Why military planes have wings on top, commercial underneith?

Question

Why do a lot of military planes such as the c-17 have their wings above the fuselage while most of the commercial aircraft have the wings underneith?

Answer 1

Nice answers above...but the major reason has been missed.....(with the exception of SteveL who hit the second major rational)

For the most part..because military transport aircraft must be able to operate of unprepared landing areas...this includes gravel, sand, grass, composite mat etc...With the engines mounted higher up....there is less chance of injustion of FOD (foreign object damage)

Answer 2

Military aircraft such as the C-130, C-5 and C17 are designed for quick loading and unloading as you do not want the planes sitting on the ground for long periods of time as they make easy targets. The capability of "ro-ro" (roll on, roll off) loading therefore is a big advantage. You can not do that with a low wing plane as the supports for the wings are in the way.

All three of them can do air drops. But they also can do low level extractions of cargo, dumping the cargo right onto the runway without having to land. For that to be safe and prevent a large BANG as the cargo hits the runway, a high wing design puts the cargo closer to the runway so there is less of a drop when it comes out of the plane.

Military planes are designed specifically for emergency water landings. With a low wing plane, such as an airliner, as soon as the plane hits the water, the wings generate a ton of Resistance and often either get ripped off or cause the plane to flip. End of plane, death of crew and loss of cargo. Plane sinks like a rock. With a high wing, the plane hits the water with the fuselage first, losing speed until it slowly sinks into the water with the wings on top floating, holding the plane on the surface. All the military planes have emergency exits and life rafts at the top of the wing so you exit up and out.

The high wing design is a more stable design. The weight is hanging under the wing helping to keep the plane stable. If the weight is on top, the natural tendency is for the plane to want to turn over so the weight is on the bottom. This advantage is why many of the small civilian private planes ALSO have the wing on top. You can also see better under you as the wing is not in the way.

Lastly, it is cheaper to make a low wing design. That is a primary concern with civilian aircraft. With a military planes, cost is a secondary consideration. The primary consideration for military planes is the ability to complete the mission and survive damage.

Answer 3

First off, not ALL military airplanes have their wings above the fuselage, and not ALL commercial airplanes have their wings below the fuselage.

Most military cargo transports (like C-5s, C-130s, C-17s, etc.) have high wings, becuase that keeps the engines higher above the ground and thus less likely to ingest debris (like dust from an unpaved runway). It also allows more room for flap clearance.

Some commercial airliners and freighters do have high wings as well, but most jet-powered airliners have low wings. With low wings, the main landing gear usually retracts into the wing, while with a high wing , it retracts into the belly of the fuselage. This means that the main landing gear units are spread wider apart with a low wing. With turboprop-powered airliners, the landing gear usually retracts into pods in the engine nacelles, rather than into the wings or the belly of the fuselage (but their are exceptions- like the ATR family and the Dornier 328). There are many airliners with high wings, most of them are turboprop-powered. Some high-wing commercial turboprops include: the Dornier 328, Dash 7, Dash 8, ATR-42, ATR-72, An-24, An-140, Shorts 330, Shorts 360, Fokker 50, F27, and there are many others as well. There are not many jet-powered airliners with high wings, but their are a few, theres the BAe-146/RJ/RJX family, the Fairchild/Dornier 328JET, and the An-148. Also there are some commercial jet-powered freighters with high wings, like the An-124.

Answer 4

Military cargo aircraft are designed with wings above the fuselage for several reasons...

1) to place the engines higher off the ground for operating from unimproved (dirt) runways.

2) The high wing positions the fuselage floor closer to the ground to make cargo loading/unloading easier, and

3) it locates the center section of the wing above the load floor, so the airplane can have a flat load floor all the way from front to back.

Answer 5

The Military cargo planes are designed with higher mounted wings to sit lower to the ground for easier loading and a lower approached angle for the loading ramp. While Commercial planes are designed with lower mounted wings because loading height is not an issue and it also provides a better view from the windows for the passengers.

Answer 6

When dealing with Military transport as in the C130/ C17, this aircraft was designed for insurgent action into inhospitable environments. As such the high wing with a deep cord value gives greater lift and allows for STOL Short Take Off & Landing. this also means there is a higher stall factor allowing for steep climbs off of the runway /airfield without the aircraft losing stability. Secondly this lifts the motive power above the dust storm and FOD Foreign Object Debris which could get sucked into the engine intakes.
High wing also allows for quick and easy cargo discharge without the wings cluttering up the exit routes. In flight with discharge of cargo the high wing reduces the turbulent back pressure near to the cargo doors so reducing the likelyhood of the chute being compressed when being deployed. However high wing deep cord values reduce the high speed manouverability so making the vehicle a sitting duck. so either armourment or defensive strategy is required when flying.
Commercial aircraft require a higher degree of comfort and do not require STOL capability, runways are long and clear of debris therfore low wings of a low cord value and a wider section give adequate lift for a greater payload on takeoff with better high altitude speed and longer range. However you will have noticed that both the UK and the USA armed forces hire/rent/ charter domestic airliners to carry troups to distant shores. Some are even converted to inflight refueling to accomodate greater haul values, reduced fuel load on takeoff means higher payload then refueled in flight means greater endurance. (This is because your average "grunt" Jarhead" "Pongo" carries more luggage than than average"barry" on his way to malaga for a sun sea sangria and sex week) and in comfort.. When disembarked they then get onto the C130 or C17 globe master for transport onto the line. Hope this answers your question

Answer 7

The F4 and Eurofighter are low wing planes. The BAe 146 and De Havilland Dash 9 are high wing commercial planes. There's no hard and fast rule.

Answer 8

One subtle reason that I read in AOPA flight training magazine once, was that wings underneath the fuselage gives the illusion of stabilty. The passengers are more comfortable seeing wings below them rather than above them. I'm certain that's not a primary factor though.

Answer 9

having wings up brings the fuselage to the ground. so is the cargo bay accesable through the tail ramp and front ramp, like you can see it on Galaxy. this is very useful for quick unloading and loading of bulky cargo, such as armors, trucks, etc.

Answer 10

Its a function of aircraft dynamics and purpose. Not all military aircraft have wings on top, F-16, F-17 Harrier, etc. It's all an engineering trade-off.