In this tutorial, I will explain how to create a rocket fin using the engineering design process. The goal of this project is to produce a working rocket fin while learning how the process of design influences your final product.
This is what you need in order to make this project happen:
- A hobby rocket kit (any kind of basic model rocket kit should suffice)
- 3D modeling software. I used SolidWorks at my school, but you could use TinkerCAD (free online modeling software) or any other program
- Rocket engines (something similar to a ESTES A8-3 engine)
- Material to build the rocket fin. I 3D printed my fins, so this would require access to a 3D printer, but you could make the fins out of balsa wood, fiberglass, cardboard, etc. It is up to you to determine what to use and what material is best for you.
- Glue- superglue, epoxy, white glue, wood glue, etc.
- Hobby knife or utility knife
Step 1: Research Rocket Basics (Conceptual Modeling)
The first step of designing your rocket fin is to understand the basics of how rockets work. There is a lot of information that goes into rockets, but since we are not all aerospace engineers, I will keep it simple.
List of helpful information that I have learned from this project:
- There are several forces acting on the rocket during flight. The main ones are weight (gravity), drag, thrust/lift.
- The weight of the fins will influence how high the rocket will travel, because the force of gravity pulls the rocket back towards the earth.
- Drag also acts in the opposite direction of travel to the rocket. You want to minimize the value of this force.
- Thrust is the only force that is propelling the rocket positively in the vertical direction. Thrust is created by the engine.
- The number of fins used and design of the fin you choose affects the stability of the rocket
- The stability is determined based on surface area, the number of fins used, and weight of the fin.
- Make sure that when you mathematically model the design, you understand what happens when you change certain parts of the fin.
- Other factors influencing the design are the center of mass and center of pressure
- The center of mass is the balancing point of the rocket. If you hold the rocket horizontally on your finger, the point that it balances on is your center of mass.
- The center of pressure is where all the forces of the air (drag) meet.
- It is ideal to have the center of pressure located closer to the bottom of the rocket. This provides the best stability during flight.
- The material that you create your fins with will affect how well it performs
- I chose to make my fin out of 3D printed plastic. I did this because it was going to be the most accurate way for me to get a physical representation of my graphical model.
- If the fins are not smooth, there will be more drag
- If the fin is too heavy or light, this will influence stability and thrust
See this website for more information:
It is very helpful to take notes on everything you learn, even if you do not understand it yet. Start sketching very basic ideas for your fin. The more you can come up with, the better. Try not to look up other designs until you come up with several ideas of your own. After learning more about the way to make your fin more efficient, you can revise your original sketches.
Step 2: Design Your Fin (Graphical Modeling)
In this step, you will take what you have learned about the basics of rocket fins and start designing your fin! This part can often be the most fun, but remember that you will eventually need to justify your reasons for your design to make sure that it will be a viable solution.
- Using SolidWorks (or another 3D modeling software) start drawing the basic shape of your fin
- Extrude the fin to your desired thickness. Mine was between 2 and 3 millimeters wide.
- Fillet, round, and taper edges to desired shape. This will affect drag. I decided to round my edges on the leading edge so that they would be more aerodynamic, reducing the amount of drag on the fins.
- Make sure that the fin model is fully defined so that you know that it will work with the full rocket assembly model.
In my first design, shown as the first picture, I had not researched as much as I should have before starting. I jumped into graphically modeling the fin, and made a design that looked cool. After mathematically modeling the first fin, I realized that I could have made a more efficient design, so I came back and ended up with the fin on the right.
The difference between the fins is that the second design has a bit more surface area that is farther away from the body of the rocket. This serves two purposes; it keeps the fin away from the engine to prevent it from burning, and it makes the rocket more stable. Also, the placement of the fin on the body is in such a way that more of the fin is lower to the ground. This brings the center of mass and center of pressure towards the bottom of the rocket, which is desirable.
Step 3: Make Sure Your Fin Will Work (Mathematical Modeling)
After designing your fin, you need to make sure that the fin is going to perform as expected. This could be for different reasons. Anything from achieving highest altitude, flying the straightest, wanting the rocket to rotate, or even just having the coolest looking fins can be mathematically modeled. Do not worry, mathematical modeling is not as scary as it sounds!
As pictured, I ran a flow diagram on my model in SolidWorks. This shows me where there are areas of high and low pressure, representing the drag on the body and fins. While not necessary, this helps you refine your design and minimize drag to achieve the best results.
I also used SolidWorks to evaluate the center of mass, center of pressure, and drag coefficient (see pictures). These values all show me if this design is going to provide a usable rocket fin.
You can also use the Barrowman Equations sheet, formulated in excel to check your location for center of pressure. This gives you a pretty good estimate to the location of the center of pressure on the body. It is ideal to keep your center of pressure between one and two times of the rocket diameter below your center of mass. This ensures the greatest stability during flight.
The other page on this excel file show the apogee equations. My predicted altitude is 76 meters or 249 feet.
This step involves a lot of back and forth work with the graphical modeling step. You will take measurements to calculate the CoP and then modify the design to achieve better results. Do this until you are pleased with the estimated CoP.
See this link for more information to calculate stuff:
Step 4: Build Your Rocket (Working Model)
Now comes the part where you will actually assemble your rocket. Follow the steps provided in the kit to build the rocket. The only difference here is that for my project, I will use my 3D printed fins instead of the balsa wood. I chose to 3D print my fins because it was going to be the easiest way for me to create my fins. I knew that there would be a lot of inaccuracies if I tried to shape the fin out of balsa wood or another material. Also 3D printing is very cool, and I like to use it as much as I can while I have access to a 3D printer.
I decided to attach my fins using super glue instead of white glue. This is because it creates a stronger bond for the materials, and it dries much faster. Many decisions made in this design were based on the ability to actually be able to assemble the rocket.
I also painted the rocket to make it fly higher.
Make sure your rocket is packed well before you launch it.
Make an extra fin or two for when you launch. Your fins most likely will break and/or detach from the body, so bring some more super glue to attach another fin if necessary.
Step 5: Launch That Rocket (Results and Altitude Calculation)
Finally, you can launch the rocket!
Pack your parachute and attach the engine carefully. Make sure that the ignition wires do not cross on the launch pad, use safety glasses and other safety equipment, and make sure that you launch in a very open area. The wind likes to catch the parachute on the descent, taking it far away from the launch site.
If you would like to calculate how high the rocket travels, you need to measure the angle that the rocket peaks at, just before the parachute ejects. You also need to measure the distance between where the rocket launches and where you measure the angle. From there, use simple trigonometry to calculate the height.
I used 300 feet for my distance between launching and angle measuring. The angle that my rocket achieved was 39 degrees. Using the equation below, I calculated that the peak altitude was about 243 feet.
Y = Xtan(A)
X = the distance from the launchpad
A = the angle your rocket peaked at
Y = approximated max altitude
To calculate percent error for the height, take the predicted height (P), subtract it from the actual value (A), and then divide by the predicted value (P). This will give you a decimal that you multiply by 100 to give you your percent error (E).
E= ((A - P)/P) x 100
243 - 249 = (-)6
6 / 249 = .0241
.0241 x 100 = 2.41% error
This is a very reasonable percent error. I am actually quite impressed with how well this turned out! Factors involved are weight differences in the graphical and physical models, drag, craftsmanship, wind conditions during launch, and a 10% error for the engines.
Step 6: Final Thoughts
If I were to do this project again, I would have made the fill density on the fins less. I did not change the default fill density on the computer before printing. The result was a sturdy fin, but it was also about 10 times heavier than a similar sized fin made from balsa wood. I think that the stability would have stayed the same with a less dense fill, but the weight would have decreased, resulting in a higher peak altitude due to less overall weight.
Make sure that you take your time on a project like this, because the more time you spend learning and researching, the less time you have to spend on trial and error designing like me.
I definitely learned the value of the engineering design process. It is a cycle that you may have to repeat several times before finalizing your design. This process can be applied to many other things in life, so it is great to learn. It is also important to remember that things will not go according to plan every time, so you must be flexible and problem solve with time constraints.