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using
         one of the methods discussed in the section on High Power Construction
         Techniques. Be sure to completely sand off the glassine coating of
the
         body tubes prior to applying the fiberglass.
      3. Also fiberglass-reinforce the thick paper centering rings supplied
         with the kit. Glass both sides of the rings. If you want to build a
         payload section in the Shadow, then leave the center cut-out in one
         of the rings and glass over it.
      4. If you plan to use only 24x70 disposable motors (including Aerotech
         E's) and/or 24mm reloads, then yellow glue or epoxy a motor block
         2.5" into one end of the 6" motor tube. If you install the motor hook,
         file down the part that sticks into the tube. This will let you
         fit in 24mm reloads. Be sure and lightly sand the motor tube prior
         to installing motor hook. [NOTE: If you plan to use non-standard 24mm
         Aerotech motors than skip this step.]
      5. Epoxy one fiberglass-and-epoxy-reinforced centering ring 1/2" from the
         rear end of the motor tube. Be sure there is a notch in the ring to
         allow some movement of the motor hook. Epoxy a second centering ring
         in the middle of the motor tube. Epoxy a third ring 1/8" from the
         front of the motor tube. Install the motor tube into the main
         body tube with the motor tube flush with the bottom of the main body
         tube.
      6. Fiberglass-reinforce all of the fins. Apply the glass to both sides
         of the fins. Be sure that the fins are completely sanded (and any
         airfoiling/rounding completed) before applying the cloth. An optional
         step is to apply some 1/2" wide strips of glass along all of the
         fin edges EXCEPT the root edge.
      7. Rough up the epoxy on the main body tube along the lines where the
         fins will attach. Use 220 or coarser sandpaper. You really want the
         smooth epoxy coating roughed up. You can also drill a few 'rivet'
         holes along the fin attachment lines.
      8. Apply epoxy where the fins will attach and attach the fins. Do not
         fillet at this time.
      9. When the fins are dry, apply 1/2" strips of fiberglass cloth along
         each fin root edge, with 1/4" on the body tube and the other half of
         the width along the fin side. Coat this will coating epoxy. When
         dry, YOUR FINS WILL NOT COME OFF.
     10. Couple the bottom two body tube sections together. An option step
         is to make a payload section out of the third body tube section that
         comes with the Shadow. Use the LOC coupler to make a payload section.
         You can sand down the solid centering ring to slide inside the LOC
         coupler to form a bulk-head. Epoxy a 2"x 2" piece of scrap 1/16"
         plywood or 1/8" balsa to the inside surface of the bulkhead to add
         strength. Install either a large screw-eye or small eye-bolt to the
         center of the bulkhead, to be used to shock cord and parachute
         attachment.
      The end result of the above is a model which is really too heavy to
      fly on a D12. My modified Shadow came out to about 14 oz (I built it
      VERY heavy and added the payload section). My modified Broadsword came
      out to about 12 oz. Both have been flown on motors as small as composite
      D's (D21-4, D13-4R). The Shadow has flown on E15-4 (perfect), E30-4
      (a -5 is really needed), F24-7R, F39-7R, and G42-8. The Broadsword
      has just been test-flown on the D21-4 and E15-4. It WILL be flown on
      G42's, though.

      If you want to use 29mm motors in BT-80 based models, I would recommend
      either switching to plywood centering rings or sticking to low-thrust
      motors, such as the F14. In the end, if you want to fly 29mm, you would
      really be better off getting a kit designed as a Large Model Rocket from
      the start.
---------------------------------------
6.13   How can I prevent balsa fins from breaking off on landing (especially
       for models with swept fins)?

     From: Bob Craddock (craddock1@aol.com)
       Take your fin pattern, reduce it by ~90% on a xerox machine, and make
       as many copies as you need to glue one pattern on both sides of each
       fin.  Put about two coats of sanding sealer on the new paper surface,
       sand, and then paint the fins all over again.  A friend of mine was
       having the exact same trouble on his Super Big Bertha, and the paper
       reinforcement was his solution.  It worked great, but next time I
say use
       bass wood on everything.

     From: The Silent Observer (silent1@ix.netcom.com)
       There's a variation on this technique, that needs to be applied during
       building, that can make balsa fins stronger than bass (and still
lighter).
       What you need to do is simply to cover the fins before painting.
       I used silk tissue (like model airplane tissue made from silk
fibers) on my
       Big Bertha, and in a dozen flights (before it lodged high in a tree)
never
       had so much as a crack, even when flown on a D21 (and including one
       "plastic wad" recovery when the rocket hit the ground fairly hard).
You
       could use ordinary Japanese tissue, or Silkspan (R), or you could
even use
       something like nylon cloth or very light fiberglass (attached with
epoxy or
       CA in this case).
       With tissue, you need to cover the entire surface -- I simply
wrapped it
       over the rounded leading edge, and trimmed it off at the tapered
trailing
       edge, leaving the square "bottom" edge and the root uncovered.  You can
       attach Silkspan with almost any glue, but silk tissue (as I found)
"fuzzes"
       if you get it damp and handle it, so something like Testor's model
airplane
       glue or thick, clear nitrate dope might be a better choice; it won't
soften
       the binder that holds the fibers in the tissue together.
       Any of these, done after sanding (and filling, in the tissue cases)
will add
       significantly to the strength of the fin, while adding very little
weight.
       Making fins out of basswood or ply is probably okay with a Bertha
derivative
       -- they tend to be overstable in any case -- but may lead to an
unstable
       model if you have a design with less margin.

     From: David Bucher  (dbucher@mcn.org)
       There are two things you can do, both of which lower the rocket
       in a "fin up" attitude.  The first works by making a "yoke" or
harness for
       lowering the rocket body horizontally ( if you choose).  Install an
anchor
       (screw eye, inch worm shaped brass wire clip  etc.) through the body
tube
       wall between the fins at the rear end of the body.  Attach a squid
line or
       kevlar thread to the anchor and run it up the outside of the body
(tightly)
       and attach to the nose cone or 'chute.  Configure it to lower rocket as
       above.
        The other (and better!) way for the rocket you describe is to use rear
       ejection.  This will not help you with the present rocket, but any other
       rocket with sufficient body width will work just fine.  When making the
       motor mount assembly.  substitute a longer motor tube (29mm LOC
       tube for instance) and make up some ply or G10 centering rings
including
       two with a fair spread between where you can wrap the 'chute around
       the motor tube.  Install a solid bulkhead with cable lanyard to serve
       as a thrust ring and pressure block.  Make sure the motor mount unit
       slides well in the body and attach elastic to the cable lanyard and now
       you've got a rocket that ejects to the rear. Just cut a small notch
in the
       farthest forward centering rings to allow the shock cord to pass.
This me-
       thod works great and if you're confused by what I just wrote (a not un-
       heard of possibility!) just think of the internal "power pod" in some
       BGs.  It works the same way except you must make provision to conn-
       ect ALL parts together.  There are two things you can do, both of which
       lower the rocket in a "fin up" attitude.  The first works by making a
       "yoke" or harness for lowering the rocket body horizontally ( if you
       choose).  Install an anchor (screw eye, inch worm shaped brass wire
clip
       etc.) through the body tube wall between the fins at the rear end of
the
       body.  Attach a squid line or kevlar thread to the anchor and run it up
       the outside of the body (tightly) and attach to the nose cone or
'chute.
       Configure it to lower rocket as above.
---------------------------------------
6.14   I just lost my favorite rocket and the kit is discontinued.  How can I
         make another one just like it?

    From:  and 
      I don't know if everyone else already does this, but I've started
saving the
      kit card, instructions, and a copy of the fin shape or shapes for
every kit
      I build -- rockets have a way of getting lost or broken, and model
rocket
      companies have a way of discontinuing my favorite kits. Getting a
color copy
      of the decal sheet (or better yet, a color scan) is also a good idea.
---------------------------------------
6.15  How can I reduce damage to the booster stage of two stage models caused
      by the engine exhaust of the second stage?

    From: phunter@numill.com (Perry Hunter)
      Try scotch tape instead of masking tape. It should release fractionally
      faster and >might< reduce scorching of the lower stage.

      In some cases, it's possible to line the inside of the top of the lower
      stage with 20lb xerox paper, and it will take the damage rather than
      the exposed section of the stage. It's not possible to cover everything
      (slip fit couplers , etc. prevent lining all of it) but it can help.
---------------------------------------
6.16  Is there a way to increase the stability of a model with near
      neutral stability?

    From: Peter "My views are not to be confused with those
          of a rabbit librarian" Alway (alway@pooh.physics.lsa.umich.edu)

      Sounding rockets that are aerodynamically stable are often spun at a
      slower rate that insures that any off-axis thrust will cause the
      rocket to corkscrew, rather than follow an arc.  The corkscrew may
      be subtle--but it beats an equally subtle arc.  A sounding rocket
      that naturally describes an arc with a 20-mile radius due to its
      asymmetries cannot reach higher than 20 miles.  But if the rocket
      is spun through 360 degrees every few hundred feet, the
      20-mile-radius arc turns into a very suble corkscrew.

      Imageine the modeler puts a very slight misallignment between the
      forward and rear fins of a sidewinder.  Suppose it's just one degree.
      also suppose the fins are 1 foot apart.  the rocket will naturally
      arc in a circle with a 360-foot circumference and a 57-foot radius.
      That's instant doom!   make the error half as bad and you are in
      trouble.  But if the rocket spins every 10 feet, the path will be
      a generally upward corkscrew, less than ideal performance, but
      a safe flight.

      So with model rockets, a spin on ascent is a good way to make a
      marginal or asymmetrical model safe.  Estes used to sell a space
      shuttle orbiter kit that had a spin tab for this reason, and the
      old Astron Space Plane had spin tabs as well.
---------------------------------------
6.17  How can I build a rocket with less wind resistance?

    From: John DeMar (smdemar@mailbox.syr.edu)

      The best thing you can do is to NOT use launch lugs.  Use a
      launch tower instead.  A polished, smooth finish makes a big
      difference too.  If the design allows, use a boattail and make
      sure all transitions are smooth (from nosecones/payload sections,
      etc.).  Fin shape is a minor affect if they are relatively thin,
      otherwise make sure the edges are at least rounded.

      Here are some numbers for comparison:
         Standard finish, no transitions, with lug:    Cd = 0.88
         Standard finish, no lug:                           0.68
         Polished finish, no lug:                           0.61
         Standard finish, no lug, 2:1 boattail:             0.52
---------------------------------------
Copyright (c) 1996 Wolfram von Kiparski, editor.
Refer to Part 00 for the full copyright notice.

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