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Sprint ABM rocket prior to its successful launch using a J415 rocket motor
Sprint ABM Streaking Skyward
| MAIN PAGE | PRODUCTS | CONSULTING | MISSION | RESUME | ORDER |
Copyright © 1999-2008 John Cipolla/AeroRocket
Sprint ABM High Power
Rocket back
The construction of
a semi-scale high power model of the Sprint ABM has been a challenging design
project. Development started by generating the rocket's airframe
geometry using a CAD (Computer Aided Design) program to determine
the diameter and spacing of each centering ring to support the
booster outer shell. Accurate determination of centering ring
spacing and diameter are important to achieve total outer shell
contact with the airframe support structure. If total contact
between the airframe and outer shell is not achieved the structure
will fail due to aerodynamic loads experienced during liftoff.
Another important consideration in the development of rocket
airframe geometry was placement of the launch rod holes through
each centering ring from the base to the exit point just below
the nose cone. Hole placement was critical because I wanted to
have the launch rod exit the vehicle below the nose cone but
within the solid basswood collar at the top of the booster. Development
of the model's geometry using a CAD package was the only way
to assure that launch rod holes were placed correctly the first
time to avoid trashing an expensive basswood collar. Attaching
launch lugs to the exterior of the booster was not an option!
This is because a heavy conical model rocket like the Sprint
will exert a relatively large normal force to the launch rod
during liftoff causing the rod to "whip" severely.
The resulting unstable flight would be a nightmare. Using a CAD
program also made it possible to size and locate the bay for
the electronics required to deploy the recovery system. By using
Computer Aided Design it has been possible to identify all possible
interferences between major components and avoid trial and error
construction.
Another important design consideration in the development of
the Sprint model was sizing and placement of fins to achieve
stable flight. It was my intention to adhere as closely as possible
to the actual geometry of the Sprint missile. However, even with
a solid basswood nose cone relatively large fins were required
to make the vehicle stable. AeroDRAG & Flight Simulation™ was valuable in its ability to interactively
size the fins to minimize nose cone ballast and reduce overall
vehicle weight. A relatively small amount of weight is required
to achieve stability for the high power motors I intend to use
in this model.
However, the outer shell or skin bending operation would not
be made easy even with all the design tools at my disposal! Using
a cardboard template I cut the .062" basswood plywood to
the shape required to cover the airframe. Then, after soaking
the skin for two days I wrapped it into a little tube about 6
inches in diameter and let it dry that way. The skin almost fit
the diameter of the airframe. Then, I used 15 minute epoxy to
attach one edge of the skin to the airframe at a stringer location.
The edge was secured using 6 small C-Clamps and allowed to dry.
After a few hours I applied plenty of Elmers Wood glue to all
airframe surfaces. Then my wife and I wrestled the skin into
position around the airframe. The process took almost an hour
and a half to achieve complete adhesion with the airframe.
Sprint ABM rocket prior to its successful launch using a J415 rocket motor Sprint ABM Streaking Skyward | MAIN PAGE | PRODUCTS | CONSULTING | MISSION | RESUME | ORDER | Copyright © 1999-2008 John Cipolla/AeroRocket |