Engine Electrical System

This is a computer drawing of the electrical system of the Wright brothers' 1903  aircraft engine. This engine powered the first, heavier than air, self-propelled, mane uverable, piloted aircraft; the Wright 1903 Flyer at Kitty Hawk, North Carolina, in  December, 1903. To generate thrust for their aircraft, the brothers used twin,  counter-rotating propellers at the rear of the aircraft. To turn the propellers, the  brothers designed and built a water-cooled, gasoline powered, four-stroke, four c ylinder,internal combustion engine. Mechanical Operation The figure at the top shows the major components of the electrical system on  the Wright 1903 engine. In any internal combustion engine, fuel and oxygen are  combined in a combustion process to produce the power to turn the crankshaft  of the engine. The job of the electrical system is to provide the spark which initiates  combustion. Electrical power is generated by the magneto at the rear of the engine. The magneto  relies on the physics principle ofelectrical inductance to produce electricity;  when a wire is moved through a magnetic field an electrical current is inducedin  the wire. The magneto has a large, U - shaped, permanent magnet at the top.  Between the arms of the magnet, a wire is rotated on a shaft which is turned by  the friction drive wheel rubbing on the engine flywheel. An electrical current is  induced in the moving wire. The power to turn the magneto is provided by the  running engine. The magneto is very similar to the alternator or generator on a  modern automobile. The Wright brothers purchased their magneto and it  provided a very modest 10 volts at 4 amps in operation. Two wires connect  the magneto to the engine; a ground wire to the leg of the crankcase, and  a power wire to the bus bar on the outside of the four combustion  chambers of the engine. On each combustion chamber, the bus bar conducts electricity to an ignition  plug which is screwed through the wall of the chamber. The plug is insulated  from the wall of the chamber. Inside the chamber, there is a contact  switch which is movable. When the switch is closed, a circuit is created  and electricity flows through the wires, bus bar and plug. When the switch  is opened quickly, a spark is generated. You can see this effect if you  pull the plug on an operating appliance at home. Spring levers  mounted on the outside of the chamber are used to open and close  the contact switch by an insulated shaft which passes through the wall  of the combustion chamber. The spring levers are attached to the crankcase  of the engine which is grounded to the magneto. The levers are activated  by cams which turn on a cam shaft under the engine. The cam shaft is  linked by gears to the exhaust valve cam shaft which is turned by the  timing chain. The gears and cams insure that the contact switch is  opened, and the ignition spark occurs at just the proper moment of  the engine cycle. Here's a computer animation of the action of the levers  and contact switch: In this animation, we have cut open cylinder #3 so that you can watch the motion of the valves, cams, rocker arms, and electrical contacts and switches. The spring which  moves the electrical contact  inside cylinder #3 is partially hidden by the cylinder itself. The spring is barely visible  behind the blue exhaust valve spring. You can better see the action of the electric cam  and spring on the adjoining cylinder #4 to the right. But notice that the timing of the motion of the switches and valves is different between adjoining cylinders. On the animation, we have cut the bus bar to allow us to see inside cylinder #3; the bar wraps around cylinder  #3 in the same way that it wraps around cylinder #2 to the left. How Does It Work? To understand how the electrical system works, we have drawn a simplified wiring diagram of the engine: We have numbered the cylinders (and combustion chambers) from 1 to 4 going  from the front of the engine to the back. The magneto, wires, contact switches, and grounded cylinders produce an electrical circuit, which you have heard about in school. This particular type of circuit is called a parallel circuit because  there are parallel lines running through the four cylinders. The contact switch on any cylinder can be opened or closed without affecting the neighboring cylinders.  (If the cylinders were wired in series, opening any switch would cut the current to ll the cylinders.) Throughout nearly all of the cycle for a given cylinder, the contact switch is held opened and no current flows through the system. But when the cam pushes  the levers, the contact switch in one cylinder is initially closed which produces a current of electricity from the magneto through the bus bar, switch, and levers, to the crankcase and back to the magneto. This condition for cylinder #1 is shown at the top of the figure. As the cam continues to move, the contact switch is suddenly pulled open, as shown at the bottom of the figure. A small spark occurs as the switch is opened (you can see this effect if you pull the  plug on an operating lamp in your home.) Inside the combustion chamber, this spark is used to ignite the fuel/air mixture at the end of the compression stroke. The contact switch is kept open inside the cylinder until the next firing. The opening of the switch is called an electrical break (of the circuit) and this firing  technique is called a "make and break" system. The four cylinders of this engine  fire one at a time in a firing order which is repeated. The brothers used a 1  - 3 - 4 - 2 firing order to balance out the firings and make the engine run as smooth  as possible.