head & tail wind

[Brave]

Is turbulence usually stronger with a head or tail wind? Also, the monitor on my recent Northwest trans pacific flight (will detail in another thread) indicated a head wind of -12, what does this mean? The numbers ranged from -12 to +120 to and from my destination.

The flight went from Portland to Japan via the Canadian coast and Arctic circle (~11 hours), but a "lower" arc on the return (~9 hours), why?

 

[kingpenguin78]

Flying east to west up across the Arctic circle follows what is known as a great circle route and thus is a shorter flight distance then heading across the ocean directly. Because of head winds that would be encountered flying West it is faster to fly this great circle route then it would be to go across the ocean and burn more fuel. If the jet you were in flew at (lets say) 500mph, encountered a headwind of 120mph, its ground speed would be 380mph which would add at least a few hours on a long flight like that. Depending on the season, flying this far North would also take you out of some of the jet stream regions and reduce your headwinds even further.

However, on the way back, the aircraft can make use of the wind (in this case now it is a tailwind at 120mph) which will increase your groundspeed and thus make the overall trip shorter. So, the 500mph jet now would be travelling at a groundspeed of 620mph, which from the viewpoint of someone on the ground would be approaching the speed of sound. This would cut off a few hours and make it worth while to head across the ocean instead of following a great circle back.

Making use of a tailwind almost always makes for a shorter flight...

As for is turbulence stronger during these head/tail wind situations, I am not really 100% sure. Turbulence would in theory be more pronounced when you crossed boundries between regions of wind that was moving at different speeds, but I suspect that if you were in a consistenly moving airmass you would would experience very little turbulence.

 

[tb_neg]

I think you are right. It's the borders you have to worry about. Just like water sloshing over rocks.

As for is turbulence stronger during these head/tail wind situations, I am not really 100% sure. Turbulence would in theory be more pronounced when you crossed boundries between regions of wind that was moving at different speeds, but I suspect that if you were in a consistenly moving airmass you would would experience very little turbulence.

 

[Brave]

So what does a negative, e.g., -12, tail wind indicate? Is there more turbulence potential with a higher/lower number?

 

[kingpenguin78]

How was the wind referred to in the cabin display that you were watching? Was it always headwind, or did it change from headwind to tailwind? I have never been on a flight where they let you know the head/tailwind speeds, so that is pretty cool. What airline was it on?

I would suspect that since it ranged from -12 to 120, it was only presenting you a headwind calculation and -12 would mean there was a 12mph tailwind at the time of the measurement.

As for turbulence potential with higher wind speeds I would say there is more chance of turbulence within a moving air mass, but it would not be completely dependent upon what the wind speed is. You could experience sever turbulence at a low wind speed and not have anything at a higher windspeed. It all depends on where you are travelling in an airmass as well as your angle of attack and direction in reference to the wind.

Turbulence is generated due to eddies and inconsistencies in different moving air masses, not specifically the wind itself. I have been on flights that have landed is severe winds (Calgary can have some intense wind storms) and have not felt a bump.

-Jon

 

[Brave]

It was an Airbus 330 to/from Portland/Tokyo. On the eastbound flight, I remember the number being -12, so maybe the negative refers to a tailwind. On the outgoing westbound flight, it ranged from 60 to 120. Curious if the higher number means more wind, thus possibly more turbulence?