On the bevel

On most of the rockets I’ve built so far, the leading edges of the fins are rounded. On some the trailing edges are too… maybe even the tips. Generally that’s as ambitious as I’ve gotten with fin shaping.

The exception, which may seem odd, was the Tail Burner Habanero. I had a reason. The supplied ⅛” balsa seemed way too chunky for such a little rocket, so I decided to make lemonade by beveling the trailing edges.IMG_3094

I thought the results looked pretty good.IMG_3218

But that’s as far as I’ve gone, until today.

Here’s my first attempt at a fully tapered fin:IMG_3621

I found Chris Michielssen’s article in Peak of Flight #357 pretty helpful. This fin certainly isn’t perfect. For one thing I was too aggressive on the leading edge and ended up making it too sharp — the edge is so thin, I’m sure it’d splinter if someone looked at it crosswise.

Not that I’m going to use this fin on a rocket. That wasn’t the intention. This was just a practice piece.

So what am I doing this for? Well, I’d had a thought. A thought about putting tapered fins on an Excelsior Honest Goon.

A ridiculous thought, right? But goonies are supposed to be ridiculous.

The instructions don’t call for tapered fins, of course. The instructions don’t even call for rounding the leading edge. (Nor do the instructions for the Baby Bertha kit one normally would bash into a goony.) But I figured it might be a fun idea, for certain values of fun.

Then I took another look at the Honest Goon and said “Oh… yeah…”. The fins, unlike those on an Honest John, are mounted with the trailing edge back behind the body tube, and the Honest Goon is a much heavier rocket than the Tail Burner Habanero. Tapered trailing edges would have a life expectancy of about 0.9 flights.

Okay, so it was too ridiculous a thought even for a goony. But at least now I’ve had some practice at fin tapering. Who knows, maybe I’ll make an Honest John sooner or later.



2 thoughts on “On the bevel

  1. HI Rich,
    Thanks for the acknowledgement and link to the Apogee POF.
    I may have mentioned in the Apogee article, it takes a few tries to get it right.
    Sometimes I make extra fins and pick the best ones for the model.
    You are on the right track though! Just don’t make the edges too thin!

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