Tina wrote in news:621fed62-d178-4edc-9850-
:

On Jun 3, 7:56 pm, Frank Olson
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!

"Negative dihedral" may have more to do with keeping the landing gear
legs shorter. I know that's how they solved the problem they
encountered with the longer gear legs required on the Avro Arrow. On
the original mock-ups, when they first tried to retract the main gear
legs, they "crunched together" with each other at the point where
they
entered the fuselage.

Dihedral (whether "positive" or "negative") does tend to *add*
stability, not take it away. Fighter jets and large airliners use
"fly
by wire" because the stick forces required to move the control
surfaces
may be too much for the average pilot (or might cause a good deal of
fatigue which, on longer flights, could be detrimental to the safe
operation of the aircraft). "Fly by wire" does little toward
enhancing
the overall stability of an aircraft. "Stability" has more to do
with
the overall design of the aircraft (and it's intended use).

well what occurred to me is, with negative dihedral, as one wing lifts
it generates MORE lift, while the wing going down generates less. I
thought that would encourage the roll, but maybe the wing design
itself somehow takes that into account..



Yes, if you had a striaght wing airplane like that it would tend to do
it left to its; own devices, but a swept wing airplane well tend to
resist yaw, and by association, roll by virtue of the sweep alone.



Bertie