Flytech

While I was in France, I was freindly with a Swedish artist named Woytek.

(It's a Polish name, and the W is pronounced V. Those of you who are, like me, John Hegley fans may remember that 'Wojtek' is the name of his schoolground villain. Our Woytek showed no signs of villainy, or schoolgrounditude.)

Anyway, one day he asked me the following question:
What G-force does a fly go through when it turns in flight?

I'd never thought about it, but if you watch flies they do indeed make sudden right-angle turns.
I'd never thought about it because flies revolt me.

When a plane turns, the pilot feels a force. This is because the engines exert a force to change the direction of the plane's motion. In principle, it's exactly the same for a disease-bag fly.

As any physicist knows, the first thing to do is to make up a mathematical construction that's similar to the real problem. Therefore think of the fly changing direction by flying part of a circle- rather like a car on a roundabout. A bit of messing around with geomtery and momentum vectors shows that the force the fly feels is given by the formula
V²/R
where V is the speed of flight and R is the size of the arc- roughly, how sharp the turn is.
The V squared means that if you travel twice as fast, you feel four times the force. This is why the effect is just noticeable when you drive around a corner, but makes fighter pilots black out.

From observations, I estimate that for the fly it's about one foul metre a second. It's harder to estimate R- they seem to be turning almost instantly, and at random. Of course, that's a survival trait: flies that are easy to watch are flies that are easy to catch on your tongue. If you're a chameleon, I mean. I've never tried to catch flies with my tongue.

I think though, that it's in the neighbourhood of a millimetre. Put that in the formula, and you get an acceleration of 1 000 Newtons. Gravity on Earth surface is 9.8 Newtons, so I'm estimating that a manouvering fly feels about 100 G. 3 or 4 G is more than enough to make me want to have a sit down and think seriously about my kidneys.

If you put a human through 100 G, they'd probably, well, burst.

We don't deal with G-forces very well for two main reasons.

1) We're full of blood
2) We have big, important brains (with the exception of Le Pen, Haider, Ian Paisley, etc.)

When pilots bank sharply, loads of blood suddenly finds itself pushed to one side of the body. Too much blood in the brain puts pressure on the grey matter, and we don't like this at all. Incidentally, slightly raised blood pressure in the brain often causes headaches, which is why stress can cause them. If there's not enough blood getting up top, say because it's all partying in your feet, then you feel light-headed and pass out. It's like suffocating.

I don't know much about the disgusting anatomy of flies, but they're evidently built to take sharp corners. Do they have blood? I don't know. They certainly don't have lungs like us big animals. And they certainly don't have much in the way of brains. Allow me to quote Bill Bryson (from memory, and therfeore a bit wrong).
Instructions for being a train station pigeon
1. Peck aimlessly at the ground in the hope that it is edible
2. Take fright at someone walking along the platform and fly up to a girder
3. Shit
4. Repeat.

And flies, of course, are even more moronically mechanical than pigeons. Even if they can corner in a way that makes Schumacher driving through the mountains look like a planetary orbit.

And now I think I need to go and take a shower.

Song in my head: Would you believe, "Mr. Blue Sky" by ELO