Building a Semroc V-2 (part 1)

Last August, Carl McLawhorn died. At the time I was new enough to rocketry not to recognize his name, but I soon found out his significance. I had the Semroc V-2 on my wish list at the time, and as a token of support — as well as out of uncertainty as to Semroc’s future — I bought the kit that week.

This winter it was the oldest un-begun rocket in my build pile. Time to fix that.

This is one of Semroc’s xKits, which means it’s essentially a piece for piece reproduction of a classic OOP kit, in this case the Estes V-2 (K-22 or 1222) produced from 1965 to 1977. According to Semroc’s insert the only changes are laser-cut fins (thank you!!) and a larger washer weight for the semi-scale version.

Here’s what’s in the bag:

IMG_2281

What isn’t in the bag is instructions. Instead they point you to http://www.spacemodeling.org/jimz/k-22.htm (there’s a PDF version at http://www.spacemodeling.org/jimz/estes/k-22.pdf) for a scan of the original Estes instructions.

Another thing that doesn’t come in the bag is a decision: Scale or semi-scale fins? The scale fins give a more accurate appearance, but they’re pretty small for the rocket’s size. The semi-scale fins are larger. Even with those you’re supposed to use the supplied washer to add weight to the nose for stability. With the scale fins the insert recommends “up to 1/2 oz. of weight (not included) … deep into the nose cone”. In a YORF post Carl McLawhorn recommended “1/2 to 3/4 oz weight” in a hole 2.5″ deep and 1/2″ diameter.

All this time I’ve been waffling about whether to use the scale or semi-scale fins. Truthfully I still am, a little, though I’ll probably bite the bullet and go scale. So I figured I’d start by drilling out the nose cone.

That wasn’t bad. I started out with a Forstner bit in my drill press, which got me to a depth of about 1.5″. From there I switched over to a twist bit in a handheld drill, with some blue tape on the bit marking the 2.5″ point so I wouldn’t drill too far and out the far end. Actually I deliberately went a little further, to about 2.75″. I weighed out 3/4 oz (21.25 g) of lead BBs. They’ll fit easily in the hole.

IMG_2282

I haven’t glued them in, though. Later. Keeping options open.

Next, I started following the Estes directions: Glued in the motor block. Next the motor mount tube is supposed to be glued into the boat tail, but first…

It would be an educational experience to build this model exactly as it would have been done in 1965, right up through the educational experience of learning why people don’t build them that way these days. The shock cord mount back then consisted of a piece of gauze which you’d glue over the knotted shock cord inside the end of the body tube. And indeed, Semroc supplies a little square of gauze.

They also supply a piece of Kevlar and a piece of braided elastic! They don’t say anything about that on the insert, but that’s what I got instead of an Estes style rubber band. And that’s fine with me. I decided to follow Dick Stafford’s example and used CA to tack the Kevlar around the motor mount tube.IMG_2286Once that was dry I used a rat tail file to ease the boat tail hole a bit. I spread 30 minute epoxy inside the boat tail, fed the Kevlar back through the the motor mount tube, stuck an empty motor casing inside, and screwed the tube (following the Kevlar spiral) into the boat tail. The trick here is to keep track of which end of the tube and which end of the boat tail is which! After removing the casing and pulling the Kevlar back through, the latter comes out at the wide end of the boat tail, and the motor block is at the same end, so we’re good.IMG_2287

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