Time, Speed, and Distance Problems
The rate arrow on the disk is always set to indicate a value per hour on the outer scale. There are three basic
To find the Time En Route, let’s assume you know your airspeed is 150 knots (nautical miles per hour).
1.Set the rate arrow to 150. See Figure 3.
2.You have determined the distance to your destination to be 245 nautical miles. Speed and distance are always on the outer scale; 245 is halfway between 24 and 25.
3.Look directly opposite to that value on the inner scale to find the Time En Route. It is between 1:35 and 1:40. There are five cali- bration marks on the middle scale between 1:35 and 1:40, and 245 NM on the outer scale is closest to the third calibration, or one hour and 38 minutes.
To find out how far you can go if your fuel endurance is 4.5 hours and your ground speed is known to be 125 knots:
1.Set the rate arrow at 125 on the outer scale. See Figure 4.
2.Find 4:30 on the inner scale.
3.The value on the outer scale is slightly more than 55. You know that 4 hours at 125 knots should cover 500 miles, so the outer scale is read as 500, not 50 or 5,000, which makes each large calibration mark worth 10 nautical miles. The answer is 564 nautical miles.
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