THE YELLOW JACKET

Mapp Gas Cylinder Steam Rocket

   Some of you may know what yellow jacket wasps are, or even had the honor
of witnessing their ferocious hive-protection battle tactics first hand.
This latest steam rocket was named in their honor.

   YELLOW JACKET and GREEN MONSTER are similar in design.  Machine shop work
and welding are required.  Start by burning out every bit of Mapp gas or
propane when a tank is nearly empty by lighting the torch or camp stove and
letting it burn until the flame goes out.
   Check that the tank fitting is square with the tank body. If it isn't, tap
the high side with a hammer lightly and keep checking it until it is.
The hold-down plate.
   The steel hold plate needs to have a 7/8" hole cut into it with a hole saw.
The rest can be cut with a hacksaw, power jig saw or a metal-cutting bandsaw.
(This hold plate was 1/4", but 3/16" would have been lighter.)
Turning the tank fitting to match the hold plate.
   You will probably need to turn the unthreaded part of the tank fitting to
fit the "7/8 in. hole" because hole saws do not cut precise diameters.
Drill out the tank fitting to 1/2" in the lathe or a drill press.
Drilling the nozzle throat.
   After drilling the nozzle throat, the inlet valve will fall free inside.
Turn the tank upside down and keep shaking it until the pin, which is normally
inside the tank, is seen in the hole.  Get pliers on the pin and pull it out.
Remove the label.
   There will be a sharp edge left around the hole inside the tank.  Remove it
with a ball burr in a drill, drill press or Dremel tool.  (It would be even
better to taper the fitting to 90 degrees inside.)  Holding it upside down,
use an air gun to blow the metal chips out.
The tank with hold plate and exit cone.
   The hold plate was welded onto the tank fitting threads and the center was
pipe-reamed 30 degrees.  Leave about 3/16" straight for the O-ring seat.
   The exit cone seam was TIG-welded and then the exit cone was silver-brazed
into the hold plate. (Two propane torches were required.) It is very important
to get the nozzle throat and exit cone aligned precisely with the tank.
   A brass disk was also silver-soldered over the relief valve fitting after
removing the paint and then fluxing.
The fin supports and fin mounts.
   The 1/4" x 1/4" fin supports were TIG-welded to the hold plate and the 1/4"
ring around the tank. (A 3/16" ring would have been lighter.)  The 1/16" fin
mounts were TIG-welded to the fin supports.
The nozzle plug, hold-down bar and pressure gauge.
   This is the same base used for the GREEN MONSTER but with a 1/2" by 9 foot
stainless guide rod.  The O-rings are Dash 012, MSC #06840128.
The battery and switch compartment.
   The white bead at left is the Safe/Arm push-pull.  The microswitch finger
is next, swinging out to burn the delay fuse ignitor when the rocket rises up
off the trigger wire. At the bottom is the ignitor tip near the end of the
fuse.  (These will be taped together.)  The 3-foot chute is deployed by a 12-
second delay (4" pyro fuse). The chute charge is a slightly-rounded 1/8 tsp.
of FFFFg black powder.
The ignition system set for launch.
   The Safe/Arm pin still has the safety clip on it. The trigger wire is now
in the copper-wire loop, holding the switch finger back. Next is the guide rod
screw eye. Then the fuse, fuse hook and ignitor tip.  At the bottom is the
chute cable spring clip on the hose clamp.  The rocket hangs from this clip
while descending under the chute.
   The trigger wire, launch rod, fuse and chute cable are opposite the torch.
YELLOW JACKET seen from launch control.
   At 500 PSI, the hold-down force required is 98 pounds minus the dead weight
of 3 lbs. 6 oz. for the rocket plus 2 pounds (2 pints) for the water.
(At 600 PSI, the hold force is 118 pounds and 132 pounds at 700 PSI.)
The continuity tester.
   This is the same one used for all the other steam and chemical rockets.
The primary and secondary chute savers.
   The primary chute saver is an aluminum muffin cup.  The secondary uses a
coffee bag cut to 8 & 1/2" by 12 & 1/2" and then formed over a bottle into a
cup 2 & 3/4" wide x 7 & 1/2" deep and taped on the bottom.  The two chute
savers are then taped bottom to bottom.
   The YELLOW JACKET is 38 & 1/4 in. ( 3.19 ft.) long.  In the video, the
rocket is 7/16" high or 14/32".  Scale is 1/32" = .2278 feet.
Frame number 228 of the video.
YELLOW JACKET launch.
   Measurements from the video frames indicate that the rocket has gone 1.82
ft. from the starting-point frame to the next frame 1/30 sec later, which is
54.6 ft/sec or 37 MPH.  Then 51 MPH, 70 MPH, 87 MPH, 112 MPH and 126 MPH
before going out of view.
   The pressure was about 625 lbs at explode-off. The Quest How High altimeter
in the nose cone gives the apogee as 735 ft.
The final descent.