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6 Answers

How Gusts Work

Asked by: 2466 views Aerodynamics

I understand normal wind, but I can't figure out how gusts increase/decrease an aircraft's speed. It's counter-intuitive for me to think a headwind gust would decrease the airspeed, since I think that more air flow would increase lift and airspeed. Is a headwind gust, in essence, pushing the aircraft backwards in the air mass, thereby reducing its airspeed? 

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6 Answers



  1. Mark Kolber on Oct 14, 2016

    Where did you read that? What does the rest of the thought say? I ask because there is probably more to it that what you are saying.

    A transient increase in headwind from a horizontal shear (aka gust), will produce a similar transient increase in airspeed.

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  2. Kris Kortokrax on Oct 14, 2016

    Drew,

    You seem to be talking about two separate issues. If the headwind is “pushing the aircraft backwards”, it is slowing the ground speed. However, as Mark said, the momentary increase in headwind will give a momentary increase in airspeed.

    You can easily see this if you sit in the airplane on the ground during gusty wind conditions and watch the airspeed indicator needle move in response to wind changes.

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  3. Drew on Oct 14, 2016

    I suppose the underlying question is why we fly a higher approach speed in gusty conditions. I’ve heard as if gusts could reduce the airspeed on approach. If a headwind gust will increase the airspeed, there is no fear of getting too slow; if anything, the approach would be too fast. Thank you for the feedback.

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  4. Koehn on Oct 14, 2016

    The reason you fly an approach faster in gusty conditions is so that when you’re on the right approach speed and the gust you’re in ends, you don’t suddenly find yourself low and slow and out of options.

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  5. Mark Kolber on Oct 17, 2016

    Yes, Drew. As Koehn says, the problem with gusts isn’t the transient increase in airspeed they produce but the transient decrease in airspeed that occurs when they end.

    I think the conceptual issue is, we picture ourselves turning final when the winds are steady and then being hit by a gust. But they don’t have to be all that momentary. They can last up to 20 seconds and still be considered a “gust” – more than enough time to turn final when the peak is taking place and then have the lull remove a bunch of airspeed very quickly.

    Plus, try not to think of a gust as being a purely frontal condition. The fact that they are reported that was, “10G20”, doesn’t mean the gust has to be from the same direction as the steady wind. These are unstable wind conditions in which negative shear is just as likely as positive gust. Just two sides of the same coin.

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  6. Drew on Oct 17, 2016

    That helps a lot, Mark.

    Thank you all for your responses.

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