INSTRUMENT FLIGHT RULES WORKBOOK
507. THE WIND SIDE OF THE CR-2 COMPUTER
Ground speed computation is basic to flying. Being able to compute accurate ground speed is
important when determining times and fuel requirements. The variables to be considered during
preflight planning that affect ground speed are TAS, Wind, Crab Angle, and True Course. For
the purposes of this course we will only concern ourselves with TAS and WIND.
As you work through a problem, make sure you keep the following in mind:
1. Winds obtained during a weather brief or from a winds-aloft chart are given in degrees
True. Only the winds given by Approach/Departure Control or a tower are magnetic.
2. As the winds are True, the desired course to be flown must also be True. A Magnetic
course is converted to a True course by accounting for Magnetic Variation (MAG VAR). This
conversion is easily made with the CR-2.
You will be converting MAG course to True course solely for use
on the wind side of the CR-2 in determining ground speed.
3. Ground Speed is computed with the CR-2 by adding or subtracting a wind component to or
from the aircraft's TAS.
Prior to using the CR-2, make sure you are familiar with its makeup. If you require more
detailed information, refer to your AI pubs, CR-2 Instruction Manual, or consult your RI
Use your CR-2 and work through the following examples:
TAS = 140 knots
Wind = 220º at 35 knots
MAG Course = 085º
Place MAG Course of 085º over the TC index.
Find 220º (wind direction) on degree scale.
Plot the wind dot at 35 (wind speed).
Determine whether a head, tail or no-wind condition exists.
CR-2 COMPUTER 5-9