A few weeks ago I completed the construction of my newest rocket: The MachMobile38. The MachMobile38 is a minimum diamter 38mm rocket, capable of flying on anything from an E to 800 feet, to a large I motor to around mach 1.8.
The MachMobile is both light and strong. It weighs around 7oz and is capable of flying on most E motors. The tube is a 1.5in shipping tube with 2 wraps of 6oz fiberglass. The fins are 1/8in plywood sandwiched between a layer of 6oz fiberglass. The nosecone is the LOC Precision 1.5in plastic one.
The finish looks great! Nice and smooth and the fiberglass covers the spirals in the cardboard tubes nicely. However, it didnt always look that way. The fiberglassing was very rough. The upper (payload) tube was the hardest. I peeled off a few layers of cardboard before beginning to glass. Big mistake. The inconsistency in the tube created air bubbles in the fiberglass layup and peel ply. In some parts of the tube the ply didnt touch the fiberglass, leaving a rough texture.
The bottom tube went a little more smoothly. I used teflon coated peel ply from Aircraft Spruce. It didn't leave a peel ply texture. However, The Teflon coated ply wouldn't absorb epoxy and the fiberglass was not fully saturated so I got lots of little air bubbles where the epoxy should have been.
Next up was the fins. I laminated 2 peices of 6oz fiberglass to some 1/8in crap-plywood and clamped them between a board for eight hours. Voila' 3 stiff, light fiberglass and lite ply fins. Nice and strong.
I tacked the fins in with 5 minute epoxy using a fin guide.
Next up was fillets. I wanted to deviate from the normal route of 30min epoxy and go with a stronger solution. The fillets are chopped carbon fiber and proline 4100 epoxy. Carbon fiber fillets are the strongest kind commonly used so why not! I need these fins to be strong to stand up to the mach monster. I chopped up some carbon fiber and mixed it with epoxy until it turned into the black sludge of death. This was smeared along the root of the fin and the body tube. Lastly, I used a dowel and parchment paper to form the fillet shape. The one drawback to carbon fiber fillets are: they are REALLY UGLY. The carbon fiber hardens rock solid and is darn near impossible to sand.
Finishing these fillets was pretty treacherous. First, I wrapped sandpaper around the dowel that I used to originally make the fillets. I slid the dowel up and down the fillet to get rid of any high spots. After this, a second fillet of Bondo body filler was applied. Automotive filler can bu used for just about any rough spot in the rocket's body. You smear it on and sand it down after it cures. After the bondo had cured on my fins I wrapped sandpaper around the same dowel and began sanding again. I repeated the process with any rough spots in the tube.
I primed the rocket with Rustoleum 2x primer and wet-sanded.
I gave it 2 coats of Rustoleum gloss orange
I added some monokote trim for a little visibility. Looks nice!
Next up was the decal. To make these you just need a little time, patience, a sharp hobby knife and some monokote.
Finished!
This will fly at Hellfire on an H400 vmax. I should get about Mach 1.3 out of it. That, plus a 4500ft flight would make it a pretty impressive flight.
Thanks for reading!
