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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.
Still, the B-25 has mostly negative dihedral and is one of the nicest flying, stable airplanes I've eve flown. Go figure.
Still, the B-25 has mostly negative dihedral and is one of the nicest flying, stable airplanes I've eve flown. Go figure.
Only know what I was taught in aerodynamics, maybe I got it wrong, but I got an A anyway.The idea that dihedral causes the lower wing to have a higher "vertical" component of lift is incorrect. It has to do with the airplane's movement through the air...angle of attack.
requoted from above from the Pilot Handbook ..."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."
I know on paper it looks like the lowered wing is now perpindicular to the horizon so it has more lift pulling it up, but lift is only relative to the angle of attack/oncoming air. Nothing helps keeps the "wings level" other than an autopilot. The only way dihedral helps keep the wings level is once you put the airplane there, it will tend to stay there.
The idea that dihedral causes the lower wing to have a higher "vertical" component of lift is incorrect. It has to do with the airplane's movement through the air...angle of attack.
requoted from above from the Pilot Handbook ..."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."
I know on paper it looks like the lowered wing is now perpindicular to the horizon so it has more lift pulling it up, but lift is only relative to the angle of attack/oncoming air. Nothing helps keeps the "wings level" other than an autopilot. The only way dihedral helps keep the wings level is once you put the airplane there, it will tend to stay there.
BAM! ..never thought of that before. Great stuff!As the lowered wing begins to produce an increased AOA and more lift than the raised wing, a yawing moment will take place in the form of adverse yaw which helps restore lateral balance. As the lowered wing begins to produce more lift, it incurs a drag penalty and yaws the nose towards the lowered wing which begins to rise. As this yaw towards the lowered wing (albeit rising) takes place, it assists in lifting the raised wing (which is now lowering) to continue the cycle of oscillation. This is due to the acceleration of the raised wing as it begins to lower so that it can rise abd roll back towards the originally lowered wing. Both wings will experience this until the oscillations completely dampen out.
The Pilot Handbook quote isn't about the vertical/horizontal component of lift. It is the poorly worded explanation of the increasing AoA as the lowering wing descends. If the last sentence said "strikes the lowering wing at a much greater AoA than the rising wing", it would be more technically accurate - and understandable.requoted from above from the Pilot Handbook ..."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."