Space Grant Consortium - University of Wisconsin - Green Bay

Design Features
The chief requirements of this design problem were to optimize the weight of the dart and to
ensure a stable flight. These design efforts, among others, are detailed in this report.
Booster A layout showing the features and components of the booster and dart is shown in
Figure 1.
Figure 1: Layout of Sounding Rocket, showing internal components
All kinetic energy imparted to the booster is wasted energy as far as the final altitude of the dart
is concerned. Thus the primary goal in the design and construction of the booster was to keep its
weight to a minimum, allowing the transmission of a maximal fraction of the motor’s energy to
the dart. This goal was accomplished by using clean fillets to reduce epoxy use, installing the
smallest safe size of hardware, and minimizing the length of the body tube. The fully loaded
weight of the booster was 4.3 lbf.
Dart The primary design objective for the dart was to minimize drag and ensure stable flight.
Each of these design efforts is explained in turn.
The drag coefficient is minimized primarily by streamlining the shape of the dart. The principle
sources of drag are friction drag and pressure drag, but since rockets are of fairly blunt shape and
fly at very high Reynolds numbers, pressure drag is the dominant drag source. Pressure drag is
generated by flow separation at the rear of an object. Thus the best way reduce pressure drag is
to prevent flow separation by installing a boattail.
The second geometric feature that affects drag is the cross sectional area of the dart. Although it
is clear that the area should be minimized, an additional design constraint is present—a certain
volume of components (parachute, shock chord, fire blanket, and electronics) must be contained
within the body. At first, we built a 2.1-inch (54mm) diameter dart to ensure that all these
components would fit. After successfully constructing and flying the 2.1-inch dart, we
endeavored to further reduce the diameter to 1.5 inches (38mm). This diameter change reduced
the cross sectional area by a factor of 2.0. Since drag force is directly proportional to cross
sectional area, the diameter reduction cut the dart’s drag exactly in half! We were able to
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