Monday, 24 August 2015

Some basic terms related to Aircraft - Part 5

8. Stall
  • So far the lift is concerned, it increases as we increase the angle (provided the air speed remains constant) but only up to certain limit; after this it begins to fall off.
  • The actual amount of lift given by wing when this maximum limit is reached varies with shape of aerofoil section.
  • Most of the wings, whatever their aerofoil shape and whatever the air speed, reach their maximum lift at about 15deg to 20deg.
  • After certain angle the wing loses its lift and drag dominates. This phenomenon is called stalling. 
9. Aspect Ratio
  • Aspect Ratio is a measure of how long and slender a wing is from tip to tip.
  • The Aspect Ratio of a wing is defined to be the square of the span divided by the wing area and is given the symbol AR.
  • The formula is simplified for a rectangular wing, as being the ratio of the span to the chord length as shown on the figure below.

10. Wing Dihedral 
  • Wing Dihedral refers to the angle of wing panels as seen from the aircraft's front view. 
  • Dihedral is added to the wings for roll stability; a wing with some Dihedral will naturally return to its original position if it is subject to a briefly slight roll displacement.
  • Most large airliner wings are designed with Dihedral. 
  • On the contrary the highly maneuverable fighter planes have no Dihedral.
  • In fact, some fighter aircraft have the wing tips lower than the roots, giving the aircraft a high roll rate.
  • A negative Dihedral angle is called Anhedral. 
See the Dihedral of 5 deg in the above given Izicraft-400 trainer aircraft.

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