Sponsor Message:
Aviation Technical / Operations Forum
My Starred Topics | Profile | New Topic | Forum Index | Help | Search 
High Wing Vs. Low Wing  
User currently offlineFlexo From St. Helena, joined Mar 2007, 406 posts, RR: 0
Posted (5 years 11 months 19 hours ago) and read 20931 times:

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?

140 replies: All unread, showing first 25:
 
User currently offlineBAe146QT From United Kingdom, joined Sep 2006, 996 posts, RR: 0
Reply 1, posted (5 years 11 months 19 hours ago) and read 20958 times:



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.



Todos mis dominós son totalmente pegajosos
User currently offlineFuturecaptain From , joined Dec 1969, posts, RR:
Reply 2, posted (5 years 11 months 19 hours ago) and read 20926 times:



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.


User currently offlineSlamClick From United States of America, joined Nov 2003, 10062 posts, RR: 68
Reply 3, posted (5 years 11 months 19 hours ago) and read 20909 times:



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.



Happiness is not seeing another trite Ste. Maarten photo all week long.
User currently offlineUAL747 From , joined Dec 1969, posts, RR:
Reply 4, posted (5 years 11 months 18 hours ago) and read 20891 times:

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.

UAL


User currently offline2H4 From United States of America, joined Oct 2004, 8955 posts, RR: 60
Reply 5, posted (5 years 11 months 18 hours ago) and read 20886 times:
AIRLINERS.NET CREW
HEAD DATABASE EDITOR



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



Intentionally Left Blank
User currently offlineFlexo From St. Helena, joined Mar 2007, 406 posts, RR: 0
Reply 6, posted (5 years 11 months 17 hours ago) and read 20868 times:



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?


User currently offlineSlamClick From United States of America, joined Nov 2003, 10062 posts, RR: 68
Reply 7, posted (5 years 11 months 17 hours ago) and read 20864 times:



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



Happiness is not seeing another trite Ste. Maarten photo all week long.
User currently offline2H4 From United States of America, joined Oct 2004, 8955 posts, RR: 60
Reply 8, posted (5 years 11 months 17 hours ago) and read 20867 times:
AIRLINERS.NET CREW
HEAD DATABASE EDITOR



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:


View Large View Medium
Click here for bigger photo!

Photo © Mel Lawrence
View Large View Medium
Click here for bigger photo!

Photo © Robert Roggeman



View Large View Medium
Click here for bigger photo!

Photo © Peter de Jong
View Large View Medium
Click here for bigger photo!

Photo © Joeri Turk



Signed,

Tupolev



Intentionally Left Blank
User currently offline2H4 From United States of America, joined Oct 2004, 8955 posts, RR: 60
Reply 9, posted (5 years 11 months 17 hours ago) and read 20857 times:
AIRLINERS.NET CREW
HEAD DATABASE EDITOR



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.

2H4



Intentionally Left Blank
User currently offlineRoseFlyer From United States of America, joined Feb 2004, 9375 posts, RR: 52
Reply 10, posted (5 years 11 months 17 hours ago) and read 20838 times:

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.


If you have never designed an airplane part before, let the real designers do the work!
User currently offlineFuturecaptain From , joined Dec 1969, posts, RR:
Reply 11, posted (5 years 11 months 16 hours ago) and read 20821 times:



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.


User currently offline2H4 From United States of America, joined Oct 2004, 8955 posts, RR: 60
Reply 12, posted (5 years 11 months 16 hours ago) and read 20819 times:
AIRLINERS.NET CREW
HEAD DATABASE EDITOR



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

2H4



Intentionally Left Blank
User currently offlineFlexo From St. Helena, joined Mar 2007, 406 posts, RR: 0
Reply 13, posted (5 years 11 months 16 hours ago) and read 20804 times:



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"?


User currently offline2H4 From United States of America, joined Oct 2004, 8955 posts, RR: 60
Reply 14, posted (5 years 11 months 16 hours ago) and read 20801 times:
AIRLINERS.NET CREW
HEAD DATABASE EDITOR



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.

2H4



Intentionally Left Blank
User currently offlinePihero From France, joined Jan 2005, 4143 posts, RR: 76
Reply 15, posted (5 years 11 months 13 hours ago) and read 20773 times:
Support Airliners.net - become a First Class Member!



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.



Contrail designer
User currently offlineGolfOscarDelta From India, joined Feb 2008, 169 posts, RR: 0
Reply 16, posted (5 years 11 months 13 hours ago) and read 20777 times:

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.


User currently offlineStarlionblue From Greenland, joined Feb 2004, 16908 posts, RR: 67
Reply 17, posted (5 years 11 months 12 hours ago) and read 20743 times:

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]


"There are no stupid questions, but there are a lot of inquisitive idiots."
User currently offlineViscount724 From Switzerland, joined Oct 2006, 24061 posts, RR: 22
Reply 18, posted (5 years 11 months 11 hours ago) and read 20724 times:



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.


User currently offlineTdscanuck From Canada, joined Jan 2006, 12709 posts, RR: 80
Reply 19, posted (5 years 11 months 11 hours ago) and read 20725 times:



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?

Tom.


User currently offlineMD-90 From United States of America, joined Jan 2000, 8494 posts, RR: 12
Reply 20, posted (5 years 11 months 10 hours ago) and read 20716 times:



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.


User currently offlineSlamClick From United States of America, joined Nov 2003, 10062 posts, RR: 68
Reply 21, posted (5 years 11 months 6 hours ago) and read 20672 times:



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

Okay, when's the last time you saw a low-wing ornithopter?



Happiness is not seeing another trite Ste. Maarten photo all week long.
User currently offlineFlipdewaf From United Kingdom, joined Jul 2006, 1540 posts, RR: 1
Reply 22, posted (5 years 10 months 4 weeks 1 day 20 hours ago) and read 20565 times:
Support Airliners.net - become a First Class Member!



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.

Fred


User currently offlineBAe146QT From United Kingdom, joined Sep 2006, 996 posts, RR: 0
Reply 23, posted (5 years 10 months 4 weeks 1 day 19 hours ago) and read 20561 times:



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.



Todos mis dominós son totalmente pegajosos
User currently offlineFlexo From St. Helena, joined Mar 2007, 406 posts, RR: 0
Reply 24, posted (5 years 10 months 4 weeks 1 day 13 hours ago) and read 20512 times:



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:

View Large View Medium
Click here for bigger photo!

Photo © Dave Sturges
View Large View Medium
Click here for bigger photo!

Photo © Andres Contador



25 Flipdewaf : 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 aircra
26 Thegeek : 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
27 Starlionblue : Nope. The "rules" regarding anhedral are a bit different for high wings. It is quite positively stable. Yes. Significantly larger.
28 Thegeek : 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 no
29 Tdscanuck : 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 po
30 Point8six : 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
31 Thegeek : 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
32 BAe146QT : That may well explain my confusion in the matter. That'll be another one for my Borders shopping list...
33 SeaBosDca : 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 o
34 Flexo : 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 b
35 HaveBlue : 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 th
36 HercPPMX : 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 ru
37 SEPilot : 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, bu
38 SlamClick : Approximately just about exactly like that. Sorry, I somehow missed your post until just now. Thank you. You have diminished my ignorance ever so sli
39 Thegeek : 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 c
40 BAe146QT : Looks to me like an F-35.
41 GolfOscarDelta : Yep, F-35 it is.
42 SEPilot : This was possible with props; it is basically impossible with jets. Prop engines (even some turboprops) generally have some empty space in the nacell
43 Post contains links and images Starlionblue : 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
44 Post contains links HaveBlue : Cool second picture Starlionblue, but the first one gives me this: Forbidden You don't have permission to access /Oregon/Birds/Avian-Skeleton.jpg on t
45 Starlionblue : That's funny. I see it fine. Hmmmmm. Anyway it doesn't really show anything new.
46 CanadianNorth : 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 l
47 Kukkudrill : 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.
48 2H4 : 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. 2H4
49 Kukkudrill : 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.
50 HaveBlue : True, but even though it was a design requirement for most military cargo planes to be able to operate from unimproved runways, I doubt they see much
51 Vzlet : This might explain the occasional catastropic failure of C-130 wings.
52 BAe146QT : I have no data on this, but I suspect you're right. They were probably designed as contingency against a forward airfield being bombed out, forcing a
53 DocLightning : Not so simple. It's also an accident of evolution. First of all: dorsum=back/top and ventrum=front/bottom Birds are evolved from a common ancestor wi
54 HaveBlue : Interesting post DocLightning
55 Mir : Yes and no. You are correct in thinking that anhedral will make an airplane less stable, but an airliner or cargo plane with anhedral is still going
56 Rwessel : Because almost all muscles are more efficient in contraction, or work exclusively in that mode, a dorsal wing mount would drastically reduce the leng
57 Nomadd22 : Good luck boarding it while it's running. Part of the advantage for high wing on large cargo military aircraft is the need to load extremely heavy ob
58 Post contains links HaveBlue : Although technically the C-5 can carry 2 Abrams at one time, I think operationally that doesn't happen very often. The best I could find online was t
59 DocLightning : Well all muscles contract. There are no muscles that expand in any known organism. And you raise a good point. The downstroke is more important than
60 L-188 : The 60 ton tank in the cabin. The reason you see a lot of anhedral on those big military transports is that you have a center of mass below the cente
61 Nomadd22 : I'm not so sure about that. A plane with a tank in the belly won't roll about the wing attach. It will roll around the center of gravity. Pendulums w
62 Starlionblue : Just guessing here that the lift on the wing will shift the CG very far up on a high winged transport. Essentially the aircraft hangs from the wing s
63 JetMech : Fascinating input Doc, many thanks! Although I have studied much about engineering, it is always most interesting to learn about another area of know
64 FredT : Pendulum effect is all fine - if you have a net acceleration which is always acting in the vertical in the earth-fixed frame of reference. The local
65 Thegeek : So, while the anhedral moves the centre of lift below the wing box, it's still above the centre of gravity? That's what I've been able to gather from
66 FredT : The vertical position of the centre of lift doesn't really matter a whole lot when looking at lateral stability. It will still be pointing straight up
67 DocLightning : I'm no zoologist, but it's probably the pectoralis muscles.
68 Post contains links JetMech : This website gets into good detail about various issues to do with aerodynamics and flight dynamics; http://www.aeroexperiments.org/sitemap.shtml In
69 Tdscanuck : Yes. That's why having a high-wing tends to increase roll stability...if you roll, the couple between lift and gravity tends to roll the airplane bac
70 Post contains links FredT : Just in the way a pendulum in the cabin will hang straight down towards the center of the earth in a turn... If you have water next to a pendulum, th
71 Tdscanuck : No, not at all in the same way. A pendulum hanging in the cabin has a hinge can't can't "see" aircraft roll. When the aircraft itself rolls, there is
72 Blackbird : GolfOscarDelta, Hey that's a good fuselage structural set-up.. looks like the loads would be distributed through very nicely and it would be very stur
73 SpeedyGonzales : How about Tu-154? It has low wing and anhedral.
74 FredT : Gravity is acceleration. We are normally accelerated straight up against gravity, from being supported by the ground. This is how a pendulum will kno
75 Tdscanuck : No, gravity is a force. It causes an acceleration if, and only if, you don't have a counteracting force. Sitting at my desk, I am subject to the forc
76 DocLightning : Actually, you are incorrect. You are not moving, but you are accelerating. Einstein explains it this way: If you are in a spaceship in open space not
77 Tdscanuck : Not in a ground reference frame, I'm not. The position vector isn't changing. Relative to spacetime, sure, but I don't think that gets us closer to t
78 Post contains links JetMech : I'd suspect we are actually accelerated down towards the centre of the earth with gravity, and supported in place against it by the ground. I suspect
79 FredT : A force is measured in Newtons. Acceleration is measured in meters per second squared. Now, which unit do you use for gravity? Yes indeed, meters per
80 JetMech : Of course not, that's why I accounted for it in my original post . Regards, JetMech
81 FredT : OK, you remove it in one paragraph to create a righting force couple. Then you reintroduce it in the next paragraph to cause side slip. But you have t
82 David L : Wasn't Tdscanuck simply expressing Newton's Second Law? I may be missing something obvious but doesn't free-fall require acceleration, e.g. towards t
83 Post contains images FredT : Ahem, how to put it... I'd like to compliment you on an excellent choice of signature! Google, wikipedia or any physics text book should provide you
84 David L : Oh well, so much for a degree in Physics. However, it was quite a while ago (and I haven't used it much) so the definitions may well have changed. Mo
85 Tdscanuck : Bingo. Rather, the pendulum couple still exists in a coordinated turn (gravity didn't go away) but it's directly counteracted by the centripedal acce
86 JetMech : I prefaced that paragraph by stating that the aircraft was in a steady state side-slip. Thus, you still require a horizontal component of the lift fo
87 David L : Correct. You can't have acceleration without force(s) but you can have forces without acceleration... if those forces are balanced.
88 Post contains links FredT : The pendulum couple created by a force acting in line with the centre of mass of the aircraft? Moment = force times moment arm. Moment arm length zer
89 Post contains links FredT : Some interesting reading for those who want to see just how pronounced the effect of wing position is on lateral stability.
90 Tdscanuck : The moment arm isn't the same. The moment arm isn't the absolute distance between the CP and the CG (unless you're banked 90 degrees), it's the proje
91 FredT : The projected distance, as well as the perpendicular distance (which is the moment arm) will indeed double if the distance CL - CoG doubles, everythi
92 Tdscanuck : Take a look at the moment arm on the gravity force, which is *not* perpendicular to the wings if you're banked. It's non-zero. You need to look at th
93 JetMech : Fred, I wholeheartedly agree, that in a co-ordinated turn, the arm of the couple would indeed be zero as you have asserted. However, in a side slip s
94 Post contains images FredT : But where is the 'gravity force', aka 'weight', acting? At the center of mass. You're not getting a force couple out of that one. An aircraft is not
95 Tdscanuck : That's the effective definition of center of lift, actually. I fully agree that the sum of moments about the CG is zero. However, as is extremely eas
96 Post contains images JetMech : If we resolve the overall lift vector into the side slip element, and the element balancing lift we get the following. The dark green line represents
97 Tdscanuck : Wow. That was a lot more elegant than all that blather that I wrote. Nicely done! Yeah, what JetMech said. Tom.
98 Starlionblue : Great drawing JetMech! Anyone have a clue on this one though?
99 Post contains links and images JetMech : I should have added that the drawing is only strictly valid for the brief interval in time where we have a steady (zero lateral acceleration) side sl
100 Starlionblue : Wow. Jetmech. Great illustrations. Thank you.
101 David L : I'm still reading, too, but I can't add anything you and JetMech haven't - I just couldn't let the basics go. May the Acceleration be with you.
102 FredT : You cannot, I repeat, CAN NOT, break a force down into it's components and ignore one component while considering the other. You are effectively sayi
103 Tdscanuck : Bingo. I think that one distinction is behind this entire debate. He's not ignoring it. The moment from the remaining component doesn't balance the c
104 Tdscanuck : I was pondering this today (my mind wanders when I mow the lawn) and I got this wrong. JetMech isn't ignoring the other component, but my comment is
105 XT6Wagon : Haveblue, The origional M1 was 60 tons. The early M1A1 is about 63 tons. The later ones with more armor is 67tons, and the M1A2 is even heavier with
106 JetMech : I actually thought about it more and I think I got it ass about. The anhedral would actually exacerbate any excessive roll tendency ! True, Fred, I a
107 FredT : This thread is no longer about aircraft configurations. It is now about fundamental physic, without the understanding of which it is nigh impossible t
108 Smeg : Wow, My eyes are starting to bleed, and my brain has been reduced to mush! It brings back horrible memories of ATPL principles of flight OK, round 2.
109 Tdscanuck : Yes. The couple between gravity and the vertical component of lift has a moment arm equal to the horizontal distance between the CL and the CG. The c
110 Post contains links and images Tdscanuck : Since diagrams seem to be working better here, let's try that, building on what JetMech had. Here's our basic airplane. We've got three points of inte
111 JetMech : Lovely pictures Tds! Your even doing better than me with this part of the explanation! I forgot to mention that when you get hit by a side gust, the
112 Post contains images FredT : First off, it makes life a whole lot easier if you let the lateral force be a lateral force rather than a horizontal force. I suspect being guilty of
113 Tdscanuck : We can pick whichever we like, I think. It just depends on whether we want to use an aircraft centered coordiante system or a ground centered one (an
114 Post contains images JetMech : I not too sure if I agree with this. It is the lateral component of lift that works against the lateral component of drag. I'm really not too comfort
115 Post contains links FredT : You can, of course, use any system of reference. You can use that of the moon. Or why not try something different and solve it in a non-orthogonal co
116 FredT : Sorry, can't help you with that one. It's just the way it is, you'll have to get comfortable with reality on your own. Only that lift is acting along
117 Rheinwaldner : Interesting. IMHO too many variables mixed. When talking about lateral stability we strictly speak about a banked aircraft, not coordinated turning, t
118 Tdscanuck : I agree the reference system doesn't change reality. I don't agree with you that it's inherently simpler to use airplane centered (for this problem)
119 Post contains images FredT : Considering how I posted the aircraft centered free body diagrams and showed that there is no pendulum affect (which is not at all the same answer),
120 Tdscanuck : Nice analysis. It's good to hash out the math because it keeps us from getting twisted up in terminology. Yep. However: and If you sum the moments ar
121 Tdscanuck : I made an algebra goof here and didn't notice until the edit window closed. The derivation should be as follows: M_CG (clockwise positive) = -Fh*s2*c
122 JetMech : Fair enough. I now see that your diagrams in reply 112 were with respect to an aircraft reference system in side slip. The diagram I drew in reply 11
123 FredT : Moments on a rigid body has a trick to them, as you should be aware. Here's the math for that one as well: M_CG = Lh*s1*cos(phi) - Lv*s1*sin(phi) - F
124 FredT : Missed a couple of posts while writing. For the non-steady level case, we add a reaction force at the CG, Fa, positive to the left in the diagram. For
125 FredT : Thank you for the kind words. The analysis was for a steady-state side slip, but you now have both. No, it wouldn't. If you added energy it would not
126 Tdscanuck : You show me how you can roll around the CG and not move the CL. We're agreeing about the CG...if you rotate around the CG the CG doesn't move. The *C
127 Tdscanuck : Edit: remove stupid comment[Edited 2008-06-19 22:41:30]
128 JetMech : Wouldn't crossed controls represent a constant addition of energy to maintain a steady state side slip? It's the same as a car. I can be proceeding a
129 Rwessel : Hardly. You're not doing any work (in the physics sense of the word) just holding the controls crossed. Consider what would happen if you crossed the
130 FredT : I'll spell it out. Factors affecting lateral stability, in no particular order. Keel effect An interaction between lateral aerodynamic forces, and acc
131 FredT : You will only need to input energy in order to maintain your velocity. No energy goes into accelerating or decelerating in any direction. A slip will
132 Starlionblue : Showoff. Seriously though I like how this discussion is developing, especially in comparison to the degenerating catfight about autolands. I might be
133 Post contains images JetMech : Aren't you thus agreeing with this statement of mine? A side gust represent a transient addition of energy, which dihedral, keel effect and other air
134 Post contains links Rheinwaldner : We are by far not through. ************************************************************************************** *** Fact is: *** Vertical displaceme
135 Post contains images JetMech : I think this may be the crux of the situation. The "pendulum" effect ( for high wing configuratrion ) is important during a transient sideslip, where
136 FredT : You covered all the bases on your own, I think. Yes, more power will be required lest you descend or decrease airspeed. This would, in the larger pic
137 FredT : They do not. They do not. Oh, and completely different aerodynamic properties. Could matter in an aircraft, I don't know... OK, go check the literatu
138 Tdscanuck : I'm in this boat too, but I'm about 95% in line with FredT now. Actually going through the math (which I'd considered but hadn't actually executed un
139 JetMech : Me too. I've learnt plenty from Fred during the course of this thread. Can't argue with the numbers! To add further to the discussion of reply 119. I
140 Post contains links FredT : I would like to point out to new readers of this old thread that the above statement says exactly the opposite of what I intended, as found by Vikkyv
Top Of Page
Forum Index

Reply To This Topic High Wing Vs. Low Wing
Username:
No username? Sign up now!
Password: 


Forgot Password? Be reminded.
Remember me on this computer (uses cookies)
  • Tech/Ops related posts only!
  • Not Tech/Ops related? Use the other forums
  • No adverts of any kind. This includes web pages.
  • No hostile language or criticizing of others.
  • Do not post copyright protected material.
  • Use relevant and describing topics.
  • Check if your post already been discussed.
  • Check your spelling!
  • DETAILED RULES
Add Images Add SmiliesPosting Help

Please check your spelling (press "Check Spelling" above)


Similar topics:More similar topics...
Minimum Fuel Vs. Low Fuel posted Sat Dec 2 2000 19:25:57 by A7700
Low Vs High Wing Aircraft posted Sat Jul 6 2002 07:53:47 by Trent_800
Wing Flex, 757 Vs A320 posted Fri Sep 14 2007 04:23:12 by N9JIG
Wing-loading Vs Ride & Turbulence posted Fri Mar 9 2007 11:43:26 by Redcordes
Crosswind Crab Landing VS Lowering One Wing? posted Thu Mar 8 2007 00:15:34 by SSTsomeday
High/Low Wing Aircraft Advantages/disadvantages posted Mon Mar 27 2006 22:46:21 by Hcpunx99
Nose High Vs. Nose Low Approaches posted Wed Mar 22 2006 03:57:47 by FlyingNanook
Clean Wing Vs. Cluttered Wing posted Tue Dec 28 2004 15:48:34 by Thrust
Pilot Positions Helicopter Vs Fixed Wing posted Tue Jul 6 2004 17:51:32 by NORTHSEATIGER
737NG Vs Classic Wing Sweep posted Wed Jun 5 2002 20:30:17 by Barney captain
Minimum Fuel Vs. Low Fuel posted Sat Dec 2 2000 19:25:57 by A7700
Low Vs High Wing Aircraft posted Sat Jul 6 2002 07:53:47 by Trent_800
Normal Airbridges Vs. Over-wing Airbridges (AMS) posted Tue Oct 25 2011 09:01:36 by Pacific
Pressure Above Vs Below Wing posted Thu Sep 15 2011 04:44:29 by faro
The 717 Wing Vs. The MD-80/MD-90 Wing posted Thu Sep 16 2010 09:36:32 by tsugambler
A330 Vs A340 Wing posted Thu Jul 30 2009 12:50:51 by DocLightning
Elliptic Wing-Tips Vs Winglets posted Wed Apr 22 2009 06:10:58 by Faro
Ditching With A High-wing Plane. Possible? posted Tue Jan 20 2009 04:44:17 by Rheinwaldner

Sponsor Message:
Printer friendly format