I finally finished my rendition of the Crossfire DX. Instead of starting a new build thread I thought I'd just put a mini-build here--hope nobody minds.
Conical Nose Cone
I decided to do mine with BT-55 so that I could keep the transition on the bottom of the rocket. I have a hefty supply of low-power stuff, body tubes, couplers, nose cones, etc., but I did not have a conical nose cone for a BT-55, so that had to be handmade. I will try and attach a pdf with the template below.
I use the usual roll the bristol paper over ever smaller dowels to get the curvature, but I could never stick a tab in a single step, so I work my way up from the bottom, taping as I go and then glue a tab on from the inside with the tape and some rubber bands holding everything in place. I follow that up with a soak in thin CA. Sand. I epoxied the bottom of the nose to some BT-55 to keep the curvature right.
I've never made a paper nose cone before, but I did make a really long boattail once and it looked good for awhile, but eventually somehow got out of round. As a safeguard, I used the template again and glassed the nose. (8.5 oz, west systems). After a full 24 hour cure, I sanded and filled any gaps with epoxy clay and finally applied a thin layer of my usual filler (Equal parts West Systems epoxy, colloidal silica, and phenolic microballoons).
After that cured I sanded until it looked right. Finally, primer and paint red.
Transition
I used a section from a BT-55 elliptical nose cone for the transition/inverse boattail at the bottom. That's 1/4" pin striping for the cutting mask--works nicely on non-uniform surfaces like nose cones and boattails.
Motor Tube and Motor Retention
I decided to put in a motor retainer (24 mm) because I had one and I don't often build 24 mm. I configured the motor tube to accommodate up to 90mm of motor but did put in an engine block so that I could fly motors like the D-12 that doesn't have a thrust ring--just add a couple of spacers and screw on the cap. The centering rings are from an Estes Designer's Set.
Fincan
I decided to make these through-wall fins. I used the fin guide from openrocket to cut the slots into the body tube after I epoxied in the motor tube. I just wasn't in the mood to fill and prime so I papered the fins (even the strakes). The procedure I have outlined elsewhere, but basically rubber cement on both fins and paper, let dry a few minutes, slap on the fins, using the fins as a guide cut the paper. Do the same for the other side. Let soak in thin CA and once it dries, sand until smooth (120 followed by 320 grit).
I used a posterboard fin jig to mount the fins. For fillets I used dripless carpenters glue and one-at-a-timed them, because it does drip a little. Also had to do a little filling with Bondo glazing and spot putty. After the fins were cured, I attached the strakes with wood glue. Fins are 1/8" basswood. Strakes are 1/8" balsa.
Final Product
It came in at 513 mm long, a gross weight of 131 grams, and a margin of 2.56. I added clay to the nosecone before attaching the bulkhead (1/8 basswood) to match the margin on the Crossfire ISX. Any details missing from this mini-build, assume they were standard practices.
Here's a side-by-side of the ISX and DX. I couldn't get the waterslide decals to look very gray. They came out a bit bluish despite having designated the color as black with transparency, killing off the C,Y,M values entirely.
I'll post a video of its maiden flight when that happens. Probably fly it on a D12 first. Openrocket sims suggest a D12 would take it to almost 700 feet, but a G55 might see 2700. I used the square fin profile instead of rounded because of the drag from the strakes, so the apogees could be higher.