dihedral - any good explanations?

[Checks]

Any good, simple explanations of why dihedral works you guys/gals can share?

Thanks in advance,

Mike

 

[nismo611]

Think about it like a bowl it also kind of has dihedral if you drop a marble in it it stops at the bottom. The same bowl flipped over would allow the marble to roll off a side.

 

[VW Pilot]

In other words it creates more stability along the roll axis of an aircraft. (Piper Cherokees, Beech Bonanzas, Mooneys, Cirrus)

 

[TxPilot0878]

Also done for "Gravity Fueling" of aircraft! Most small aircraft sump from the main tank and this is the best way to assure it gets there! But positive Dynamic stability as well!

 

[pilotyip]

With both wings having a slight upward bend as one wing drops, its competent of vertical lift becomes greater than the vertical lift component of the opposite wing. Thus having a tendency to lift the wing that dropped giving the airplane positive stability. Where is Avbug when you need him?

 

[Amish RakeFight]

From the FAA Pilot Handbook of Aeronautical Kowledge:

Dihedral. The positive acute angle between the lateral axis of an airplane and a line through the center of a wing or horizontal stabilizer. Dihedral contributes to the lateral stability of an airplane.

The most common procedure for producing lateral stability is to build the wings with an angle of one to three degrees above perpendicular to the longitudinal axis. The wings on either side of the aircraft join the fuselage to form a slight V or angle called “dihedral.” The amount of dihedral is measured by the angle made by each wing above a line parallel to the lateral axis.

Dihedral involves a balance of lift created by the wings’ AOA on each side of the aircraft’s longitudinal axis. If a momentary gust of wind forces one wing to rise and the other to lower, the aircraft banks. When the aircraft is banked without turning, the tendency to sideslip or slide downward toward the lowered wing occurs. Since the wings have dihedral, the air strikes the lower wing at a much greater AOA than the higher wing. The increased AOA on the lower wing creates more lift than the higher wing. Increased lift causes the lower wing to begin to rise upward. As the wings approach the level position, the AOA on both wings once again are equal, causing the rolling tendency to subside. The effect of dihedral is to produce a rolling tendency to return the aircraft to a laterally balanced flight condition when a sideslip occurs.

The restoring force may move the low wing up too far, so that the opposite wing now goes down. If so, the process is repeated, decreasing with each lateral oscillation until a balance for wings-level flight is finally reached.

Conversely, excessive dihedral has an adverse effect on lateral maneuvering qualities. The aircraft may be so stable laterally that it resists an intentional rolling motion. For this reason, aircraft that require fast roll or banking characteristics usually have less dihedral than those designed for less maneuverability.

 

[nosehair]

Imagine this:

A giant hand is holding your airplane up in the sky, with no forward motion.

The giant hand releases, and your airplane falls straight down. The wings have a 90 degree angle of attack as it falls straight down.

Now imagine that the airplane is moving forward 1 foot for each 1 foot downward movement. That would produce a 45 degree angle of attack.

Continue increasing forward movement to 10 feet forward for each 1 foot drop. That would make a 10 degree angle of attack, (I think!).

Anyway, you see the picture? Each time a wing drops, the dropping action increases angle of attack which increases lift to bring the wing back up.

 

[Donsa320]

Exception to the rule.

Still, the B-25 has mostly negative dihedral and is one of the nicest flying, stable airplanes I've eve flown. Go figure.

 

[jak378]

Still, the B-25 has mostly negative dihedral and is one of the nicest flying, stable airplanes I've eve flown. Go figure.

I'm not sure, but off the top of my head: Does it matter whether the diledral is positive or negative for it to have the desired effect. Never thought about that before.

 

[LR25]

Still, the B-25 has mostly negative dihedral and is one of the nicest flying, stable airplanes I've eve flown. Go figure.

If you let go of the controls, does the b-25 stay in the general direction, or does it right itself?

If you let go of the controls of a champ, it will right itself. Even if the champ wasnt in trim, it will find a point to where it will oscillate between nose up nose down as speed increases and decreases. Dihedral, combined with an asymmetrical airfoil increases stability. It creates dynamic stability, the B-25 probably does not have this property, especially with the anhedral wing.