The Plumber's Delight Launch Pad
Bill Owens, NAR#61063

Reprinted electronically from The Upstate Rocketeer, the section 
newsletter of MARS (NAR Section 136)

Good launch pads are expensive, and I'd rather spend my money on body
tubes and whoosh generators. But the slickest pad designs I've seen all
involve metalworking, welding, or some other craft which is beyond my
limited resources. Therefore, I've worked out a design for a strong,
stable, versatile pad which can be built with simple hand tools out of
inexpensive materials but which has the features of the better
commercial pads. The design borrows some ideas from commercial pads
(Quest and Hobbylabs have simpler, tripod designs) and uses a variation
on a tilt head detailed in a recent issue of Sport Rocketry.

The Plumber's Delight is a 4-legged pad design with a wide stance for
maximum stability, but which stands almost two feet off the ground for
convenience. It has an easy to use tilt head and can accept launch rods
up to 1/4" diameter with quick and easy rod changes. It can be broken
down into a very small package for transport (about 6" dia x 28" long,
without the launch rods) and assembled at the field in seconds. It can
also be made light or have weight added to make it as heavy as desired.
Finally, all the parts can be easily obtained (in Rochester, Builder's
Square has all the parts except the rod and the steel plate, and Chase
Pitkin has those). I purchased everything necessary for under $20.


Construction

The base of the PD is a 1" CPVC pipe 4-way crossover fitting. It looks
like a cross, with four female fittings at 90 degrees to each other.
Each leg consists of a 24" piece of 1" CPVC pipe, with a cap at one end
and a 45 degree elbow at the other. If you can find street elbows
(female one end, male the other), so much the better; if not, cut 2"
lengths of pipe and attach them to the elbows (see Figure 1). Using
CPVC cement, glue the caps and elbows on the legs, and glue the 2"
sections into the elbows. For your own sake, please do this in a very
well ventilated area or outside, the cement consists of some nasty
chemicals!

To make the tilt head, assemble the eyebolts, rubber and steel washers
as shown in Figure 1 (fender washer, eyebolt, two small steel washers,
large rubber washer, two small rubber washers, eyebolt, large rubber
washer, two small steel washers, eyebolt, fender washer) and clamp the
whole stack together with the 1/4x20 bolt and wingnut. The small rubber
and steel washers are optional; they help to keep the eyebolts centered
on the 1/4x20 bolt. If you leave them out, check that the stack is
centered before tightening (or use a larger center bolt, with
correspondingly larger washers).

With the tilt head assembled, swing the outside eyebolts so that they
face one direction, with the middle eyebolt facing opposite. Measure
the distance between the ends of the outside bolts (should be about
1/2") and drill two 1/4" holes in the center of the 4-way fitting
(through one side of the fitting only). Check the inside of the fitting
before drilling; the one I used was molded with thicker plastic in one
direction, so I chose that location for the holes. Place a nut on each
bolt and insert them into the holes, then place nuts on the inside and
tighten both bolts. The nuts on the outside of the fitting help to lock
the bolts in place (and are easier to reach with a wrench).

Next, clean any oil or dirt off one end of the launch rod and wrap it
with about 9 layers of masking tape.  The resulting cylinder of tape
should be about 1/4" in diameter. Using pliers if necessary, twist the
taped end of the rod halfway into the 1/4" rod coupler. The rod should
project straight out of the coupler, and should fit quite tightly.

To make the blast deflector, cut your choice of shape (round, square,
rectangular, whatever) out of the steel sheet and drill a 1/4" hole in
it. Place a nut on the middle eyebolt and drop the deflector on the
bolt, then thread the launch rod onto the bolt. It might be necessary
to trim the eyebolt somewhat to make everything fit correctly. Finally,
attach the legs to the 4-way fitting and your pad is complete!


Options

If you don't need a tilt head, just drill one hole all the way through
the center of the 4-way fitting and insert a 1 3/4" long 1/4x20 bolt.
Place a nut on the bolt to hold it in, drop the blast deflector on and
attach the launch rod.

Depending on your philosophy of blast deflectors, you may wish to use a
drop on deflector, in which case the rod coupler nut is better
protected from the hot exhaust gases. You might also want to bend the
deflector at an angle to deflect burning particles away from the tail
of the rocket.

For a heavier, more stable pad, fill the legs with your choice of steel
shot, sand, or concrete and plug the open ends if necessary.
Personally, I use clothes hangers bent to form U-shaped stakes, and
simply stake the legs down.

Additional launch rods can be added by the tape wrap method above for
up to 3/16" dia; 1/4" rods can simply be threaded with an appropriate
die.


Parts List

Description			Quantity

For pad:
1" CPVC pipe			10'
1" CPVC 4-way crossover		1
1" CPVC 45 degree elbow		4
1" CPVC cap			4
CPVC cement			1 bottle
1/8"x3' steel rod		1
1/4" threaded rod coupler	1
16ga steel sheet		1

For tilt head:
1/4"x20 eyebolt			3
1/4"x20x1 1/4" bolt		1
1/4" fender washer		2
1/4" steel washer		4
1/4" large rubber washer 	2
1/4" small rubber washer 	2
1/4"x20 nut			6


