Height:  20.5"
Width:  1.14"
Weight:  7 oz
Motor:  29mm
Recovery:  Parachute

Brief:  This is a three-finned, single-staged machbreaker inspired by Impulse Aerospace's Machbuster, but made of lighter materials and greater diameter to allow use of standard 29mm motors.

Construction:  Since its overall length is short, the rocket needed weight in the nose, so I ordered a solid urethane conical nose from Red Arrow Hobbies.  The body tube is 14.5 inch length of LOC MMT 1.14 spiral wound paper tubing.  The launch lug is 1 inch long and is 1/4 inch paper tubing  stock. 

The fins are delta shaped, and are 1/8 inch birch, available in many hobby stores.  I cut it with a band saw.  Epoxy was used to bind them to the body tube, and generous fillits were made.  The fins themselves have a root edge(length that runs along the body tube) of 2 1/2 inches, zero chord edge (it's pointed, thus), and span of 1.75 inches (body tube to the point).  The trailing edge runs perpendicular to the body tube, thus it has no forward or aft sweep relative to it.  The fins were aligned using a measuring tape around the body tube to trisect the circumference and decide where to place the fins. 

The chute is 10 inches in diameter, and is thin nylon material.  There is no spill hole.  It is a 6-gored hemisphere and its 15-inch braided nylon shroud lines are sewn into the seams between the gores.  The shock cord is 2 feet long and is 1/4 inch flat white elastic.  It ties to the hook that came embedded in the nose cone and is mounted to a 1/8 inch wide Kevlar® cord loop  mounted into a folded paper mount inside the main body tube. 

Finishing was unique for sure.  Every other fin face is silvered with Testor's enamel paint.  The other faces are blaze orange Testors.  The body is blaze orange too. and I ran stripes of green, gold glitter, and red [aint up the body tube on one side, with the words in black, "Mach My Words" in the middle of the stripe pattern.  At the top of the body tube is a 1 inch band of holographic silver craft paper available in Michaels and other hobby stores.  This stuff refracts various colors from different viewing angles and helps with visibility.  The nose cone is Testor's enamel red.

Flight:  When I built this, I was inspired more by the altitude claims made by Impulse Aerospace and was tinkering with math to see if minimizing weight would increase altitude.  Well, speed increased dramatically.  On just an Aerotech G35-7, the model took off with a bang.  No, I'm not joking.  It sounded like a gunshot and scared people over a quarter of a mile away.  They came out of their houses to see what the matter was.  So, kids, don't try this in a park.  Do it in the open desert, please.  It flew straight, judging by the straight smoke trail.  Thank goodness for the obnoxious yellow color of the nylon chute, or else I never would have gotten this bird back.  A friend swore that it went up a mile.  I had to get into my car and chase it down the road, recovering it off a golf course.  I apologized profusely to the golfers, who burst out laughing as I left.  Hmmm.  It was undamaged, and the chute unburnt.  However, I think that a longer delay would be better, because I think ejection occurred before apogee, pulling the mount a bit.  I'll try a G25-10 or 14 next time. 

In fact, Rocksim 3.0 predicts that the G25-10 would eject at apogee with an altitude of 6234.32 feet and a speed of 1024 feet per second.  Sheesh!  The program predicts that the Apogee F10-8 will work nicely as well and so will the Aerotech G80-13.  In fact, you'll exceed mach by about 300 feet per second with this motor.  Better epoxy the heck out of those fins!!!

Summary:  Fun to design, rewarding for people who like to dare speed and altitude with a lot of noise.  But don't do this in a park.  It'll cause too much consternation.