The Rocket - Structure
The total length of the rocket is 124 inches and the weight is approximately 39 pounds. The body tube, nosecone and fins of our rocket are made of fiberglass, which has a high strength to weight ratio. Fiberglass gets its name from its production process, where it is made from glass that has been melted into long, thin fibers that are then layered to create greater tensile strength (Fiberglass). The tube must be strong because it will be used to support the fins and nosecone and will encase the payload device, recovery system, and motor mount. The structure of the rocket is shown in the figure below.
The rocket is designed with a tangent ogive nosecone, which has a diameter of 6 inches and length of 24 inches. This gives the nosecone a caliber, length to diameter ratio, of 4 (Ogive Nose Cones). This shape is named due to the relationship between the rocket body and the nose cone, as the body is tangent to the curve of the cone at its base. The shape provides the rocket with more internal volume when compared to a strictly conical shape. More importantly, the tangent ogive is efficient, as it increases laminar flow. This means that the surrounding fluid will travel more smoothly around the nose cone, that flow properties such as velocity and pressure will remain more constant, and that drag will be dramatically decreased (Encyclopædia Britannica, 2012). This increase in laminar flow will further increase the rocket‟s stability.
G-10 fiberglass clipped delta fins will be attached in slits and then bonded to both the interior and exterior of the body with 3M Scotch Weld high-strength adhesive. Fins are important because they give the rocket a greater restoring lift force at the small angles of attack made by air hitting each fin (Nakka, Fins for Stability, 2001). The clipped delta fins will reduce the turning momentum of the rocket and maintain a straight, stable ascent as well as maintain flexibility and resilience for the impact of landing. G-10 fiberglass was chosen because not only is it characteristically lightweight, it is also very strong.
Bulkplates and Centering Rings
The vehicle will contain a total of six bulkheads in different sections of the body. The different bulkheads will serve as to fasten and transfer the load within the rocket. They must be exceedingly strong and secure, as they hold in place the U-bolts that are used to connect the shock cord of the recovery system to the rocket body. Our bulkplates, also known as bulkheads, are approximately half an inch thick and made of birch plywood. The large thickness of the bulkplates, paired with lower rigidity of the birch plywood material allows us to epoxy them securely into place. This becomes particularly important with the addition of the U-bolts to the bulkplates.
There are also four birch plywood centering rings used to align the motor tube along the longitudinal axis of the airframe, with the Booster Section of our rocket. The centering rings are, like the bulkplates, half an inch thick and also very sturdy. The first ring is located two and a half inches from the forward end of the motor tube, the second centering ring is located above the fins, the third centering ring is located below the fins, and the fourth is flush with the aft end of the motor mount. These rings serve as a method of centering the motor tube within the body tube.
To increase the durability of the rocket body and the security of the fins, the team decided to build a fin can assembly. The assembly is composed of the fins, the motor mount, and four centering rings. The bottom centering ring will have the outside diameter of the airframe and will be placed directly above the motor retainer. Two centering rings will be placed above and below the fins and will have slots cut into them to prevent radial movement of the fins within the rocket body. The fins will be evenly spaced around the motor mount, which will be ensured with the fin alignment jig. The last centering ring will be placed approximately one inch from the forward end of the motor mount to ensure the security of the motor mount in the airframe. The airframe will have fin slots cut to the end as shown in the figure below so the fin can assembly will slide into the airframe once it is completed. The assembly will be secured in the airframe using epoxy and machine screws.
The payload is designed so it can be easily inserted and removed from the airframe. In order to accommodate for the payload, a coupler and two bulkplate will be epoxied at the aft end of the payload airframe as shown in Figure 9. The aft bulkplate will have a U-bolt that will be attached to the main shock cord. Holes will be drilled in the airframe that will allow machine screws to hold the payload in place.