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Mostly, the high-wing and landing gear configuration on many cargo aircraft designs is intended to facilitate a low loading floor and the ability to load and un

Mostly, the high-wing and landing gear configuration on many cargo aircraft designs is intended to facilitate a low loading floor and the ability to load and unload the aircraft on rough fields without special ground equipment (e.g. by means of a ramp integrated with the the rear doors of the aircraft like a C-130 or with a deployable forward ramp and kneeling front gear like the An-124.) Another benefit is providing extra ground clearance for the engines to reduce foreign object ingestion. Everything else flows from this. The wing spar and structural supports needed in a cantilever monoplane (i.e. not a biplane with a truss structure) take up a fair amount of room. By moving these structural elements to the top of the aircraft, it's possible to get a low floor and still hang engines from pylons beneath the wings. The wings themselves will be angled downward from root to tip (known as anhedral) to partly counteract the pendulum stability caused by having a center of gravity so far below the center of pressure. Passenger aircraft do not usually use this configuration because it is heavier - the sides of the fuselage must be built stronger to support the load, compared to a low-wing configuration. Weight costs performance costs fuel costs money, so you don't build a large aircraft like this unless it has to operate at fields without ground equipment.

vlehto 11y ago
There are lot of bombers with high wing (B52, almost anything several engines from WWII). About half of all propeller driven passenger planes have high wing. >Unlike the An-124, the An-225 was not intended for tactical airlifting and is not designed for short-field operation It still has high wing. And U2 has high wing. It's probably the plane with most carefully calculated weight ever. If it was inherently heavier, this would make no sense.
- lotsofactors 11y ago
  > There are lot of bombers with high wing (B52, almost anything several engines from WWII). Most bombers dispense ordnance from their undersides, ideally near the center of gravity; limiting the structural members needed in those parts simplifies things. > About half of all propeller driven passenger planes have high wing. These are designed not to require ground vehicles for loading and unloading. Propellor ground clearance is also an issue for the larger types. > Unlike the An-124, the An-225 was not intended for tactical airlifting and is not designed for short-field operation > It still has high wing. The An-225 carries cargoes of unusual bulk to unusual places. Being able to get these cargoes on and off the aircraft without some sort of lift has advantages. Low-wing freighters, which are all variants of passenger types these days, almost always carry palletized cargo of standard dimensional units (See https://en.wikipedia.org/wiki/Unit_load_device https://en.wikipedia.org/wiki/Unit_load_device) - this allows for standardized ground handling equipment for most loads. > And U2 has high wing. It's probably the plane with most carefully calculated weight ever. > If it was inherently heavier, this would make no sense. The U2 is not a high-wing aircraft, it is a mid-wing aircraft with its spar roughly running through its center of gravity. This is actually the most efficient and aerodynamically cleanest configuration, and many high-performance aircraft use this arrangement. The main problem with it for passenger or cargo use is that the wing structure ends up interfering with the middle of the fuselage volume near the center of gravity, which tends to be valuable space in a transport aircraft.
  - deleted 11y ago
    [deleted]
  - vlehto 11y ago
    Why should I believe you. Do you design airplanes?
    - zwiteof 11y ago
      Because his answers are accurate. While weight and aerodynamic performance are very important, aircraft design is inherently multi-disciplinary and requires tradeoffs depending on the design requirements.
      - vlehto 11y ago
        With no sources or authority. While my answer seems logically just as good to explain this stuff. Seems like the argument is won purely by asserting certainty. But I'm not objective of course.
        zwiteof 11y ago
        > While my answer seems logically just as good to explain this stuff. It sounds logical if you don't have a background in aerospace, but otherwise it's relatively inaccurate. For example: > So far my best guess is that it's related to landing gear. Landing gear makes significant portion of the total weight Landing gear makes up roughly 3% of the total takeoff weight. Hardly significant compared to fuel and cargo/passengers. [1] > you want to keep it short and compact. This is certainly true from a structural standpoint. > Engines are the heaviest things in passenger planes, so landing gear is close to engines. Compared to a person, yes. Compared to the total cargo/passengers, not really. The 787 MGTOW is ~500,000, of that, the two GE GEnx-1B engines weight about 26,000 lb combined. The landing gear is "close to the engines" in your example picture, but this is because you typically place the main landing gear such that it is near the center of gravity. The nose gear only supports 8-15% [2] of the aircraft weight to make steering possible while taxiing. Some commercial aircraft have tail mounted engines such as the MD-80 (https://upload.wikimedia.org/wikipedia/commons/2/25/Allegiant_MD-80_at_McCarran_International_Airport_(6334695369).jpg https://upload.wikimedia.org/wikipedia/commons/2/25/Allegian...). The wing (and landing gear) are indeed further aft since the CG is moved back further due to the engine placement. In addition, comparing the number of wheels is a red herring for a commercial jet v. a cargo plane. The CG location relative to the wheelbase will be remarkably similar in both cases. However, military cargo planes often operate out of poor and/or shorter airfields. This limits the amount of weight you can put on each wheel if you're landing on asphalt rather than reinforced concrete, so you have more wheels with less load per wheel to keep from sinking into the ground. In addition, more wheels allows you to slow down quicker since you can spread out the braking action. > With cargo plane the heaviest part of the plane is the cargo. The cargo/passengers are a significant portion for commercial transports as well. Again for the 787, you've got around 100,000 in cargo/passengers (about 20% mass fraction). The C-17 carries 170,000 lbs of cargo with a 585,000 MGTOW giving a mass fraction of 29%. Not too surprising they have a higher mass fraction there since they're not adding any parasitic mass for things like passenger comfort. lotsoffactors' comments on cargo loading/unloading considerations and the U-2 being a mid-wing aircraft are correct as well. Sources: Aerospace Engineer and Raymer's Aircraft Design textbook (basically the bible of aircraft design). [1] Chapter 15 of Aircraft Design: A Conceptual Approach (3rd Edition) by Daniel Raymer [2] Chapter 11 of Raymer

vlehto 11y ago

There are lot of bombers with high wing (B52, almost anything several engines from WWII). About half of all propeller driven passenger planes have high wing. >Unlike the An-124, the An-225 was not intended for tactical airlifting and is not designed for short-field operation It still has high wing. And U2 has high wing. It's probably the plane with most carefully calculated weight ever. If it was inherently heavier, this would make no sense.

lotsofactors 11y ago
> There are lot of bombers with high wing (B52, almost anything several engines from WWII). Most bombers dispense ordnance from their undersides, ideally near the center of gravity; limiting the structural members needed in those parts simplifies things. > About half of all propeller driven passenger planes have high wing. These are designed not to require ground vehicles for loading and unloading. Propellor ground clearance is also an issue for the larger types. > Unlike the An-124, the An-225 was not intended for tactical airlifting and is not designed for short-field operation > It still has high wing. The An-225 carries cargoes of unusual bulk to unusual places. Being able to get these cargoes on and off the aircraft without some sort of lift has advantages. Low-wing freighters, which are all variants of passenger types these days, almost always carry palletized cargo of standard dimensional units (See https://en.wikipedia.org/wiki/Unit_load_device https://en.wikipedia.org/wiki/Unit_load_device) - this allows for standardized ground handling equipment for most loads. > And U2 has high wing. It's probably the plane with most carefully calculated weight ever. > If it was inherently heavier, this would make no sense. The U2 is not a high-wing aircraft, it is a mid-wing aircraft with its spar roughly running through its center of gravity. This is actually the most efficient and aerodynamically cleanest configuration, and many high-performance aircraft use this arrangement. The main problem with it for passenger or cargo use is that the wing structure ends up interfering with the middle of the fuselage volume near the center of gravity, which tends to be valuable space in a transport aircraft.
- deleted 11y ago
  [deleted]
- vlehto 11y ago
  Why should I believe you. Do you design airplanes?
  - zwiteof 11y ago
    Because his answers are accurate. While weight and aerodynamic performance are very important, aircraft design is inherently multi-disciplinary and requires tradeoffs depending on the design requirements.
    - vlehto 11y ago
      With no sources or authority. While my answer seems logically just as good to explain this stuff. Seems like the argument is won purely by asserting certainty. But I'm not objective of course.
      - zwiteof 11y ago
        > While my answer seems logically just as good to explain this stuff. It sounds logical if you don't have a background in aerospace, but otherwise it's relatively inaccurate. For example: > So far my best guess is that it's related to landing gear. Landing gear makes significant portion of the total weight Landing gear makes up roughly 3% of the total takeoff weight. Hardly significant compared to fuel and cargo/passengers. [1] > you want to keep it short and compact. This is certainly true from a structural standpoint. > Engines are the heaviest things in passenger planes, so landing gear is close to engines. Compared to a person, yes. Compared to the total cargo/passengers, not really. The 787 MGTOW is ~500,000, of that, the two GE GEnx-1B engines weight about 26,000 lb combined. The landing gear is "close to the engines" in your example picture, but this is because you typically place the main landing gear such that it is near the center of gravity. The nose gear only supports 8-15% [2] of the aircraft weight to make steering possible while taxiing. Some commercial aircraft have tail mounted engines such as the MD-80 (https://upload.wikimedia.org/wikipedia/commons/2/25/Allegiant_MD-80_at_McCarran_International_Airport_(6334695369).jpg https://upload.wikimedia.org/wikipedia/commons/2/25/Allegian...). The wing (and landing gear) are indeed further aft since the CG is moved back further due to the engine placement. In addition, comparing the number of wheels is a red herring for a commercial jet v. a cargo plane. The CG location relative to the wheelbase will be remarkably similar in both cases. However, military cargo planes often operate out of poor and/or shorter airfields. This limits the amount of weight you can put on each wheel if you're landing on asphalt rather than reinforced concrete, so you have more wheels with less load per wheel to keep from sinking into the ground. In addition, more wheels allows you to slow down quicker since you can spread out the braking action. > With cargo plane the heaviest part of the plane is the cargo. The cargo/passengers are a significant portion for commercial transports as well. Again for the 787, you've got around 100,000 in cargo/passengers (about 20% mass fraction). The C-17 carries 170,000 lbs of cargo with a 585,000 MGTOW giving a mass fraction of 29%. Not too surprising they have a higher mass fraction there since they're not adding any parasitic mass for things like passenger comfort. lotsoffactors' comments on cargo loading/unloading considerations and the U-2 being a mid-wing aircraft are correct as well. Sources: Aerospace Engineer and Raymer's Aircraft Design textbook (basically the bible of aircraft design). [1] Chapter 15 of Aircraft Design: A Conceptual Approach (3rd Edition) by Daniel Raymer [2] Chapter 11 of Raymer