How do I get dead reckoning?

Answered by Willie Powers

To calculate dead reckoning, you need to consider the distance traveled, the speed of the aircraft, and the effects of wind on heading and airspeed. The basic formula for dead reckoning is Distance = Speed x Time. Let’s break down the process step by step.

1. Determine the airspeed of the aircraft: Airspeed is the speed at which the aircraft is moving through the air. It is typically measured in knots. In this example, let’s say the aircraft is flying at an airspeed of 250 knots.

2. Calculate the time spent flying: Time is the duration for which the aircraft has been in the air. Let’s assume the aircraft has been flying for 2 hours.

3. Use the formula to find the distance traveled: Distance = Speed x Time. In this case, the distance would be 250 knots (airspeed) x 2 hours = 500 nautical miles.

4. Consider the effects of wind: Wind can affect both the heading and airspeed of the aircraft. To account for this, we use the wind triangle.

5. Determine the wind direction and speed: This information can be obtained from various sources such as weather reports, onboard instruments, or communication with air traffic control. Let’s say the wind is coming from the northeast at a speed of 20 knots.

6. Draw the wind triangle: The wind triangle is a graphical representation used to calculate the effects of wind on heading and airspeed. It consists of three sides: True heading (TH), True airspeed (TAS), and Groundspeed (GS).

7. Calculate the True heading (TH): TH is the direction in which the aircraft needs to be pointed to counteract the effect of wind. To calculate TH, use the formula: TH = Magnetic heading (MH) + Wind correction angle (WCA). The magnetic heading can be obtained from a compass or navigation instruments. The wind correction angle is determined based on the wind direction and speed. In this example, let’s assume the magnetic heading is 360 degrees.

8. Calculate the Wind correction angle (WCA): WCA is the angle between the desired heading and the actual heading needed to counteract the wind. To calculate WCA, use trigonometry. In this case, the wind is coming from the northeast, which means the desired heading (TH) should be adjusted to the left. The WCA can be calculated using the formula: WCA = arcsin (Wind speed / True airspeed). In this example, WCA would be arcsin (20 knots / 250 knots) = 4.77 degrees.

9. Calculate the Groundspeed (GS): GS is the speed at which the aircraft is moving over the ground. It takes into account both the airspeed and the effect of wind. To calculate GS, use the formula: GS = TAS – Wind speed. In this example, GS would be 250 knots (airspeed) – 20 knots (wind speed) = 230 knots.

10. Steer the aircraft: Now that you have the True heading (TH) and Groundspeed (GS), you can steer the aircraft in the direction of TH and maintain the GS. This will ensure you stay on track and reach your destination.

Remember, these calculations are based on theoretical examples. In real-life situations, there might be additional factors to consider, such as variations in wind speed and direction, weather changes, and navigation system inaccuracies. It’s always important to cross-check with other navigation methods and stay vigilant during the flight.

While I don’t have personal experiences as an aircraft pilot or navigator, I hope this detailed explanation helps you understand the process of dead reckoning and how to calculate it effectively.