Calculating flight time is a bit more complicated than calculating driving time, but nevertheless, it is a relatively simple calculation to make. Electronic calculators can do this for you, but it is still a good idea to understand the calculation you are making before relying on such devices. This calculation is a major part of any flight plan. You will also need access to current weather information along your route. Be aware that, if weather conditions change, it will be necessary to recalculate your flight time based on updated information.
Things You'll Need
- Calculator with cosine function
- Flight calculator (optional)
Plan your flight, and make note of the following information: geographic distance of your planned route, the planned cruising altitude, the planned cruising airspeed, current wind conditions and expected wind conditions for the approximate duration of your flight.
Determine your planned time en route without wind. To do this, simply divide the geographical distance of your route by your planned cruising airspeed.
Determine the headwind or tailwind component of the wind at your cruising altitude. This refers to the portion of the wind speed that will be with or against you (as opposed to the crosswind portion, which is blowing sideways to your course). This is a trigonometric calculation. Using a paper map, measure the angle between the direction of the wind and the direction of your planned course. Use a calculator to determine the cosine of that angle. Multiply the result by the known speed of the wind. The result will be the headwind or tailwind component. Headwinds are expressed as positive numbers, and tailwinds are expressed as negative numbers.
Alternatively, you can use a flight calculator (E6B) to make this calculation simply by entering the speed and direction of the wind, your planned course and airspeed.
Multiply the headwind or tailwind component by your estimated flight time expressed as a decimal, such as "3.2 hours."
Add the result (don't forget that tailwinds are negative numbers) to the geographic distance of your route. The resulting number will be total nautical air miles of your trip. This is the distance of your trip adjusted for wind. This is the distance you should use for fuel planning, as well as for calculating flight time.
Divide the nautical air miles by your cruising speed to get an accurate estimate of your time on route. Keep in mind that this does not include the time you will spend climbing away from your point of origin, or the time you will spend descending to your destination.