HoCaDart1 - Hollow Carbon fibre Dart No. 1
Since quite a while I was working on a dart rocket. Last winter I collected
a broken ski pole as a dart body. It was used as a hollow tube - I hoped
for a low Cd value if I just rounded the front rim. Of course it should become
a backgliding dart, because it could be a harmful projectile coming down
like an arrow from great altitude. During the backglide test phase it drilled
itself repeatedly deep into the earth and took long soil samples in its belly.
For the booster, I took a rocket from my early WR days, a
S. W. R. rocket ("merci" to Jean Berthelot), which was very
easy to make. A simple wooden stick on top of it acted as a start rod for
the dart. It is held in place by two bottle caps.
It turned out that it would be good to make the booster backglide as well,
otherwise the wooden stick hits the surface first and eventually breaks,
unless the soil is soft. Two test launch sessions were necessary to make
both rockets backglide and resolve minor problems. See below for the third
and last test flight.
||Construction of the HoCaDart #1:
(1) dart body: a conical tube of carbon fibre; I used a piece of a broken
(2) weights, taped to the tube to make it backglide, during the optimization
process (explained on the BackMax page)
(3) three small laminated cardboard
(4) wooden stick, acts as a guidance for the dart
(5) neck of a 2 liter Coke bottle, used both as a nose cone and stick base
(6) a 2 liter Coke bottle, the booster vessel
(7) tube fin with taped on weights(yellow) to make the booster backglide,
Detail of the optimized dart:
(8) The weight (2) was replaced with a short piece of a lamp rod with a nut,
glued into the back of the dart. The weight was adjusted to get the same
CG as in the test version with the taped on weights.
Launch Report of the last test flight
On 20th May 2002 the dart/booster combination was sent into the final test
phase. I sent them up with 400 ml water and 5 bar pressure. It was cool to
see them leave the launcher together. Like in slow motion, the dart separated
slowly from the booster, which slowed down more and more due to its much
higher Cd. Our eyes followed the flight of the dart, which went up HIGH,
considering the lowish 5 bar start pressure. Almost invisible at apogee,
it started backglide soon after. Up there the winds must've been a little
higher than down here, the dart landed some 80 m away from the launch site.
||However, the dart was never to be seen again. In the landing area, the
grass was less than knee high. We searched until the lack of daylight forced
us to stop. Next morning, early before work, co-launcher Peter Mappes (on
the right) and myself went back to the spot, armed with pitchforks to comb
through the grass, without sucess.
Yes, we were very unlucky to loose this promising piece of water rocketry
right after the the last of it's test flights, just before the first launch
with its designed pressure, going for altitude.