negative dihedral

"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

"Bertie the Bunyip" wrote in message
...

That's right. I never flew it but the guys who did said ............


Bertie

Starting to sound like your little brother Anthony.

"Bertie the Bunyip" wrote in message
...


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

WOW! Buttlipps, that's waaay coool. Do you have to like soak your head in
cold water after such radical processing? Cooling or something?

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

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.

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, 11:35 pm, Bertie the Bunyip wrote:
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

The everything that can be tried had been tried notion is out of
fashion, I don't think the patent office will be closing anytime soon,
or that Ratan's Scaled Composites will be closing up his shop. You can
bet someone will be trying an airplane with one wing over the other
soon. What would you call such a thing -- a redundant winged airplane?
For sure, in these days of political correctness, it would not be
called bi, would it?

Where are my meds?

Tina wrote in news:d86791d1-d1cd-4256-8c9e-
:

On Jun 3, 11:35 pm, Bertie the Bunyip wrote:
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

The everything that can be tried had been tried notion is out of
fashion, I don't think the patent office will be closing anytime soon,
or that Ratan's Scaled Composites will be closing up his shop. You can
bet someone will be trying an airplane with one wing over the other
soon. What would you call such a thing -- a redundant winged airplane?
For sure, in these days of political correctness, it would not be
called bi, would it?

Well, years ago a hypersonic bipe was looked at, believe it or not, but
even Beurt Rutan will tell you that none of his creations were
completely original. Not to detract from his talent, whihc is monstrous,
but there's nothing on any of his airplanes that hadn't been done
before. Even that mad boomerang has precedants and quite a lot of them
dating back to the first world war (Caproni). Getting it all arranged
right to make it go better than anything before it is his gift. Having
said that, Spaceship one was pretty unique, but you'll probably find
that mad recovery system was done in boost glider in an old issue of
American Aircraft Modeler or similar. I never cease to be astounded at
the massive number of airplanes constructed in th elast century and the
variety. it hardly seems possible sometimes that there were enough
people to make them all!


Bertie



Bertie

Where are my meds?