UAL747
Topic Author
Posts: 6725
Joined: Mon Dec 13, 1999 5:42 am

Anhedral Vs Dihedral

Mon Mar 29, 2010 8:06 am

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
"Bangkok Tower, United 890 Heavy. Bangkok Tower, United 890 Heavy.....Okay, fine, we'll just turn 190 and Visual Our Way
 
kiwiandrew

RE: Anhedral Vs Dihedral

Mon Mar 29, 2010 8:37 am

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 .
 
UAL747
Topic Author
Posts: 6725
Joined: Mon Dec 13, 1999 5:42 am

RE: Anhedral Vs Dihedral

Mon Mar 29, 2010 8:50 am

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.
"Bangkok Tower, United 890 Heavy. Bangkok Tower, United 890 Heavy.....Okay, fine, we'll just turn 190 and Visual Our Way
 
GST
Posts: 808
Joined: Wed Jun 11, 2008 10:27 am

RE: Anhedral Vs Dihedral

Mon Mar 29, 2010 9:28 am

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.
 
Mir
Posts: 19092
Joined: Mon Jan 05, 2004 3:55 am

RE: Anhedral Vs Dihedral

Mon Mar 29, 2010 9:31 am

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
 
cobra27
Posts: 939
Joined: Wed May 23, 2001 6:57 pm

RE: Anhedral Vs Dihedral

Mon Mar 29, 2010 7:37 pm

Fi you have anhedral, you need a big vertical tail, (an-124). But then again A380 and 747 tails are huge, even withouht anhedral
 
LONGisland89
Posts: 542
Joined: Sun Jan 22, 2006 3:34 am

RE: Anhedral Vs Dihedral

Tue Mar 30, 2010 3:05 pm

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).
 
Part147
Posts: 385
Joined: Tue Dec 16, 2008 3:13 pm

RE: Anhedral Vs Dihedral

Tue Mar 30, 2010 3:13 pm

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!
 
FredT
Posts: 2166
Joined: Thu Feb 07, 2002 9:51 pm

RE: Anhedral Vs Dihedral

Tue Mar 30, 2010 8:11 pm

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.
 
tdscanuck
Posts: 8572
Joined: Wed Jan 11, 2006 7:25 am

RE: Anhedral Vs Dihedral

Wed Mar 31, 2010 12:22 am

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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