Space Grant Consortium - University of Wisconsin - Green Bay

Our Design
Our rocket uses the basic laws of physics in concept and design. The booster is simply meant to
push the dart upwards. Knowing this we wanted to design it as aerodynamically and light as possible.
We decided to use a boattail on the booster because this makes the booster, and the rocket in its
entirety, more aerodynamic. It does this by minimizing the disturbance as the air comes back together
at the end of the rocket. In keeping with the light design we went with a plastic boattail instead of a
fiberglass one. We believe that it will be strong enough. At the end of the boattail we have a threaded
cap for motor retention. It allows for easy retention without having to deal with threaded rod through
the boattail going to nuts holding a washer.
The body is the required 4” body tube. We choose a phenolic airframe. This again is because we want a
very light design and believe that a phenolic tube will still be strong enough. We cut the tube very
short, roughly a foot; to make the booster light. More importantly however is the aerodynamics of the
design. We want the booster to create as little drag as possible thus making it short. Simply put, drag is
directly proportional to surface area; the more surface area the more drag. Within the body of booster
we used as few centering rings and bulk plates as possible. This reduces weight. We will be using
motor eject for the booster. This is because it is the simplest and is all we need for the booster.
The nosecone for the booster is different from most rockets. Because the rocket has a dart
coming out of it we decided to turn a plastic nosecone into a custom boattail. What this allows us to do
is to recede the dart into the nosecone making the overlap length longer. Having a longer overlapping
length makes the rocket less flimsy where the dart comes out. Having the rocket less flimsy reduces the
amount of energy lost when the rocket ascends.
The dart consists of a plastic nosecone on each end. This is for the same reason as the boattail
on the booster. It makes the dart more aerodynamic. The airframe is made of phenolic tube same as the
booster; this is due to the weight advantage. We made the dart three feet long. Inside the airframe we
have two electronics bays. The judges’ is in the back end of the dart, just in front of the fins. In the
front of the dart are our electronics. We are using Missile Works’ RRC2-mini Rocket Recovery
Controller 1.2 This will record altitude, but more importantly it will ignite the charges the blow the
chute after apogee. Between the two electronics bays is a parachute connected by a shock cord. In the
front is a plastic nosecone.
The back nosecone was converted into a slight boattail. We cut off the tip of the back nosecone,
turning it into the slight boattail. We cut it so that the hole was just large enough for the brass tube to
fit. The other end was secured by a bulk plate with a hole cut into the center. In the front boattail of the
booster is a long nail, roughly ten inches long. This nail is held in the front bulk plate with epoxy. The
brass tube slips over the nail. The rod will be used to guide the dart off the booster. This allows for a
relatively frictionless separation between the booster and the dart. This is key in our design.
The difficult part of designing the rocket was to ensure balance the center of pressure and center of
gravity at specific ratios. It was calculated that for the utmost performance the center of pressure
should be located 1.5 to 2 times the diameter behind the center of gravity. This will allow for the most
efficient thrust and achieve the highest altitude/performance possible. The center of pressure is
determined by the geometry of the rocket and was checked using the simulation program RockSim 8.
The center of gravity; however, was found by locating the point on the rocket where it balanced on a
fulcrum.
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