The Rocket Motor...What Makes
It Go?
Featuring the Conklin Comet
The propulsion system for the CONKLIN COMET Rocket Car is composed of
three basic subsystems. These are the fuel, control and motor subsystems.
The fuel is 90% or 98% hydrogen peroxide. No other chemical takes part
i the thrust producing process. This fact puts the CONKLIN COMET Rocket
motor in the liquid monopropellant classification of rocket systems. The
peroxide is a clear, odorless, non-volatile, non-explosive, non-flammable
and non-toxic liquid. It is easily decomposed by most materials into water
and oxygen gas. this decomposition produces energy in the form of heat.
This heat energy is what is utilized in generating the power in the CONKLIN
COMET rocket motor. Because the fuel is easily decomposed, all materials
it comes in contact with must be of the type with which it does nor react.
In the CONKLIN COMET rocket fuel system these materials are 300 series stainless
steel, teflon, tygon, and polypropylene. these materials must be kept free
of such contaminants as dirt, oil, grease, or other organic materials.
The peroxide is purchased in 26 gallon drums made of a special alloy
of aluminum and is not removed  from
these drums until time for use. It is then transferred from the storage
drums to the fuel tank in the CONKLIN COMET rocket by means of a polypropylene
pump. In some cases when the specific volume of fuel is required for a specific
vehicle performance characteristics, this predetermined volume is measured
out in a separate polypropylene bottle and then transferred to the CONKLIN
COMET fuel tank. Care must be taken not to spill any fuel on the vehicle
since it is very corrosive.
The fuel tank has a high capacity of 17 gallons and weighs 100 lbs. It
is fabricated of 316 stainless steel. It is shatterproof and rated at 800
psi with all interior welds sandblasted and subjected to nitric acid rinse.
The fuel is transferred from the pump to the fuel tank in Tygon hose, the
fuel tank has pressure vent and rapid-drain systems.
The control system is composed of storage tanks for nitrogen gas, plumbing
for distributing the gas, a nitrogen pressure regulator, burst diaphragm
and the throttle valve. The nitrogen gas is used to push the fuel from the
fuel tank into the rocket motor. The nitrogen is an inert gas which is odorless,
colorless, non-toxic and non-flammable. It is stored at a pressure of 2500
psi in two spherical tanks (SEE ABOVE PHOTO) each about one cu. ft. capacity.
These containers at the rear of the vehicle are fabricated of steel and
wrapped in fiberglass fiber to increase their strength to weight ratio.
These containers are filled from the standard type of gas bottles used in
welding. The nitrogen storage containers are rated at 3000 psi, as is all
plumbing used in the distribution system.
When the rocket motor is to be fired, the high pressure nitrogen gas
is released from the storage containers by a foot actuated ball valve and
allowed to proceed to the nitrogen regulator where the pressure is reduced
to and maintained at 525 psi. on the downstream side of the regulator. This
pressure regulator is a Victor model GD-97 which is used in many space age
applications. The downstream pressure loading is set by the driver while
in the vehicle just before the run and can be varied by means of a valve.
By actuating another valve the driver can deliver the nitrogen gas to the
fuel tank and pressurize it to the required pressure of 425 psi. Although
625 psi is the optimum fuel pressure at which to operate, the driver may
load the fuel tank to 675 psi. At this pressure the burst diaphragm on the
tank will burst releasing all the tank pressure. This safety device prevents
overloading the fuel tank.
 Ky was also the owner & builder
of the Conklin Comet
The thrust of the motor is regulated by controlling the flow rate of
the fuel into the motor. This control is accomplished very simply by a Hills-McCanna
ball valve. This ball valve is located in the fuel line between the fuel
tank and the rocket motor. The valve handle is connected to the throttle
stick in the driver compartment by means of a series of linkages. Pulling
the throttle to the rear opens the valve. The distance the throttle is pulled
back determines the amount the valve is opened. If the valve is full open,
enough fuel reaches the the motor to give a full thrust condition. Of course
the fuel flow takes place when the valve is opened because the fuel tank
has been pre-loaded to a pressure of 525 psi but the nitrogen gas and this
loading is kept constant during the run by the nitrogen regulator. When
the valve is closed the fuel flow to the motor is stopped and the motor
shuts down instantly. After firing the motor, the pressure in the fuel tank
is released by means of a vent valve actuated by the driver. In case the
throttle valve should not close after turning on the motor, the motor can
be instantly stopped by opening the fuel tank vent valve and releasing the
tank pressure.
The rocket motor is constructed of 316 stainless steel. The catalyst
pack is a mix of silver and nickel wire cloth packed into a mat and positioned
just behind the fuel injector plate. The total length of the motor is just
24" and it is 12" in diameter at the point of maximum diameter.
The principal of operation of the motor is simple. The fuel enters the fuel
manifold and is evenly distributed over the catalyst pack by a plate perforated
with hundreds of small holes much the same way the water comes out of a
bathroom shower head. This spray of fuel is forced through a maze of catalyst
pack and is completely decomposed to superheated steam and oxygen gas. This
decomposition liberated a great deal of heat causing the temperature inside
the motor to reach 1370 Fahrenheit degrees. This temperature rise causes
the pressure inside the motor to soar to 300 psi.
This combination of heat and pressure results in the steam and oxygen
being forced out the exhaust nozzle at a speed of 4000 feet per second.
At full thrust the motor consumes 3 gallons of fuel per second with each
gallon weighing 11.6 lbs. Since the decomposition of the 34.8 lbs. of fuel
per second also produces 34.8 lbs. of gases per second, a situation exists
where the motor is expelling 34.8 lbs. of gas at the enormous speed of 4000
feet per second. This results in a forward shove on the CONKLIN COMET rocket
of 3000 lbs. which is applied constantly ad long as the driver has the stick
to the wood. If the throttle is only partial opened, he gets only partial
thrust. So it is possible to drive the vehicle at any speed desired up to
the maximum.
The affect of fuel decomposition by the catalyst pack is very similar
to throwing a bucket of water on red hot chunk of metal. The water constantly
flashes to steam as does the peroxide when it is forced through the silver
and nickel of the catalyst pack. The exhaust from the rocket motor is not
visible and since it is composed of steam and oxygen, it is not toxic. Because
there is no burning taking place i the motor, there is no flame produced.
The only sign of action on the part of the motor is a great deal of noise.
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