Go to Home Depot or Lowes Home Improvement Center and buy a $50.00 stack of polystyrene foam sheets (shown below).
It's 4ft x 50ft x 0.25 inches thick and it's fan-folded into a stack of 2ft x 4ft sheets.
One 2ft X 4ft sheet weighs just 6 ounces.
The finished rocket with motor weighs 3 pounds.
Go to Staples and purchase a roll of Staples clear 2-inch wide packaging tape (item 609139).
Also purchase a package of 3 poster board sheets 14in x 22in (item 846923).
This is a thinner type of poster board good for making a motor-mount tube.
Purchase Elmer's Glue-All (white all-purpose glue).
Purchase a small spool of 18-gauge steel wire from a hardware store (for launching lugs).
Purchase G40-4W motors and First Fire Junior Igniters from www.hobbylinc.com .
Use caution when choosing high-power motors. High thrust and high velocity can tear the rocket apart.
Aerotech motors H115 and I140 are okay.
Aerotech motor H45 is excellent (slow 7-second burn) but it has no ejection charge.
Cesaroni "Mellow" motors such as I55 and J94 are excellent (slow 7-second burn).
Using a utility knife or box cutter, cut off a 2ft x 2ft foam sheet.
Use a sharp blade and the foam will cut very easily.
Make 90 degree square cuts, not beveled cuts.
Use a metal or wooden yardstick as a guide for the blade to make nice straight edges.
Roll the 2ft x 2ft foam sheet into a tube. The tube will have a length of 2ft, a circumference of 2ft and a diameter of 7.5 inches.
Roll the foam sheet so that the plastic-coated side is on the outside.
The foam sheet is too stiff to roll directly; it needs to be pre-shaped on a curved surface such as a 3-inch diameter pipe.
The pole of an outdoor basketball net makes a good surface to pre-shape the foam.
Press the foam firmly against the pole with both hands and wrap it 180 degrees around the pole, one section at a time.
Take care to curve the foam uniformly; try not to make any kinks or creases.
Work your way from one edge of the foam to the other until it is uniformly curved and roughly holds the shape of the letter-C.
Another way to curve the foam sheet is to use a bending tool as shown below made from a firring strip (wood) purchased at Home Depot.
Cut the firring strip into 2 pieces that are each 3 feet long.
Place 1-inch by 2-inch pieces of 1/4-inch thick foam between the ends of the two pieces of wood and wrap elastic bands around the ends to hold it together.
Place a 2ft x 2ft foam sheet between the 2 pieces of foam and put a 60 degree bend in the foam every 2 inches working from one end to the other.
To bend the foam, hold the bending assembly at the 2 ends, press the foam against the floor or table top while using a little rolling action.
Using the floor, 2 knees and 2 hands, carefully force the foam sheet into the shape of a tube.
Try not to kink or crease the foam. Butt the 2 opposing edges of the foam together; do not overlap them.
Bend the 2 opposing edges of the foam inward to form a heart-shape as shown on the figure below,
then apply a 2in x 2in piece of clear tape across the mating edges near the middle of the tube.
Press the tape firmly onto the foam as you release your grip on the tube and it goes from a heart-shape to a round shape.
It is important that the tape pull the 2 opposing edges of foam as tightly together as possible in order to obtain a smooth round tube.
Don't get discouraged if the tube is not perfectly round with the first piece of tape.
Repeat the heart-shape and taping procedure with additional 2-inch pieces of tape until the entire 2-foot length of tube is fully taped.
If the tube has kinks and is not round, work the tube with your hands until it is round.
If the taped seam is not smooth and round, the tape did not pull the foam together tight enough.
Forming perfectly round tubes is difficult and may take some practice.
If making a 2-foot section of tube seems too difficult, make two 1-foot sections of tube or four 6-inch sections of tube.
It is easier to make shorter tubes. Tape the shorter tubes together to form a 2-foot long tube.
Make 3 more 2-foot sections of body tube as described above.
Using clear packaging tape, tape the 2-foot sections together to make two 4-foot body tubes.
Cut off a 4.5-inch by 12-inch strip of the thinner poster board purchased in step-1 above.
Wrap it once around a G40-4W motor, apply Elmer's Glue uniformly across the remainder of the poster board and wrap it around the motor to form a 1.1-inch diameter tube.
Tape it, if necessary, to prevent it from unraveling. Leave the tube on the motor over night to dry and harden.
Using a utility knife, cut two round 7.5-inch diameter foam disks.
Cut a 1.1-inch diameter round hole at the center of each disk.
Verify that the 1.1-inch motor mount tube fits snugly inside these holes.
Form a 2-foot by 3-inch strip of foam into a 7.5-inch diameter 3-inch long cylinder.
Use Elmer's glue to glue one disk near one end of the 1.1-inch diameter motor-mount tube.
Slide the 3-inch long cylinder over the motor-mount tube.
Slide the 2nd disk onto the motor-mount tube and glue in place.
Use clear packaging tape to tape the disks to the cylinder along the outside edges.
Tape the motor mount to one end of a 4-foot body tube.
Using a utility knife, cut three 12-inch by 12-inch foam squares for fins.
Fold the square pieces in half with plastic-coat on outside to form 6-inch by 12-inch fins.
Cut 1.5-inch by 0.5-inch tabs and tape them to the base of the fins as shown in the figure below.
These notches will be inserted into slots cut into the main body tube to hold the fins in place.
Cut 1.5-inch by 0.2-inch slots into the bottom of the main body tube to support the fins by the notches.
The fins should be arranged uniformly 120 degrees apart and should be located at the very bottom of the main body tube
so that they help hold the rocket upright when it is standing on a level surface.
Verify that the fins fit snuggly into the slots.
The size of the slots can be adjusted by scraping with the blade of a screwdriver.
Glue the fins to the body tube using Elmer's Glue or DAP Quick Seal Clear Adhesive Caulk.
Consider painting the fins and body tube before gluing if they are to be different colors.
Use caution with spray paints. Most spray paints will melt the foam.
Fast-Drying spray paints such as Rustoleum American Accents Ultra Cover 2X are usually okay.
......
Cut a 6-inch square piece of screen material such as 6-inch wide plastic gutter guard.
Thread four pieces of kite string though four 0.5-inch to 0.75-inch diameter plastic buttons (shirt buttons).
Using the string and buttons (buttons on outside of body tube), anchor the screen horizontally inside the body tube about 1-foot below the top of the upper body tube.
This screen will support the rocket's parachute and any other payload objects.
The screen is porous so it will allow the ejection charge to eject the parachute, payload and nosecone.
The payload and parachute are far enough away from the rocket motor that recovery wading isn't needed.
Cut two 5-inch long wires from a spool of 18-gauge wire. Bend the wires as shown in the figure above.
Verify that the loops fit loosely around a 1/2-inch diameter launching rod and verify that the 1-inch straight sections can lie flat against the side of the body tube.
Use clear packaging tape to tape one of the launching lugs to the lower part of the main body tube near the fins.
Tape the other launching lug near the top of that same 4-foot section of main body tube.
Line up the launching lugs so that the launching rod goes through one of the fins.
The rocket will be sit better on the launch pad if one fin wraps around the launching rod.
Reinforce the launching lugs by anchoring them to the body tube with buttons and string.
Cut six long thin foam equilateral triangles 12-inches long and 4-inches wide at the base.
Curve the long edges of the triangles to produce a curved nosecone.
Bevel the long edges so that the gaps will be minimized when the triangles are assembled into a cone.
Bevel the edges so that the clear plasti-coated side of the foam is outward.
Place the six triangles edge to edge with plasti-coated side upward and tape them together with clear packaging tape.
Curve the triangle foam assembly into the shape of a cone and tape the final seam.
Cut a 4-inch x 23-inch strip of foam and tape it into the shape of a cylinder as was done to make the main body tubes.
Tape the 4-inch long cylinder to the bottom of the nose cone.
Insert the bottom of the nose cone into the top of the main body tube and verify that it fits loosely.
A nosecone with transparent payload section can be made from a large bottle of pretzels.
Glue a styrofoam hemisphere (from a craft store) to the top of the bottle.
Use a strip of foam sheet, if necessary, to adapt the bottle to the body tube.
Cut another 4-inch x 23-inch strip of foam and tape it into the shape of a cylinder as was done to make the main body tubes.
Insert this 4-inch long cylinder 2-inches into the top of the lower main body tube and tape it into place.
The purpose of this coupler is to make it easier to line-up and connect the two 4-foot long sections of main body tube just before launch. The two 4-foot long sections should then be taped together before launch. The two 4-foot long sections can be un-taped and separated after launch.
Cut a 24-inch diameter circle from a plastic garbage bag. Wipe the plastic with a fabric softener towel to eliminate static cling. Use small pieces of duct tape to attach six 30-inch long pieces of kite string uniformly along the perimeter of the circle. Tie the ends of the six pieces of string together with a 2-foot piece of a thicker string. Use clear packaging tape to attach the end of the thicker string to the outside and top of the main body tube.
Tape a 10-foot long streamer to the base of the nose cone. The purpose of the streamer is to slow the descent of the nose cone and to make it possible to calculate the height of the flight. To calculate the height, record the nose cone by digital video as it strikes the ground. Count the number of frames that it takes the nose cone to fall 10 feet. Count the number of frames that it takes the nose cone to fall from the peak of the flight. The ratio of the two counts gives the altitude of the flight.
Slide a G40-4W rocket motor into the Motor mount tube and use a small strip of duct tape to tape it into place. Simply over-lap the tape partly around the base of the motor and partly around the base of the motor mount tube.
Tie a piece of string to the main body tube so that the foam rocket can be suspended horizontally outdoors in the presence of some wind. Verify that the rocket turns naturally by itself and points into the wind. If the rocket turns away from the wind, it needs more weight in the payload area. Purchase some 6-inch tall plastic action figures from a dollar store if weight is needed. Make a 1-foot diameter parachute for each action figure. Tennis balls with or without streamers can also be used for ballast.
Video: Foam rocket with high-power Aerotech I140 motor.
Photos & Video: This is what happens if you don't glue the fins properly.