1312
2
Divide 120 by 4. Place 120 on outer scale opposite 4 on the inner scale. Read
answer, 30, on outer scale opposite unit index (numeral «10» on inner scale).
CALCULATING GROUND SPEED
The mobile outer and fixed inner scales are used for determination of
ground speed problems. Two of the following quantities are available
for its solution: time, distance, ground speed.
3
Known: Distance and Time. Required: Ground speed.
A pilot finds by the use of check point that he has travelled 104 miles in 35 minutes.
What is the ground speed?
Solution:
Move the mobile scale until 104 on the mobile scale is set opposite 35 on
the fixed scale. Opposite the hour index (the arrow marked «MPH» directly over the
hour 12) read 178 miles per hour on the mobile scale.
4
Known: Distance and speed. Required: Time.
A pilot wants to know how long it will take to go 486 miles at a ground speed of 156
miles per hour.
Solution:
On the mobile scale set 156 opposite the hour index on the fixed scale.
On the inner scale opposite 486 on the mobile scale read 187 minutes (or 3 hours
and 7 minutes).
CALCULATING MILES PER MINUTE
This may be read after the speed in miles per hour has been obtained. The speed
given in miles per hour on the mobile scale when set opposite the hour index on
the fixed scale can be readily converted into miles per minute by reading the
number on the mobile scale appearing opposite the figure «10» on the fixed scale.
The figure «10» is often referred to as the unit index.
5
In Example 4, the ground speed was 156 miles per hour. With the 156 on the mobile
scale set opposite the hour index, what is the speed in miles per minute?
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