Re: Home make launchers

From: Pat Flannery (flanner_at_daktel.com)
Date: 07/22/04 

Date: Thu, 22 Jul 2004 01:46:39 -0500

Bryan Ashcraft wrote:

>Hehehe, believe it or not I have tried using oranges when there was a
>personal potato shortage. There didn't appear much difference with flight
>characteristics, however the barrel did get a little sticky and attracted
>wasps! This is where a toilet brush and some warm saopy water came in handy.
>

Grapes out of PVC plumbing pipe blowguns work great also; the grape's
flexability lets it seal well with the tube, but the grape ruptures on
impact with the target, transfering its energy into the foe with a
satisfieng wallop that can be heard from over fifty feet away, and
leaving a bruise that lasts many days.

>
>Another thing I tried once was tipping some frozen peas on top of the spud
>to be fired. This made marvelous birdshot ;-)
>

That would probably be "Birdseye" shot; as they make frozen peas.
A big Foster's Lager can with its top removed, filled with gravel, and
covered with aluminum foil fired from a homemade gunpowder cannon works
great. 3/8" thick plywood ends up looking like Swiss Cheese, and in my
test ended up with a rectangular hole in it as the can passed through it
going sideways.

>
>
>Ok, I'll bite, how did you manage to blow yourself up?
>
By trying to reload a 175 mm siege morter without swabbing out the
barrel; I had a one-pound can of gunpowder detonate in my right hand.

I wrote about this and some of my other world class screw-ups:

The foot-long plumbing-pipe rocket motor:

"I was standing in the Blockhouse (our enclosed porch) safely behind one
of the glass windows, when the countdown reached zero, and the plug of the
20,000 volt furnace ignition coil went into wall socket, sending the power
to the spark plug located at the bottom of the rocket motor (buried in the
heap of mud to contain shrapnel in case of a casing failure) and the little
dab of You-Know-What that was applied overits spark gap- in earlier tests,
with a fuse igniter (which made the device scarily resemble a pipe bomb)
The grain was ignited at the bottom of the central hole, leading to a second
or so until full thrust was achieved, as the fire propagated up the inside of
the grain- but I knew that that wasn't very effective, and would lead to a
slow liftoff when it had grown fins.
The engine started nicely, blew the buried sparkplug out of its hole (this making
a _downward_ facing hole of larger diamiter than the upward facing exhaust
nozzle), and then, like a Minuteman missile, rose majestically from it's mudpile,
straight up, breathing fire at both ends, finless, and rising rapidly out of my
field of vision through the window- this occurred as my father was leaving in the
family car to investigate the fire at a building we owned and rented out.
I didn't know how high it was going to go, or in which direction, but the
"launch technicians"; my somewhat smarter friends, cowering behind the
concrete wall into the alley, saw it reach an altitude of around 75 feet,
and head on a trajectory toward the departing car. My father saw the impact
of the motor about thirty feet from the car, as he waited at the corner
yield sign, completely ruining any chance of "plausible deniability" of the
incident. Around a half hour later he got back from the fire, which had been
minor, and had a little talk with me.
But I had learned my lesson, and only did tests from then on when my parents
were far away from the house. After the flaming birch tree incident caused by
the fuze-ignited/gunpowder down center grain bore boosted ignition strapdown
test which shattered the fuel grain and led to the giant blast of exhaust
going up to the tree above it under the tree (I blamed the somewhat blackened
condition of the upper branches on a possible case of tree blight.), it was
time to start the aerial tests, from a shooting range at one of the local
reservoirs,
By then it was winter, and the motor had aluminum fins, made from bookshelf
supports attached to it with the aid of two hose clamps. As it stood there,
in it's proud red primer paint scheme, ready to challenge the heavens from
the pie tin that was its launch pad and blast deflector perched on a snowbank
the hissing of the waterproof fuse gave announcement of the beginning of a
new age, as our launch team cowered behind the families other, more beat up car.
The fire slowly reached the bottom of the rocket, and the cocktail straw full of
gunpowder waiting inside it, as we all cringed in gleeful expectation- A
terrific roar! A vast cloud of white smoke! Something traveling upwards
hundreds of feet in a blink of an eye; then the long futile search for the
rocket, which could give eternal evidence of my technical virtuosity...and
more importantly, could be used as evidence in a court of law if found by
someone "not in the loop" of the experiments.
No luck, but I had learned my lesson, and swore that from now on, I would
wear gloves when handling my rockets, so as not to leave possibly
incriminating fingerprints on them. It was only when we examined the piepad
that we noticed an odd hole in the center of it, with three rips, each 120
degrees apart, radiating from it. The body of the rocket, minus it's
screw-on nosecap, was found about a foot under the pad. Apparently, the high
pressure gas of the burning propellant had seeped out around the top joint
(I should have gotten in touch with NASA about this: Cold Weather + Leaky
Joint On Solid Rocket Booster = No Go.), "lubricating" it with hot gas, so
that it unscrewed nearly instantaneously, or simply tore off the threads.
The Pipe Motor program ended on that embarrassing note, the one intended to
stay put having gone into the air; the one that was to have gone into the
air descending through the launchpad.
But I had learned my lesson- Gunpowder, not You-Know-What, was the wave of
the future- and my 100 mm cannon, 175 mm siege mortar, and trip to the
emergency room were just around the corner!"

The Great Big Cannons.

"Mine never blew- just lifted off backwards from the strap-down test minus
stabilizing fins, and unscrewed the nosecap on high pressure gas- these were
the "Caramel Candy" variety... on the other hand I cannot possibly stress
the importance of swabbing out the barrel of a siege mortar before you begin
pouring black powder into it from a 1 pound can...still it could have been
worse...it could have gone off when I was leaning over it putting the
projectile into it- making a 7 inch diameter hole through me, rather than
merely setting me on fire and partially blowing my thumb off."

Lightning Death To The Ants.

Then there was the destruction of the anthill by driving the two rods from the anode
and cathode of the 20,000 volt furnace ignition coil into the ground on either side of it,
and letting the current flow through the intervening ground; a plan that worked well until
I reached down and removed one of the rods; thereby allowing the current to flow through the
ground into my tennis shoes and out via my hand, which surprisingly was not insulated
by the oven mitt covered with the plastic bread bag as I thought it would be...my
friend said I cut a most striking figure as I bounded down the boulevard, leaving
lightning flashes each time my shoes touched the ground, until the wires pulled off
of the ignition coil; and allowed the muscles in my hand to relax.
But it was after the siege mortar explosion that my friends started referring to
me as "Wile E. Coyote", or "Professor Fate"; and showed their deep concern for my
condition by eating two large pizzas between the three of them as well as drinking
a case of beer, before they arrived at the hospital to visit me- laughing hysterically."

The Bomb In The Basement Sink

"You can take a large empty tin for percussion caps, fill it with black
powder, put a length of waterproof fuze in it, and sink it to the bottom
of your forty gallon square shaped cast-concrete sink in the
basement...with a submerged air-filled glass Christmas tree ornament
next to it to demonstrate how depth charges destroy submarines by
shockwaves traveling through water...
The experiment will demonstrate many things:
1.) Water is basically incompressible.
2.) It is an excellent tamping compound for any explosive.
3.) Properly tamped, even a small amount of gunpowder packs a great deal
of energy.
4.) It is fully possible to move a cubic block of water of about forty
gallons volume in a vertical direction at high velocity while
maintaining it in an approximately cubic form.
5.) Glass Christmas Tree ornaments are far stronger that they would
appear to be... strong enought to rise up in a vertical column of
explosivly driven water intact...but not so strong that the can survive
being driven into a ceiling joist at around a hundred miles per hour.
6.) As well as worrying about spilling water and have it leak through
the floor into the downstairs story, it is also possible to have
"spilled" water emerge _through_ the floor of the story above you.
7.) Barnes Wallis was quite correct when he realized that even small
explosions can crack concrete when the blast is tamped by water, and the
explosive is in direct contact with the concrete...such as the concrete
of the face of the Mohne dam...or the concrete at the bottom of a
cast-concrete basement sink. It only leaked around a pint or two a
minute after that- from the hairline cracks in the bottom."

Pat