Owleye From , joined Dec 1969, posts, RR: Posted (8 months 5 days 17 hours ago) and read 2547 times:
Antonov's aircraft have drooping designed shoulder wings. Okay, the Avro BAe has a simular droop-design and the 328 a little bit aswell but overal shoulder wing aircraft have upward standing wings. What is the 'big secret' behind this way of droop-wing designing?
Oly720man From United Kingdom, joined May 2004, 4857 posts, RR: 12 Reply 1, posted (8 months 5 days 16 hours ago) and read 2499 times:
There are aerodynamic/stability reasons why you want wings pointing upwards, but there are structural and operational reasons why high wing aircraft have the wings drooping.
Don't forget that wings rise under the effect of aerodynamic loading (lift) and droop further under the weight of the fuel they contain so the cruise wing position will be different from what you see on the ground. And for something like the An225, and the B52 for that matter, the wings can bend quite a long way, more than 10m at the wing tip of a B52 before they break, IIRC
Compare these B52 photos for example and how much the wings are bent upwards with the flying aircraft.
Owleye From , joined Dec 1969, posts, RR: Reply 2, posted (8 months 5 days 15 hours ago) and read 2473 times:
Thanks Oly720man, that makes sense. I have been thinking of it aswell but especially for the Antonovs the drooping wings are almost their signature (...as they have almost all shoulder wing aircraft built).
Kukkudrill From Malta, joined Dec 2004, 1063 posts, RR: 6 Reply 4, posted (8 months 5 days 13 hours ago) and read 2416 times:
Quoting Owleye (Thread starter): What is the 'big secret' behind this way of droop-wing designing?
I once asked this question on the forum. The answer I got then was that high wings make for greater roll stability, and this is accentuated if the wings are swept back. The result is that it can be difficult to roll especially if you're a freighter with a heavy load of cargo, and the reason for the droop is to counteract that. (Wing dihedral or upward slant makes for greater roll stability while wing anhedral or droop does the opposite.)
Starlionblue From Greenland, joined Feb 2004, 13702 posts, RR: 67 Reply 5, posted (8 months 5 days 7 hours ago) and read 2307 times:
Quoting Viscount724 (Reply 3):
What aircraft types with wings mounted at the top of the fuselage have upward-angled wings? I am having trouble thinking of any.
My model glider did. Seriously though, I think an aircraft with high mounted wings and dihedral would be too stable in roll.
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Vikkyvik From United States of America, joined Jul 2003, 3964 posts, RR: 25 Reply 6, posted (8 months 5 days 5 hours ago) and read 2276 times:
Quoting Viscount724 (Reply 3): What aircraft types with wings mounted at the top of the fuselage have upward-angled wings? I am having trouble thinking of any.
Can't say for sure, but the following appear to have upward-angled wings:
2H4 From United States of America, joined Oct 2004, 8277 posts, RR: 64 Reply 8, posted (8 months 4 days 2 hours ago) and read 2003 times:
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Quoting Viscount724 (Reply 3): What aircraft types with wings mounted at the top of the fuselage have upward-angled wings? I am having trouble thinking of any.
SEPilot From United States of America, joined Dec 2006, 4149 posts, RR: 26 Reply 9, posted (8 months 2 days 21 hours ago) and read 1860 times:
The issue, as others have pointed out, is how much stability you want. With dihedral, as you start to roll the lower wing becomes more perpendicular to the force of gravity, and hence has more lift. This counteracts the roll, and hence stabilizes the aircraft. Anhedral works opposite, and on first glance would appear to be undesirable. But with a high winged aircraft, the center of mass is lower than the center of lift, and hence the aircraft has stability from that. It is up to the aircraft designer to determine exactly how much stability he wants, and easiest way to adjust it is with dihedral or anhedral. Note that both are at the expense of efficiency; the lift vectors from the two wings will fight each other to some extent and so the total lift needed is greater than the lift required to fly the plane. For modest amounts of dihedral or anhedral this effect is small, however.
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2H4 From United States of America, joined Oct 2004, 8277 posts, RR: 64 Reply 11, posted (8 months 2 days 4 hours ago) and read 1699 times:
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Quoting DocLightning (Reply 10): Eww. That's disgraceful. You should beg to be pardoned.
Ah, grasshoppah, but it is you who must beg to be pardoned. For that airplane was designed by none other than the maestro of aerodynamics himself....Burt Rutan.
FredT From United Kingdom, joined Feb 2002, 2130 posts, RR: 30 Reply 12, posted (8 months 2 days 1 hour ago) and read 1674 times:
Quoting SEPilot (Reply 9): With dihedral, as you start to roll the lower wing becomes more perpendicular to the force of gravity, and hence has more lift.
Often quoted and completely wrong.
Quoting SEPilot (Reply 9): But with a high winged aircraft, the center of mass is lower than the center of lift, and hence the aircraft has stability from that.
Also often quoted and completely wrong.
We discussed it all in length in this thread. A lot of length, in fact. I'd start reading from the end.
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Vikkyvik From United States of America, joined Jul 2003, 3964 posts, RR: 25 Reply 13, posted (8 months 1 day ago) and read 1506 times:
Quoting FredT (Reply 12):
We discussed it all in length in this thread. A lot of length, in fact. I'd start reading from the end.
Thanks for that link, Fred. Made a great (if lengthy) read.
However, there are a couple of comments I'm having a hard time reconciling. If you'll allow me to pull a couple of your quotes from that thread:
"Dihedral means the upwind wing in a side slip will have an increased angle of attack, giving lateral stability. Anhedral does the opposite."
That's what I've always been told, and it makes sense to me. However, near the end of the thread, you say:
"Anhedral will give the windward wing an increased angle of attack and the leeward wing a decreased angle of attack in a slip, adding to lateral stability.
Dihedral will do the opposite."
I'm assuming windward = upwind, and leeward = downwind, for the case of a sideslip. So are those two comments in conflict with each other, or am I missing something?
Thanks a bunch - I thought I'd just ask that question here instead of adding more length to an already lengthy thread
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VirginFlyer From Australia, joined Sep 2000, 4318 posts, RR: 54 Reply 14, posted (8 months 22 hours ago) and read 1496 times:
Quoting Vikkyvik (Reply 13): "Anhedral will give the windward wing an increased angle of attack and the leeward wing a decreased angle of attack in a slip, adding to lateral stability
That is the incorrect comment. Let's avoid terms like windward or upwind or whatever for fear of confusing people (especially myself!), and describe it from first principles, as you would see it sitting in the aircraft, or following right behind it.
You have an aircraft. The aircraft is rolled to the left by a gust of wind, such that the left wing is "down" and the right wing is "up". The aircraft will begin slipping towards the left. If you have dihedral, the left wing will see a greater angle of attack than the right wing, and the resulting difference in lift from each wing causes a moment which tries to roll the aircraft to the right - this is a stabilising effect. If you have anhedral, the right wing will see a greater angle of attack than the left wing, and the resulting difference in lift from each wing causes a moment which tries to roll the aircraft to the left - this is a destabilising effect.
I've always wondered about the low wing Tupolev transports, which up untill the Tu-204 all had anhedral, and the Yakovlev Yak-42. I'm struggling to think of any other low wing subsonic designs which featured anhedral. What was the rationale behind these aircraft being designed that way?
Starlionblue From Greenland, joined Feb 2004, 13702 posts, RR: 67 Reply 16, posted (8 months 17 hours ago) and read 1441 times:
Quoting VirginFlyer (Reply 14): I've always wondered about the low wing Tupolev transports, which up untill the Tu-204 all had anhedral, and the Yakovlev Yak-42. I'm struggling to think of any other low wing subsonic designs which featured anhedral. What was the rationale behind these aircraft being designed that way?
The only reason I can think of is short and sturdy main gear legs. On the Tu-154, for example,t the mains are housed in wing pods. But it still doesn't seem like a good enough reason.
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FredT From United Kingdom, joined Feb 2002, 2130 posts, RR: 30 Reply 17, posted (8 months 16 hours ago) and read 1431 times:
Oh, about the Tupolevs, keep in mind that wing sweep will also add to lateral stability. Add enough wing sweep and you'll get too much stability, in which case anhedral is one way to decrease the lateral stability again.
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Seriously though, I think an aircraft with high mounted wings and dihedral would be too stable in roll.
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