NOTE: While the basic design has flown, some tolerances and features have been changed since the initial version. These changes have not been test printed, but should improve the fit and durability of some parts.
Checked Baggage, named for its notional method of transport to launches, is a medium complexity high-power model rocket. It is designed to fly on 38mm rocket motors. The motor mount is designed to have a short section of Blue Tube or other suitable 38mm motor tubing glued into the mount as thermal protection. A “No Insulator” motor mount that does not use the insulating tube is included but has not been tested. A rail is required for launching this model.
Additional required materials:
- One 4” x 3 foot Shipping Tube
- Masking tape
- Thin superglue
- 15 feet of 5/16 tubular nylon or equivalent
- Suitable parachute (48 to 60 inch)
- 38mm Blue Tube or equivalent (possibly optional)
- Two (2) #6-32 x 5/8” Phillips Flat Head Screws
- Thirty-five (35) #6-32 x 3/8” Phillips Flat Head Screws
- Thirty-two (32) #6-32x 1/2” Socket Head Screws
- Sixty-nine (69) #6-32 Heat-Set Inserts (McMaster-Carr P/N: 93365A132 or equivalent)
- Pen or pencil
- Drill bits for #6 screws
It is recommended to print all rocket components using PETG. All components are able to be printed without support material. The Top Solid layer, Bottom Solid layer, and Perimeter Shell settings were set at 4 with a 50% rectilinear infill.
The airframe is a 4-inch diameter, 3-foot long shipping tube purchased from Staples. Any tube will work, as long as the inside diameter is 4 inches with a wall thickness of around 0.1 inches.
The first step is drilling the screw holes in the cardboard airframe. Mark out the hole locations for the 32 fin attachment screws, the lower rail button, and the 8 recovery hardpoint attachment screws. The base of the recovery hardpoint should be around 20 inches from the base of the body tube, and should be clocked so set of screw points is inline with the rail button screw point on the motor mount. Drill and deburr the holes out so a #6 screw will easily pass through. If they are slightly out of alignment, it is ok to oversize the holes to make everything fit. Strengthen the holes by applying a few drops of thin CA glue to the edges of the holes.
Heat-set inserts are used to provide attachment points for the screws. Use a soldering iron to install the inserts in to the motor mount, recovery hardpoint, and nose sections.
Tie one end of the tubular nylon to the recovery hardpoint using the hole in the center. Alternatively, a 5/16 eyebolt may be used. The recovery hardpoint is installed in the airframe with the slightly protruding end facing aft. Slide the hardpoint into the body tube and secure with 7 #6 x ½” flat head screws with screw fairings. Use a 5/8 #6 flat head screw and rail button for one of the holes that is inline with the lower rail button.
The nose cone assembly is fairly straightforward, with the three sections bolting together with #6 x 3/8” flat head screws. The payload bay section is bolted to the bottom of the nosecone, followed by the nose shoulder. Thread the free end of the shock cord through the recovery piston, with the flat side facing aft. Tie the free end to the mount on the bottom of the nose shoulder.
There are two motor mount models included in the download. “CB-Motor Mount v2” is designed to have a section of Blue Tube or other suitable 38mm motor mount tubing glued into the printed motor mount. This is done purely for thermal reasons (to try to prevent the plastic from softening) and may not be necessary. An optional motor mount, “CB-Motor Mount_No Insulation” has been included that does not required a thermal insulator tube. It has not been tested and should be used with caution.
To make and install the 38mm insulator tube, cut a section that is even with the end of the printed motor mount when fully inserted. Apply epoxy to the tube and insert it into the printed motor mount. The rest of the assembly is the same for both versions.
The motor mount is held in the airframe by the fin attachment screws and lower rail button screw, with no glue required. It is important that the end of the motor mount has a snug fit in the airframe to prevent gas from escaping. Gas leakage could prevent the parachute from properly deploying. If it has a lose fit, wrap the end with masking tape to provide a better seal.
Insert the motor mount and position it so all the holes are aligned. If there are some misalignments, enlarge the holes in the airframe. The hole diameters are not critical (within reason). Attach the fins to the motor mount with #6 socket head cap screws, and the lower rail button with one #6 x 5/8 flat head screw.
With the shock cord pulled tight, the piston should be outside of the airframe, about 6 inches from the end. Tie a knot in the shock cord on either side of the piston to keep it from sliding up or down the shock cord. Attach the parachute to the shock cord near the nose cone.
No recovery wadding or dog barf is required to fly Checked Baggage. Insert the piston into the airframe, followed by the shock cord and folded parachute. Insert the nose cone into the end of the airframe. You should just be able to lift the rocket by the nose without the nosecone sliding out of the tube. Use sandpaper or masking tape to adjust the fit as necessary. Insert your motor of choice in the motor mount and secure with the motor retainer. The rocket is now ready to fly!
Checked Baggage has been test flown on an Aerotech I218 with an 8 second delay.