What does an E6B flight computer compute?
An E6B is a pilot's pocket calculator for flight planning. The classic version has no battery: it is a circular slide rule on one side and a sliding wind grid on the other. It answers questions about time, fuel, altitude and wind.
The calculator side
The round side is a circular slide rule. Line up two numbers on the scales and it gives you a third, because most planning problems are one multiplication or division. A student's first problems are usually these:
- Time, speed and distance. 145 nautical miles at 112 knots of ground speed takes about 1 hour 18 minutes.
- Fuel. A burn of 8.5 gallons per hour for 2.5 hours uses 21.25 gallons. With 40 gallons usable, the same burn gives about 4.7 hours to dry tanks, before any reserve.
- True airspeed. Set pressure altitude against temperature in the window and read true airspeed against your calibrated airspeed.
- Density altitude. The same window shows it. Use the density altitude calculator to check your work.
- Conversions. Nautical to statute miles, Celsius to Fahrenheit, gallons to pounds of fuel, using marks printed on the scales.
A slide rule keeps no decimal point, so you place it yourself. Reading 18 on the scale could mean 1.8, 18 or 180. That is why instructors ask for a rough estimate first.
The wind side
The other side solves the wind triangle, the question every cross-country flight starts with: what heading do I fly to stay on my course, and how fast will I actually go over the ground? You mark the wind on a rotating disc, slide the grid to your true airspeed, and read the wind correction angle and ground speed.
For example, a true course of 345° at 120 knots true airspeed, with the wind from 030° at 15 knots, gives a heading of about 350° and a ground speed of about 109 knots. You can run those numbers in the wind triangle calculator and see the triangle drawn out.
The same geometry gives the wind components for a runway. A wind 30° off the runway at 18 knots is 9 knots of crosswind. There is a separate crosswind calculator for that.
What the problems have in common
None of this needs an E6B in particular. Time is distance over speed. Crosswind is wind times the sine of the angle. The tool exists because pilots needed these answers on a kneeboard, in a cockpit, long before phones. Once you see the formula behind a problem, the scale makes more sense, and so does a wrong answer.
Manual or electronic?
They answer the same questions, and many students use both.
- A manual E6B needs no battery and shows the shape of the problem. Many instructors want you to be able to use one.
- An electronic one or an app is faster and has no scale to misread. It can also show the steps, which helps when your manual answer and the book's disagree.
Before a written test, find out what you are allowed to bring. Test centers have their own rules and they do change. Phones are commonly not allowed in the room, so ask your instructor or the test center in good time and practice with what you will actually use.
Where Headwind fits
Headwind is an E6B for Android that solves as you type, with no equals key. The wind triangle, finding the wind, runway wind, time, speed and distance, fuel, cloud base and conversions are free. Headwind Pro, a single purchase, adds pressure and density altitude, true airspeed and Mach, weight and balance, the nav log, descent planning, turns and glide, and holding entries. Each calculator has a "How it's calculated" section with the formula behind the answer, so you can follow along with your manual one.
For planning and training only, not for navigation. Check every result against your aircraft's flight manual and official sources before you rely on it.