DRAG review

the ones starred are the topics i still need eventually double check eventually.

1.) the coefficient of an airfoil is determined by its shape and area, its minimum value is found at zero degrees angle of attack.
2.) the three types of drag experienced by a helicopter in forward flight are profile, parasite and induced.
*3.) when the speed of a helicopter increases from 20 knots to 60 knots, parasite drag increases by a factor of four.
*4.) form drag can be reduced by shaping.
5.) skin friction drag is caused by friction between molecules in the turbulent layer which is a retarded layer of air between the airfoil and the wake.
6.)a laminar boundary layer is normally thin, it produces little skin friction drag and is not readily subject to separation from the airfoil surface.
7.) a turbulent boundary layer is normally thick, it produces much skin friction drag and it is readily subject to separation from the airfoil surface.
8.) the point where the laminar boundary layer changes into the turbulent boundary layer is called the transition point.
9.) with an increase in airspeed, skin friction drag increases because the transmission point moves forward and the boundary layer thickens.
10.) induced drag is the result of the differences in lift above and below the airfoil and is directly proportional to induced flow.
11.) with an increase in airspeed, induced drag decreases, and parasite drag increases.
12.) an increase in aspect ratio tends to increase induced drag.
13.) wash out is a structural design which decreases the blade angle from blade root to blade tip.
14.) total drag of a helicopter is low at zero airspeed, it increases with an increase in airspeed.