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View Full Version : CFI Pop Quiz #104

Chris Burgess
01-05-2006, 06:34 AM
That portion of the aircraft's total drag created by the production of lift is called

A) induced drag, and is not affected by changes in airspeed.
B) induced drag, and is greatly affected by changes in airspeed.
C) parasite drag, and is greatly affected by changes in airspeed.

Udi
01-05-2006, 08:10 AM
We gyronauts should know this better than anyone!

Udi

chuter
01-05-2006, 08:47 AM
I'll go with B.............:o

gyropilot
01-05-2006, 09:01 AM
From Chapter 2 of the Rotorcraft Flying Handbook:

"INDUCED DRAG

Induced drag is generated by the airflow circulation around the rotor blade as it creates lift. The high-pressure area beneath the blade joins the low-pressure air above the blade at the trailing edge and at the rotor tips. This causes a spiral, or vortex, which trails behind each blade whenever lift is being produced. These vortices deflect the airstream downward in the vicinity of the blade, creating an increase in downwash. Therefore, the blade operates in an average relative wind that is inclined downward and rearward near the blade. Because the lift produced by the blade is perpendicular to the relative wind, the lift is inclined aft by the same amount. The component of lift that is acting in a rearward direction is induced drag.

As the air pressure differential increases with an increase in angle of attack, stronger vortices form, and induced drag increases. Since the blade’s angle of attack is usually lower at higher airspeeds, and higher at low speeds, induced drag decreases as airspeed increases and increases as airspeed decreases. Induced drag is the major cause of drag at lower airspeeds."

JByrd
01-05-2006, 10:25 AM
Hi Chris,

Good quiz.

B) induced drag, and is greatly affected by changes in airspeed.

Implied: nominal angle of attack, turbulent boundary layer, constant Reynolds number.

automan1223
01-05-2006, 10:55 AM
There is usually a chart in the books that shows the curves of both types of drag, parasitic and induced and they vary greatly, If I remember they reach a point of equlibrium and then reverse.

Jonathan

Chris Burgess
01-05-2006, 05:16 PM
B is the correct answer. Good responses all.