| Rocket Day |
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AME 309 Blasts Off on Rocket Day
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The basic water rocket consisting of fins glued onto plastic soft drink
bottle. This rocket sitting atop the laucher is partially filled with
green-dyed water. The black plug seals the rocket exhaust (bottle opening)
as air is pumped in. Releasing the 3 metal clamps launches the rocket.
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As part of the undergraduate Fluid Mechanics class (AME 309) in the
Fall, 2004 semester, the students worked in eight groups of four or
five on a project to design and analyze a water rocket.
The rocket consisted of a 20 oz. drink bottle partially filled with water
and pressurized up to 4 atmospheres with air. The students were
allowed to design appendages, i.e. fins, a nose cone, etc., to
streamline and stabilize the rocket in flight. The project required
each group to develop equations to analyze the internal gas expansion and
the motion of the liquid propellant to predict the thrust. The thrust
produced during the boost phase of the flight occurred over on a small
time scale compared to the total flight time. The students were also
required to develop the fluid mechanical equations for the external
aerodynamics of the rocket and predict the rocket’s height. The addition
of the drag calculations made the rocket equation non-linear. The goal
of the project was to optimize the amount of internal propellant and
external appendages to attain the maximum height of the vehicle in
flight.
Reality was faced on chilly (It was 40°F the night before!)
December 3rd when the students flew their
rockets on the Intramural Field west of Heritage Hall. Two different
rocket launchers were busy between 12:30 and 3pm testing the
students' designs and analyses. Each group was able to launch
their rocket multiple times, varying the amount of propellant and the
pressure. The maximum height attained by the rockets was measured by
triangulation. Many of the rockets reached heights in excess of 120
feet. After acquiring the required data towards the end of the test
flights, several of the groups increased the pressure to 7 atmospheres
and altered the propellant load to explore the maximum altitude
attainable. The results were interesting; a maximum height of 170
feet was achieved by one group but one rocket exploded on the launcher
due to the higher pressure. Each group prepared a written report
after launchday, explaining
their design and analysis as well as comparing their flight results
with their predictions.
--Ron Blackwelder
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Students at the preparations table, where they weigh their rockets,
measure the amount of water--propellant--to be used and wait for
their turns at the launch pad. The soft drink
cans contain propellant for students, not for their rockets.
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An interesting side note to the testing was that no one got wet
(except when the rocket exploded). Examination of the launch photographs
afterward revealed the exhaust from the rockets produced a very cohesive
jet of water but virtually no spray. The jet consisted of intermittent
lumps of water interspersed between liquid strings as seen in the
accompanying photo. A more advanced project will be to study a similar
water jet and explain the mechanism that produces the lumps and strings
of water as observed.
-RB |
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Angela Shibata, and Richard Taras watch their rocket
head skyward immediately after Angela launched it.
Phillip Prejean (on the left) watches the rocket as
Jerry Chen watches from a safe position behind the netting.
In the foreground the photo has captured the water jet consisting of
water streaks and lumps left by the rocket a few milliseconds
after it has moved out of sight.
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