This is a Skill Level 1 rocket that really doesn’t need any sort of detailed build description, except that I wanted to document how I modified the motor mount for a replaceable Kevlar shock cord leader.
I won this kit at last month’s club launch’s helicopter duration contest. Since the Razor kit has “pre-finished” tubes it doesn’t need painting, so I decided to put this together now for possible launch in our club’s demo at Walt’s Hobbies’ Secret Santa Sale later this month. (“Pre-finished” is in quotes, because, yes, the tubing is yellow, but it also has very visible spiral seams, and the insides of the tube fins are unfinished. And that’s just how it’s going to be.)
Like the Bohica’s Dead Ringer, this is a BT-50 rocket with an 18 mm motor mount, so doing replaceable Kevlar is a little tricky; I tried a slightly different approach this time.
Yes, there are decals, or rather stickers; they were still tucked into the instructions when I took the picture.
I started off by marking the motor mount tube for the positions of the centering rings, motor hook, and guide straw. Then I put a 1/4″ wide strip of blue tape along where the motor hook and guide straw will go.
I had a spent motor casing in the tube to prevent deforming it. Usually when I make a motor mount I put the forward centering ring flush with the end of the tube, but the Razor instructions have you put it 1/2″ back, and I decided to do that. They also have both rings going over the motor hook, with no notching or filing, which strikes me as odd.
Next I cut notches in the rings to accommodate the motor hook and guide straw. This is the first time I’ve done it in this order. Cutting the rings after they’ve been glued down keeps them from expanding and not fitting into the body tube. But I’m not happy about doing it this way; seems too dangerous. I didn’t do any damage to the motor tube, but that may have just been luck. I’m hoping there’s a better solution to the expansion problem.
I put the motor hook in place, secured it with duct tape, and glued down the guide straw. In the past I’ve used yellow glue for the straw but today it didn’t seem to want to hold very well, so I used CA.
I installed the motor mount, using as before a piece of blue tape over the guide straw to keep epoxy out of it. And then I realized there was a problem: with the centering rings both cut to accommodate the motor hook, there’s a fairly large opening the full length of the motor mount. That’s not good; it may prevent the ejection charge from creating enough pressure to push the nose cone off. Had the forward ring been flush with the tube end, as on the Dead Ringer, essentially the only opening would have been the guide straw which is small enough not to cause trouble. And I’m having trouble thinking of a way to plug the forward hole without plugging the guide straw too. The rear hole, maybe, can be plugged with glue soaked paper. I haven’t done that yet but I might try it.
I attached the tube fins and launch lug, applied the stickers, and glued the nose cone together more or less per the instructions. Then I ran a piece of 100 lb Kevlar through the guide straw and out the forward end of the body tube.
I tied the kit elastic to the Kevlar,
then pulled the Kevlar back until the knot was just inside the top of the body tube. I marked the Kevlar with a Sharpie at the base of the motor tube.
Pulling on the forward end of the Kevlar tightened it around the motor tube securely.
And that’s it. Check out the ugly fillets on the tube fins! I forgot Titebond No-Drip No-Run dries brown. Between that and the body tube spirals and the unfinished insides of the tube fins this one will win no beauty contests. But, hey, it’s a rocket.