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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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