Wind Calm and Human Performance

Mmmm Cold Beer
Mmmm Cold Beer
Mmmm Cold Beer

Finally, good weather and finances permitted me to get over to Sherburn today to get some flying done. It was one of those very rare days when the weather forecast says “Wind = CALM”. Which means, as it says, there was little or no significant wind – at least from the surface to where I was flying (not above 1000 feet today).

Why the picture of beer? I thought this post was about calm wind, flying and PPL exams (even though beer is much more interesting than exams)? Well… I’ll get to that in less than a minute.

Flying with no wind is quite an odd experience. Usually we have a headwind on take-off and landing. There are many reasons for this but the bottom line effect is that it slows down your ground speed.

Imagine that you throw a ball at 100mph. Imagine the wind blowing towards you at 50mph. The ball would actually move relative to the ground at approximately 50mph (ground speed). Although it would still be travelling through the air at 100mph (air speed).

So (Don’t worry I’ll be quick – before you fall asleep)… The air speed used for take-off and landing is always roughly the same (depending on the type of plane and some other factors) but depending on the wind velocity and angle the ground speed will be different.

Normally we approach to land at 70 Knots (air speed) but if there is a 15 Knot head wind and I look down, I will be travelling across the ground at 55 Knots (ground speed). Today – when you look down – you are travelling across the ground at 70 Knots too. So it seems to take longer to descend (when in fact it just takes more distance) and you use up more runway when landing and more when taking off too.

I took some video today but it is not very exciting. If you really are having trouble sleeping, have a look here. There is no in-flight footage I’m afraid. I can’t hold the camera and fly solo. I’ve had an idea for next time though so stay tuned.

Incidentally – This video is my entry for most boring, ugly video ever posted on YouTube. I think it’s a winner.

So… Why the beer?

Well one of the questions in the Human Performance and Limitations exam is:

How long does it take the body to eliminate one unit of alcohol? One unit of alcohol is equivalent to a half a pint of beer, one glass of wine or one measure of regular spirit.

The answer is one hour.

I passed by the way.

Special thanks to Julia at Sherburn and the Great Circle iPhone app for much revision help.