systems were not installed for 40 years after the crash of Pan Am 214. Here's an article describing the state of the art in 2004: airspacemag.com/how-things-work/safer-fuel-tanks-5883916
                – David K
                Dec 11 at 13:15










              • @DavidK Yes, it looks like I've exaggerated what actually happened. I'll come back and edit when I have time, or you're welcome to propose an edit yourself if you have the time. Thanks for letting me know.
                – David Richerby
                Dec 11 at 14:50












              • @DavidK Edited.
                – David Richerby
                Dec 13 at 23:35






              • 1




                @summerrain Do you have any examples of planes that have made successful emergency landings after fuel tank fires? It feels like your argument is completely hypothetical.
                – David Richerby
                Dec 14 at 16:50






              • 1




                @summerrain I already explained why there aren't fuel tanks under the cockpit. Your question amounts to "In an alternate universe, would..." and we're not in an alternate universe so there's no value in addressing your question. As for an example, you are claiming that putting fuel tanks in different places would give more time for emergency landings. I suggest to you that fuel tank fires are so catastrophic that no emergency landing is going to be possible. A great way for you to argue against that claim would be to say "But it happened on flight XYZ."
                – David Richerby
                Dec 14 at 17:19














              10












              10








              10








              • added weight increases the structural load applied to the wings




              Only when the plane's on the ground. When it's in the air, it decreases the load on the wings because their lift balances the weight.





              • different gravitational forces and wing-bending between full and empty tanks result in repeating stresses shortening the aircraft life-span




              At the rate of one cycle per flight. And the wings already go through a stress cycle once per flight (flexed down when the plane's on the ground and up when it's in the air).





              • higher risk of catastrophic damage to wings in case of in-flight fuel ignition




              The fuel tanks catching fire in flight is catastrophic wherever you put them.





              • higher risk of fire when lightning strikes a wing




              When did that last happen? Wikipedia's list of plane crashes suggests LANSA flight 508 in 1971. Such incidents are now even rarer, because fuel tanks are fitted with inerting systems. This was originally recommended after the crash of Pan Am flight 214 in 1963 but it took a long time for it to actually happen.






              share|improve this answer
















              • added weight increases the structural load applied to the wings




              Only when the plane's on the ground. When it's in the air, it decreases the load on the wings because their lift balances the weight.





              • different gravitational forces and wing-bending between full and empty tanks result in repeating stresses shortening the aircraft life-span




              At the rate of one cycle per flight. And the wings already go through a stress cycle once per flight (flexed down when the plane's on the ground and up when it's in the air).





              • higher risk of catastrophic damage to wings in case of in-flight fuel ignition




              The fuel tanks catching fire in flight is catastrophic wherever you put them.





              • higher risk of fire when lightning strikes a wing




              When did that last happen? Wikipedia's list of plane crashes suggests LANSA flight 508 in 1971. Such incidents are now even rarer, because fuel tanks are fitted with inerting systems. This was originally recommended after the crash of Pan Am flight 214 in 1963 but it took a long time for it to actually happen.







              share|improve this answer














              share|improve this answer



              share|improve this answer








              edited Dec 13 at 23:35

























              answered Dec 10 at 20:53









              David Richerby

              9,64733478




              9,64733478








              • 1




                This answer seems to imply that inerting systems have been used since sometime shortly after 1963, or at least that inerting systems are responsible for the lack of lightning-induced fire since 1971. The link you provided, however, says inerting systems were not installed for 40 years after the crash of Pan Am 214. Here's an article describing the state of the art in 2004: airspacemag.com/how-things-work/safer-fuel-tanks-5883916
                – David K
                Dec 11 at 13:15










              • @DavidK Yes, it looks like I've exaggerated what actually happened. I'll come back and edit when I have time, or you're welcome to propose an edit yourself if you have the time. Thanks for letting me know.
                – David Richerby
                Dec 11 at 14:50












              • @DavidK Edited.
                – David Richerby
                Dec 13 at 23:35






              • 1




                @summerrain Do you have any examples of planes that have made successful emergency landings after fuel tank fires? It feels like your argument is completely hypothetical.
                – David Richerby
                Dec 14 at 16:50






              • 1




                @summerrain I already explained why there aren't fuel tanks under the cockpit. Your question amounts to "In an alternate universe, would..." and we're not in an alternate universe so there's no value in addressing your question. As for an example, you are claiming that putting fuel tanks in different places would give more time for emergency landings. I suggest to you that fuel tank fires are so catastrophic that no emergency landing is going to be possible. A great way for you to argue against that claim would be to say "But it happened on flight XYZ."
                – David Richerby
                Dec 14 at 17:19














              • 1




                This answer seems to imply that inerting systems have been used since sometime shortly after 1963, or at least that inerting systems are responsible for the lack of lightning-induced fire since 1971. The link you provided, however, says inerting systems were not installed for 40 years after the crash of Pan Am 214. Here's an article describing the state of the art in 2004: airspacemag.com/how-things-work/safer-fuel-tanks-5883916
                – David K
                Dec 11 at 13:15










              • @DavidK Yes, it looks like I've exaggerated what actually happened. I'll come back and edit when I have time, or you're welcome to propose an edit yourself if you have the time. Thanks for letting me know.
                – David Richerby
                Dec 11 at 14:50












              • @DavidK Edited.
                – David Richerby
                Dec 13 at 23:35






              • 1




                @summerrain Do you have any examples of planes that have made successful emergency landings after fuel tank fires? It feels like your argument is completely hypothetical.
                – David Richerby
                Dec 14 at 16:50






              • 1




                @summerrain I already explained why there aren't fuel tanks under the cockpit. Your question amounts to "In an alternate universe, would..." and we're not in an alternate universe so there's no value in addressing your question. As for an example, you are claiming that putting fuel tanks in different places would give more time for emergency landings. I suggest to you that fuel tank fires are so catastrophic that no emergency landing is going to be possible. A great way for you to argue against that claim would be to say "But it happened on flight XYZ."
                – David Richerby
                Dec 14 at 17:19








              1




              1




              This answer seems to imply that inerting systems have been used since sometime shortly after 1963, or at least that inerting systems are responsible for the lack of lightning-induced fire since 1971. The link you provided, however, says inerting systems were not installed for 40 years after the crash of Pan Am 214. Here's an article describing the state of the art in 2004: airspacemag.com/how-things-work/safer-fuel-tanks-5883916
              – David K
              Dec 11 at 13:15




              This answer seems to imply that inerting systems have been used since sometime shortly after 1963, or at least that inerting systems are responsible for the lack of lightning-induced fire since 1971. The link you provided, however, says inerting systems were not installed for 40 years after the crash of Pan Am 214. Here's an article describing the state of the art in 2004: airspacemag.com/how-things-work/safer-fuel-tanks-5883916
              – David K
              Dec 11 at 13:15












              @DavidK Yes, it looks like I've exaggerated what actually happened. I'll come back and edit when I have time, or you're welcome to propose an edit yourself if you have the time. Thanks for letting me know.
              – David Richerby
              Dec 11 at 14:50






              @DavidK Yes, it looks like I've exaggerated what actually happened. I'll come back and edit when I have time, or you're welcome to propose an edit yourself if you have the time. Thanks for letting me know.
              – David Richerby
              Dec 11 at 14:50














              @DavidK Edited.
              – David Richerby
              Dec 13 at 23:35




              @DavidK Edited.
              – David Richerby
              Dec 13 at 23:35




              1




              1




              @summerrain Do you have any examples of planes that have made successful emergency landings after fuel tank fires? It feels like your argument is completely hypothetical.
              – David Richerby
              Dec 14 at 16:50




              @summerrain Do you have any examples of planes that have made successful emergency landings after fuel tank fires? It feels like your argument is completely hypothetical.
              – David Richerby
              Dec 14 at 16:50




              1




              1




              @summerrain I already explained why there aren't fuel tanks under the cockpit. Your question amounts to "In an alternate universe, would..." and we're not in an alternate universe so there's no value in addressing your question. As for an example, you are claiming that putting fuel tanks in different places would give more time for emergency landings. I suggest to you that fuel tank fires are so catastrophic that no emergency landing is going to be possible. A great way for you to argue against that claim would be to say "But it happened on flight XYZ."
              – David Richerby
              Dec 14 at 17:19




              @summerrain I already explained why there aren't fuel tanks under the cockpit. Your question amounts to "In an alternate universe, would..." and we're not in an alternate universe so there's no value in addressing your question. As for an example, you are claiming that putting fuel tanks in different places would give more time for emergency landings. I suggest to you that fuel tank fires are so catastrophic that no emergency landing is going to be possible. A great way for you to argue against that claim would be to say "But it happened on flight XYZ."
              – David Richerby
              Dec 14 at 17:19











              1














              More weight on the wings is actually good as it makes the aircraft more balance and more resistant to unnecessary swerving during turbulence or wind current, like a person walking on tight rope carrying a horizontal rod(bar) for balancing. Check out radius of Gyration in mechanics.






              share|improve this answer


























                1














                More weight on the wings is actually good as it makes the aircraft more balance and more resistant to unnecessary swerving during turbulence or wind current, like a person walking on tight rope carrying a horizontal rod(bar) for balancing. Check out radius of Gyration in mechanics.






                share|improve this answer
























                  1












                  1








                  1






                  More weight on the wings is actually good as it makes the aircraft more balance and more resistant to unnecessary swerving during turbulence or wind current, like a person walking on tight rope carrying a horizontal rod(bar) for balancing. Check out radius of Gyration in mechanics.






                  share|improve this answer












                  More weight on the wings is actually good as it makes the aircraft more balance and more resistant to unnecessary swerving during turbulence or wind current, like a person walking on tight rope carrying a horizontal rod(bar) for balancing. Check out radius of Gyration in mechanics.







                  share|improve this answer












                  share|improve this answer



                  share|improve this answer










                  answered Dec 12 at 15:38









                  Integral Master

                  112




                  112























                      -2














                      There is no other reason.
                      The engine is attached to the wing and They are trying to design a fuel tank to fuel the engine,
                      There is no space on the torso. So they make a hole in the wings.






                      share|improve this answer



















                      • 1




                        welcome to aviation.SE. Please be aware that this is an english-only website. as such, we will have to remove the part of your answer written in Korean. Moreover, please be aware that we like answers that contain a bit of detail, and possibly references.
                        – Federico
                        Dec 16 at 8:24


















                      -2














                      There is no other reason.
                      The engine is attached to the wing and They are trying to design a fuel tank to fuel the engine,
                      There is no space on the torso. So they make a hole in the wings.






                      share|improve this answer



















                      • 1




                        welcome to aviation.SE. Please be aware that this is an english-only website. as such, we will have to remove the part of your answer written in Korean. Moreover, please be aware that we like answers that contain a bit of detail, and possibly references.
                        – Federico
                        Dec 16 at 8:24
















                      -2












                      -2








                      -2






                      There is no other reason.
                      The engine is attached to the wing and They are trying to design a fuel tank to fuel the engine,
                      There is no space on the torso. So they make a hole in the wings.






                      share|improve this answer














                      There is no other reason.
                      The engine is attached to the wing and They are trying to design a fuel tank to fuel the engine,
                      There is no space on the torso. So they make a hole in the wings.







                      share|improve this answer














                      share|improve this answer



                      share|improve this answer








                      edited Dec 16 at 8:25









                      Federico

                      25.2k15100151




                      25.2k15100151










                      answered Dec 16 at 4:37









                      최인철

                      1




                      1








                      • 1




                        welcome to aviation.SE. Please be aware that this is an english-only website. as such, we will have to remove the part of your answer written in Korean. Moreover, please be aware that we like answers that contain a bit of detail, and possibly references.
                        – Federico
                        Dec 16 at 8:24
















                      • 1




                        welcome to aviation.SE. Please be aware that this is an english-only website. as such, we will have to remove the part of your answer written in Korean. Moreover, please be aware that we like answers that contain a bit of detail, and possibly references.
                        – Federico
                        Dec 16 at 8:24










                      1




                      1




                      welcome to aviation.SE. Please be aware that this is an english-only website. as such, we will have to remove the part of your answer written in Korean. Moreover, please be aware that we like answers that contain a bit of detail, and possibly references.
                      – Federico
                      Dec 16 at 8:24






                      welcome to aviation.SE. Please be aware that this is an english-only website. as such, we will have to remove the part of your answer written in Korean. Moreover, please be aware that we like answers that contain a bit of detail, and possibly references.
                      – Federico
                      Dec 16 at 8:24




















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