For the forty years following the
of the Wright brothers, airplanes used
internal combustion engines
Today, most general aviation or private airplanes are still
powered by propellers and internal combustion engines, much like your
We will discuss the fundamentals of the
internal combustion engine using the
Wright brothers' 1903 engine, shown in the figure, as an example.
The brothers' design is very simple by today's standards, so it is a good
engine for students to study and learn the
fundamentals of engines
The figure at the top shows the major components
of a combustion chamber
on the Wright 1903 engine.
In any internal combustion engine,
fuel and oxygen are combined in a
to produce the power to turn the
crankshaft of the engine.
The combustion takes place in the combustion chamber. There is a combustion
chamber for each cylinder of the engine.
On the figure we show cylinder #4 at three different times during the engine
We have peeled open the side of the chamber and the
which sits on top of the chamber and we have color coded the parts
for easy identification.
The figure on the left shows the parts during the
of the cycle. The intake valve (red) is normally held snug against the
valve seat (yellow) by the intake valve spring. The seat and the
edge of the valve are carefully machined so that gases can not pass between themwhen the valve is closed. During the intake stroke, the intake valve is pulled
open and a small gap exists between the valve and the seat. Fuel and air in the
intake manifold flows through the gap and into the combustion chamber.
The valve can only move up and down because the intake valve cage
holds the stem of the valve.
The middle figure shows the parts during the
power strokes of the cycle.
The intake valve is now closed and the chamber forms a totally closed vessel with
piston and cylinder.
Protruding through the walls of the chamber are the
ignition plug (green) and
The switch is normally held open. The switch is closed against the plug,
and opens quickly to generate a
spark to ignite the fuel/air mixture during the
The figure on the right shows the parts during the
The exhaust valve (blue), like the intake valve, is normally held snug against
its valve seat by the exhaust valve spring. During the exhaust stroke,
the valve is pushed open by a cam-driven
Like the intake valve, the exhaust valve is held in place by a valve cage which
wraps around the valve stem. When the exhaust valve is opened, the hot exhaust gas
is pushed through the open valve and exits the engine. The movement of all theseparts is coordinated by the
timing system and is shown in this animation:
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