The Sparking Tankers

It's time for the new puzzler. You're ready. You probably know I have an interesting puzzler. What's more interesting is that we're not sure of the answer, but we will have it.

I remember when I was but a wee lad, going for Sunday drives anywhere in Our Fair City that we would see large tanker trucks loaded with flammable or inflammable fluids.

And they all had somewhere, attached to the underpinnings of this thing from the carriage, a chain or some metal conductive contraption that went from the frame of the vehicle and touched the ground. And it would throw off a shower of sparks as this chain dragged along the ground when the vehicle was in motion.

The question is, part one: what are those big trucks that have these things?

And part B, I will preface the question with the statement that I see these trucks nowadays, but I don't see the chain. So part B is how do they make invisible chains?

Or Part B is, why don't they have them anymore? They used to have them, why? That's part one. And part B, they don't have them anymore. Why?

Answer the Puzzler »

Remember last week's puzzler?

Jimmy Cagney's Assistant

It's time for the puzzler.

You've all seen those old movies? Those old movies with Jimmy Cagney, you know, "You dirty rat. You're the guy who sent up my brother!"

And he's got a leather jacket and a scarf around his neck climbing into a plane. Remember the great line? "I can fly the crates they come in."

Everyone's seen those movies. So, he climbs into the plane and his assistant prepares for takeoff.

And all those planes were started by hanging on the prop and pulling it, starting it much like you would crank an old-timey Model T Ford. And of course, they had electric starters, later on. But that was the way they were all started back then. And once the plane was started, they'd remove the chocks from the wheels and they'd fly off into the sunset and do whatever they did.

But the question is about the starting procedure. You'll notice if you watch those movies that the assistant always takes a hold of the prop. And when he starts it, what he's going to do is he's going to snap the prop, and that's what gets the crankshaft turning and gets the pistons all moving and that's what starts it. But before he snaps the prop, he will turn the prop, sometimes an entire revolution, very slowly. And then once he has done that, then he will start the engine. So, the question is, why?

Why what? Why did he always turn the prop very slowly at first?