What is total drag?

Total drag is the sum of parasitic drag, profile drag, and induced drag.diagram of total aerodynamic drag

Parasitic drag is caused by non-lifting portions of the aircraft, such as the rotor mast, landing gear, etc.  Parasitic drag is present anytime the aircraft is moving.  Parasitic drag increases significantly with airspeed.

Profile drag develops from frictional resistance as the rotor blades passing through the air.  Profile drag is comprised of form drag and skin friction.  Overall, profile drag increases moderately with increases in speed, but does not change significantly with changes in the airfoil’s angle of attack.  Form drag is the result of turbulent wake caused by separation of airflow from the surface of a structure.  A flat plat creates more form drag than a symmetrical airfoil (teardrop).

 

Diagram of various profile-form drag combinations

Skin friction is caused by surface texture.  The smoother something is the less skin friction.  Dirt, ice, and other items that impact the surface texture have a significant effect on friction drag.

Induced drag is a result of the production of lift.  Lift production generates downward velocities and vortices that increase induced drag.  As the aircraft increases forward speed, induced drag decreases.

Reference(s):

FAA-H-8083-21A – Helicopter Flying Handbook pg. 2-5
Principles of Helicopter Flight, 2nd Edition, pg. 28
FM 3-04.203-2007 Fundamentals of Flight pg. 1-28

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