It does seem logical that a 10-knot tailwind on the way back will ‘pay you back’ for the 10-knot headwind you had on the way out. But it doesn’t work that way. Many flights that we take are ‘out and back’ trips. We takeoff from one airport headed for a meeting, an instructional period or just lunch, and then return back to where we started. Often these flights take place with a prevailing wind. Have you ever reasoned that a headwind on the way out will be made up for on the way home by the return tailwind? In fact you could say that any wind acts like a headwind!
Example 1 — 100kts, No Wind: If you have a groundspeed of 100 knots and you fly to an airport 100 nautical miles away with no wind, it should take you one hour to get there. The return trip, also with no wind, should also take one hour.
Result: The out-and-back flight takes a total of two hours.
Example 2 — 100kts, 25kt headwind/tailwind: On the outbound leg, with a 25-knot headwind, the 100 mile trip will take 1 hour and 20 minutes. The groundspeed during that outbound leg would be only 75 knots. On the way home however, you will enjoy a tailwind — and a groundspeed of 125 knots. At that speed the 100 mile trip will take 48 minutes.
Result: Adding both legs together (1:20 + :48) equals 2 hours and 8 minutes — eight minutes longer than with no wind at all!
The Lesson
The headwind took more away from us than the tailwind gave back. Having any wind at all therefore acts on the airplane like a headwind will act: it delays our arrival and makes us burn more fuel.
What’s Going On?
It still does not seem logical that this headwind/tailwind scenario is not an even trade-off. But here is why it is not: When the headwind acts on the airplane, it reduces the groundspeed and prolongs the flight. This means that the headwind will have a longer time period to act on the airplane than a tailwind will. This also means that the airplane is exposed to the advantage of a tailwind for a shorter period of time and therefore gets less of a good thing. So a headwind is more bad, than a tailwind is good!
Important: Fuel starvation is a leading cause of off airport landings. We must keep the “net headwind effect” in mind when making our fuel plans for long round-trips.
