Guide: Wind Drift & Ground Speed
Long before GPS screens dominated the cockpit, pilots relied on the E6B "Whiz Wheel"—a complex mechanical slide rule—to calculate the effects of wind on their aircraft. While modern avionics do this automatically, understanding the "Triangle of Velocities" remains a mandatory requirement for written exams and fundamental airmanship. An aircraft flies through a moving body of air. If the wind is blowing from the left, the aircraft will be pushed to the right. To fly a straight path over the ground (True Course), the pilot must turn the nose of the aircraft slightly into the wind. This angle is known as the Wind Correction Angle (WCA). Furthermore, the wind will either push the aircraft forward (tailwind) or slow it down (headwind). This digital E6B uses vector trigonometry to instantly resolve the Triangle of Velocities, providing the exact compass heading to fly and the actual speed you will travel over the earth.
How to Use This Tool
Input your True Airspeed (TAS)—the actual speed your aircraft is moving through the air mass, which can be found in your POH cruise performance charts. Next, enter your True Course (Deg); this is the line you drew on your map relative to True North. Input the forecasted Wind Direction (the direction the wind is blowing FROM) and the Wind Speed in knots. Finally, input the local Magnetic Variation (found on your VFR sectional chart) to convert your True Heading into a Magnetic Heading that your compass can actually read.
The Math Behind It
The engine utilizes advanced vector trigonometry to resolve the wind triangle. It calculates the angular difference between the wind direction and the true course. Using sine and cosine functions, it separates the raw wind vector into a direct crosswind component and a direct headwind component. The Wind Correction Angle (WCA) is found by taking the arc sine of the crosswind divided by the True Airspeed. The WCA is added to the True Course to find the True Heading. Finally, the Magnetic Variation is subtracted or added to find the Magnetic Heading, and the headwind/tailwind component is applied to TAS to find Ground Speed.
Understanding Your Results
Mag Heading (MH) is the most critical output; this is the exact number you must point the nose of the aircraft at using your magnetic compass to compensate for the wind drift. Ground Speed is your actual velocity over the surface of the earth, which you must use to calculate your fuel burn and ETA. Headwind Comp indicates how much aerodynamic resistance you are fighting.
Real-World Example
A pilot plans to fly a True Course of 090° (due East) at a True Airspeed of 110 knots. The winds aloft forecast reports the wind is coming from 045° at 20 knots. The local magnetic variation is -5° (5 degrees West). The calculator determines that the wind is hitting the aircraft from the front-left. To avoid being pushed south, the calculator determines a Wind Correction Angle of 7° left. The True Heading becomes 083°. Applying the -5° magnetic variation (East is least, West is best, so we add 5°), the Magnetic Heading becomes 088°. The 20-knot wind at a 45-degree angle also creates a 14-knot headwind, reducing the aircraft's Ground Speed to 96 knots.
Frequently Asked Questions
What is the difference between True Course and Magnetic Heading?
True Course is the physical line drawn on a map relative to the geographic North Pole. Magnetic Heading is the direction the nose of the airplane points relative to the Magnetic North Pole (which moves). You cannot steer a True Course on a compass; you must calculate the Magnetic Heading.
What does 'East is least, West is best' mean?
It is a memory mnemonic for applying Magnetic Variation. If the variation is East, you subtract it from your True Heading. If the variation is West, you add it to your True Heading to find your Magnetic Heading.
Why is Ground Speed important?
True Airspeed dictates how the airplane feels aerodynamically, but Ground Speed dictates how fast you reach your destination. If you have a 110-knot airspeed but a 40-knot headwind, your ground speed is 70 knots. You must use 70 knots to calculate whether you have enough fuel to reach the runway.
How do I know the wind direction?
Before the flight, pilots consult the Winds and Temperatures Aloft Forecast (FB). In the air, modern glass cockpits (like the Garmin G1000) calculate real-time wind vectors by comparing the GPS track to the air data computer's heading.