BigJimFX
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High Wing Airliner

Mon Apr 10, 2006 1:12 pm

Ok I did a search and couldn't find anyone discussing it so here it goes...

How come there are no new airliners with a high wing design. The only one I can think of off the top of my head is the BAE 146 (avro) and the Dash 8. Is there a particular reason why, or is just because nobody really thinks about it anymore?
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Zkpilot
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RE: High Wing Airliner

Mon Apr 10, 2006 1:46 pm

For Turboprops they are a good design, for larger aircraft not so much, exceptions being Cargo military types (Antonovs, Galaxies, Hercs etc). Anhedrels vs dihedrels... designers have debated this in the past.
One downside of the high wing design in larger aircraft is crosswind landings. This is because the wingtip is lower than on a low wing design thus higher chance of striking the ground if not flown properly, for smaller aircraft its not so much of an issue because the wings don't extend out so far.
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BigJimFX
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RE: High Wing Airliner

Mon Apr 10, 2006 1:54 pm

Quoting Zkpilot (Reply 1):
One downside of the high wing design in larger aircraft is crosswind landings. This is because the wingtip is lower than on a low wing design thus higher chance of striking the ground if not flown properly

I'm not quite sure I understand. I recal it being an issue for X-wind landings due to the fact that air can get between the wing and fuselage and push up... That could be a problem in a cessna (IS a problem in a cessna) But if the weight is increased, would it still be an issue? ( to a certain extent of course)
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pelican22
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RE: High Wing Airliner

Tue Apr 11, 2006 3:52 am

What about the AN-72 and the new AN-148,this is in flight test at the moment,it seats about 90-110 passengers,it is a high wing design,powered by PS-90 turbofan engines and d'ont forget the Donier 328 jet,high wing and two jet engines.
 
OldAeroGuy
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RE: High Wing Airliner

Tue Apr 11, 2006 4:02 am

Three quick reasons I can think of:

Interference of the wing spar in the passenger cabin plus wing center section fuel over the passenger cabin.

Difficulty with integration of the landing gear. It pretty much has to go in external pods.

Airplane flotation in the event of a ditching. Although this event is very remote, it's still a design consideration.
Airplane design is easy, the difficulty is getting them to fly - Barnes Wallis
 
BigJimFX
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RE: High Wing Airliner

Tue Apr 11, 2006 4:30 am

Quoting Pelican22 (Reply 3):
d'ont forget the Donier 328 jet,high wing and two jet engines

I did forget... I apologize. It didn't come to me cause the only donier that popped into my head at the time was the turbo prop that looks just like it.

Quoting OldAeroGuy (Reply 4):
Three quick reasons I can think of:

Interference of the wing spar in the passenger cabin plus wing center section fuel over the passenger cabin.

Difficulty with integration of the landing gear. It pretty much has to go in external pods.

Airplane flotation in the event of a ditching. Although this event is very remote, it's still a design consideration

Ok that makes sense. I didnt think about any of those considerations. Thanks!
I'd like to thank me for flying Me Airways...
 
flydreamliner
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RE: High Wing Airliner

Tue Apr 11, 2006 5:20 am

Quoting Pelican22 (Reply 3):
What about the AN-72 and the new AN-148,this is in flight test at the moment,it seats about 90-110 passengers,it is a high wing design,powered by PS-90 turbofan engines and d'ont forget the Donier 328 jet,high wing and two jet engines.

The Do 328 sold very few examples, and the line was closed. AN-72 and An-148 aren't the best sellers either......
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Arrow
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RE: High Wing Airliner

Tue Apr 11, 2006 5:27 am

Quoting Zkpilot (Reply 1):
One downside of the high wing design in larger aircraft is crosswind landings.

I'm no engineer, but I think you've got this backwards. It's the low-wing that has the limitations because the vertical distance between the main gear and the wing tip is less than it is for a high wing, meaning its ability to lower the wing in a slideslip is reduced as the ground gets closer. I don't think there's enough dihedral on the main wing to overcome the high-wing advantage on that score. Correct me if I'm wrong. Any engineers out there?
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BigJimFX
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RE: High Wing Airliner

Tue Apr 11, 2006 8:36 pm

Quoting Arrow (Reply 7):
I'm no engineer, but I think you've got this backwards. It's the low-wing that has the limitations because the vertical distance between the main gear and the wing tip is less than it is for a high wing, meaning its ability to lower the wing in a slideslip is reduced as the ground gets closer. I don't think there's enough dihedral on the main wing to overcome the high-wing advantage on that score. Correct me if I'm wrong. Any engineers out there?

I was thinking the same thing, but I didn't want to point it out because I wasn't sure

Another thing...

Quoting OldAeroGuy (Reply 4):
Difficulty with integration of the landing gear. It pretty much has to go in external pods

Wouldn't this almost be cheaper, I mean adding all the gear stuff into the wing has to be some kind of an issue. Not to mention, now you dont have to make tall gears for normal engines(airbus) or make De De Der looking engines (737).

Quoting OldAeroGuy (Reply 4):
Interference of the wing spar in the passenger cabin plus wing center section fuel over the passenger cabin

Can't you just put the center tank in the belly and just us a pump system. Plus without the gear in the wing, theres more space for fuel.
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OldAeroGuy
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RE: High Wing Airliner

Tue Apr 11, 2006 10:24 pm

Quoting BigJimFX (Reply 8):
Wouldn't this almost be cheaper, I mean adding all the gear stuff into the wing has to be some kind of an issue. Not to mention, now you dont have to make tall gears for normal engines(airbus) or make De De Der looking engines (737).

What track do you want to have on the gear and how do you stow it?

A wide track is desireable for both ground handling and pavement loading. For a high wing airplane (assuming you don't want to make the gear wing mounted so it's long and spindley), the gear will be mounted in the lower body. To get a wide track, the gear must be either housed in external fairings (ala military transport) or have a complex retraction mechanism (ala military fighters).

The external fairings create extra drag that puts the high wing airplane at a disadvantage. The complex retraction mechanism adds an additional reliability risk and a maintenance burden. Either of these solutions create economic costs that a low wing airplane doesn't have.

Quoting BigJimFX (Reply 8):
Can't you just put the center tank in the belly and just us a pump system. Plus without the gear in the wing, theres more space for fuel.

Where do you route the fuel lines? Either they need to run external to the body (a drag penalty and potentially subject to damage) or they need to run through the passenger cabin, inside the pressure vessel. Flammable fluids in the pressure vessel are never a good idea. The APU fuel line is an exception, but it needs to be inside a double walled fuel line. This is acceptable because the line is rather small and it stays below the cargo floor. Your lower lobe-to-wing fuel lines need to be large and run through the passenger cabin if they're not external. The certifying authorities will probably take a dim view of this arrangement.

By the way, putting the gear in the wing of a low wing airplane does not impact the fuel volume. The fuel is carried between the forward and aft spars. For structural reasons, the gear does not penetrate the spars. Instead, it is housed in the inboard portion of the wing aft of the rear spar.

Now as a counterpoint, what do you think the advantages of a high wing airliner would be?
Airplane design is easy, the difficulty is getting them to fly - Barnes Wallis
 
HiFi
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RE: High Wing Airliner

Wed Apr 12, 2006 5:12 am

Both high-wing and low-wing designs have lots of advantages and lots of disadvantages.. The conclusion you get after spending hours and hours thinking about it is: it just doesn't matter (unless you have a very specific mission or constraint).

Manufacturers that usually go with high-wing will probably continue designing high-wing... the same goes for low-wing... simple as that, because you already know what to do to compensate for the disadvantages. It's not lack of imagination or creativity, it's just that for the majority of design cases there's no real gain in preferring one option over the other.
no commercial potential
 
787engineer
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RE: High Wing Airliner

Wed Apr 12, 2006 6:09 am

There's also a structural advantage with a low-wing airplane. By podding the lading gear against the fuselage (a la military transports) the gear mechanism is simpler (less weight), but the fuselage must now be strengthened. The fuselage must support the landing gear loads whereas earlier it is integrated into the wingbox structure. With a high wing not only must the fuselage be strengthened up top so the fuselage will "hang on to" the wing, but the fuselage walls have to be strengthened to support the wing and plane especially on landing. Also note the "flattened bottom" of most military transports, this is to achieve the desired cargo-floor height but really isn't as optimal as a circular fuselage, and is generally heavier. In the end gear stowage is probably the primary advantage of low-wing planes.

Most military transports use the high-wing design mostly because of its advantages in landing/takeoff: 1) engines higher up to avoid FOD when landing on rough unpaved runways, 2) the high wing position allows for larger flaps which improves STOL performance 3) A high wing tends to prevent a "floating" effect (ground boundary layer), which makes it easier for pilots to nail their landings right where they want to.
 
BigJimFX
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RE: High Wing Airliner

Wed Apr 12, 2006 8:11 am

Quoting OldAeroGuy (Reply 9):
Now as a counterpoint, what do you think the advantages of a high wing airliner would be?

Your gonna hate me..... I think it looks cool hyper , and people who sit on the wing seats have a good view.

Quoting OldAeroGuy (Reply 9):
Where do you route the fuel lines? Either they need to run external to the body (a drag penalty and potentially subject to damage) or they need to run through the passenger cabin, inside the pressure vessel. Flammable fluids in the pressure vessel are never a good idea

Where are the fuel lines routed in a rear engined aircraft? Through the cabin, outside the pressure vessel I guess. I'm not an engineer (obviously) I just think with modern technology, it seems like we have hit a wall with aircraft design. After composites and super-efficient engines... where do we go? Maybe thats the way some felt just before jets. I just think we could use technology to do something different.

Quoting OldAeroGuy (Reply 9):
What track do you want to have on the gear and how do you stow it?


Any way we can put them into miniature lifting surfaces? Kinda like a helicopter?
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m404
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RE: High Wing Airliner

Wed Apr 12, 2006 8:26 am

BIGJIM I understand your preference. I loved the 146 and F-27.

I'm thinking that possibly engine accesibility on a large hi-wing would be more difficult.
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OldAeroGuy
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RE: High Wing Airliner

Wed Apr 12, 2006 10:44 am

Quoting HiFi (Reply 10):
Both high-wing and low-wing designs have lots of advantages and lots of disadvantages.. The conclusion you get after spending hours and hours thinking about it is: it just doesn't matter (unless you have a very specific mission or constraint).

Manufacturers that usually go with high-wing will probably continue designing high-wing... the same goes for low-wing... simple as that, because you already know what to do to compensate for the disadvantages. It's not lack of imagination or creativity, it's just that for the majority of design cases there's no real gain in preferring one option over the other.

Compare the number of A320/737 or larger airliners that are low wing vs high wing. Low wing airplanes far out number the high wings. This says that there are more low wing airplanes says that for airliners, low wings have fewer design compromises and/or are more efficient. If it were a toss up, there would be a more even distribution. There are real advantages for a low wing airliner and the market is skewed accordingly.

Quoting BigJimFX (Reply 12):
Where are the fuel lines routed in a rear engined aircraft? Through the cabin, outside the pressure vessel I guess.

Nope, they're just like APU fuel lines. Inside the pressure vessel but below the passenger and/or cargo floor. Not through the passenger cabin. And while rear mounted engine airliners are more numerous than high wing airliners, they are still very much in the minority. The market is skewed by efficiency here as well.

Quoting BigJimFX (Reply 12):
Any way we can put them into miniature lifting surfaces? Kinda like a helicopter?

Is there any mechanical flying object with more drag than a helicopter?
Airplane design is easy, the difficulty is getting them to fly - Barnes Wallis

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