We're still in the thick of the summer heat here in the desert Southwest. To pass the time, I'm taking on another kit, this time the SA-14 Archer from North Coast Rocketry. I was actually looking at two other NCR kits—the Bounty Hunter and the Lance Delta—and was trying to make up my mind between those two when I took a look at the Archer. I liked the fin shape, and man, check out those strakes. Sign me up.
The kit has nice body tubes (LOC tubes maybe?)—a 24" lower and 10" upper—with clean, straight fin slots. The coupler and motor tube are thick-wall. Wood parts are decent—a little warping on the fins and strakes, and some splintering on one leading edge, but nothing serious.
The kit has a shock cord system NCR is famous for—an .063" steel cable 18" long that anchors to the aft CR, then 12' of braided Aramid cord (looks like 2mm), and, at the top end, 4' of 1/2" black elastic, which would stretch to around 12'.
Full-color stickers and instructions compliment the kit.
I weighed and measured all components, then entered that data into the OpenRocket design file I had already started. Then I plugged in two motors—the AT G-74-6 and AT G80-7—to check stability. It's overstable on both—2.82 on the G80, and 3.03 on the G74. And it pitches quite a bit in the sims.
I had been thinking about narrowing the fin semispan from the first time I saw a picture of the rocket. I liked the shape, but it stuck out too far for me. Now, with an accurate OR file to run comparisons, I cut the semispan from 5.35" down to 3.45", then ran the sims again. Stability with the G74 dropped to under 2.00, and pitch rate was cut in half.
So, I'm running with that. Once I had the fin shape where I wanted it, I printed out a template and marked the fins. I planned on using a razor saw to do the cutting, so I set up a guide with a straight edge and a clamp. Then I made a couple of passes with a heavy hobby knife, making it easier for the razor saw to settle in without jumping out of the cut.
These turned out nice, with smooth, straight cuts.
Then I clamped the fins and block sanded the edges to even everything up.
The kit has nice body tubes (LOC tubes maybe?)—a 24" lower and 10" upper—with clean, straight fin slots. The coupler and motor tube are thick-wall. Wood parts are decent—a little warping on the fins and strakes, and some splintering on one leading edge, but nothing serious.
The kit has a shock cord system NCR is famous for—an .063" steel cable 18" long that anchors to the aft CR, then 12' of braided Aramid cord (looks like 2mm), and, at the top end, 4' of 1/2" black elastic, which would stretch to around 12'.
Full-color stickers and instructions compliment the kit.
I weighed and measured all components, then entered that data into the OpenRocket design file I had already started. Then I plugged in two motors—the AT G-74-6 and AT G80-7—to check stability. It's overstable on both—2.82 on the G80, and 3.03 on the G74. And it pitches quite a bit in the sims.
I had been thinking about narrowing the fin semispan from the first time I saw a picture of the rocket. I liked the shape, but it stuck out too far for me. Now, with an accurate OR file to run comparisons, I cut the semispan from 5.35" down to 3.45", then ran the sims again. Stability with the G74 dropped to under 2.00, and pitch rate was cut in half.
So, I'm running with that. Once I had the fin shape where I wanted it, I printed out a template and marked the fins. I planned on using a razor saw to do the cutting, so I set up a guide with a straight edge and a clamp. Then I made a couple of passes with a heavy hobby knife, making it easier for the razor saw to settle in without jumping out of the cut.
These turned out nice, with smooth, straight cuts.
Then I clamped the fins and block sanded the edges to even everything up.