Flashes of Panic

I heard the telltale “Sssss” of the liftoff last night, and looked out the window to see smoke in the park across the street: someone else was launching rockets in the park! I looked up, but didn’t see it come down; I did hear what I thought was a little voice saying, “Daddy, do it again!”

As I made dinner, I picked out the man doing the launching, and what was probably his son sitting on the ground not far from the launcher. I watched them fuss over something which was probably the rocket; I saw the streamer. Eventually they had it set up to launch again, and I thought, it really looks like they’ve got the pad at quite a dramatic angle, don’t they?

Well, apparently they weren’t *ahem* exactly rocket scientists. (Granted, most hobby rocket launchers aren’t, myself included.) I watched it launch, then flinched even though I was across the park from them: it did a tight loop, then drove straight into the ground about twenty meters away from them, still blazing. Then it puffed smoke (the tracking smoke) and popped the ejection charge. Don’t know what that did; I expect it may have ruptured the body tube. I heard someone shouting; there were others on the field, who probably weren’t too thrilled to have this landshark flying nearby.

There are some pretty cool photos of this sort of thing on Flickr; this is the best one, and contains a pretty good explanation of what happens:

… Luckily, that setting perfectly captured the full trajectory of this chaotic flight of instability. The rocket had too heavy a motor in the back, a J-class motor in this case if I recall.

For those of use who have set off a bare Estes rocket engine as kids and watched it skip randomly through space, you have a sense of what happened here. You can add a nose cone and some fins to a motor, and it will be still be unstable. You need a proper balance of weight and thrust vectors. … To be stable, the rocket’s CP (Center of Pressure) should be one or two body diameters behind the CG (Center of Gravity).

The fins are there to streamline the flow of air and provide a large surface area and help to keep the center of pressure below the center of mass of the rocket.

This is why I didn’t fly my newest rocket this week; I don’t know where the center of gravity is, and I haven’t tested its stability yet.

Now Playing: Americans in Corduroys from Ghost Repeater by Jeffrey Foucault