flexo
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High Wing Vs. Low Wing

Fri May 23, 2008 4:23 pm

Hi Everyone,

It seems for current plane makers there is a consensus that low wing is the best way to go for passenger aircraft.

However, for military transports it seems that high wing is the way to go. I can't think of any modern transporter with low wings.

So why is that? Wouldn't a high wing also have significant advantages for passenger aircraft? It seems that you could place the wing attachment in the currently wasted space in the crown area of the fuselage and gain valuable cargo space in the lower part.

The only downside I can think of is more difficult engine maintenance. Obviously I must be missing something or it would be done, so what is it?
 
BAE146QT
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RE: High Wing Vs. Low Wing

Fri May 23, 2008 4:36 pm



Quoting Flexo (Thread starter):
Obviously I must be missing something or it would be done, so what is it?

I don't know what benefits low-wing design has over high-wing (though stall characteristics come to mind) but the reason why so many military transports are high-winged is probably due to;

1) Keeping the engines away from FOD.
2) increasing the options for loading at ground level.

Airliners have the luxury of known fields usually. A military transporter might not do.
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futurecaptain
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RE: High Wing Vs. Low Wing

Fri May 23, 2008 5:00 pm



Quoting Flexo (Thread starter):
Obviously I must be missing something or it would be done,

High wing airliners can be found in several turboprops, some small regional jets, and flying boats. I know you probably mean more mainline aircraft though.

Quoting BAe146QT (Reply 1):
I don't know what benefits low-wing design has over high-wing (though stall characteristics come to mind)

Stall characteristics are going to deal more with wing design then wing position.
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SlamClick
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RE: High Wing Vs. Low Wing

Fri May 23, 2008 5:10 pm



Quoting BAe146QT (Reply 1):
1) Keeping the engines away from FOD.
2) increasing the options for loading at ground level.

I'm pretty sure the design choices would lie in these areas and not in aerodynamics. Military transports might have to operate in unimproved areas, amid ground clutter etc. Besides they don't have to make a profit for their stockholders.

Now what I don't understand is this: Why is it that a high-wing has to have its wings mounted farther forward? They all do. Compare Aero Commander with Queen Air or try to reconfigure a C-141 as a low-wing and see if it wouldn't just look like the wings needed to be moved aft.
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UAL747
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RE: High Wing Vs. Low Wing

Fri May 23, 2008 5:42 pm

For larger airliners, the wingbox would become a problem in a high-wing configuration. It would cut into the cabin roof too much. In a low-wing configuration, you can hide that down in the cargo hold and not disrupt the cabin height.

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RE: High Wing Vs. Low Wing

Fri May 23, 2008 5:54 pm



Quoting UAL747 (Reply 4):
For larger airliners, the wingbox would become a problem in a high-wing configuration. It would cut into the cabin roof too much.

Why would that design challenge be specific to larger airliners? If the Q400 can fit the wingbox up there and maintain a relatively comfortable cabin, it seems to me the same could be accomplished with a larger wing and fuselage.

2H4
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flexo
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RE: High Wing Vs. Low Wing

Fri May 23, 2008 6:21 pm



Quoting Futurecaptain (Reply 2):
High wing airliners can be found in several turboprops

True, but from what I heard that is mainly due to the propeller diameter which would be limited too much in a low wing configuration.

Quoting SlamClick (Reply 3):


Quoting BAe146QT (Reply 1):
1) Keeping the engines away from FOD.
2) increasing the options for loading at ground level.

I'm pretty sure the design choices would lie in these areas and not in aerodynamics. Military transports might have to operate in unimproved areas, amid ground clutter etc. Besides they don't have to make a profit for their stockholders.

You are right of course that military aircraft have a much different objective where efficiency and making profit are not top of the list. However, that would imply that high wing designs are not as efficient to build / operate. Is that really so?
 
SlamClick
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RE: High Wing Vs. Low Wing

Fri May 23, 2008 6:25 pm



Quoting 2H4 (Reply 5):
Why would that design challenge be specific to larger airliners?

It certainly would be a 'challenge' but challenges exist to be overcome, sometimes without regard for benefits or pricetags. It would, at least, require a solution very unlike what is done in the current flock of Boeing and Airbus offerings. On those, take a peek at a fuselage cross-section where the wing carries through. The wing is very deep - maybe five or six feet deep on a jumbo. The cabin deck is pretty much always flat, in a plane* above the uppermost camber. The carry-through is shaped a lot like just another bit of wing. It's worked for a long time. Viewed from fore-aft, the wing's frontal area is masked by spaces used for cargo compartments in the lower lobes.

Now picture that same wing-section passing through up high. Unless you want to step down a few feet in the area of the wing, you will have to drop the entire passengers deck down enough to give you the required headroom there. Now where do the bag pits go? Does the electrics, hydraulics, pneumatics, conditioned air, etc. all get rerouted through the overhead? Is that as safe as? What impact does that have on routine maintenance? How ever will we load the bags? Etc?

Or we completely redesign the manner in which the wing-structure is mated to the fuselage-structure. I can envision ring-bulkheads incorporating hardpoints to attach outer wing panels, and structures to mate to fuselage tubes, but they would have to be quite substantial and they would, no doubt, be complex to manufacture - when compared with just resting the tube on the wing, then bolting them together.

Here's yet another area where I am blissfully ignorant, but I suspect that there are different load-carrying characteristics for a stiff wing-attached-to-fuselage arrangement like I describe above vs. the wing being a single structure from tip to tip. My uneducated, but broadly experienced eye tells me that the traditional design the load is distributed pretty uniformly from tip to tip, but in the former there would be a lot of concentration of the load, the stress, in the area of the attach points. I suspect that is true, I cannot back it up and will yield to my academic betters on this, but that is what I think.

* Geometry plane, not airplane.  Smile
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2H4
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RE: High Wing Vs. Low Wing

Fri May 23, 2008 6:28 pm



Quoting Flexo (Reply 6):
True, but from what I heard that is mainly due to the propeller diameter which would be limited too much in a low wing configuration.

Just install 45-foot high landing gear:


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2H4
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RE: High Wing Vs. Low Wing

Fri May 23, 2008 6:34 pm



Quoting SlamClick (Reply 7):
Now picture that same wing-section passing through up high. Unless you want to step down a few feet in the area of the wing, you will have to drop the entire passengers deck down enough to give you the required headroom there. Now where do the bag pits go? Does the electrics, hydraulics, pneumatics, conditioned air, etc. all get rerouted through the overhead? Is that as safe as? What impact does that have on routine maintenance? How ever will we load the bags? Etc?

Absolutely, and I was wondering why, if the Q400 can overcome those challenges, why larger aircraft wouldn't also be able to do so. I'm not of the opinion that they can or should....just curious what technical challenges stand in their way.

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roseflyer
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RE: High Wing Vs. Low Wing

Fri May 23, 2008 7:09 pm

High wing designs actually aren't more efficient. No one has really addressed that. Military cargo planes are high wing so that they can have easy loading. Whether it is a C17 or Antonov AN124, it's easy to roll or even drive equipment onto the airplane with the cargo ramp. Passenger aircraft don't need this capability and thus can have a more optimized configuration, which I believe is a low wing configuration. It's been a while since I learned about this stuff in college, but I believe less weight is required for a low wing design for the structural components. I'm not sure about the aero differences.
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futurecaptain
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RE: High Wing Vs. Low Wing

Fri May 23, 2008 7:40 pm



Quoting RoseFlyer (Reply 10):
I'm not sure about the aero differences.

For one a high wing is going to be more inherently stable. For instance, when was the last time you saw a low winged bird?

But with a high wing you have the question of "where do I put the landing gear?" Wider gear allows for a greater crosswind component. Unfortunately with most high wing airplanes the main gear goes into the fuselage and ends up being very closely spaced.
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2H4
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RE: High Wing Vs. Low Wing

Fri May 23, 2008 7:47 pm



Quoting Futurecaptain (Reply 11):
But with a high wing you have the question of "where do I put the landing gear?"

The obvious solution is, of course, hover gear:





 Wink

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flexo
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RE: High Wing Vs. Low Wing

Fri May 23, 2008 7:59 pm



Quoting 2H4 (Reply 12):
The obvious solution is, of course, hover gear:

Wow, they actually built a prototype with that kind of gear? How cool is that, I guess it could also land on water?

Begs the question though: How do you retract that "gear"?
 
2H4
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RE: High Wing Vs. Low Wing

Fri May 23, 2008 8:00 pm



Quoting Flexo (Reply 13):
Begs the question though: How do you retract that "gear"?

Just turn off that aux jet engine and deflate it, I think.

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Pihero
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RE: High Wing Vs. Low Wing

Fri May 23, 2008 10:52 pm



Quoting SlamClick (Reply 3):
Now what I don't understand is this: Why is it that a high-wing has to have its wings mounted farther forward? They all do. Compare Aero Commander with Queen Air or try to reconfigure a C-141 as a low-wing and see if it wouldn't just look like the wings needed to be moved aft.

I asked the very same question to an aerodynamicist friend of mine and his answer was that the aircraft fuselage top becomes influenced by the *aerodynamic field* of the wing and it becomes lift generating (that's also the reason why military transporters have a smaller wing than they would normally have). As a result, the center of lift is further forward than it is with the wing taken alone. Hence the wing position and the increased tailplane surface.
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GolfOscarDelta
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RE: High Wing Vs. Low Wing

Fri May 23, 2008 11:00 pm

Two other reasons i think of, that cause most passenger aircraft to have low wing rather than high wing are:
1. Noise sheilding - in a low wing airliner the wing usually shields the cabin from (at least some) engine noise
2. Landing Gear: This itself is a two part problem
a. A landing gear is usally attached to the wing carrythrough box in a low wing config. Thus requiring little structual reinforcement unlike in a high wing config where the fuselage has to be strengthened to accomadate landing gear loads.
b. Landing gear Stowage: In low wing config it is usually stowed in the part of the fairing just behind the wing carrythrough box and hence does not cause any extra drag as compared to a high wing config which will require blister fairing along the fuselage to accomodate the landing gear and thus cause extra drag.

Quoting SlamClick (Reply 7):
I can envision ring-bulkheads incorporating hardpoints to attach outer wing panels, and structures to mate to fuselage tubes

Did you mean something like this?
http://www.jsf.mil/images/gallery/cdp/lockheed/manufacturing/cdp_loc_manf_007.jpg

Quoting SlamClick (Reply 7):
suspect that there are different load-carrying characteristics for a stiff wing-attached-to-fuselage arrangement like I describe above vs. the wing being a single structure from tip to tip



Quoting SlamClick (Reply 7):
experienced eye tells me that the traditional design the load is distributed pretty uniformly from tip to tip, but in the former there would be a lot of concentration of the load, the stress, in the area of the attach points

To add to SlamClick's comment's
IIRC, the carry through wing (i.e wing being single structure end to end) is mainly used because the torsional loads on one wing can be balenced by the loads on the other. In case of the wing-attached-to-fuselage-structure the torsional loads have to be passed through the fuselage structure to the other side, while the bending/torsional loads of the fuselage itself have to be accomodated by the fuselage structure. The point is, you have two loads now (wing loads and fuselage loads) to consider at the wing/fuslage intersection, and this area would need to be beefed up considerably, leading to weight incease as compared to the wing-wingbox-wing structure with the fuselage sitting on it. Uh and if i'm worng feel free to correct me on that.
 
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Starlionblue
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RE: High Wing Vs. Low Wing

Fri May 23, 2008 11:44 pm

Quoting Futurecaptain (Reply 11):
For instance, when was the last time you saw a low winged bird?

Birds use muscles for propulsion and they need those muscles to be long enough and big enough. They ones for the power stroke (down) attach at the breastbone. With a low wing, these muscles would become very short. High wings allow more flapping range. So it's not quite the same.

[Edited 2008-05-23 16:45:07]
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RE: High Wing Vs. Low Wing

Sat May 24, 2008 12:41 am



Quoting UAL747 (Reply 4):
For larger airliners, the wingbox would become a problem in a high-wing configuration. It would cut into the cabin roof too much. In a low-wing configuration, you can hide that down in the cargo hold and not disrupt the cabin height.

Although that's not a problem on some later turboprops, it's one of the few things I don't like about the BAe146/Avro RJ since the wing structure results in very shallow overhead bins for several rows of seats under the wing, only big enough for a thin briefcase or soft items. If you have a larger carry-on bag you have to hope the bins forward of or behind the wing aren't full.
 
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RE: High Wing Vs. Low Wing

Sat May 24, 2008 1:02 am



Quoting Flexo (Thread starter):
Wouldn't a high wing also have significant advantages for passenger aircraft? It seems that you could place the wing attachment in the currently wasted space in the crown area of the fuselage and gain valuable cargo space in the lower part.

The crown on current airliners isn't deep enough for the wing box. The cabin floor is typically near the mid-point of the fuselage and the top of the wing is only a few inches under the cabin floor. In other words, the wing is about as thick as the cargo hold, which is a *lot* thicker than the crown space.

Quoting Flexo (Thread starter):
The only downside I can think of is more difficult engine maintenance. Obviously I must be missing something or it would be done, so what is it?

Landing gear and crashworthiness.

Quoting 2H4 (Reply 5):
Why would that design challenge be specific to larger airliners? If the Q400 can fit the wingbox up there and maintain a relatively comfortable cabin, it seems to me the same could be accomplished with a larger wing and fuselage.

The Q400 doesn't have nearly the cargo requirements that a larger airliner does.

Quoting Futurecaptain (Reply 11):
For one a high wing is going to be more inherently stable. For instance, when was the last time you saw a low winged bird?

When was the last time you saw a statically stable bird?

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RE: High Wing Vs. Low Wing

Sat May 24, 2008 1:46 am



Quoting RoseFlyer (Reply 10):
High wing designs actually aren't more efficient.

Peter Garrison in Flying wrote a Technicalities column about high-vs-low wings. On piston aircraft, at least, high wings are actually more efficient due to having less wing/fuselage interference.
 
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RE: High Wing Vs. Low Wing

Sat May 24, 2008 5:51 am



Quoting Starlionblue (Reply 17):
So it's not quite the same.

Okay, when's the last time you saw a low-wing ornithopter?
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flipdewaf
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RE: High Wing Vs. Low Wing

Sat May 24, 2008 4:16 pm



Quoting Futurecaptain (Reply 11):
For one a high wing is going to be more inherently stable.

Being more stable in roll is actually a hindrance as the aircraft get big, you either need massive ailerons or a huge amount of anhedral, so much in fact that in some cases the ground clearance of the high wing is worse than the low wing. This would definitely be the case on an A380 sized aircraft.

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BAE146QT
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RE: High Wing Vs. Low Wing

Sat May 24, 2008 4:33 pm



Quoting RoseFlyer (Reply 10):
Military cargo planes are high wing so that they can have easy loading. Whether it is a C17 or Antonov AN124, it's easy to roll or even drive equipment onto the airplane with the cargo ramp. Passenger aircraft don't need this capability and thus can have a more optimized configuration, which I believe is a low wing configuration.

Now - wasn't the B-747 originally designed with - at least at first - a military cargo lifter role in mind? It was up against the Lockheed C-5, (although it wasn't a stand-up fight like the YF-16 vs YF-17 or the YF-32 vs the YF-35), if I recall correctly.

It's clear that the C-5 'won', but I have never known the reasons why and I can't help but wonder if their wing design was a major factor.

Quoting SlamClick (Reply 21):
Okay, when's the last time you saw a low-wing ornithopter?

That's not quite fair, chap, but it's a heck of a loaded question.

Birds/bees/whatever are 'designed' to accommodate the limitations of their powerplant, meaning they have to have a high wing, since the power stroke is down and muscles are stronger in contraction than expansion. Just ask a crocodile, once you have taken the rubber band off his mouth.

Knowing that an ornithopter is specifically designed to imitate those creatures, in spite of not being similarly limited, could give the answer. They're built that way because they are an imitation of life.

But an ornithopter's wings rely on a constantly changing angle of attack. Whether there would be a negative aerodynamic effect of having a significant portion of the wing root drop below the line of the fuselage (or body) with every flap, I'm not sure. This may also be a limitation of the design though.
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flexo
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RE: High Wing Vs. Low Wing

Sat May 24, 2008 10:57 pm



Quoting Flipdewaf (Reply 22):
Being more stable in roll is actually a hindrance as the aircraft get big, you either need massive ailerons or a huge amount of anhedral, so much in fact that in some cases the ground clearance of the high wing is worse than the low wing. This would definitely be the case on an A380 sized aircraft.

Isn't the AN-225 of an even greater size than the A380? It seems that the ground clearance of the AN is greater than the A380:

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flipdewaf
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RE: High Wing Vs. Low Wing

Sat May 24, 2008 11:45 pm

In the recent large aircraft design project we had at university the anhedral on the high wings to get the roll rate meant that the high winged aircraft required longer gear to move the engines up. The ground clearance problems (especially fro a crosswind landing constraint) the angle is limited by the outboard engine or even wing tip on the low wing it is the inboard engine normally and the gulling can take this away. The Engines on the AN-225 are considerably smaller than the A380 and on the AN225 the max payload (taking the MTOW up to around that of the A380F is when the buran was carried which raises the CofG of the aircraft to make the wing effectively lower.

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thegeek
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RE: High Wing Vs. Low Wing

Sun May 25, 2008 12:01 am

Does the anhedral of the An-225 result in negative stability? The only way I can see that it wouldn't is if the bending of the wings under load gives some dihedral.
 
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Starlionblue
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RE: High Wing Vs. Low Wing

Sun May 25, 2008 12:28 am



Quoting Thegeek (Reply 26):
Does the anhedral of the An-225 result in negative stability? The only way I can see that it wouldn't is if the bending of the wings under load gives some dihedral.

Nope. The "rules" regarding anhedral are a bit different for high wings. It is quite positively stable.

Quoting Flexo (Reply 24):
Isn't the AN-225 of an even greater size than the A380?

Yes. Significantly larger.
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thegeek
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RE: High Wing Vs. Low Wing

Sun May 25, 2008 1:16 am



Quoting Starlionblue (Reply 27):
Nope. The "rules" regarding anhedral are a bit different for high wings. It is quite positively stable.

Hate to ask endless and annoying questions, but why? With 2 degrees of anhedral on each side, if you roll 2 degrees to port, the starboard wing is now producing more lift and the port wing less lift, exacerbating the roll. What complication am I missing?
 
tdscanuck
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RE: High Wing Vs. Low Wing

Sun May 25, 2008 4:58 am



Quoting BAe146QT (Reply 23):
Now - wasn't the B-747 originally designed with - at least at first - a military cargo lifter role in mind? It was up against the Lockheed C-5, (although it wasn't a stand-up fight like the YF-16 vs YF-17 or the YF-32 vs the YF-35), if I recall correctly.

You recall wrong. Boeing was working on a competitor to the C-5, but it wasn't the 747. Joe Sutter (747 Chief Engineer) is extremely clear on this point. The 747 was designed from the outset to be a freighter, because Boeing assumed that the SST would take over the passenger role. However, the military cargo mission was a different airplane.

Quoting Thegeek (Reply 26):
Does the anhedral of the An-225 result in negative stability?

No.

Quoting Thegeek (Reply 28):
Hate to ask endless and annoying questions, but why? With 2 degrees of anhedral on each side, if you roll 2 degrees to port, the starboard wing is now producing more lift and the port wing less lift, exacerbating the roll. What complication am I missing?

You're missing the pendulum effect of the fuselage. You have a lot of weight (huge weight, for a cargolifter) below the wing, which causes substantial roll stability. It's so pronounced on large cargolifters that they introduce anhedral in order to lessen the roll stability to something reasonable (but still positive). Otherwise you'd end up needing absolutely gigantic ailerons and paying a drag penalty for essentially no return.

Tom.
 
point8six
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RE: High Wing Vs. Low Wing

Sun May 25, 2008 8:05 am

Boeing's entry for the USAF large freighter - won by Lockheed's C5 Galaxy - was a high wing, conventional tail aircraft. The An124 resembles Boeing's entry!
In "747" Joe Sutter states that the 747 was designed as a pax a/c and freighter from the start -page 90.
High wing military a/c ( C5, An124,An225, C141,IL76 etc.) are for use on unconventional runways, such as Tundra and gravel and therefore the need to mount the engines as far off the ground as possible, is obvious.
 
thegeek
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RE: High Wing Vs. Low Wing

Sun May 25, 2008 10:00 am



Quoting Tdscanuck (Reply 29):
You're missing the pendulum effect of the fuselage. You have a lot of weight (huge weight, for a cargolifter) below the wing, which causes substantial roll stability. It's so pronounced on large cargolifters that they introduce anhedral in order to lessen the roll stability to something reasonable (but still positive). Otherwise you'd end up needing absolutely gigantic ailerons and paying a drag penalty for essentially no return.

Interesting. Even with the very short moment arm of that pendulum, yes I can see that.

There you have it, there is an advantage: Anhedral wings will be more level at the tips than dihedral wings, and therefore the lift will be more directly upwards. At least that's what I think would happen.
 
BAE146QT
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RE: High Wing Vs. Low Wing

Sun May 25, 2008 1:59 pm



Quoting Tdscanuck (Reply 29):
Boeing was working on a competitor to the C-5, but it wasn't the 747.



Quoting Tdscanuck (Reply 29):
The 747 was designed from the outset to be a freighter, because Boeing assumed that the SST would take over the passenger role. However, the military cargo mission was a different airplane.

That may well explain my confusion in the matter.

Quoting Point8six (Reply 30):
In "747" Joe Sutter states that the 747 was designed as a pax a/c and freighter from the start -page 90.

That'll be another one for my Borders shopping list...
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seabosdca
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RE: High Wing Vs. Low Wing

Sun May 25, 2008 4:43 pm



Quoting Flexo (Reply 24):
Isn't the AN-225 of an even greater size than the A380? It seems that the ground clearance of the AN is greater than the A380:

Look at those pictures carefully and imagine that you have GP7000s on the An-225, with the outboard pair mounted as far out on the wing as they are on the A380. I don't think there would be much if any difference in ground clearance. The difference is because the D-18s are so much smaller and mounted further inboard.
 
flexo
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RE: High Wing Vs. Low Wing

Sun May 25, 2008 4:55 pm



Quoting SeaBosDca (Reply 33):
Look at those pictures carefully and imagine that you have GP7000s on the An-225, with the outboard pair mounted as far out on the wing as they are on the A380. I don't think there would be much if any difference in ground clearance. The difference is because the D-18s are so much smaller and mounted further inboard.

After looking at those pictures for a while I think you might be right. Although it seems that the pictures are not the same scale. The AN seems to be further away from the photographer.

The lower ground clearance of the high winged aircraft brings up another question: It was earlier mentioned high wings in military aircraft are also due to keeping the engines away from FOD. Now that seems to be not working so well!
 
HaveBlue
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RE: High Wing Vs. Low Wing

Sun May 25, 2008 9:20 pm

On top of the need to operate in and out of unimproved runways, I've always thought the single biggest reason for high wing transports was the fact that they can stop, pop open the tail (and nose on some) and drive the cargo on and off. Can you imagine how much more difficult it would be to move an M-1 Abrams off the C-5 if it couldn't just drive on? And some planes make this even easier by 'kneeling' to where the fuselage is literally almost on the pavement (C-5 kneels, think the An-225 does at the front). Anyhow driving tanks and pushing helos up ramps to nearly ground level cargo holds was the key imo.
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RE: High Wing Vs. Low Wing

Mon May 26, 2008 10:48 am

Most of these points have already been brought up. Just my thoughts. The higher wings on Military cargo aircraft allow for 1. Landing on unimproved runways, helps to prevent FODing out engines. 2. On a/c such as the C-130 it also allows for 13'+ props to still maintain a good amount of ground clearance. 3. aircraft such as the the C-130, C-17, and C-5 have there cargo floors very close to the belly of the a/c to allow for taller objects to be transported in the a/c. My guess is that if the A/C had low wing designs the wingbox might force the cargo floor to be placed up higher in the A/C limiting the ability to carry over sized cargo. i.e. CH-46; UH-60; AH-1W, M1A1.
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SEPilot
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RE: High Wing Vs. Low Wing

Mon May 26, 2008 2:05 pm



Quoting Futurecaptain (Reply 11):
For one a high wing is going to be more inherently stable. For instance, when was the last time you saw a low winged bird?

The stability of high winged aircraft comes from the pendulum effect, as Tdscanuck says. I had always thought this was why birds were high winged, but Starlionblue's explanation of the muscle location makes sense as well, and is something I had not thought of. The point is using the pendulum effect to get stability is marginally more efficient than using dihedral, as with dihedral you have the lift vectors from each wing working against each other to a small degree. But it is pretty small in the overall scheme of things, and the structural considerations favoring low wings far outweigh it. The reason almost all jetliners are low winged is that the structure necessary to support the landing gear is incorporated into the wingbox, making it much more compact and efficient (i.e. light), as well as not requiring as much fuselage space. With a high winged design you have to connect the wingbox with the landing gear structure, which would have to be through the fuselage walls. The landing gear would also have to be mounted to the fuselage, making it narrower than when mounted on the wings. The weight penalties of the structure necessary for the high winged design far outweigh the slight aerodynamic efficiency. And, if you end up with too much stability on a high winged design the anhedral that you then have to introduce has the same aerodynamic penalty as dihedral does.

Quoting BAe146QT (Reply 23):

Now - wasn't the B-747 originally designed with - at least at first - a military cargo lifter role in mind?

As Tdscanuck stated, that was a different plane. The 747 wasn't even conceived until Boeing lost that competition, and they started from clean paper.
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RE: High Wing Vs. Low Wing

Mon May 26, 2008 3:23 pm



Quoting GolfOscarDelta (Reply 16):
Did you mean something like this?

Approximately just about exactly like that.

Sorry, I somehow missed your post until just now. Thank you. You have diminished my ignorance ever so slightly while validating something I formerly could only suspect to be true.

By the way, that is a rather complex jig. I'd like to see how they get the airframe out of it when it is completed.
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RE: High Wing Vs. Low Wing

Mon May 26, 2008 7:04 pm



Quoting SEPilot (Reply 37):
The landing gear would also have to be mounted to the fuselage

An interesting alternative is to make it DHC-8 like, and connect the landing gear to pods under the engines. At least this takes care of cross wind concerns of high wings. I doubt it helps the weight penalty too much though.

Quoting GolfOscarDelta (Reply 16):
Did you mean something like this?

At the risk of asking a stupid question, what is that picture of?
 
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RE: High Wing Vs. Low Wing

Mon May 26, 2008 7:12 pm



Quoting Thegeek (Reply 39):
At the risk of asking a stupid question, what is that picture of?

Looks to me like an F-35.
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RE: High Wing Vs. Low Wing

Mon May 26, 2008 7:32 pm



Quoting Thegeek (Reply 39):



Quoting BAe146QT (Reply 40):
Looks to me like an F-35.

Yep, F-35 it is.
 
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RE: High Wing Vs. Low Wing

Mon May 26, 2008 10:12 pm



Quoting Thegeek (Reply 39):

An interesting alternative is to make it DHC-8 like, and connect the landing gear to pods under the engines. At least this takes care of cross wind concerns of high wings. I doubt it helps the weight penalty too much though.

This was possible with props; it is basically impossible with jets. Prop engines (even some turboprops) generally have some empty space in the nacelle behind the engine; jets do not, as the airflow through the engine uses up all of the space behind it. You would have to add a substantial bulge to the engine, which would be horribly inefficient. On top of that, the landing gear would have to be quite a bit longer than standard gear, which adds weight. It would actually help reduce requirements on the wingbox slightly, as putting the landing gear weight and loads partially out on the wing would actually reduce stress, but not enough to overcome the disadvantages.
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RE: High Wing Vs. Low Wing

Tue May 27, 2008 12:46 am



Quoting SEPilot (Reply 37):
Starlionblue's explanation of the muscle location makes sense as well,

Most birds elongate the chest (flying) muscles even more by having a keeled breastbone. This allows a strong attachment point far out from the chest cavity.

http://www.paulnoll.com/Oregon/Birds/Avian-Skeleton.jpg
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HaveBlue
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RE: High Wing Vs. Low Wing

Tue May 27, 2008 2:13 pm

Cool second picture Starlionblue, but the first one gives me this:

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You don't have permission to access /Oregon/Birds/Avian-Skeleton.jpg on this server.


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RE: High Wing Vs. Low Wing

Wed May 28, 2008 12:35 am



Quoting HaveBlue (Reply 44):
You don't have permission to access /Oregon/Birds/Avian-Skeleton.jpg on this server.

That's funny. I see it fine. Hmmmmm. Anyway it doesn't really show anything new.
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CanadianNorth
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RE: High Wing Vs. Low Wing

Wed May 28, 2008 4:18 am

The way I learned it back in level 1 of AME school:

High wing:
-less chance of damage from both FOD and ground equipment
-more stable
-can allow for large diameter props without having to raise the fuselage up as much
-can allow for easier loading/unloading
-better view during level flight
-most high wing jet powered aircraft need some anhedral to counteract the fact that they can be too stable to maneuver

Low wing:
-easier access for maintenance, in some cases easier access for fueling
-lighter
-allows for better placement of landing gear
-for engines mounted under wings this design can make for a quieter cabin
-better view during turns
-most low wing aircraft need some dihedral to make up for lack of stability in the overall design



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RE: High Wing Vs. Low Wing

Wed May 28, 2008 12:55 pm



Quoting Flexo (Reply 34):
The lower ground clearance of the high winged aircraft brings up another question: It was earlier mentioned high wings in military aircraft are also due to keeping the engines away from FOD. Now that seems to be not working so well!

Aren't the inner engines most at risk of FOD since they are closest to the aircraft's wheels? Being higher up means they are less in harm's way.
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RE: High Wing Vs. Low Wing

Wed May 28, 2008 2:51 pm



Quoting Kukkudrill (Reply 47):
Aren't the inner engines most at risk of FOD since they are closest to the aircraft's wheels? Being higher up means they are less in harm's way.

But it's more likely that the inner engines will be over pavement, while the outer engines will be hanging out over dirt, gravel, etc.

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RE: High Wing Vs. Low Wing

Wed May 28, 2008 9:43 pm

True, assuming you're on a paved runway. I imagine FOD is much more of an issue when you're operating from an unpaved surface.
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