Wing dihedral

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

"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."

I used to think that, but it was pointed out that the issue isn't
"raising the wing" as "rotating the aircraft" and that the higher wing
still has a moment that will tend to rotate the aircraft.

Jose
--
Money: what you need when you run out of brains.
for Email, make the obvious change in the address.

Give some thought to the components of lift, on both wings, and to which
direction lift acts. ;-)


"Dallas" wrote in message
nk.net...
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

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.

"William Snow"
Give some thought to the components of lift, on both wings, and to which
direction lift acts. ;-)
http://makeashorterlink.com/?B25A35DCC

I have. I see no forces presented in this illustration that would change
the components of lift on the wings or it's direction that would cause the
aircraft to roll back to horizontal.

Why would a horizontal wing create "more effective lift" than a banked wing?

This thread began in another group and some interesting points were
discussed, but I honestly expected a few belly laughs here on the absurdity
of this book's explanation.


Dallas

On Wed, 15 Mar 2006 23:13:03 GMT, Jose
wrote:

"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."

I used to think that, but it was pointed out that the issue isn't
"raising the wing" as "rotating the aircraft" and that the higher wing
still has a moment that will tend to rotate the aircraft.

Try both. The lower wing is trying to come back up as it has move
vertical component of lift than the other wing. The higher wing has
more lift in the direction of the lower wing so the plane will start
to turn that direction at the same time.

If you don't believe me, Get in the back seat of a Bonanza on a day
with lots of thermals. It doesn't have to be a V-tail, the F33 will
do the same thing. As the seat is behind the center of lift you get
some strange and exaggerated sensations and a high barf factor.

OTOH it makes the plane quite stable for the pilot even though it has
a wing loading on par, or slightly less than some Cherokees.

Cherokees which have a lot of dihedral also do pretty well on the
bumps and do not have quite the barf factor of the Bo's rear seat.

Roger Halstead (K8RI & ARRL life member)
(N833R, S# CD-2 Worlds oldest Debonair)
www.rogerhalstead.com

Jose

The higher wing has less AOA.

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