Wing dihedral

The higher wing has less AOA.

Only because the a/c is slipping - the vertical/horizontal component of
lift stuff misses the point

Chris Wells wrote:
The higher wing has less AOA.

On Wed, 15 Mar 2006 23:02:58 GMT, "Dallas"
wrote:

Would anyone care to comment on the accuracy of this illustration of how
wing dihedral works from a 1981 Jeppesen Sanderson book.

http://makeashorterlink.com/?B25A35DCC

The accompanying statement reads:
"When an aircraft with dihedral rolls so that one wind is lower than the
other, the lower wing will have more effective lift than the raised wing
because it is not tilted from the horizontal as much. The imbalance in lift
tends to raise the lower wing and restore level flight."

Try this illustration from NASA:

http://history.nasa.gov/SP-367/f144.htm

Don

That gave me some problem for a while when I read about it as well.
Here's how I deicded to understand it. (Well, it works for me whether
it's the truth or not...)

Take it to an extreme--an airplane with a 90 degree dihedral. The
fuselage in in the "corner.
Now imagine one wing horizontal, the other wing vertical. All of the
lift component is on the horizontal wing, but the fuselage is at the
corner. The wing is pushing up, the fuselage is being pulled down by
gravity, and the plane rotates. The vertical wing is attempting to
push the airplane sideways. However, the fuselage isn't fixed in space
to rotate in just one place, so the sideways force actually does push
the airplane sideways rather than just rotating towards the horizontal
wing. Therefore, the fuselage "sinks", until it is in the low point
between the two wings (which would then be both pointing upwards at 45
degree angles.

Clear as mud? Oh well, I tried.

I'm not sure what the question is.

I think I do....

Lift is a vector. If a wing drops a little bit, the vertical
(lift)component of the wing is greater than the vertical component of
the raised wing. (The raised wing now also has a horizontal component.)

Having the greater vertical component helps it to raise itself. This is
just a stability aid, not a wing leveller. Some airplanes are anhedral,
to improve the "rollability" of it.

John




Dallas wrote:

Would anyone care to comment on the accuracy of this illustration of how
wing dihedral works from a 1981 Jeppesen Sanderson book.

http://makeashorterlink.com/?B25A35DCC

The accompanying statement reads:
"When an aircraft with dihedral rolls so that one wind is lower than the
other, the lower wing will have more effective lift than the raised wing
because it is not tilted from the horizontal as much. The imbalance in lift
tends to raise the lower wing and restore level flight."


Dallas

I haven't looked at the illustration but what happens is that if the a/c
rolls to the left, it will begin to slip to the left. The left wing
will have a greater angle of attack than the right, therefore more lift
and it will tend to correct the roll.

By the same token, if it is yawed the left it will begin to skid to the
right. The right panel has a higher angle of attack and it roll left.
That's how rudder-only model a/c manage to roll and turn.

You fly enough models - especially free flight - and the value of
dihedral for stability becomes quite evident. Dihedral produces
stability in roll. Most full size a/c don't have enough to produce what
I guess would be called static roll stability. Left alone, they go into
a spiral and either hit the ground or break up. Free flight models
have enough dihedral (or polyhedral) to remain stable in roll.
Typically they are set up for stable circling flight. Take too much
dihedral out and they will spiral in.

Dihedral was key to controlling early RC models. With a properly setup
rudder-only non-proportional control model, you could not only turn, but
climb, dive, and even loop. I wonder what Jepp says about that?

Dallas wrote:
Would anyone care to comment on the accuracy of this illustration of how
wing dihedral works from a 1981 Jeppesen Sanderson book.

http://makeashorterlink.com/?B25A35DCC

The accompanying statement reads:
"When an aircraft with dihedral rolls so that one wind is lower than the
other, the lower wing will have more effective lift than the raised wing
because it is not tilted from the horizontal as much. The imbalance in lift
tends to raise the lower wing and restore level flight."


Dallas

I've often wondered how 2 channel R/C works without ailerons (obviously
well enough, right?)

I know a guy with a Yak-52, and I've noticed what looks like an almost
complete lack of dihedral on its wing. I suppose that has a lot to do
with its stability (or lack thereof?) The Chinese version (Nanchang)
has dihedral starting on approx the outer 1/3rd of its span IIRC.

2 channel (w/o ailerons) works great. You'll never see a aileron-less
model without dihedral (I understand swept wings work too but I've never
seen that).

single channel works too - how does one do a loop with rudder-only?
Quite well thank you.

Acrobatic R/C with a normal configuration a/c are often straight winged
or close too it. That's to isolate the function of the rudder so it
causes yaw only. Works pretty well except for some effects from
fuselage blanking and such.

But that's when R/C aircraft were mosting just trying to model full
scale aircraft. That balloon was busted a long time ago. What is this?

http://youtube.com/watch?v=K6besEwoR...c%20hydroplane

wrote:
I've often wondered how 2 channel R/C works without ailerons (obviously
well enough, right?)

I know a guy with a Yak-52, and I've noticed what looks like an almost
complete lack of dihedral on its wing. I suppose that has a lot to do
with its stability (or lack thereof?) The Chinese version (Nanchang)
has dihedral starting on approx the outer 1/3rd of its span IIRC.

Take a look at "Aerodynamics for Naval Aviators" NAVWEPS 00-80T-00, Page
295....

"Maule Driver" wrote in message
m...
2 channel (w/o ailerons) works great. You'll never see a aileron-less
model without dihedral (I understand swept wings work too but I've never
seen that).

single channel works too - how does one do a loop with rudder-only? Quite
well thank you.

Acrobatic R/C with a normal configuration a/c are often straight winged or
close too it. That's to isolate the function of the rudder so it causes
yaw only. Works pretty well except for some effects from fuselage
blanking and such.

But that's when R/C aircraft were mosting just trying to model full scale
aircraft. That balloon was busted a long time ago. What is this?

http://youtube.com/watch?v=K6besEwoR...c%20hydroplane

wrote:
I've often wondered how 2 channel R/C works without ailerons (obviously
well enough, right?)

I know a guy with a Yak-52, and I've noticed what looks like an almost
complete lack of dihedral on its wing. I suppose that has a lot to do
with its stability (or lack thereof?) The Chinese version (Nanchang)
has dihedral starting on approx the outer 1/3rd of its span IIRC.

Do you have a link?

Andrew included this explanation in his response which is the one I was
trying to recite (excerpt):

What, then, is the real explanation as to why a dihedral angle is an
aid to lateral stability? When the wings are both equally inclined the
resultant lift on the wings is vertically upwards and will exactly
balance the weight. If, however, one wing becomes lower than the other,
then the resultant lift on the wings will be slightly inclined in the
direction of the lower wing, while the weight will remain vertical.
Therefore the two forces will not balance each other and there will be
a small resultant force acting in a sideways and downwards direction.
This force is temporarily unbalanced and therefore the aeroplane will
move in the direction of this force - i.e. it will sideslip - and this
will cause a fow of air in the opposite direction to the slip. This ahs
the effect of increasing the angle of attach of the lower plane and
increasing that of the upper plane. The lower plane will therefore
produce more lift and a restoring moment will result. Also the wing tip
of the lower plane will become, as it were, the leading edge so far as
the slip is concerned; and just as the center of pressure across the
chord is nearer the leading edge, so the center of the pressure
distribution along the span will now be on the lower plane; for both
these reasons the lower plane will receive more lift, and after a
slight slip sideways the aeroplane will roll back into its proper
position. As a matter of fact, owing to the protetcion of the fuselage,
it is probably that the flow of air created by the sideslip will not
reach a large portion fo the raised wing at all; this depends very much
on the position of the wing relative to the fuselage.

William Snow wrote:
Take a look at "Aerodynamics for Naval Aviators" NAVWEPS 00-80T-00, Page
295....