Sunday, August 12, 2012

24mm Paper Honest John, Part 2

I made good progress on the 24mm paper Honest John today. As I mentioned in the previous post, I attached three centering rings to the 24mm tube. I didn't fully think out the recovery harness but attached a short Kevlar leader to the top ring so I could keep going.

I recently found a small plastic bottle that I thought would make a good el-cheapo, DIY motor retainer.  I got the idea from Chris Michielssen on his Model Rocket Building blog.. This mainly involves cutting the neck of the bottle off and drilling/grinding a hole in the cap.  I installed a sliver of a spent 24mm case as a motor block. Its location was set using a E9 with the DIY retainer pushed into place. I should have just positioned it with a quarter-inch overhang because the motor is perfectly flush with the motor tube.  This won't affect the rocket's flight but the motor will have to be extracted with a dowel.  Luckily, my range box is pre-loaded with this item.

I attached the neck of the bottle to the motor tube using 5-minute epoxy.  Since I mixed a bit too much, I also used it to tack the motor mount into the tube and slathered the rest inside of the nose cone tip.

After I installed the main fins, I found that they are still fairly floppy despite the fin tabs being attached to the body.  If I build another large paper model conversion, I'll opt for thicker foam board rings.  I had trimmed the top of the body off since it is longer than scale (in the flight position, the nose of the stomp version sits above the scale position so it can slide down on landing). This gave me some spare printed paper.  So, I cut 'L' shaped strips to further reinforce the ends of the fin roots (the fin tabs are shorter than the root).

I ran the Honest John design through RockSim and found it to be quite stable.  However, that changes when an E9 is loaded.  Since the nose cone section has no internal structure, I was concerned about how to install nose weight. I added a small bulkhead near the tip of the cone and one of the laminated 24mm-2.6" rings at the joint of the top two sections of the cone.  I added a short section of 24mm tube to provide a housing for any nose wight that might be needed. By the time I'm done adding bits and pieces to the nose cone assembly, it may not need any extra weight!

I glued another one of the bulkheads in the base of the bottom section of the nose cone.  I guess I'll use another as at the base of the shoulder that I'll be building.  As it turns out, I won't have any spare rings after all!