I got my G12 motors a couple of weeks ago, and Northern Colorado Rocketry is finally going to get to launch this weekend (albeit at the Atlas site with a 12k waiver), and I have a new and improved tower, so let's make a record attempt rocket!
I have a mandrel for a nice skinny Von Karman nosecone, and a very worn-out silicone mold, but I'm going to take the easy way out for now and just use the Apogee 29mm plastic cone. If the altitude is disappointing I'll invest the time to work on a the VK. I think I'll want it for the H record attempt because of its faster max speed.
For tubes, the Apogee 29mm cardboard tube isn't a bad choice. After all, it appears to have been used for the H record recently. It weighs almost exactly 1 gram per inch in length. Today I made my own thin-wall carbon tube so that I could integrate a little boat tail, and sand it down smooth. I'm also curious how the mass compares. For the mandrel, I'm using a CTI 6-grain case with a tapered rear closure, covered with mylar:
This time I remembered I needed to tape the mylar together with the sticky side out. For the tapered rear closure, I used some separate flash-breaking tape and a bunch of grease between the closure and the motor case. I taped the mylar down at the other end to make sure I didn't get any epoxy underneath it.
Next, a simple single-layer braided sleeve. I taped it down at the forward end, which I will discard. Taping it down helps to stretch it lengthwise to take out the slack. The +/- 45 degree fiber orientation is far from ideal, but in this application we're talking about a cardboard replacement where it's not going to be stressed much at all. It just needs to be light and smooth.
After the shrink tube:
I used Soller 1.25" light carbon sleeve, and one of their shrink tubes, which did a pretty nice job on this tube. I taped it on the front end and found that it helped to keep some tension on it while I used a hot air gun to shrink down the tube, which went down smooth and pushed the epoxy along the length of the tube as I went. But every layup has to have some moment of desperation. In this case I let the excess epoxy pool up at the back and, and then when I tilted the tube the other way, the epoxy ran down inside the motor case that I'd like to use again. I washed it out with some acetone and a bottle brush while the wet layup was still going on the outside.
I the tube into the oven at 125F, went out to put up Christmas lights, and came back in to a finished tube that came off the mandrel pretty easily. After I pulled out the mylar, the tube came out to 12.8 grams for about 12" of length. So no mass savings over the cardboard tube, but the boat tail is already taken care of.
Packing in the electronics is where things will get interesting, but that's for tomorrow. I'll be using a Featherweight GPS Tracker and a Blue Raven prototype altimeter.
I have a mandrel for a nice skinny Von Karman nosecone, and a very worn-out silicone mold, but I'm going to take the easy way out for now and just use the Apogee 29mm plastic cone. If the altitude is disappointing I'll invest the time to work on a the VK. I think I'll want it for the H record attempt because of its faster max speed.
For tubes, the Apogee 29mm cardboard tube isn't a bad choice. After all, it appears to have been used for the H record recently. It weighs almost exactly 1 gram per inch in length. Today I made my own thin-wall carbon tube so that I could integrate a little boat tail, and sand it down smooth. I'm also curious how the mass compares. For the mandrel, I'm using a CTI 6-grain case with a tapered rear closure, covered with mylar:
This time I remembered I needed to tape the mylar together with the sticky side out. For the tapered rear closure, I used some separate flash-breaking tape and a bunch of grease between the closure and the motor case. I taped the mylar down at the other end to make sure I didn't get any epoxy underneath it.
Next, a simple single-layer braided sleeve. I taped it down at the forward end, which I will discard. Taping it down helps to stretch it lengthwise to take out the slack. The +/- 45 degree fiber orientation is far from ideal, but in this application we're talking about a cardboard replacement where it's not going to be stressed much at all. It just needs to be light and smooth.
After the shrink tube:
I used Soller 1.25" light carbon sleeve, and one of their shrink tubes, which did a pretty nice job on this tube. I taped it on the front end and found that it helped to keep some tension on it while I used a hot air gun to shrink down the tube, which went down smooth and pushed the epoxy along the length of the tube as I went. But every layup has to have some moment of desperation. In this case I let the excess epoxy pool up at the back and, and then when I tilted the tube the other way, the epoxy ran down inside the motor case that I'd like to use again. I washed it out with some acetone and a bottle brush while the wet layup was still going on the outside.
I the tube into the oven at 125F, went out to put up Christmas lights, and came back in to a finished tube that came off the mandrel pretty easily. After I pulled out the mylar, the tube came out to 12.8 grams for about 12" of length. So no mass savings over the cardboard tube, but the boat tail is already taken care of.
Packing in the electronics is where things will get interesting, but that's for tomorrow. I'll be using a Featherweight GPS Tracker and a Blue Raven prototype altimeter.
