Topic Author
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Low Vs High Wing Aircraft

Sat Jul 06, 2002 2:53 pm

Is there any aerodynamic reason why nearly all airliners adopt the low wing design instead of the high wing C17 type design. I may be wrong but it seems to me that most of the heavy lifting transport aircraft have the high wing design (C17, Hercules, Anotov)
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RE: Low Vs High Wing Aircraft

Sat Jul 06, 2002 3:29 pm

Loading cargo is easier and needs less ground equipment on a high wing/low floor heighth type aircraft. Also easier to roll on/roll off wheeled and tracked vehicles, ie, military operations.

RE: Low Vs High Wing Aircraft

Sun Jul 07, 2002 12:28 am

Why no high-wing airliners? In a few cases, it wasn't for the lack of trying. I'm not sure about the Russian airplanes, but Lockheed either certified or had civilian versions of the C130, C141, and C5 on the drawing board. Boeing is trying to lease a fleet of C17's to a 121 freight/cargo operator as we speak. Civilian operations have evolved to use a jetway, military operations favor "drive on, drive off" loading. (Hmmm... That's the way they load ferry boats. Maybe some startup airline will... Naw dumb idea, very dumb.)

I believe that Lockheed has made a few civilian C130's - as I remember, they were known as L100's. I don't believe that any civilian C141's were ever built, nor were there ever any civilian C5's. However, I had an instructor at FlightSafety, who in a former life flew C5's in the Air Force. This guy got a "civilian" C5 type rating and it was on his ATP certificate. I believe it was listed as a "L500", but it's been a long time, so I'm not positive. It seemed that at one point, Lockheed was real serious about selling them on the civil market and the FAA (or who ever does things like that) assigned the civilian type designator to it in anticipation. He was simply at the right place and at the right time and got the type-rating added to his license by way of his military competency. Shortly there after Lockheed dropped the program and the FAA quit giving C5 type-ratings.
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RE: Low Vs High Wing Aircraft

Sun Jul 07, 2002 2:47 am

It would seem to me that low-wing aircraft would also be at risk of FOD when landing on the poor runways most airlift a/c frequent. High wings keep the engine intakes higher of the ground.

Then again, it could be coincidental...

Top Gun
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RE: Low Vs High Wing Aircraft

Tue Jul 09, 2002 11:15 pm

The only thing I can think of is the posistion of the Wing Spar.

In a Semi Cantilever wing (high wing) the spar would run over head and still give you ample room to put cargo. In a Full Canitlever wing (you guessed it, a low wing) there is a space on the "floor" that the spar goes through. You could either have a bug bump in the floor or have two cargo "holds" (or three if you think about it) instead one one giant one.
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RE: Low Vs High Wing Aircraft

Sat Jul 13, 2002 12:54 am

As has been pointed out, military airlifters use the high wing layout because of the low load floor it provides. But now, if you look at those airlifters, you will see large sponsons sticking out of the lower fuselage to contain the landing gear. These cause drag. The low wing layout allows the landing gear to be tucked into the wing and wing-fuselage junction, economizing on frontal area. The gear is attached to the wing, which is already strong to hold up the fuselage; with the high wing, both the upper and lower fuselage must be strengthened.
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RE: Low Vs High Wing Aircraft

Sat Jul 13, 2002 8:53 am

Look at the Bae146/Avro/and i'll fated RJX
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RE: Low Vs High Wing Aircraft

Sun Jul 14, 2002 4:00 am

Quite frankly, after viewing pix of the 146/ARJ, it seems to me as if the landing gear problem is not really as bad as Areopagus sees it to be. These aircraft do have landing gear bumps, but not any worse than low-winged airliners do.

Have a looksie:

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Photo © Derek Ferguson

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Photo © Derek Ferguson

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Photo © Derek Ferguson

Of course, I had to throw this pic in, because it's just cool.

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Photo © Chris Sheldon

Twin Cessna 812 Victor, Minneapolis Center, we observe your operation in the immediate vicinity of extreme precipitation
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RE: Low Vs High Wing Aircraft

Sun Jul 14, 2002 8:20 pm

There are pro's and con's to high- and low-wing designs. Here are some significant ones off the top of my head.

Wing spar:
For pax a/c, having a wing spar through the top part of the cabin is unwanted. It will reduce space in the cabin. A wing spar below the floow won't. Having the wing spar above the fuselage (ATR) sacrifices aerodynamics to get around this problem.

Structural reasons:
In a low wing aircraft, you will have the aircraft standing on top of the wing. The loads put on the floor of the aircraft can be transmitted through the wing without going through the fuselage structure. This means that the fuselage can be made lighter.

Landing gear:
With a high wing, you either have a landing gear in the lower part of the fuselage (C130, BAe146) or a tall gear in the wings (F50).

With the gear in the fuselage, you get a narrow gear which is less stable and you'll probably have to add bulges on the fuselage which will be less aerodynamically effective. Much of the weight of an aircraft is in the wings and all this weight will have to be transmitted down to the gear while on the ground and especially when landing. This means lots of added weight in the fuselage.

As was mentioned before, a tall gear in the wings means a heavier landing gear and larger pylons to house it while retracted.

Engine placement:
A high wing will enable you to have the engines farther off the ground, reducing the risk of pod strikes and FOD ingestion from the surface. A high wing is especially attractive for a turboprob, as an underslung engine on a low wing isn't possible if you have a propeller. You want a clean upper surface of the wing for maximum aerodynamical efficiency. The junk you hang off the bottom of the wing won't reduce the lift by much, it will just add to drag. Junk on top of the wing (such as engines) will reduce lift.

Wing/stabilizer interaction:
With a high wing, you'll probably be forced to have a T tail to get the stabilizer out of the downwash from the wing. This adds structural weight.

I thought I was doing good trying to avoid those airport hotels... and look at me now.
Topic Author
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RE: Low Vs High Wing Aircraft

Wed Jul 17, 2002 2:40 pm

Thanks People,
Good logical answers like usual. I had my own thoughts on this but i dont work in the industry so i thought i would ask the experts.
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RE: Low Vs High Wing Aircraft

Wed Jul 24, 2002 4:34 am

Sorry I'm a bit late on this one - I've been up to the eyeballs.

I think you hit the nail on the proverbial head when you gave the list of heavylift aircraft. All of them were designed initially for military service. In these cases, they are designed with extremes in mind:

1. Poorly prepared strips - high risk of FOD damage.

2. Outsized loads that have to be loaded/offloaded as quickly as possible.

3. Short runways

4. Risk of Surface to Air Missiles (SAMs) - you want to get down as quickly as possible and then up again as quickly as possible.

If you apply the same principles to the civil world (except maybe for the bit about people shooting at you... normally), you may well end up with a high wing design.

The Avro/BAe 146/RJ series (whatever you want to call them) merely applies these principles. It gets off the ground quickly (see the airfields in Nepal...) and can carry relatively large loads, considering the rest of the design specification.

I'd be interested on the structural engineers view (sorry - I do cockpits) on whether it's easier to fit a high lift wing (thick, higher AoA) to a high wing design, or whether the same problems arise.

As a final curiosity, compare the following pictures:

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Photo © Andrew Brooks

View Large View Medium
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Photo © Derek Ferguson

Any similarities?
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