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The
"Coney"
Backslider
Water Rocket
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Robert
Youens
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Please see
Ulrich Hornstein's site for more information on Backsliding:
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The cone is 2.5
feet long and made from paper twisted into the cone
shape. The paper I used was labeled for use as school book covers. It
is 15 inches wide and 20 foot long. The cone is simply taped to the
bottle with scotch tape.
Reason may
indicate that the Center of Gravity is way to far back on this rocket
for it to have stable flight. It was discovered years ago that in
long skinny rockets the relationship of the Center of Gravity and Center
of Lateral Area can be very different than the required one caliber
(dimeter) distance of Center of Gravity ahead of Center of Lateral Area.
A fellow name
Barroman mathmatically calculated a new point which has become
know as the Barrowman Center of Pressure. In long skinny
rockets with the Center of Gravity located behind the Center of Lateral
Area, stable flight is still possible as long as the Center of Gravity is
ahead of the Barrowman Center of Pressure.
This rocket will
fligh well and will maintain vertical flight to apogee. At
apogee, rather that nose over and head for the ground, the rocket slides
downward tail first. At a point the fins catch the air and put the rocket
into a horizontal recovery. This ballance is maintained by the angle of
the fin. If the tail is lifted up too much the fins stall and the back of
the rocket goes back into
the horizontal position until the fins catch enough
air to get back into the horizontal glide angle.
It is a beautiful
thing to watch and a dependable form of recovery.
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This rocket has 4
fins which are almost too much surface area to keep the
Center of Lateral Area ahead of the Center of Gravity. When you
think about it, another fin or larger fins add little weight, but the
additional cross sectional area does dramatically move the Center of
Lateral Area backward while the Center of Gravity stays in place.
When the Center of Lateral Area gets behind the Center of Gravity you are
almost insured a nose down attitude as the rocket progresses
through apogee. You may find if you used three fins or smaller fins
you would get a smooth recovery with a slightly steeper backward
glide angle.
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The paper fins used on this rocket are of my own
design and you can find
instructions on how to make them by clicking on the picture of the fin
next to this text.
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