FLIGHT (Rocket Motor)

19.

A Basic Stick Rocket

To test a rocket motor in-flight, the simplest configuration is a stick-rocket. Be aware, however, that most states classify “stick-rockets” as fireworks. If fireworks are illegal, then stick-rockets will be illegal too. Also, because a stick-rocket has no parachute, it falls straight back to the ground when spent. Because it is still hot when it lands, it can set fire to anything flammable. Therefore, when flying these motors on sticks, remember that the largest has a range of more than a mile. Fly them only in an area where there’s absolutely nothing that might catch fire, and check with local authorities before you proceed.
Aside from the legal and safety concerns, the first thing you should know about a stick-rocket {Figure 19-1) is that it will not fly as high as a rocket with an aerodynamic body. A stick-rocket has a blunt nose, and it’s center of thrust is not aligned with its center of gravity. It therefore flies at a slightly cocked angle, and the resultant turbulence creates an excessive amount of aerodynamic drag that prevents the rocket from performing as well as it should. To streamline the rocket and alleviate some of the drag, you can fit the front of the motor with a paper nose cone.
MATERIALS LIST
1. A sheet of stiff paper (Like an old file folder.)
2. A strip of masking tape
3. Some white glue
4. A pair of scissors
1. From a sheet of stiff paper, cut a semicircle (half of a circle) about 4 times the outside diameter of the motor, and lay a strip of tape from the center to the outer edge (Figure 19-2).
2. Bend the semicircle into a cone. Stick it together with the tape, and make the diameter of the cone’s base a little larger than the diameter of rocket motor (Figure 19-3).
3. Firmly press the cone down over the front of the motor, so that the motor’s front edge marks the paper with a circular crease (Figure 19-4).
4. With the scissors, trim away the paper below the crease (Figure 19-5). Run a small bead of glue around the front of the motor (Figure 19-6). and press the cone firmly into place (Figure 19-7).

Figure 19-1. A basic stick rocket. The blunt nose and the off center stick generate excessive drag that degrades both speed and altitude.

Important note. Do not make a stick-rocket with a motor whose burn time is longer than 3 seconds. Most of the motors in this topic have a low starting thrust. If the bum time exceeds 3 seconds, the longer period of low thrust can allow a stick-rocket to wander off course, and thereby increase the danger of flying downrange and setting a fire. A motor with cm extended bum time needs a properly balanced, aerodynamic body to establish and maintain vertical flight.
When mounting a motor on the stick, it is important to mount it firmly, because the twisting forces generated during flight are powerful. If the stick is not firmly affixed, the motor will twist out of alignment, and the rocket will fly off-course. Also, the entire stick-motor assembly has to be properly balanced. If the stick is too long, the rocket will weathervane into the slightest wind. If the stick is too short, the rocket will fly in a gyrating spiral that generates drag and degrades performance. Finally, the stick has to be strong enough to withstand the rigors of flight at speeds up to 400 miles per hour. If the stick is too thin or too weak, it will break.
In the early 1980s I experimented with sticks made of pine and fir. but they broke too easily, so I changed to hardwoods like maple, mahogany, and alder. Hardwoods are expensive if you buy them at a lumber yard, but fortunately, the back roads of America are littered with a free supply. If you take a drive on the dirt roads outside of any city, you’ll find places where people illegally dump trash, and that trash usually includes old. upholstered couches. These couches are made of cloth and padding stretched over hardwood frames. The wood is of poor cosmetic quality, and not good enough for making nice looking furniture. But its fine for making rocket sticks, and one couch provides enough wood to make dozens.
Some couches have wider and thicker boards than others, so don’t grab the first one you see. Turn each couch over, and look at the frame inside. With a little practice, you’ll learn to spot the ones that are best for salvaging. When you take one of these couches, be a good citizen, and don’t tear it apart at the side of the road. This leaves a mess for other people to clean up. The proper etiquette is to load it onto your truck, take it home, and knock it apart in the back yard. Then remove the nails, tacks, and staples, cut the long boards into the sticks you need with a table saw. and throw the leftovers in the trash.
When I did this many years ago. I used 1/2″ square sticks for the 1″ and 1-1/8″ i.d. motors. 3/8″ square sticks for the 3/4″ i.d. motors, and 1/4″ square sticks for the 1/2″ i.d. motors. Some trial and error will be involved. If a stick breaks during a flight, make the next rocket with a thicker stick. To assemble a stick-rocket, and balance it for flight, proceed as follows:

MATERIALS LIST
1. A finished rocket motor with a paper nose cone
2. A stick of the proper size and length
3. Some masking tape
4. Some white glue

1. Select a stick of the size and length that you think you will need, and temporarily tape it to the side of the motor.
2. The exact location of a stick rocket’s balance point can vary depending on the weight of the motor, the length of the motor, and the weight of the stick. But most of the stick rockets I’ve made seem to balance best on the stick, about one motor-diameter behind the motor’s nozzle. The motor in this example is 1″ o.d.. so I’ve made a mark on the stick exactly 1″ behind the nozzle. At this mark. lay the rocket across a round, wooden dowel. If the rocket tilts forward (Figure 19-8). the stick is too short, and you’ll have to use a longer stick. If the rocket tilts backward (Figure 19-9). die stick is too long. and you’ll have to make it shorter. When the rocket rests level across the dowel (Figure 19-10). the stick is probably the correct length for proper balance and stable flight.
3. Remove the temporary tape, run a bead of glue lengthwise along the side of the motor (Figure 19-11). and press the stick into place (Figure 19-12). Notice in this photo how I’ve cut the front of the stick at an angle. This further reduces drag, and improves performance even more. Wrap the stick to the motor with two bands of masking tape several layers thick (Figure 19-13). and the rocket is finished.

Launching a Single Stage Stick Rocket

You can make an inexpensive launcher from a scrap of schedule 40 PVC plastic pipe, a 2-foot length of steel rod. and two stainless steel hose clamps. The pipe should be longer than the rocket’s stick. Cut the pipe and the rod to length, and clamp them together with the hose clamps (Figure 19-14). Then position the launcher at the angle you want, and push the rod into the ground (Figure 19-15 ). Insert the rocket’s stick into the pipe (Figure 19-16 ). insert an electric igniter, hook up the firing system, retire to a safe distance, and fire the rocket. If the rocket flies straight and true, and stays on course, you correctly estimated the length of the stick. If it weathervanes into side-winds as it flies, make the stick on your next rocket shorter. If it gyrates or spirals as it climbs into the air. make the stick on your next rocket longer.