Space Grant Consortium - University of Wisconsin - Green Bay

though a strong crosswind was present during the launch. This verified that the CP and CG
calculations were accurate.
Competition Flight
Team Narwhal’s competition launch was, in most respects, very successful. The flight was
extremely straight and stable, in spite of the high wind speeds. Both sections separated and
deployed according to plan, descended safely to the ground at a near-perfect rate, and were
recovered with no damage. The only unfavorable outcome from the competition was that our
achieved altitude (3600 ft) was drastically lower than the expected altitude (5500 ft). However,
analysis of the flight data demonstrated that two primary factors caused this discrepancy.
First of all, the cross sectional area of the dart that was used for altitude predictions was too
small. The outer diameter of the dart was used to compute the cross sectional area, which failed
to account for the area of the substantial fillets at the roots of the fins. Out post-flight analysis
indicated that the fillets add 25% to the cross sectional area of the dart. Accounting for the actual
cross sectional area brings the predicted altitude much closer to the actual altitude.
Secondly, we were unable to accurately predict the drag coefficient of the rocket. For our
prediction, we used a value of 0.3 for the dart and 0.35 for the dart + booster assembly. Analysis
of the flight data indicated that the actual drag coefficient on the dart is 0.45. When the
numerical simulation was re-run with the updated cross sectional area and drag coefficients, the
predicted altitude was within 400 ft of the actual altitude. The remaining difference can be
explained by launch rail friction.
The results of this competition highlighted one key principle—the importance of obtaining good
test data. At the level of sophistication of which we are capable, we were unable to accurately
predict the flight performance. Had our attempts to take data earlier in the year been more
successful, we would certainly have come much closer to correctly predicting the peak altitude.
Conclusion
The goal of this year’s Wisconsin Space Grant Consortium Collegiate Rocket Design Contest
was to develop, build, and fly a boosted dart rocket. Our team met these goals with a solution
that was robust yet nearly optimized. Our entry flew safely and successfully, and logged the
highest flight of the day at 3600 ft. Although this altitude fell short of our predictions, post-flight
analyses indicated that the cause was a poor estimate of drag coefficient.
We feel that this competition was quite successful for team Narwhal. We enjoyed seeing our
hard work pay off with a beautiful flight and a perfect recovery. As we designed, built, and tested
our rocket, we learned valuable lessons about rocketry, testing, analysis, and teamwork.
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