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6 Answers

Headwind vs. Tailwind

Asked by: 4365 views Aerodynamics

Hello,

Reading Chapter 12 of FAA's PHAK book, I came across this statement, "A tailwind quickly changing to a headwind causes an increase in airspeed and performance.
Conversely, a headwind changing to a tailwind causes a decrease in airspeed and performance."

Can someone please explain this to me? I thought tailwinds increased your speed during cruise portion of flight and vice versa. 

Thank you,

Nima

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6 Answers



  1. Mark Kolber on Dec 11, 2020

    I’ll leave more technical explanations to others. It’s the difference between airspeed and ground speed. When you talk about a tailwind increasing speed, that’s speed over the *ground*, not aircraft performance.

    What the PHAK is talking about is a sudden change in wind direction – wind shear. With that in mind, question back to you: You are on final. The wind quickly changes from a headwind to a tailwind. What happens?

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  2. Nima on Dec 11, 2020

    Hi Mark,

    Thank you for your answer and explanation. To answer your question, if the wind quickly changes from a headwind to a tailwind on final, one would lose speed, lift, and sink. That is why I think it is safer to fly a bit faster with headwind gusts but I could be wrong. Thanks again.

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  3. Paul H. on Dec 11, 2020

    Think about the momentum and inertia of your aircraft.

    You’re going 100 kias against a 10 kt headwind. You have 100 knots of wind over your wings, holding you up.

    Suddenly, that headwind changes to a 10 kt tailwind. Instantly, you only have 80 knots of wind over your wings.

    Yes, over the course of several seconds at the same power setting your plane will speed up and regain an indicated airspeed of 100 kias.

    Yes, once this change has happened your ground speed will be 20 knots faster, making the tailwind a good thing.

    During those several seconds, though, your airspeed has suddenly dropped from 100 kias to 80. Your plane will be sinking.

    Now imagine it when you’re on final, going maybe 70 kias. 10-knot headwind shifting to 10-knot tailwind drops your indicated airspeed to 50 kias, and if you don’t change power settings quickly, you’re dropping like a rock, at or near stall speed. Those several seconds it takes for your airplane’s momentum and inertia to allow a rebalance of thrust and drag are more seconds than you can really afford. You’ll have to make fairly quick adjustments to pitch and power to stay anywhere near your approach profile.

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  4. Mark Kolber on Dec 12, 2020

    Answering my question answered yours. too, didn’t it?

    That loss of airspeed and lift is the reason why on with reported gusts (which can change from headwind to tailwind to headwind to tailwind….) , we add 1/2 of the gust factor to our landing speed.

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  5. Nima on Dec 12, 2020

    Thank you Mark and Paul for the thorough explanations. It now makes sense.

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  6. Mackey on Dec 13, 2020

    100 KIAS –10K Head Wind= 90K ground speed.
    100 KIAS + 10K tail wind = 110K ground speed.
    110K–90K = 20K

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