Building the BOILING MAD Steam Rocket
This steam rocket uses an aluminum tank from a 15-lb. CO2 fire extinguisher
for the motor. A 500,000 Btu weed burner torch heats the water. The guide rod
and main chute anchor cable are opposite the 2000 F torch flame.
The 1/4" steel holddown plate had mill scale, so the O-ring seat was milled.
The 16-ga. exit cone is TIG-welded. It could also be silver-brazed, but first
grind off the zinc galvanizing at the joint and overlap the seam 1/8".
The nozzle has a thread of 1 & 1/8" x 12 TPI to fit the tank, a 3/4" throat
diameter and an exit cone diameter of 2.5".
Only silver braze can be used, NOT common solder or even "silver-bearing"
solder. Silver solder melts at 1205 F and is VERY strong, used for exotic,
featherlight racing bicycles. Harris Safety-Silv45 is similar, sold at
welding supply stores. Use the flux made for each one. A propane or Mapp gas
plumber's torch works great.
The nozzle and fins are one unit that screws into the tank. The 1/4" ply
fins are bolted to 1/8" steel mounts that are welded to 3/8" square steel bars
welded down at the hold plate and at the 5/16" circular "halo" around the
tank. The tank seal silicone O-ring is Dash 216, MSC stock #06842165. Silicone
(high-temperature) O-rings must be used, NOT common black neoprene ones.
The pressure gauge is Northern Tool #53689 (4", 0 - 600 PSI) or #53690 (4",
0 - 1000 PSI). At 500 PSI, the hold-down force required is 221 lbs. minus 39
lbs. dead weight. At far left is the guide rod socket. Then the nozzle plug
with the copper line to the pressure gauge. On the nozzle plug is an O-ring
lubed with silicone grease. At the far right is the launch lever which pulls
away the support bolt. The nozzle plug (silicone) O-ring is Dash 016, MSC
The rocket motor with the nozzle/fins unit (with O-ring installed) screwed
in is filled with water upside down. The launch base is turned upside down
and the nozzle plug (with O-ring installed) is put into the nozzle with the
guide rod socket lined up with the "hook" on the nozzle/fins unit. Both are
now turned rightside up together. The rocket body is seated onto the bottom
of the motor with the upper guide rod guide lined up with the "hook" and the
guide rod socket. Then the hose clamp is tightened.
Over the main chute charge (1/2 level tsp FFFFg black powder in a masking
tape pouch) is the primary chute protector, an inverted 6" paper picnic bowl.
Over the paper bowl is this Bernzomatic Heat Cloth, intended to protect things
behind copper pipes that are being "sweated" (soldered) with a torch.
The nose cone cable goes through the heat cloth grommets and is attached to
the end of the friction rope. The chute shrouds are attached to the chain
link on the rope friction brake. The inner chute cable is attached inside to
a bolt on the upper part of the body tube. It exits the body tube as shown and
another cable goes from the bolt to the chain link on the holddown plate.
A 15 pound friction force is put on the 6 ft. rope to prevent any hard jolt
or bungee-cord rebound. The chute shrouds are put into the chain link on the
rope friction brake. The rope is tied to the anchor cable with a bowline and
there must be a figure eight knot at the end of the rope.
There is a 9-volt battery, a 4700 mFd cap, an LED and a switch in the nose
cone. When the rocket rises a bit up the guide rod, the delay fuse for the
chute charge is lit. The nose cone anchor cable and the (not yet taped over)
chute delay ignition wires are only outside the body tube here for display.
A paper clip taped to the guide rod is holding the delay-fuse-ignition
switch open. The clip will pass through the open part of the "hook".
The thumbscrew adjusts the flame. The adjuster is pulled off the handle by
a cord when launch pressure is reached. Pulling more slides the torch back
so that the rocket fin does not hit the wind guard.
The end of the torch must be 8 to 10 inches away from the motor. So it is
imperative to have a wind guard that keeps the flame on the tank. This is a
similar steam rocket.
All set to go at the NEFAR rocket club near Buell, Florida. This first
version, BOILING OVER, had a different nose cone and also used a drogue.
Pressure was monitored using a 20X spotting scope. The apogee on this first
launch was 790 feet. From the book we had on steam rockets, we expected more.
This is the no-drogue BOILING OVER seen from a different angle. This is at
the South Florida Rocket Club at Florida City. But it was too windy to launch.
The launch at Dan Griffin's sod farm, a perfect launch site, went to only
712 feet because there was a chute-deployment glitch. So the nose cone was
redesigned for pyro-fuse delay instead of using altimeter chute deployment.
This is one frame of the launch video. Measuring the length of the rocket
(4 ft), the distance gone in 5 frames and the time of those frames (5/30 sec),
it is going 78 ft/sec or 53 MPH here.
Rocket weight full: 39 lb.
Water: 2 gallons
Rocket weight empty : 24 lb
Main chute size: 8 feet
Nozzle throat: 3/4"
Exit nozzle diameter: 2.5"
Specific impulse : 45 sec (half that of black powder)
Impulse: 720 lb-sec (L)
Thrust duration: .93 seconds (28 video frames)
Total cost per launch: $2.00!