, the zero-lift drag coefficient
<math>C_</math> is a dimensionless parameter which relates an aircraft's zero-lift drag force
to its size, speed, and flying altitude.
Mathematically, zero-lift drag coefficient
is defined as <math>C_ = C_D - C_</math>, where <math>C_D</math> is the total drag coefficient for a given power, speed, and altitude, and <math>C_</math> is the lift-induced drag
coefficient at the same conditions. Thus, zero-lift drag coefficient is reflective of parasitic drag
which makes it very useful in understanding how "clean" or streamlined an aircraft's aerodynamics are. For example, Sopwith Camel
biplane of World War I
festooned with wires, bracing struts, and fixed landing gear, had a zero-lift drag coefficient of approximately 0.0378, compared to 0.0161 for the streamlined P-51 Mustang
of World War II
which compares very favorably even with the best modern aircraft.
The zero-lift drag coefficient can be more easily conceptualized as the drag area
) which is simply the product of zero-lift drag coefficient and aircraft's wing area (<math>C_ times S</math> where <math>S</math> is the wing area). Parasitic drag experienced by an aircraft with a given drag area is approximately equal to the drag of a flat square disk with the same area which is held perpendicular to the direction of flight.... Read More