Space Grant Consortium - University of Wisconsin - Green Bay

Discussion of Results
Acceleration
According to RockSim, based on the rocket geometry, weight, and motor thrust the anticipated
acceleration was 1119 ft/sec squared. However, this is assuming perfect conditions. The actual
acceleration was approximately 1156 ft/sec squared. This is most likely due to a loss in thrust
provided by the motor, is due to several factors. For the actual launch, separation between the
rocket and the launch rail is not frictionless, therefore acceleration is lost. The coefficient of
friction on the surface of the rocket was most likely higher than RockSim predicted. This would
create more drag and reduce acceleration. The last contribution to acceleration loss is wind. On
the day of the launch there was a strong wind. This affects the acceleration by altering the
rockets orientation slightly. This changes the rockets momentum vector. By changing the vector
some acceleration is lost. It is because of these factors that the actual acceleration was different
from the predicted value.
Altitude
Our predicted altitude at apogee was 4670 feet according to RockSIm, found in table 1; however,
the actual altitude reached was 3136 feet. The altitude is related to the acceleration in the way
that the loss of the acceleration leads to the loss of altitude. If the acceleration is lowered then the
momentum will also be lowered. With a lower momentum the dart will not travel as high after
separation from the booster.With less momentum the dart will not travel as high.
Wind will also affect the altitude. Since the center of gravity leads the center of pressure, the
rocket will turn into the wind as it travels. Ascending at an angle lowers the altitude in respect to
the vertical.
When simulating the rocket in RockSim, only model the rocket as a whole instead of a booster
and a dart. This would keep the drag the same from launch till apogee instead of the case of a
dart, where the dart has less drag thereby ascending higher.
There is also the friction when the dart separates from the booster. In our design we tried to
minimize this amount of friction however there will always be some. Because of this amount of
friction some momentum is lost during the transfer between the entire rocket and the dart. These
are the reasons for the difference between the predicted altitude and the actual altitude.
Conclusion
Ultimately, the boosted-dart rocket was a success in that it completed the primary goals of the
competition. That is, to design, build, and simulate a boosted-dart rocket that would have the dart
separate from the booster at motor burnout. The simulated values for the altitude proved to vary
from the actual, with a percent error of 32.8%. The reasons for these differences were established
in the discussion section of this report. The acceleration that was predicted showed to be close to
the actual value, with only a 3.3% error. All in all, the launch and post flight analysis showed
that results were collected and analyzed correctly.
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