11.6 What are the differences between the various HPR body tube materials used by the most HPR manufacturers?
Description
This article is from the Model Rockets FAQ, by Wolfram von Kiparski with numerous contributions by others.
11.6 What are the differences between the various HPR body tube materials used by the most HPR manufacturers?
The most common one is that material used by Estes and later by other
suppliers such as U.S. Rockets, LOC Precision, AeroTech, Launch Pad, etc.
This material is a spiral wound virgin kraft tube. Virgin kraft is stiffer
than recycled kraft and can much more easily withstand flight stresses at a
given thickness than recycled tubes as commonly found in household goods.
This material typically has an outer wrapper of "glassine" which makes the
tube smooth and accepts paint more easily. It also covers up the thicker
tube spirals of the underlayers and makes removing tube spirals with a
couple applications of sanding sealer practical.
Another common tube material is that used primarily by Public Missles. It
is a spiral wound paper with phenolic resin impregnated into it. This has
several advantages such as higher ultimate strength in aero-applications,
more waterproof out of the box and being fairly stiff. However this
material is also susceptible to cracking due to impacts and has been known
to crack during routine slow landings under overadequate parachutes.
A really good material for HPR is used only by Dynacom and U.S. Rockets and
is known as G-10 fiberglass. There are several practical variants of this
material. One can use either cloth wound or filament wound and the G-10
refers to one supplier's particular classification of a resin they use.
Even they use a dozen different resins. Among the glass's uses are
"e-glass" and "s-glass". Since one is both more expensive and stronger in
ultimate fail tests it is often used as motor casing material. However for
airframe applications, cheaper and thinner is better.
Other good but less common materials include cloth wound phenolic
impregnated, paper convolute wound phenolic impregnated, exotic composites
of kevlar, graphite, etc.
A very common material used (at one's own peril) is recycled paper style
tubes such as mailing tubes, paper towel rolls, etc. These must be over
1/8" thick to even be used for HPR at all. Even then they are easy to
damage and "unroll" on landing as they typically do not use glue except on
the edges. Rocket specific tubes are glued across the entire surface of
the superior virgin kraft material.
Plastic tubes can be used but the bonding problems of motor mounts and fins
have resulted in these having virtually no adoption among serious model or
high power rocketeers. Motor mount tubes must have an insulative element
as plastic motor tubes would quickly become the permanent owner of a motor
casing.
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