Swing Test

Okay, I've been building new additions to the fleet, you know this. I went to swing test my newest creations this evening.



It's a safety thing. I recall from the Handbook of Model Rocketry this calculus of the center of gravity and the center of pressure. The CG has to be behind the CP , if recall. I couldn't do the math. I'm sure I should be able to, but I'm not the actuary in the family, I'm the so-called artist.



But this swing test, it was the empirical demonstration of this math. And it seems like when I tried it on Dudley, He Who Must Not Be Named and Mardi Gras, that I was relieved to see they all went nose first.



What you do, and again, I'm going on memory here, is you find the balance point, which is the CG. Put a motor in and see where it balances. Tie twine around it at this point, secure it with a bit of tape, and start running it around your head like a lasso. If it flies nose first, you're in business. If it flies backward or sideways, Houston, We Have A Problem. Because when you launch, you'll have the motor propelling it forward at a huge speed and at the same time the model wanting to fly ass first. This leads to what is referred to as an unstable flight.



Or what NASA might call an anomaly. Not one as spectacular as the pros get, but when I take my kids and rockets to the park, I don't aim to fly anything into some kid's face.

So I did Crayola, and it flew ass first. Okay, I'll have to put nose weight into it, not a huge surprise with its balsa nose cone. But then Plaster, the big pink and black monster, flew sideways. Then Sunflower (the tallest rocket I've built to date, almost as tall as Em is) flew ass first. Ditto the Gardner Snake (which has a bulge in its middle, a double boat tail design like it had eaten a rocket of somewhat larger diameter).



Thing is, when I first learned of swing tests and what they demonstrate, I had already done from scratch designs that flew just fine. It was a relief to see my next-in-line models pass the test. But now, with everything I've built this spring failing, I wonder if I remember the test correctly. Maybe I'm supposed to be slightly ff the CG with my twine or something.




I have the trial version of RockSim downloaded from Apogee, but I've never been able to figure out how to use it. And in any case, my thirty days were up last October or so, and I probably couldn't even fail to evaluateCP versus CG with it today.

Oh, and when I tried to get Em to pose with a rocket, she decided to make as many faces as she could for you.

Meanwhile, the girls had McDonalds for dinner. This is truly rare. I don't eat out with them often, and when I do I avoid the Golden Arches. Nasty stuff, on the whole, and expensive to boot.




But Mo had a couple of gift cards to there from her birthday, and she and Em are too young to get all snobbish on Mickey-D's.



Then Mo wouldn't eat her dinner. For the longest time. Then, after ignoring it for a couple hours, after we'd gone outside to swing test rockets and otherwise play, she made her move.



Em had used the white plastic table to climb into a tree, and Mo went and grabbed the white plastic table. While Em, stuck up the tree, claimed her sister was just
being mean, Mo set the table by the toy plastic chair. She then went in the house and came out with her McDonalds, and proceeded to have a picnic to the consternation of her tree-bound older sister.