The Wind Side of the CR-2 Computer

CHAPTER FIVE

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.

NOTE

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

academic instructor.

Use your CR-2 and work through the following examples:

Given:

TAS = 140 knots

Wind = 220 at 35 knots

MAG Course = 085

Find:

Ground Speed

Place MAG Course of 085 over the TC index.

Find 220 (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