[BProckets] homemade rocket body material sources and techniques

[Terry McCreary]

At 10:03 AM 11/5/2004 -0500, you wrote:

>All:
>
>
>
>I haven t actually built a rocket in over twenty years and have just 
>recently zeroed in on my first BP engine a la Sleeter s book.  In 
>anticipation of getting the book I d been savings all sorts of tubes and 
>have a box of balsa sheeting scraps for fins from my other hobby 
>pursuits.  Also, I ve only built Estes kits as a youth.
>
>
>
>Questions:
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>
>
>1)       What are good web or book resources for constructing rocket bodies?

Remember the old Estes and Centuri and and other kits you made as a 
kid?  Jim Z has a lot of those plans scanned and available for download:
http://www.dars.org/jimz/rp00.htm

General books on rocketry:  Handbook of Model Rocketry, G. Harry Stine; 
Modern High-Power Rocketry, Mark Canepa.  The latter is largely for H and 
larger motors.


>2)       At what point need I be concerned about high g forces on launch 
>shredding my rockets and is this ultimately an empirical determination?

Somewhat empirical.  However, a rocket properly built with ordinary paper 
tubes, balsa nose, and basswood or thin plywood fins will stand up to I and 
even J motors.  Main point I'd suggest is through-the-wall fin mounting 
when possible.  Make a tab on each fin that reaches to the motor mount 
tube.  Slot the airframe (body) tube and glue the fin to the MMT.  Lots 
stronger than surface-mount.

Balsa fins are ok for E, even F and G motors sometimes.  I'd rather 
over-build a bit.  Good-quality carpenter's wood glue is entirely adequate 
for most rockets up to H, I, even J impulse.


>3)       What techniques are used to prep paper/cardboard tubes for final 
>painting?  (Some of my salvaged tubes have rather unattractive grooves in 
>them due to their spiral wound nature.  I may wish to fill them in and 
>paint over them sometime.)

Elmer's lightweight Fill n Finish seems to be a standard.  Automobile body 
putty, the red stuff in a tube, also works nicely.  (Thinned with lacquer 
thinner, it's also good for filling balsa fins and noses)

IMHO it's better to toss the wrapping-paper cores, etc.  Tubes are pretty 
cheap (see sources below) and a proper tube, with a smooth glassine finish, 
ends up being a lot less work than filling and smoothing a cheap tube.


>4)       What are the currently favored types of wadding to protect the 
>chute, etc.?

Rat sh*t (so called because that's what you usually find in it).  Also 
known as "dog barf" cuz that's what it looks like on the ground after it 
rains.  Proper name is "blow-in cellulose insulation".  It's already 
fireproofed.  One bag from Lowe's, four bucks, lasts a lifetime unless 
you're planning a tenth-scale Saturn V....  Nomex and Kevlar are seeing a 
lot of use as reuseable wadding, as was mentioned earlier.


>5)       What are some sources of nosecones?  (I ll ultimately make some 
>on my own from balsa and fiberglass and things like those eggs pantyhose 
>come in but assume there are lots of sources I haven t yet thought of.)

Balsa Machining Services at www.balsamachining.com has stock and 
semi-custom nose cones, as well as body tubes in all sizes.  They also do 
custom work.  They're VERY fast and very good.  Totally Tubular at 
http://www.totubular.com/ sells body tubes, centering rings, etc.  Good 
prices if you're doing a lot of rockets.  I make a lot of my own nose cones 
from balsa (smaller) or extruded styrofoam (bigger ones.  Not the white 
'beadboard' but the solid foam insulation sheets, blue or pink stuff).


>6)       Is there a quick and dirty way to calculate how much delay I 
>should build into my engines for a particular design so that I don t pop 
>the chute WAY too early or WAY too late?

wRASP is available free for download, I don't recall where.  It will model 
the flight of a rocket of given mass, diameter, etc. for commercial 
engines.  It's fun to play with.


>7)       Feel free to chime in with any other guidelines you may think I 
>should be made aware of.  (Shock cord info, fin geometry, etc.)

Shock cord need not be elastic.  In fact, guys that fly the big 'uns almost 
never use elastic.  Nylon cord, kevlar cord (heat resistant), tubular 
nylon, nylon straps, etc.

Best regards -- terry
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