Brief:
P.H.I.T.S. (Punching Holes In The Sky) is a 29mm single stage minimum diameter Mach buster with chute or streamer recovery.

Construction:
The parts list:

• 34" 29mm heavy wall motor/body tube from Balsa Machining Service
• PML conical urethane nose cone with screw eye
• 3 fins, 1/8" basswood, each with 1/8" square basswood root braces
• Estes BT55 tube coupler (1.25" long)
• 3 Estes 2.75" engine hooks
• 1/4" of 29mm tube coupler for thrust ring
• 1/4" of 29mm tube coupler for shock cord anchor
• 3 feet heavy Kevlar® covered round elastic shock cord
• 3 feet medium Kevlar® covered round elastic shock cord
• Chute or streamer
• Launch lugs
• Screw eye

Next is the shock cords and anchor, which starts with notching the anchor ring on two sides so that ring can fit into tube with shock cord anchor attached. Tie both ends of heavy Kevlar® cord to anchor at opposite sides of ring at notches, then tie slip knot on one end in medium Kevlar®shock cord around loop in heavy shock cord. With a dowel or coupler tube, slide anchor ring all the way into the body tube from the forward end until anchor ring is in contact with the thrust ring and epoxy the ring in place. Tie shock cord to PML nose cone.

For the motor retainer, an Estes BT-55 coupler fits neatly but slightly loose over BMS heavy walled 29mm tube. Mark the coupler for 3 points 120 degrees apart. Cut the top bend off Estes 2.75" engine hooks. Then bend top 1" of hooks over backwards (towards "outside") until bent over double. Place hooks on BT-55 coupler at marks so that the bottom clips face inward. CA clips onto the coupler. Test fit assembly onto the body tube and sand body tube as necessary. Again, use CA to attach BT-55 to body tube. Slide it forward until only 1/4" of motor clips are left hanging over the body tube.

Fins are cut from 1/8" basswood. Also, 6 strips 1/8" wide are cut to serve as root braces. These strengthen the body/fin joint by increasing contact area by a factor of 3 and provide additional strength by being anchored under epoxy fillets. Fins are beveled sharply with the ends of the braces beveled top and side away from fin. Braces are glued to each side of fin root with CA and with additional sanding of bevels extending line smoothly from fin, across brace. Once the fins and braces are constructed, wrap rough sandpaper around body tube with the grit facing out, and sand fin/brace root to fit curvature of tube. Fit the fins against the aft end of tube over retainer ring with the end of each fin even with end of tube. Mark fin root on each side where fin root meets forward and aft ends of retainer ring (ring makes tube thicker at this point). Use rough sandpaper taped to sanding block or emery board to sand notch in fin/brace root until fin sits tightly against body tube and retainer ring with sharp transition between the two heights. Mark body tube for three fins, 120 degrees apart and between engine hooks on retainer then glue fins in place with CA. Lay fin fillets in two layers--first layer in two parts between fin and brace and brace and tube. The second layer is a smooth layer over the top of the previous fillets, completely submerging the edge of the brace.

Lug placement requires locating between fin and an engine hook. I used two 1" pieces 1/4" styrene tube (3/16" ID), beveled sharply and tacked to the tube with CA. Small wedges of basswood were cut to act as fillet fillers. These were tacked against tube and lug with CA followed by epoxy on top to form a smooth, round, button shaped fillet.

Finishing:
I used one thin layer of white primer, one layer of white satin finish for filler/smoothing, and one layer of black Rustoleum appliance epoxy. I cannot recommend this paint enough. It is tough as nails, resists scratches and scuffs, has a finish more glossy than glossy paint, and I'd swear it glues the entire rocket together better (see flight reports). It is heavy, so it's not the best thing for a Mach buster but the strength was worth the weight trade off.

Flight:
First flight, E9-6 in 24 to 29mm adapter with mylar streamer. Estimated altitude 600 feet. Ejection at apogee, good deployment, fast descent, no damage.

Second flight, F20-7 with 12" mylar chute with spill hole plus tracking smoke. Estimated altitude 1000 feet. Ejection at apogee, good deployment, fast descent, no damage.

Third flight, F21-4 with 12" mylar chute with spill hole plus tracking smoke. Ejection before apogee and lost chute. Rocket came in hot, trailing the nose cone, and lawn darted at very high speed. I felt the thud in ground 50 yards away. Shock knocked engine adapter out of retainer and it landed 30 feet away. Rocket was embedded straight down 6" into hard packed black dirt and grass turf. Pulled rocket straight out. Tube suffered some shock cracks in paint along spiral but no bending or weakening of the tube is detected. The part below ground wiped off to its original gloss. The packed in dirt and grass inside the tube was knocked out with a 1/4" launch rod. There were no marks at all on the nose. This is what I mean about the durability of appliance epoxy paint.

The cracked paint will be sanded off with CA run into the spiral marks and the body repainted. I predict no problems due to the crash.

Summary:
This is one tough bird. It was built to handle Mach+ forces and it can handle much more.

One downside is that I used a 3/16" lug, which might bother some RSOs when I use larger engines, but it does not whip on a 4 foot 3/16" rod since it takes off so fast.