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.
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