CSV19 Pneumatic Antenna Launching System

This air-powered Tennis Ball launcher is designed to launch tennis balls over
trees towing fishing line. The fishing line is used to pull up nylon twine and
wire antennas, or heavier line and larger antennas. This design is 19 inches
long and optimized to fit in a Rubbermaid (tm) plastic tote box so that it may
be easily deployed to the field. These launchers are used by Amateur Radio
groups doing Emergency Service and other portable work, as well as installing
antennas in backyard trees.

Document Notes

Version 1.94 12/2/2005

Model TBL-CSV19 Antenna Launcher Specifications

Overall Length: approximately 19 inches.

Weight: approximately 6.5 pounds.

Barrel: 16 inches by 2.5 inches, Tennis Ball size.

Chamber: 8" by 4" dia = 100 cu in (approx 1.5 liters)

Valve: 1" sprinkler valve, modified for pneumatic actuation - no batteries
required.

Pressure Rating: materials rated to minimum 120 psi working pressure. PVC
Pipe rated to at least 200 psi working pressure. Note that Exceeding 100 psi
may damage pressure gauge.

Operational Pressure: 80 psi maximum recommended.

Performance with 4 oz Tennis Ball towing fishing line:

150 feet height at approx 50 psi.

100 feet requires approx 40 psi.

CO2 Consumption: 150 feet height requires approx 0.4 oz, or
about 30 launches per 12 oz refill.

Designed to easily fit in Rubbermaid(tm) tote.

Cost: Materials to build this launcher cost approximately $60, not
including fishing reel mount, reel or line.

NOTE: PVC is not recommended by the manufacturer for use with compressed
gasses due to potential fragmentation if it is broken while containing
pressure.
This launcher operates considerably below the rated working
pressures of the PVC materials for an extra margin of safety. The pipe and
fittings are rated at 200 psi or greater in this design.

CSV19 Antenna Launcher Performance Data

Measurements

Measurement 9/05 using SDR21 barrel, Teflon impregnated Spectra line, Zip Reel,
CO2, 4 oz ball, 5000 feet elevation, cool sunny morning - 50 psi 154 feet.

Measured 40 psi 114 feet with Dacron twisted kite line (with Schedule 40 barrel)
(Note that the line makes a significant difference, and changing to a new
Spectra based synthetic line yielded 20% higher trajectory.) (Note that trajectory
depends on many variables and will change slighly with altitude and temperature).

Computer Modelled Performance*

CSV-19 Compact Sprinkler Valve 19 inch Launcher

system Cv 5.0 Ballwt 4.0 ounces

chp oal chl bbl fps sec xbp xcp ht tofl

30 19 8 14 79 0.020 0.2 20.5 76 4.4
40 19 8 14 105 0.017 1.3 29.7 117 5.4
50 19 8 14 123 0.015 2.5 38.8 146 6.0
60 19 8 14 138 0.014 3.7 48.0 168 6.5
70 19 8 14 151 0.013 4.8 57.1 188 6.9
80 19 8 14 162 0.013 5.9 66.3 205 7.2

Cv = system flow coefficient, gpm per psi
chp = chamber pressure in psi
oal = overall length inches
chl = chamber length
bbl = barrel length
fps = velocity feet per second
sec = barrel time in seconds
xbp = exit bore pressure
xcp = exit chamber pressure
ht = peak trajectory height in feet
tofl = time of flight in seconds

* note that these performance numbers are uncalibrated and subject to change
based on measurements with your own launcher. The Cv value can be adjusted to
fit your specific results. They seem to be quite close to the Dacron line
measurement, however measurements with new synthetic line were 20% higher.
As the line ages the performance at higher heights drops slightly due to
increased drag from wear on the line.

How the CSV19 Tennis Ball Launcher Works
The Pneumatic Launcher consists
of three main elements - the Pressure Chamber, the Valve, and the Barrel. First
we will describe the system's operation, then some details of the valve.

A tennis ball with fishing line attached is pushed down the barrel using the
ramrod. Tennis balls are quite tight in the barrel. The fishing reel is set to
feed out line quickly.. The pressure chamber is pumped up with air using a tire
pump to a nominal pressure of about 40 psi. The Launcher is aimed at a steep
angle to lob the tennis ball over the desired branch or tree and triggered. The
valve opens quickly and the air flows through the valve and pressurizes the
barrel. The pressurized air expands into the lower pressure in the barrel and
places force on the tennis ball. The force on the ball is the area times the
pressure, or about 5 square inches times the pressure. For example if the barrel
pressure was 10 psi the force on the ball is 50 pounds. The force on the tennis
ball from the pressure accelerates the ball down the barrel. The force and
acceleration are substantial. In the case of 10 psi and 50 pounds the
acceleration would be 400 times that of gravity! The pressurized air continues
to flow from the pressure chamber through the valve into the barrel. As the ball
moves down the barrel the volume of the air in the barrel increases dramatically
and the pressure drops since the air coming through the valve cannot keep up
with the increasing volume in the barrel. The airlofw through the valve is
limited by the diameter of the flow path in the sprinkler valve and the speed of
sound - the air cannot flow faster. In this launcher the valve airflow is near
the speed of sound most of the time. The tennis ball is accelerated and leaves
the barrel with enough velocity to accomplish the desired trajectory, towing the
fishing line over the tree. The velocity is generally lower than a fast tennis
serve for the heights we need. A professional tennis player's fast serve would
launch an untethered tennis ball nearly 300 feet high.

The Valve we are using is a sprinkler valve, which is a type of Pilot valve.
Pilot valves use the pressure of the fluid (or gas) they are controlling to do
the work of moving the valve, using a clever pressure differential system.
Inside the valve is a diaphragm holding the valve seat closed. Attempting to
open the valve the pressure has only the 1" circular area of the valve to work
against. (The force is determined by the pressure times the area). The closing
force on the valve is developed from a small spring (very minor force) plus the
pressure acting on the larger area of the diaphragm (more than a 1" circle).
This gives more force in the direction of closing, and seals the valve tightly
to keep it from leaking. There is a small pressure equalization hole in the
diaphragm that allows the pressure on both sides to equalize to the same. Since
the areas are different, the force is not the same and the valve stays closed.

Triggering the valve is accomplished via the blowgun valve. The blowgun is on
the pilot side of the diaphragm, and when open it allows the pressure on this
side of the diaphragm to vent to atmosphere. The equalization port is attempting
to build the pressure while the blowgun is releasing it, but the equalization
port is very small and so the blowgun wins, and the pressure on the pilot side
of the diaphragm drops. The pressure on the inlet side of the valve can then
move the diaphragm and open the valve seat. This process can occur in a few
milliseconds due to the large force from the pressure. The rate is primarily
determined by how quickly the trigger system can exhaust the pilot area, the
mass of the diaphragm, the ratio of areas, etc.

If we were to actuate the valve using the electric solenoid it would be much
slower to open, and it would not open as far. The normal purpose of a sprinkler
valve is to turn sprinklers on and off, going fast is not actually desired at
all for water valves - water hammer is hard on things. The solenoid ports are
very small and cannot be opened up as much as the blowgun. The batteries and
wiring and the solenoid sticking out are not as nice a system to build and
maintain, and not as lightweight and compact. I used batteries with my first
launcher, and have since modified it for pneumatic operation. The performance
was about doubled with this upgrade (twice the height for the same pressure).
The valve oscillated and made a honking sound with electric actuation. It was
clearly not opening as effectively as it does when pneumatically actuated. In
fact, the pneumatic operation is what enables this CSV19 compact launcher to be
so small and still be so effective - able to reach well over 150 feet of height.
Electrically actuated it would not have very adequate performance for our
purpose - it would have to be made larger to do the job adequately.

How to Obtain a CSV19 Launcher
There are several ways to obtain your own
CSV19 launcher. One is to obtain the parts and build it from scratch. Another is
to purchase a kit (or a built unit) from the Online
Order Page.

EHam.net Reviews
There are two review threads on the EHam.net website
that talk about the CSV19 Launcher.

CSV19 Reviews 1

CSV19 Reviews 2

Instructions
for Building the CSV19 Launcher
The instructions have been moved to a
new page. Select the link above to load the instructions page.

Have Fun and Be Safe!

See our new Online Order Page!

The
Rest of the Story contains information about the support equipment and usage
of the Antenna Line Launchers.

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