Super Big Bertha-- Part 4: Odds and ends
The Thrifty Rocketeer continues...
While my fins dry, I thought I might address a few other items that can be prepared in preparation for the next step.
First, the kit came with two body tubes. We've been working on the bottom body tube, while the top half has been waiting patiently until now.
If you've not already done so, try fitting both the nose cone in one end, and the coupler in the other. I personally prefer to orient my body tubes so that if not perfectly round, the coupler or the body tube will stiffen and reform that roundness.
I also chose to insert half the coupler into the top body tube with a layer of wood glue smoothed on the inside of the body tube, instead of applied to the coupler. The difference is where the squeegeed glue winds up. Instead of being piled up on the coupler, it is shoved further into the tube. It doesn't hurt if it dries there. But if it's on the coupler, it could leave a ridge or form a separation between the two body tubes.
When preparing the nose cone, about the only thing needed is to very carefully slice and remove the plastic spacer that is left inside the anchor ring. You don't want to nick nor slice this ringlet where you will secure the shock cord. But by carefully stabbing the bubble of plastic spacer where thinnest, you can perforate it and allow your thumbnail to flex it and swing it out to be discarded. You may also want to write contact information with a Sharpie marker on the bottom inside shoulder of the white plastic nose cone. It will not be visible until after the nose cone is ejected.
If you're using the Estes shock cord, you can secure one end with a double knot to the nose cone, and secure it with a drop of glue. Some people prefer to replace the shock cord with a line of Kevlar string, or go half and half. That's up to you how to secure it at this late stage of the construction, if you haven't pre-planned it.
The other end of the shock cord is normally secured by a Tea-bag anchor glued inside the throat of the body tube, at least 1 3/4" inches down from the lip. This is to allow room for the nose cone to nest inside the body tube without impacting the anchor. Estes supplies a card stock anchor to be tri-folded over the end of the shock cord and glued with wood glue. Hence, the name "Tea-bag", as that's what it resembles. While the glue is still soft, mold the anchor into a semi-circle so that it will contact as much of the interior body tube as possible. And as the internal glue begins to set up, use additional glue to hold the anchor into place, holding it with your thumb or longest finger in place, again, at least 1 3/4" down inside the tube. (The instructions specify three inches.) Let dry.
If you haven't considered rail buttons, we're probably too far along to seriously consider them instead of launch lugs. The instructions indicate the launch lugs are placed along the line between two fins, one half inch up from the bottom lip of the body tube. The second one is 12 inches up from the bottom. I presume these are the best points, based upon CP and CG for the rocket, as designed and constructed.
Note: while you haven't glued the coupler into the bottom body tube yet, you still have access to the interior of the bottom body tube. Likewise, if you hadn't positioned the centering rings and glued them in, you have access from the bottom. But since we've already passed that stage, the only option I can see for adding rail buttons would be in that 1/2" lip next to the "tail pipe" but far enough away from that end of the motor mount so as not to block the screw-on motor retainer.
If you're going to add rail buttons, you can do so using almost the same measurements as the launch lungs. The top one should be along another line, 12 inches from the bottom. The bottom rail button will be as close to the centering ring as you can get it, along the 1/2" lip. You'll want to anchor these machine screw rail buttons into some scrap wood that gets glued in place along the interior wall of the body tube. Remember to sand those scrap pieces so they are smooth and will not snag or restrict the shock cord nor parachute from deploying.
And speaking of that screw-on motor retainer... the instructions tell you to rough up the interior surface of the male threaded piece so that epoxy glue will adhere better. I chose 220 grit sandpaper to wipe around and roughen the surface. I also chose 15 minute BSI epoxy glue to secure it in place. DO NOT GET THE EPOXY IN THE THREADS. And I would apply the epoxy (once mixed) sparingly to the exterior of the motor tube (tail pipe). This will allow the plastic threaded end to slip over the tube and squeegee the excess epoxy down to the centering ring where it can help secure the device. Let dry.
Now, I've ignored the placement of the parachute (typically 1/3 of the way down the shock cord), and not covered how to attach the two halves of the body tube by spreading glue on the inside 1 1/2" of the bottom body tube. I figure both of those steps are easy enough for you to accomplish on your own. I would use wood glue for both of these, and the launch lugs.
But I'm going to go back and attempt rail lugs just as a challenge, so I've held off on this last step. And then priming, painting and decals.... all waiting for us next installment.
Don't forget to cap your glue bottles and save your excess balsa scraps!
While my fins dry, I thought I might address a few other items that can be prepared in preparation for the next step.
First, the kit came with two body tubes. We've been working on the bottom body tube, while the top half has been waiting patiently until now.
If you've not already done so, try fitting both the nose cone in one end, and the coupler in the other. I personally prefer to orient my body tubes so that if not perfectly round, the coupler or the body tube will stiffen and reform that roundness.
I also chose to insert half the coupler into the top body tube with a layer of wood glue smoothed on the inside of the body tube, instead of applied to the coupler. The difference is where the squeegeed glue winds up. Instead of being piled up on the coupler, it is shoved further into the tube. It doesn't hurt if it dries there. But if it's on the coupler, it could leave a ridge or form a separation between the two body tubes.
When preparing the nose cone, about the only thing needed is to very carefully slice and remove the plastic spacer that is left inside the anchor ring. You don't want to nick nor slice this ringlet where you will secure the shock cord. But by carefully stabbing the bubble of plastic spacer where thinnest, you can perforate it and allow your thumbnail to flex it and swing it out to be discarded. You may also want to write contact information with a Sharpie marker on the bottom inside shoulder of the white plastic nose cone. It will not be visible until after the nose cone is ejected.
If you're using the Estes shock cord, you can secure one end with a double knot to the nose cone, and secure it with a drop of glue. Some people prefer to replace the shock cord with a line of Kevlar string, or go half and half. That's up to you how to secure it at this late stage of the construction, if you haven't pre-planned it.
The other end of the shock cord is normally secured by a Tea-bag anchor glued inside the throat of the body tube, at least 1 3/4" inches down from the lip. This is to allow room for the nose cone to nest inside the body tube without impacting the anchor. Estes supplies a card stock anchor to be tri-folded over the end of the shock cord and glued with wood glue. Hence, the name "Tea-bag", as that's what it resembles. While the glue is still soft, mold the anchor into a semi-circle so that it will contact as much of the interior body tube as possible. And as the internal glue begins to set up, use additional glue to hold the anchor into place, holding it with your thumb or longest finger in place, again, at least 1 3/4" down inside the tube. (The instructions specify three inches.) Let dry.
If you haven't considered rail buttons, we're probably too far along to seriously consider them instead of launch lugs. The instructions indicate the launch lugs are placed along the line between two fins, one half inch up from the bottom lip of the body tube. The second one is 12 inches up from the bottom. I presume these are the best points, based upon CP and CG for the rocket, as designed and constructed.
Note: while you haven't glued the coupler into the bottom body tube yet, you still have access to the interior of the bottom body tube. Likewise, if you hadn't positioned the centering rings and glued them in, you have access from the bottom. But since we've already passed that stage, the only option I can see for adding rail buttons would be in that 1/2" lip next to the "tail pipe" but far enough away from that end of the motor mount so as not to block the screw-on motor retainer.
If you're going to add rail buttons, you can do so using almost the same measurements as the launch lungs. The top one should be along another line, 12 inches from the bottom. The bottom rail button will be as close to the centering ring as you can get it, along the 1/2" lip. You'll want to anchor these machine screw rail buttons into some scrap wood that gets glued in place along the interior wall of the body tube. Remember to sand those scrap pieces so they are smooth and will not snag or restrict the shock cord nor parachute from deploying.
And speaking of that screw-on motor retainer... the instructions tell you to rough up the interior surface of the male threaded piece so that epoxy glue will adhere better. I chose 220 grit sandpaper to wipe around and roughen the surface. I also chose 15 minute BSI epoxy glue to secure it in place. DO NOT GET THE EPOXY IN THE THREADS. And I would apply the epoxy (once mixed) sparingly to the exterior of the motor tube (tail pipe). This will allow the plastic threaded end to slip over the tube and squeegee the excess epoxy down to the centering ring where it can help secure the device. Let dry.
Now, I've ignored the placement of the parachute (typically 1/3 of the way down the shock cord), and not covered how to attach the two halves of the body tube by spreading glue on the inside 1 1/2" of the bottom body tube. I figure both of those steps are easy enough for you to accomplish on your own. I would use wood glue for both of these, and the launch lugs.
But I'm going to go back and attempt rail lugs just as a challenge, so I've held off on this last step. And then priming, painting and decals.... all waiting for us next installment.
Don't forget to cap your glue bottles and save your excess balsa scraps!
Comments
Post a Comment