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
On this page we present a description of the basic engine parts and their function.
Individual web pages on all of the major systems and parts are provided so that
you can study each item in some detail. Just click on the hyperlink.
On the 1903 flyer, the engine is mounted on the lower wing next to the
pilot with the front of the engine, as denoted on the figure, aligned with
the front of the airplane.
The engine's only job is to turn two
propellers at the rear of the airplane.
The propellers provide the
force for the aircraft and are
connected to the engine by two power chains which are colored blue in this
animation. Notice that the left power chain has been twisted to make the
propellers rotate in opposite directions. Counter-rotating the propellers
eliminates any gyroscopic forces on the aircraft.
The chains are turned by two sprockets attached to the
at the rear of the engine. The sprockets are visible at the left of
the computer animation shown below.
The crankshaft passes though the outer
of the engine.
In this animation we have removed most of the engine parts and
removed the upper skin of the crankcase to look inside.
The view is looking down onto the engine with the front of the
engine to the right.
The brothers were worried that "slop" in the chains, and mis-fires of
the engine would cause excessive vibrations on the aircraft. So they
installed a large flywheel to the crankshaft. The flywheel is just a
large, heavy, metal wheel which damps out vibrations as it rotates.
The crankshaft is turned by four pistons which are enclosed
in cylinders contained inside the engine crankcase.
(The in-line piston arrangement used by the brothers is identical to
that used in modern four cylinder automobile engines.)
The pistons are driven by hot gases produced by the
of fuel (gasoline) and air in the
located at the end of each cylinder.
Returning to the figure at the top of the page,
fuel is fed by gravity from a
tank on a wing strut of the airplane
and enters the engine through a
Air is brought into the engine through the air intake on the
top of the engine.
The fuel is evaporated by heat from the cylinders
and mixes with the air in the carburetor
on the top of the crankcase. The carburetor for this engine is just a long,
flat, enclosed pan with no moving parts. A hole at the entrance connects to the
air intake and a hole at the exit connects to the intake manifold.
The intake manifold distributes the
fuel/air mixture to the four combustion chambers. The manifold
is also a pan with one hole at the entrance and four exit holes connected to theintake valve of each combustion chamber.
There are many, small parts associated with each combustion chamber, so here's
a figure which shows a cut through one cylinder. This view is looking from
the front to the back of the engine, with the combustion chamber at the right.
We have cut open the combustion chamber and the cylinder so that you can look inside.
The intake valve is shown in red and can open and
close to let fuel and air into the combustion chamber from the
The valve is normally held closed by a spring on top of the intake manifold,
but is pulled open during the
intake stroke of the piston.
At the end of the
the fuel is
in the combustion chamber by an electric spark.
On this figure, electrical parts are colored green.
The spark occurs very quickly by the opening of an electrical contact
inside the combustion chamber. The timing of the spark is controlled by a
cam mounted on a shaft on the bottom of the engine.
The combustion of the fuel and air produces
and high pressure exhaust gases which
are used to move the piston inside the cylinder during the
At the end of the power stroke, residual heat is
to the cooling
water jacket and the exhaust gases return to atmospheric pressure.
The exhaust gases are then pushed out
of the combustion chamber through the exhaust valve
On this figure, exhaust parts are colored blue.
The exhaust valve, like the intake valve, can open and close.
The valve is held closed by a spring during
combustion and is pushed open by a rocker arm during the exhaust stroke.
The rocker arm is moved by a
cam mounted on a shaft on the bottom of the engine.
The motion of the valves and electrical contact are shown in this computer animation.
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
of the motion of the switches and valves is different between
adjoining cylinders. There is a defined
for the cylinders.
Electricity for the ignition spark is generated by the
magneto, which is
located at the rear of the engine.
The electricity is carried to the engine along electrical wires
and distributed to the four cylinders by a band connected to the four
electrical contacts. On the animation, we have cut the band to allow us
to see inside cylinder #3; the band wraps around cylinder #3 in the
same way that it wraps around cylinder #2 to the left.
of the opening and closing of the valves and the
firing of the spark is very important and is controlled by a
on the crankcase at the front of the engine, as shown at the top of the page.
The combustion in the chambers and the friction of the pistons
and cylinders generate
a lot of heat in the engine. The parts are
by a water radiator
located on the wing strut.
A large hose at the bottom brings the coolant water into the engine
and two hoses on the top of the engine return the water to the radiator.
is also provided for the pistons and crankshaft.
- Beginner's Guide Home Page