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negative dihedral



 
 
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Old June 4th 08, 05:30 PM posted to rec.aviation.piloting
Bertie the Bunyip[_24_]
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Default negative dihedral

Tina wrote in
:

On Jun 4, 12:03 pm, Bertie the Bunyip wrote:
Tina wrote
innews:57ee2ec3-c172-4f53-96a3-cec87ee7be22

@k37g2000hsf.googlegroups.c
om:

On Jun 4, 11:23 am, Bertie the Bunyip wrote:
Tina wrote
innews:4cc0ec37-d80c-4006-9190-






m:


On Jun 4, 4:49 am, HARRY POTTER wrote:
Tina wrote:
I understand how positive dihedral helps dynamic stability in
airplanes, but some big ones, like the Russian An 124 Condor,
has a pronounced negative dihedral -- the wings have a
noticeable downward slope.


Q1: Do those airplanes need active fly by wire controls to
maintain stability, or is something else at play that keeps
them right side up?


Q2: Does anyone have a design rationalization for such a
configuration, as opposed to just zero dihedral? I can
appreciate why fighters have it -- they exploit lack of
aerodynamic stability for rapid maneuvers -- but transports
that spend their whole life being straight and level are
another issue.


Note: I have not morphed into an Mx clone!


The AN124 does not have negative dihedral. It just looks that
way when it's on the ground because the weight of the engines
bends the wings so they look drooped down. Once it's in the
air, the fuselage bends the wings the other way, so it actually
does have dihedral.


--http://onlinelogbook.net


Thanks -- didn't realize it was simply wing droop when they are
not developing lift. That's what happens when you fly in stiff
winged little airplanes, you start overlooking something as
obvious as that.


http://www.youtube.com/watch?v=WJscAaKfr7A


Bertie


OK, I see some of the downslope was washed out in flight, but it
was still obvious there. Thanks


I expect more is washed out when the airplane is at gross weight,
but your point is made, Bertie.


Um, washout is probably not the best term, being share with another
important wing feature, but yeah, it's still there even when the
airplane is very heavy. I've seen the 225 fly and it's the same.
There'a also the little BAe 146 and the C5 and the C141 and the other
little bay antonov etc. I also mentioned I had seen some striaght
wing airplanes with anhedral but couldn't remember where. Most of the
turboprop antonovs have anhedral, but not nearly as much as the jets.
He obviously liked his airplanes to be manueverable!
Even a lot of the low wing jets had anhedral. The IL 62, for
instance.and IIRC some of the Tupovlevs also had it.


There was a country music guy who had a Mitsubishi twin with what I
remember looked liked pronounced anhedral, but I did a web search and
couldn't find a photo of it. What I am remembering might have been in
the 1970s.

There's little doubt in my mind that a high wing configuration with
negative dihedral would be more stable than a low winged one -- the cg
being way under the center of lift would see to that -- but still
don't have a 'model' to explain why wing sweep is a factor: when I
have some time I'll think about that, or I suppose I could ask
Anthony.

As for new stuff in aviation? I'd say GPS, released to the general
public during the RR presidency because of the Koran jet shootdown in
Russia, is fairly new. And let us not forget the new and improved FAA.


FAA hs nothing to do with aviation! And as for GPS, it's just a tidied
up and warmed up version of a lot of older distance measured based stuff
like decca and to a lesser extent, tacan, so it's not really new, just a
more advanced and more precise system with the stations placed in space
instead of higgildy-piggildy over the landscape. It's real hard to find
something new under the sun! i can't think of anything earlier than
Decca here, but I'm sure that even that's based on something that
Polynesian sailors or somebody were doing 4,000 years ago!

Bertie

I'm doing my part to add to the recreation in rec.aviation (and trying
to not have it be wreck.aviation).


 




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