On oldrocketplans.com they have the old Centuri Nike Smoke instructions with a fin scan and ruler.
I dropped the picture into Corel Draw and messed with the sizing until the 1" ruler matched a 1" square box I drew. This got the fins size close to the Estes kit fin size.
From the Centuri instructions the fin taper measurements are shown.
The fin root edge is 1/8" thick and tapers to 1/16" at the outside edge.
I had never looked that close before and didn't realize the "diamond" taper line doesn't go to the outside corners. It starts 1/8" in from the leading and trailing corners.
The balsa grain direction runs parallel to the leading edge in the older Centuri model.
On the Estes kit the grain runs straight at a 90 degree angle to the root edge.
The Estes fin has two places where the corners could easily pop off when sanding the taper.
These are just observations. The fins are hard enough to sand to a scale taper. Most builders will probably just round the leading and trailing edges anyway.
Nike Smoke fin shaping is coming up!
Would you like a set of fins to do for the blog? I would happily loan you the fins from Danielle's kit. :)
ReplyDeleteThanks Metalhead -
DeleteBut, no! I'm just doing the one fin as an example of how to sand the correct taper. If I were Danielle, I'd cut new fins out of a slightly thinner 3/32" stock and just round the leading and trailing edges. Sharp, thin fins like this (if fully scale tapered) are just looking for nicks and dings on a hard landing.
So, I now have four 3/32" fins cut, papered and ready to be sanded. Instead of rounding the edges, I will probably put a little bevel on them, so they has some semblance of the intended shape. I will keep the kit fins for another time.
DeleteI managed to get a nice bevel and radial taper on a scratch rocket I built. I built up the fins from 1/16 inch basswood with 1/32 inch balsa skins. The difference in color of the woods made it easy to sand the taper correctly. I was surprised how easy it was. The fins were also quite strong. And I got a shape like the one above, with a nice straight edge on the fin where the bevel starts.
ReplyDeleteI need to do a post about that build, because I think people might find it useful, and it was not as hard to do as I thought it would be when I decided to try it.
Hi Daniel,
DeleteI've tapered plywood fins before and the sanded layers of wood can give a good reference (color change) for the thickness of the the fin.
Making fins like this can be rewarding if the builder slows down and doesn't give up after the first try.
I would like to see your technique Daniel. There is always more than one way to shape a fin.
DeleteSteve