Engine Fuel System
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
computer drawing of the fuel system of the Wright
brothers' 1903 aircraft 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 job of the fuel system is to mix the fuel and air (oxygen) in just the right
proportions for combustion and to distribute the fuel/air mixture to the
The fuel system of the Wright brothers is composed of
three main components; a fuel tank and line mounted on the airframe, a carburetor
in which the fuel and air are mixed, and an intake manifold which distributes
the fuel/air mixture to the combustion chambers.
In the figure, the fuel tank and line are colored blue. The tank is mounted
high because the brothers used gravity to feed the fuel into the engine.
Fuel flows through a small metal fuel line from the tank to the engine.
The flow of fuel to the engine is controlled by a fuel valve
located on the fuel line. On the Wright 1903 aircraft,
the fuel flow to the engine
was adjusted while the aircraft was sitting on the launch rail.
When the engine was running as fast and smooth as possible the aircraft
was ready for launch.
The pilot had a control stick which was connected to a cut-off valve
to stop the engine at the end of the flight. But the brothers had no throttle
or engine control during the 1903 flights.
Historical note -
automobile uses a fuel pump to move the fuel from the gas tank to the motor.
The brothers' 1903 engine had no fuel pump but they added a fuel pump to
The fuel line continues past the valve, along the top of the engine, and into the
the side of the air intake as shown on this figure.
The liquid fuel drips into the carburetor, which is a flat, enclosed
pan that sits on the top of the engine.
The floor of the carburetor is hot because it sits over the engine cylinders.
Air is drawn into the carburetor, through the air intake, because of the action
of the pistons far downstream. During the
of the engine, the piston is pulled into the cylinder, increasing the volume
in the combustion chamber. Fuel and air are pulled through the carburetor
and intake manifold to fill the increased volume.
The combination of air being drawn over the fuel and the heat of the floor of
the carburetor cause the liquid fuel (gasoline) to evaporate. The gasoline
mixes with the air as the gases move through the carburetor, as indicated by
the yellow arrow on the graphic. Near the exit of the carburetor, there is
uniform gas mixture of fuel and air, which is indicated by the green "molecules"and arrows on the figure.
Historical note -
The carburetor used by the Wrights is merely a pan in which to mix fuel and air.Modern automobiles use computer-controlled fuel injectors to accomplish
the same function. Before fuel injectors were used, automobiles and aircraft
engines used much more sophisticated carburetors to spray the fuel, mix it with
the air, and vary the fuel/air ratio for optimized performance over a range of
operating conditions. Modern carburetors have many, small, moving parts; the
Wright carburetor has no moving parts. With modern carburetors and fuel injection
systems you can throttle the engine to make it run at different speeds. Without
the moving parts,
the brothers engine ran at just one speed throughout the flights of 1903.
The fuel/air mixture leaves the carburetor and enters the intake manifold.
The job of the manifold is to distribute the fuel/air mixture to the four
cylinders. On the graphic, we have peeled open the manifold across the two center
cylinders; similar openings are found to the outer two cylinders. The flow of
the fuel/air mixture out of the manifold is controlled by the intake valve
of the combustion chamber of each cylinder.
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