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Anhedral Vs Dihedral  
User currently offlineUAL747 From , joined Dec 1969, posts, RR:
Posted (4 years 8 months 3 weeks 6 days 7 hours ago) and read 7665 times:

Most modern western aircraft have somewhat of a dihedral to their wings. It seems as we go forward in time, the more pronounced it has become, ie, the 787 and 777. The MD-11, DC-10 seem not to have much of a dihedral, in fact, they are fairly flat. However, I've noticed that some Russian Aircraft, mainly the Tu-154 has a definite pronounced anhedral and it's wings are mounted on the lower fuselage.

So I'm wondering, what are the handling differences between the two? I know part of the reason for x-hedral is to have more stability in a turn, or so I was told in the tech ops forum, but is one better than the other?

What has been the reason for the current trend for the increase in dihedral in modern aircraft, especially widebodies? Engine size?

Thanks!

UAL

9 replies: All unread, jump to last
 
User currently offlinekiwiandrew From New Zealand, joined Jun 2005, 8625 posts, RR: 13
Reply 1, posted (4 years 8 months 3 weeks 6 days 7 hours ago) and read 7658 times:
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I don't know the answer to your question , but I am blown away about the anhedral on the TU-154 , never noticed it before and if you hadn't mentioned it I would have sworn on a stack of "Airways" magazines that you only encountered anhedral on 'wing on top of the fuselage' aircraft .

Quoting UAL747 (Thread starter):
The MD-11, DC-10 seem not to have much of a dihedral, in fact, they are fairly flat.

It always seemed to me that the DC-10 had quite pronounced dihedral for the first part of the wing ( up until the engine pylon ) when view from head-on - but now that I look through the photo database it seems that it was an optical illusion caused by the undersurface of the wing .



Moderation in all things ... including moderation ;-)
User currently offlineUAL747 From , joined Dec 1969, posts, RR:
Reply 2, posted (4 years 8 months 3 weeks 6 days 7 hours ago) and read 7649 times:

Quoting kiwiandrew (Reply 1):
It always seemed to me that the DC-10 had quite pronounced dihedral for the first part of the wing ( up until the engine pylon ) when view from head-on - but now that I look through the photo database it seems that it was an optical illusion caused by the undersurface of the wing

Actually, look at the MD-11 and DC-10 from the ass-end. You will see what you are talking about.


User currently offlineGST From United Kingdom, joined Jun 2008, 938 posts, RR: 0
Reply 3, posted (4 years 8 months 3 weeks 6 days 6 hours ago) and read 7638 times:

Basically dihedral is uses in most aircraft to provide stability. Besides this, wing sweep of greater than 15 degrees (approx) will yield similar results, and since most airliners have significant sweep, this gives them all the stability they require. It is therefore most often the case that the dihedral on the wings is purely to increase the clearance between engines, and the ground. It is often the case that to counter this excessive stability due to dihedral AND sweep, that the aircraft is overly stable, and needs excessively large control surface movements to get it to do much, so I suspect that this is a reason for the occasional anhedral you see on low winged aircraft, to reduce stability to a more useful level.

User currently offlineMir From United States of America, joined Jan 2004, 21864 posts, RR: 55
Reply 4, posted (4 years 8 months 3 weeks 6 days 6 hours ago) and read 7638 times:

Quoting UAL747 (Thread starter):
So I'm wondering, what are the handling differences between the two? I know part of the reason for x-hedral is to have more stability in a turn, or so I was told in the tech ops forum, but is one better than the other?

Dihedral helps stability - not so much in a turn, but to prevent you from entering a turn. Anhedral works the other way around - it makes it easier to enter a turn. Which one you need depends on various other factors related to the airframe, and how maneuverable you want the airplane to be. You wouldn't want to put anhedral on a 777, for instance, but putting dihedral on an An-124 wouldn't be a good idea either.

-Mir



7 billion, one nation, imagination...it's a beautiful day
User currently offlinecobra27 From Slovenia, joined May 2001, 1033 posts, RR: 0
Reply 5, posted (4 years 8 months 3 weeks 5 days 20 hours ago) and read 7444 times:

Fi you have anhedral, you need a big vertical tail, (an-124). But then again A380 and 747 tails are huge, even withouht anhedral

User currently offlineLONGisland89 From United States of America, joined Jan 2006, 741 posts, RR: 0
Reply 6, posted (4 years 8 months 3 weeks 5 days ago) and read 7208 times:

Anhedral usually compromises stability in favor of controllability, but if it's a stick-fixed aircraft it won't make too muck of a difference. For example, C-130...pretty much straight wing making it a very stable aircraft. When you are low and slow in a war zone, it wont turn as quickly as a C-17 for example (pronounced anhedral).

User currently offlinePart147 From Ireland, joined Dec 2008, 529 posts, RR: 0
Reply 7, posted (4 years 8 months 3 weeks 5 days ago) and read 7206 times:

Here are some previous threads which might help further...

Dihedral Vs Anhedral? (by Part147 Dec 25 2008 in Tech Ops)

Airliner Dihedral (by BAe146QT Mar 19 2007 in Tech Ops)

Wing Dihedral (by Lehpron Apr 19 2004 in Tech Ops)



It's better to ask a stupid question during training, rather than make a REALLY stupid mistake later on!
User currently offlineFredT From United Kingdom, joined Feb 2002, 2185 posts, RR: 26
Reply 8, posted (4 years 8 months 3 weeks 4 days 19 hours ago) and read 7090 times:

And for complete understanding, including avoiding one of the most common misconceptions which is reiterated in one or two of the linked threads, also read this monster of a thread.


I thought I was doing good trying to avoid those airport hotels... and look at me now.
User currently offlinetdscanuck From Canada, joined Jan 2006, 12709 posts, RR: 80
Reply 9, posted (4 years 8 months 3 weeks 4 days 15 hours ago) and read 7010 times:

Quoting FredT (Reply 8):
And for complete understanding, including avoiding one of the most common misconceptions which is reiterated in one or two of the linked threads, also read this monster of a thread.

Recommendation: read all of FredT's posts and the last ~6 messages. The rest will make your head spin needlessly.

Tom.


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