negative dihedral

Tina wrote in news:d9fb071f-4d30-45c3-916d-
:

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.


That's called Anhedral..

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?

Nope.


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.


Well, the anhedral negates what can be excessive stability that comes
form the sweep of the wings. Sweep provides a very similar kind of
stability as does dihedral and the addition of anhedral negates some of
this and keeps the airplane form becoming so stable that it can't even
be maneuvered!
Most of the airplanes with pronounced anhedral are high wing and would
have parasol stability as well. The anhedral helps neutralise some of
that. Some low wing Russian jets have anhedral, but it's quite small
Their sweep is quite marked and the anhedral is there to ammeliarate
that. The 727 had a fairly radical sweep and you will notice, that
though it has dihedral it's very little compared to the 737 or similar.

Note: I have not morphed into an Mx clone!


We'll know for sure if you tell me this answer is completely wrong
because your MSFS 172 doesn't have anhedral.


Bertie

Frank Olson wrote in
news:3Wk1k.4381$C12.2615@pd7urf3no:

Bob Noel wrote:
In article
,
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!

Don't know why, but don't those transports with negative dihedral
also have wings above the hull? So those aircraft have the CG below
the wings.



And large transport aircraft are amongst the most aerodynamically
stable aircraft to fly.


Actually, that's not the case in every sense. They're not very speed
stable, for instance and thye have other problems with two diferent
kinds of dutch roll, related to sweep, mostly.

Bertie

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

On Jun 3, 10:25 pm, Bertie the Bunyip wrote:
Tina wrote in news:d9fb071f-4d30-45c3-916d-
:

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.

That's called Anhedral..



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?

Nope.



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.

Well, the anhedral negates what can be excessive stability that comes
form the sweep of the wings. Sweep provides a very similar kind of
stability as does dihedral and the addition of anhedral negates some of
this and keeps the airplane form becoming so stable that it can't even
be maneuvered!
Most of the airplanes with pronounced anhedral are high wing and would
have parasol stability as well. The anhedral helps neutralise some of
that. Some low wing Russian jets have anhedral, but it's quite small
Their sweep is quite marked and the anhedral is there to ammeliarate
that. The 727 had a fairly radical sweep and you will notice, that
though it has dihedral it's very little compared to the 737 or similar.



Note: I have not morphed into an Mx clone!

We'll know for sure if you tell me this answer is completely wrong
because your MSFS 172 doesn't have anhedral.

Bertie

Only after a very hard landing would a 172 develop negative dihedral.
A Mooney, on the other hand, given the placement of the wheels, would
either increase its positive dihedral, or more likely, given how
strongly they are built, put a dent in the runway.

"Kyle Boatright" wrote in
:


"Tina" wrote in message
news:d9fb071f-4d30-45c3-916d-3e4c00f89d52@
34g2000hsh.googlegroups.com..
.
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!

Dihedral (or anhedral - negative dihedral) are both used to reposition
the aircraft's Center of Lift (CL) vs the aircraft's CG. This
effectively creates a pendulum, which wants to stabilize with the
heavy part at the lowest possible position. Like a pendulum,
relatively speaking, the farther above the CG the CL is, the more
stable an aircraft will be. The whole "dihedral increases roll
stability" issue is based around this, not increased or decreased roll
due to lifting forces stemming from the attitude of the airplane. The
roll forces which create stability are due to this pendulum effect.

If you want a stable aircraft in roll, add as much dihedral as
possible to raise the CL. If you want an unstable aircraft, do the
opposite. The anhedral on some on high wing transports is probably
designed to give a desired amount of stability. Some level of
stability is great for a transport, but you don't want to create an
aircraft so stable it requires oversized ailerons to generate the
desired roll rate.


All correct! Also, anhedral helps a bit with the high alt dutch roll
case. I'd have to go into a lengthy explanation to cover it all, but
suffice it to say that swept wing airplanes are subject to a roll yaw
reversal at high altitues that can get rather unpleasnt ( complet loss
of control) Most must fly with a yaw damper, which is a gyro-controlled
rudder input that keeps the thing going straight. Anhedral offers a non
mechanical ad to ammelierating this effect. In fact, the russians are
notoriously clever at this sort of thing, which is why thye have madly
maneuverable fighters with more or less conventional control systems
while contemporary western aircraft relied on computers to achieve the
same results.


Bertie


Bertie

"Bertie the Bunyip" wrote in message
...
"Kyle Boatright" wrote in
:


"Tina" wrote in message
news:d9fb071f-4d30-45c3-916d-3e4c00f89d52@
34g2000hsh.googlegroups.com..
.
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!

Dihedral (or anhedral - negative dihedral) are both used to reposition
the aircraft's Center of Lift (CL) vs the aircraft's CG. This
effectively creates a pendulum, which wants to stabilize with the
heavy part at the lowest possible position. Like a pendulum,
relatively speaking, the farther above the CG the CL is, the more
stable an aircraft will be. The whole "dihedral increases roll
stability" issue is based around this, not increased or decreased roll
due to lifting forces stemming from the attitude of the airplane. The
roll forces which create stability are due to this pendulum effect.

If you want a stable aircraft in roll, add as much dihedral as
possible to raise the CL. If you want an unstable aircraft, do the
opposite. The anhedral on some on high wing transports is probably
designed to give a desired amount of stability. Some level of
stability is great for a transport, but you don't want to create an
aircraft so stable it requires oversized ailerons to generate the
desired roll rate.


All correct! Also, anhedral helps a bit with the high alt dutch roll
case. I'd have to go into a lengthy explanation to cover it all, but
suffice it to say that swept wing airplanes are subject to a roll yaw
reversal at high altitues that can get rather unpleasnt ( complet loss
of control)

Yep. Early 707's had a big enough dutch roll problem that it resulted in
aircraft being lost. This brought forth a redesign of the vertical stab.

Most must fly with a yaw damper, which is a gyro-controlled
rudder input that keeps the thing going straight. Anhedral offers a non
mechanical ad to ammelierating this effect. In fact, the russians are
notoriously clever at this sort of thing, which is why thye have madly
maneuverable fighters with more or less conventional control systems
while contemporary western aircraft relied on computers to achieve the
same results.


Bertie


Bertie

"Kyle Boatright" wrote in
:


"Bertie the Bunyip" wrote in message
...
"Kyle Boatright" wrote in
:


"Tina" wrote in message
news:d9fb071f-4d30-45c3-916d-3e4c00f89d52@
34g2000hsh.googlegroups.com..
.
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!

Dihedral (or anhedral - negative dihedral) are both used to
reposition the aircraft's Center of Lift (CL) vs the aircraft's CG.
This effectively creates a pendulum, which wants to stabilize with
the heavy part at the lowest possible position. Like a pendulum,
relatively speaking, the farther above the CG the CL is, the more
stable an aircraft will be. The whole "dihedral increases roll
stability" issue is based around this, not increased or decreased
roll due to lifting forces stemming from the attitude of the
airplane. The roll forces which create stability are due to this
pendulum effect.

If you want a stable aircraft in roll, add as much dihedral as
possible to raise the CL. If you want an unstable aircraft, do the
opposite. The anhedral on some on high wing transports is probably
designed to give a desired amount of stability. Some level of
stability is great for a transport, but you don't want to create an
aircraft so stable it requires oversized ailerons to generate the
desired roll rate.


All correct! Also, anhedral helps a bit with the high alt dutch roll
case. I'd have to go into a lengthy explanation to cover it all, but
suffice it to say that swept wing airplanes are subject to a roll yaw
reversal at high altitues that can get rather unpleasnt ( complet
loss of control)

Yep. Early 707's had a big enough dutch roll problem that it resulted
in aircraft being lost. This brought forth a redesign of the vertical
stab.


That's right. I never flew it but the guys who did said the high alt
departures were so violent as to be truly frightening.
The 727 was pretty wild if it lost its yaw dampers and the only cure was
to get down to where the mach margins were wide enough not to be an
issue. Fortunately I only ever had a double yaw damper failure in the
sim.



Bertie

Tina wrote in news:28472a75-654d-447f-9317-
:

On Jun 3, 10:25 pm, Bertie the Bunyip wrote:
Tina wrote in news:d9fb071f-4d30-45c3-916d-
:

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.

That's called Anhedral..



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?

Nope.



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.

Well, the anhedral negates what can be excessive stability that comes
form the sweep of the wings. Sweep provides a very similar kind of
stability as does dihedral and the addition of anhedral negates some
of
this and keeps the airplane form becoming so stable that it can't
even
be maneuvered!
Most of the airplanes with pronounced anhedral are high wing and
would
have parasol stability as well. The anhedral helps neutralise some of
that. Some low wing Russian jets have anhedral, but it's quite small
Their sweep is quite marked and the anhedral is there to ammeliarate
that. The 727 had a fairly radical sweep and you will notice, that
though it has dihedral it's very little compared to the 737 or
similar.



Note: I have not morphed into an Mx clone!

We'll know for sure if you tell me this answer is completely wrong
because your MSFS 172 doesn't have anhedral.

Bertie

Only after a very hard landing would a 172 develop negative dihedral.
A Mooney, on the other hand, given the placement of the wheels, would
either increase its positive dihedral, or more likely, given how
strongly they are built, put a dent in the runway.


I think there have been a couple of straight wing airplanes wiht
anhedral, but I can't picture one off the top of my head. Surely
everything that can be tried, has been tried at this stage!


Bertie

On Jun 3, 5:05 pm, 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.

No idea of why or how it stays upright.

From the pictures I've seen of it in the air, most of that negative
dihedral seems to go away while flying.

Yup, here's an example.
http://www.google.com/search?hl=en&q...=Google+Search
Ken

On Jun 4, 2:30*pm, Tina wrote:
On Jun 3, 10:25 pm, Bertie the Bunyip wrote:



Tina wrote in news:d9fb071f-4d30-45c3-916d-
:

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.

That's called Anhedral..

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?

Nope.

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.

Well, the anhedral negates what can be excessive stability that comes
form the sweep of the wings. Sweep provides a very similar kind of
stability as does dihedral and the addition of anhedral negates some of
this and keeps the airplane form becoming so stable that it can't even
be maneuvered!
Most of the airplanes with pronounced anhedral are high wing and would
have parasol stability as well. The anhedral helps neutralise some of
that. Some low wing Russian jets have anhedral, but it's quite small
Their sweep is quite marked and the anhedral is there to ammeliarate
that. The 727 had a fairly radical sweep and you will notice, that
though it has dihedral it's very little compared to the 737 or similar.

Note: I have not morphed into an Mx clone!

We'll know for sure if you tell me this answer is completely wrong
because your MSFS 172 doesn't have anhedral.

Bertie

Only after a very hard landing would a 172 develop negative dihedral.
A Mooney, on the other hand, given the placement of the wheels, would
either increase its positive dihedral, or more likely, given how
strongly they are built, put a dent in the runway.

With those struts I would expect polyanhedral!

Cheers