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Home > Flying the Plane > Would a plane fall if the headwind suddenly stops?
Would a plane fall if the headwind suddenly stops?
Flying - Flying the Plane
Friday, 20 March 2015 14:11
 
Ground Speed and Airspeed

Hi Captain,

My question is in regards to take off. I fly all the time for work but by no means understand any of the technical nature of flying. Keep that in mind as I write this question.

Let's say under a normal day with wind conditions at or below 10-15 miles per hour, a plane can take off at 200 mph heading into the wind.

My question is, what happens on an incredibly windy day. Let's say you take off into 70 mph wind gusts. Does the wind help the plane take off much earlier than the required hypothetical 200 mph?

Also, if it does take off at 130 mph (130mph + 70mph wind) and the wind suddenly stops, would the plane fall if the speed had not reached the 200 mph needed to fly?  

Thanks,

Mike

Hi Mike,

Your queries is quite similar to another reader who asked me on the effect of wind on a plane during the cruise ‘A Boeing 777 can’t fly this fast!here.

Here I need to explain again on what is ground speed and indicated airspeed (ie the plane’s speed). A layman is often confused over the term ‘ground speed’ and the plane’s ‘indicated airspeed’.

The ground speed is the speed at which an object travels relative to a fixed point on the earth's surface. The difference between ground speed and indicated airspeed is caused by the influence of winds on the overall speed of the aircraft.

Let’s say you are running at a constant speed of 10 mph against a walkalater (travelator) that is moving at 2 mph. Your actual movement towards your plane at the gate at the airport is 8 mph (10 - 2) but as far as you are concerned, you are still running at 10 mph!

In this hypothetical scenario, in aviation term, your ‘ground speed’ is 8 mph and your ‘indicated air speed’ is 10 mph.

In your case, the plane take-off speed is 200 mph (indicated air speed). If you have a headwind of 70 mph the groundspeed is now 130 mph and therefore you would require a shorter runway to take off. In this case, you would take off earlier.

Your assumption that the take-off speed is 130 mph is wrong. The plane needs to accelerate to 200 mph in order to take off!

Someone standing far away will see you taking off earlier at 130 mph ground speed but the pilot inside the plane will see that his plane lifted off at 200 mph.

Your assumption in the last paragraph is incorrect. The plane will not take off at 130 mph but at 200 mph indicated airspeed.

Assuming the wind speed suddenly drops to 10 mph, the ground speed of the plane is 190 mph (200 - 10)

If the wind speed suddenly stops, that means the wind speed is now zero. Your take off speed is (200 – 0) = 200 mph.

As far as the pilot is concerned, a change in the head wind, to even zero, will not affect his take off. The only difference is that he cannot take advantage of any wind to use a shorter runway!


Ground Speed versus Airspeed


Spectacular Cross Wind Landing on A380 at Zurich

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Comments (3)

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Would a plane fall if the headwind suddenly stops?
Hi Captain Lim,

Thanks so much for clarifying. Much appreciated. You are a great teacher for the many students looking to learn more on aviation.
Mike , 21 Mar, 2015
Airbus vs. Boeing
Hi Captain Lim,

I am an extremely nervous flyer. I do it because, as you have stated, it is the fastest way to get to a destination. I am scheduled to fly to Hawaii on Thursday and we will be flying on an Airbus 330-200. Over the past few weeks I have had two people - one a flight attendant - say that Airbus planes are not nearly as safe as Boeing and that they don't like flying on them. Do you have any thoughts as to whether or not one is safer than the other? I really appreciate your website and explanations and assurances for things like turbulence. I will try and keep them in mind while I'm on my next flight. Thanks for any input you might have!

Jacquie
Jacquie , 13 Apr, 2015
Would a plane fall if the headwind suddenly stops?
I find this topic very interesting and I would have imagined (by my sometimes unlogical thinking) that if the headwind of 70 knots stops "immediately and not gradually", the plane not given a chance to accelerate to 200 knots at that single point in time will stall and fall out of the sky. Effectively the IAS of 200 knots will suddenly become 130 knots and that would not enable to plane to remain aloft. Is that not true?
Adrian , 22 Dec, 2015

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