page_title: Dihedral (aeronautics)
section_title: How dihedral angle creates dihedral effect and stabilizes the spiral mode
hierarchical_section_title: Dihedral (aeronautics) / How dihedral angle creates dihedral effect and stabilizes the spiral mode
caption_attribution_description: On the explanation of the dihedral angle effect, diagram 2. Drawn by Sergey Khantsis.
context_page_description: In aeronautics, dihedral is the angle between the left and right wings of an aircraft. "Dihedral" is also used to describe the effect of sideslip on the rolling of the aircraft.
  Dihedral angle is the upward angle from horizontal of the wings or tailplane of a fixed-wing aircraft. "Anhedral angle" is the name given to negative dihedral angle, that is, when there is a downward angle from horizontal of the wings or tailplane of a fixed-wing aircraft.
  Dihedral angle has a strong influence on dihedral effect, which is named after it. Dihedral effect is the amount of roll moment produced in proportion to the amount of sideslip. Dihedral effect is a critical factor in the stability of an aircraft about the roll axis. It's also pertinent to the nature of an aircraft's Dutch roll oscillation and to maneuverability about the roll axis.
  Longitudinal dihedral is a comparatively obscure term related to the pitch axis of an airplane. It is the angle between the zero-lift axis of the wing and the zero-lift axis of the horizontal tail. Longitudinal dihedral can influence the nature of controllability about the pitch axis and the nature of an aircraft's phugoid-mode oscillation.
context_section_description: The dihedral angle contributes to the total dihedral effect of the aircraft.  In turn, the dihedral effect contributes to stability of the spiral mode.  A stable spiral mode will cause the aircraft to eventually return to a nominally "wings level" bank angle when the angle of the wings is disturbed to become off-level.
  If a disturbance causes an aircraft to roll away from its normal wings-level position as in Figure 1, the aircraft will begin to move somewhat sideways toward the lower wing.
  In Figure 2, the airplane's flight path has started to move toward its left while the nose of the airplane is still pointing in the original direction.  This means that the oncoming air is arriving somewhat from the left of the nose. The airplane now has sideslip angle in addition to the bank angle.  Figure 2 shows the airplane as it presents itself to the oncoming air.
caption: Fig. 2: Non-zero sideslip sets the lower, upwind wing to a higher angle of attack, resulting in stabilising roll moment P.
  The aircraft is shown flying directly towards the viewer.
exif: {}