Prior to designing and cutting fins for the rocket, some attention must be given to the construction of the rocket's nose cone. There are several ways to build the rocket's nose cone, including carving a cone from wood, purchasing a pre-fab plastic cone, or modifying a paper dixie cup. In this rocket project, the modified dixie cup will be the way to go. While it looks appealing, buying a plastic cone takes something away from your DIY soul! Carving a cone from balsa wood, or even cedar, or even a random dead tree branch, requires more time and the skill of carving, using sharp and potentially dangerous knives! Although I have carved a few nose cones from fallen tree branches (they work just fine), I prefer the technique of cutting and pasting for this model rocket.
Because we are relaying on dixie cup paper for the nose cone, it will need the added supporting strength of a part of the fuselage. Therefore, you will want to cut off the upper 2 inches of the fuselage. The following photo panel provides a visual* for making a clean and level cut. Now that the hard work of the engine housing assembly is complete, you do not want to mess up the fuselage when you remove the top piece!
Using a pencil and a ruler, notch the 2 inch mark down from the top of the fuselage. Take a piece of paper and wrap it once around the circumference of the fuselage at the 2 inch mark. Be sure to line up the ends of the paper, or at least where the paper begins to overlap when it wraps around the fuselage. With the pencil, draw a line around the fuselage where the paper edge meets the rocket body. This will give you a clean, straight line for cutting that is exactly 2 inches down from the top of the fuselage, in all directions. Take the paper away and make the cut with a sharp Xacto knife blade. Take your time so as not to dent or damage the fuselage.
*In this visual, (photo on the right hand side) you may have noticed that I removed part of the fuselage before attaching the engine housing. Either way is fine! This observation simply means that there are several ways to arrive at the finished rocket product!
Without fins, your rocket will simply fall over and your friends and family may laugh at you! Even a trophy rocket will want to stand out and stand on it own three or four fins in its trophy display case. Rocket fins can add a personal touch of flare to your rocket. Here is your chance to polish your rocket's glamour! This photo panel lays out the process of fin construction.
You will want to design/build three or four identical fins for your rocket, In addition to creating a stand-alone effect, fins encourage the rocket to maintain a straight-line course after lift off. Begin drawing straight and sometimes parallel lines and sometimes perpendicular lines on a piece of paper to develop an effective and easy to replicate design, as depicted in the photo on the left. A few tips and tricks to better fin construction are included in the photo on the right hand side. These tips and tricks aim to improve the rocket's strength and durability.
Pink Line: Try to maximize the gluing contact surface between the fin and the fuselage. A longer line will do this.
Purple Line: Create space between each fin and the fuselage. This added space will make it easier to load and unload the rocket engine and to position the detonator, getting ready for your rocket to launch. It will also reduce the potential of the fins getting singed by the rocket's afterburn.
Green Line: Ensure that the fins do not come to a point or a very narrow straight line here. A wider straight line will reduce any potential damage to the fins at this point.
Purple + Green Line: Finally, this combined distance is an important consideration for fin construction. The further away from the fuselage, the more damage prone the fins become. Try to keep this distance, the width, shorter than the length of each fin.
When you are satisfied with your design, use tracing paper to transfer the design to a section of corrugated (thicker = stronger) cardboard. Cutting off a flap or two from a cardboard moving box will do nicely. Carefully cut out one fin using a ruler and sharp Xacto knife. Trace two or three more fin outlines onto the cardboard using the first cut out fin as a guide. Cut out the remaining two or three fins, to produce three or four identical fins.
Pro Tip: Corrugated cardboard has a reasonable strength to it for building model rockets. However, when the cardboard is constructed, it has greater strength in one direction than in another direction. To determine which direction is stronger, hold a sample piece of cardboard so that the two opposite sides are in each hand. Press into it with your thumbs and note how easily it bends. Now, turn the cardboard 90 degrees so that you are holding the other two sides, and press in with your thumbs, noting the strength, relative to previous pressing. You should notice that one direction provides more strength than the other direction.
The longer side of your fins (usually vertically aligned) should be cut from the cardboard in the stronger direction.
Now you are ready to attach the fins to the fuselage! Follow the progression in this set of three photo panes, even though they are not in order!
Account for the number of fins in use. This rocket model will use three fins. Use the same paper technique for evenly positioning the fins as was used to cut a top section from the fuselage. Wrap a piece of paper once around the fuselage and make a pencil mark on the paper where the paper begins to overlap on the fuselage. Use a ruler to measure the circumference of the fuselage on the piece of paper. In this case, the fuselage has a circumference of 4 and one eighth inches. Divide this total by the number of fins (three) for a measurement of 1 and three eights inches. Record these measurements on the piece of paper, as depicted in the upper left photo. This measurement gives you an equal spacing for each fin.
Once again, wrap the (marked up) paper around the lower part of the fuselage and transfer the hash marks on the paper as hash marks near the base of the fuselage, as shown in the vertical right photograph. Use a protractor, positioned at the base of the fuselage, moving through each hash mark, and marking new hash marks that are in line with each original hash mark. Next, use a ruler to connect each set of two hash marks, making three straight lines around the rocket's fuselage. These straight lines represent the precise placement of the rocket's fins.
Finally, use hot glue and a glue gun (not glue-stick glue or wood glue) to attach the fins. (If you use wood glue for this process, you will experience a slow-build headache that only eases when you switch to hot glue.) You will need to work fast as the hot glue dries quickly! Glue one fin at a time, running a bead of hot glue along each of the three straight lines. While working quickly, ensure that each fin follows each straight line, in a parallel direction to the fuselage. Holding the fuselage straight out, each fin must also be set at a 180 degree angle in relation to the body tube (fuselage). Deviation in any of these two points may mean that your fin(s) will tear away during the upward thrust of the liftoff phase!
The third panel depicts a completed fin assembly.