Flying With a Turbo
That extra power doesn’t come free
BY J. MAC MCCLELLAN
TURBOCHARGING SEEMS LIKE MAGIC. With a turbo, the same size pis-
ton engine can produce more horsepower, particularly when air
density thins with high temperatures and high altitude. But, as usual
there is no free lunch, and that includes the boost from a turbo.
The full name for the technology of using exhaust gas pressure to
boost the power output from an engine is turbo supercharging. The
word “super” stands for superior because the system increases
engine intake air pressure to a value superior to ambient. As the
years have gone by the word super has largely left the pilot lexicon,
and increasingly so has charged or charging.
Now we mostly just say turbo as shorthand
for the whole system.
The device that performs the actual work
is a turbocharger, and it contains both a turbine and a compressor. The turbine and
compressor are the centrifugal type, so they
are compact in size and can be contained in a
single unit. The turbine and compressor are
mounted on a common axle that is lubricated by the normal engine
oil lubricating system.
Some or all of the high-pressure engine exhaust is forced over the
turbine before being allowed to exit the cowling. The energy in the
exhaust spins the turbine, which in turn drives the compressor
housed in the other half of the turbocharger. The compressor draws
in ambient air and pressurizes it before sending it into the cylinders
of the engine.
In a normally aspirated engine, ambient atmospheric pressure is
all that is available to force air into the cylinder when the intake
valve opens. The compressor in the turbo system can force much
more air through the intake valve, and
that’s how a turbocharging system increases
engine power output. Think of a turbo as
force-feeding the engine to get more air
and fuel into the cylinder for each stroke of
Think of a turbo as force-feeding the
engine to get more air and fuel into the
cylinder for each stroke of the piston.
engine. Producing power always generates
heat, so by making more power the turbocharged engine creates more heat that must
be dissipated by the cooling air being forced
over the cylinders. The turbo itself is also an
added source of heat.
As you will remember from science class,
when a gas or fluid is compressed it heats up,
and that’s what happens in the compressor
section of the turbo. Depending on how
much the incoming air is compressed, it can