Thinking - Slightly interesting TV helicopter factoid

When I watch helicopters shooting at people on TV, it doesn't look very real. Why dont they just hover and shoot?

Why do they keep flying past really fast and taking a few shots, then letting the escaping car escape?

It turns out there's a good reason!

Well at least I think there is, and let's face it, that's good enough for me.

There's this thing called autorotation, and it's a very fine thing indeed. It seems that when your helicopter's motor dies on you in flight, it's not just a case of "plummet to the ground and hope you land in a used marshmallow dump" or something.

It turns out there's actually something you can do.

Which is odd, and a little surprising. And also kind of pleasant if you are in a helicopter with no motor.

Helicopter blades can change the angle they sit at when they are doing their rotating thing. They can make it so they create more or less lift as required, and they can also tilt forward or backward to create thrust so you can actually go somewhere, and not just hover impressively.

Personally I think hovering is impressive enough, but it turns out other people like to derive useful function from their helicopters.

So using some sticks and pedals and things inside the helicopter, your pilot (hopefully) can make your helicopter go where they (or you if you own enough money) want it to.

But when it's falling out of the sky, it turns out they can set the blades in such a way as to make them spin a lot using the substantial breeze that they find blowing through their blades when they plummet to the ground.

As I understand it, it's a bit like strapping a ceiling fan to the front your bike and riding around the block.

The fan, despite being disconnected from any power supply, starts spinning a lot.

Now, it turns out "spinning a lot" is just the kind of thing that you want from a helicopter's blades when you dont have a motor any more.

So if your motor dies on you, as long as you have enough forward momentum, OR altitude, you dont just fall from the sky. Your skilled pilot can do the ceiling fan on a bike thing for a bit, get the blades up to pace, then just at the last minute, turn all that handy rotating blade motion into lift and actually land without everyone's blood falling out.

Way cool.

I mention that the requirement is either forward momentum, or altitude, because that's true.

I like to say true stuff where I can.

If you dont have enough forward momentum to keep the blades spinning, you can trade some altitude by falling out of the sky for a bit and pulling up. This translates into forward momentum. So you need some altitude to do a bit of a dive to get some forward momentum, or just have some forward momentum to start with.

So...

I'm guessing the reason the TV helicopters dont just hover fifty feet off the ground and shoot at Jimmy Bond a lot is because it's a really stupid thing to do.

Who knew?

120ThingsIn20Years thinks TV might have actually got it right.