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Day 170 - Water Amount Experiment
13th December 2015
Location:Whalan Reserve, NSW, Australia
Conditions:Wind ~10km/h, overcast
Team Members at Event: John K, GK,and PK.
How much water to use in a water rocket?
Since this is a question we get asked all the time, today we performed the experiment that
many students perform at school
to see what the optimal amount of water is for a
water rocket. Here is some background information on
why we use
water. A question that also often comes up is how high would a
rocket fly with air only, and so we looked at that as well.
We used our Axion III rocket for this experiment because it has
a smaller volume compared to the larger Axion rocket which meant
we would use less air from the scuba tank. The rocket parameters were:
Because the capacity of this rocket is 3.35L we chose the
following water amounts to test with: 3%,15%,30%,45% and 60%. Here are the results
including simulator predicted altitudes from two different
*Due to the weight of the 2L flight and the small
nozzle the rocket had very low acceleration and weathercocked significantly and therefore
didn't reach as high as predicted. With the simulator predicting
optimal water amount of 1.1L for this rocket we see that there
nearly equal altitudes either side of this peak. Although the
45% percentage fill gave a slightly higher altitude we must
remember that the error in our measurements is in the order of
10%. See day 159 for details of how the 10%
is arrived at.
Rolling out safety tape the easy
Mixing food colouring
Ready to launch
Visitors checking out what all
the fuss is about
Back to munching on grass
As can be seen from both the observed and simulated results the
optimal amount is about a 32% full of water and the
altitude drops off significantly when you use too little water.
With air only the rocket flew to only 37% of the altitude when
compared to the optimum.
A big thank you goes to John Beans from
Jolly Logic who
generously donated an
AltimeterThree for our experiments.
Obviously we were very keen to try it out on our rockets.
We installed the AltimeterThree App on Paul's iPod so we could download the
data. I like the fact that it not only records altitude but also
acceleration. Something we don't usually record.
We flew the Axion rocket with foam for this test to see how
well it would detect launch (because the foam flights tend to
have a slower lift-off) and then to see what the recorded flight profile
was like. The altimeter was very easy to set up and get going. We only flew it on one of two flights, because the wind
was blowing straight towards the tree-line and we didn't want the altimeter
becoming a Christmas ornament for the holidays. The second flight was similar to
the first, it flew nice and straight all the way up.
Here is a plot of the altitude and acceleration:
All the flights flew and recovered well on the day, so we