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2 Answers

Groundspeed zero but airspeed is still alive during slow flight?

Asked by: 1291 views Aerodynamics, Commercial Pilot, Flight Instructor, General Aviation, Private Pilot, Student Pilot, Weather

I remember my private pilot training days, doing slow flight in a dirty configurations, and when I practiced slow fligt into a heavy headwind, it made me realoze the plane was actually flying motionless in the air with groundspeed of zero kts but airspeed still showing airspeed. My instructor once told me we are hovering, but I still do not understand how ASI was registering some airspeed and its science behind it.

My thought is that due to the headwind, isnt more air entering pitot tube and should register higher airspeed?



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2 Answers

  1. Robert Jankowski on Apr 04, 2016

    In some training aircraft, it is quite possible to end up with a zero or even backwards ground track with a stiff enough headwind. The airplane doesn’t care about groundspeed (other than takeoff and landing), it only cares about its speed relative to the body of air that it is flying in.

    To your question:
    My thought is that due to the headwind, isn’t more air entering pitot tube and should register higher airspeed?

    Pretty close.

    I am going to make some generalized statements that may not be 100% accurate, but for this level of your training will be useful for understanding the concepts and give you the base building block for future (more complex) learning.

    Let’s say that you’re flying an aircraft in slow flight at 50 knots of indicated airspeed, in a zero wind setting, you will have a ground speed of approximately 50 knots.

    Now let’s say you’re flying at the exact same indicated airspeed but this time, you have a 10 knot headwind. Your indicated airspeed will be 50 knots, however your groundspeed will be 40 knots. If you were flying into a 50 knot headwind, you will still show a 50 knot indicated airspeed but a 0 knot ground speed.

    Going along with this, if you were flying at the same 50 knot indicated airspeed, but with a 10 knot tailwind, you will now have a 60 knot groundspeed. With a 50 knot tailwind and a 50 knot indicated airspeed, your groundspeed will be 100 knots.

    Hopefully this clears things up a little for you.

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  2. Mark Kolber on Apr 04, 2016

    Steve, I think your question reflects a basic misunderstanding of airspeed. It is the speed of the aircraft relative to the airmass, nothing else. An airplane flying at 100 KTS into zero wind has an airspeed of 100 KTS. An airplane flying at 100 KTS with a 50 KT tailwind has an airspeed of 100 KTS. And an airplane flying at 100 KTS into a headwind also has an airspeed of 100 KTS.

    To take it away from the airplane, consider a balloon, something we know has zero airspeed. Whether thje wind is zero, or 100 KTS in any direction, its airspeed is still zero.

    Watch out for the common error of confusing the speed of an aircraft relative to the ground (“ground” speed) with the speed of an aircraft relative to the airmass.

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