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Airplane Flying Handbook
Transition to Complex Airplanes
TURBOCHARGING

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Airplane Flying Handbook

Preface

Table of Contents

Chapter 1,Introduction to Flight Training
Chapter 2,Ground Operations
Chapter 3,Basic Flight Maneuvers
Chapter 4, Slow Flight, Stalls, and Spins
Chapter 5, Takeoff and Departure Climbs
Chapter 6, Ground Reference Maneuvers
Chapter 7, Airport Traffic Patterns
Chapter 8, Approaches and Landings
Chapter 9, Performance Maneuvers
Chapter 10, Night Operations
Chapter 11,Transition to Complex Airplanes
Chapter 12, Transition to Multiengine Airplanes
Chapter 13,Transition to Tailwheel Airplanes
Chapter 14, Transition to Turbo-propeller Powered Airplanes
Chapter 15,Transition to Jet Powered Airplanes
Chapter 16,Emergency Procedures

Glossary

Index

the manifold pressure decreases as additional altitude
is gained. Ground boosting, on the other hand, is an
application of turbocharging where more than the
standard 29 inches of manifold pressure is used in
flight. In various airplanes using ground boosting,
takeoff manifold pressures may go as high as 45
inches of mercury.

Although a sea level power setting and maximum
r.p.m. can be maintained up to the critical altitude,
this does not mean that the engine is developing sea
level power. Engine power is not determined just by
manifold pressure and r.p.m. Induction air
temperature is also a factor. Turbocharged induction
air is heated by compression. This temperature rise
decreases induction air density which causes a
power loss. Maintaining the equivalent horsepower
output will require a somewhat higher manifold
pressure at a given altitude than if the induction air
were not compressed by turbocharging. If, on the
other hand, the system incorporates an automatic
density controller which, instead of maintaining a
constant manifold pressure, automatically positions
the waste gate so as to maintain constant air density
to the engine, a near constant horsepower output
will result.

OPERATING CHARACTERISTICS
First and foremost, all movements of the power
controls on turbocharged engines should be slow and
gentle. Aggressive and/or abrupt throttle movements
increase the possibility of overboosting. The pilot
should carefully monitor engine indications when
making power changes.

When the waste gate is open, the turbocharged engine
will react the same as a normally aspirated engine
when the r.p.m. is varied. That is, when the r.p.m. is
increased, the manifold pressure will decrease slightly.
When the engine r.p.m. is decreased, the manifold
pressure will increase slightly. However, when the
waste gate is closed, manifold pressure variation with
engine r.p.m. is just the opposite of the normally
aspirated engine. An increase in engine r.p.m. will
result in an increase in manifold pressure, and a
decrease in engine r.p.m. will result in a decrease in
manifold pressure.

Above the critical altitude, where the waste gate
is closed, any change in airspeed will result in a
corresponding change in manifold pressure. This is
true because the increase in ram air pressure with an
increase in airspeed is magnified by the compressor
resulting in an increase in manifold pressure. The
increase in manifold pressure creates a higher mass
flow through the engine, causing higher turbine speeds
and thus further increasing manifold pressure.

When running at high altitudes, aviation gasoline may
tend to vaporize prior to reaching the cylinder. If this
occurs in the portion of the fuel system between the
fuel tank and the engine-driven fuel pump, an
auxiliary positive pressure pump may be needed in the
tank. Since engine-driven pumps pull fuel, they are
easily vapor locked. A boost pump provides positive
pressure—pushes the fuel—reducing the tendency to
vaporize.

HEAT MANAGEMENT
Turbocharged engines must be thoughtfully and
carefully operated, with continuous monitoring of
pressures and temperatures. There are two temperatures
that are especially important—turbine inlet
temperature (TIT) or in some installations exhaust gas
temperature (EGT), and cylinder head temperature.
TIT or EGT limits are set to protect the elements in the
hot section of the turbocharger, while cylinder head
temperature limits protect the engine's internal parts.

Due to the heat of compression of the induction air, a
turbocharged engine runs at higher operating
temperatures than a non-turbocharged engine. Because
turbocharged engines operate at high altitudes, their
environment is less efficient for cooling. At altitude
the air is less dense and therefore, cools less
efficiently. Also, the less dense air causes the
compressor to work harder. Compressor turbine
speeds can reach 80,000 – 100,000 r.p.m., adding
to the overall engine operating temperatures.
Turbocharged engines are also operated at higher
power settings a greater portion of the time.

High heat is detrimental to piston engine operation. Its
cumulative effects can lead to piston, ring, and
cylinder head failure, and place thermal stress on other
operating components. Excessive cylinder head
temperature can lead to detonation, which in turn can
cause catastrophic engine failure. Turbocharged
engines are especially heat sensitive. The key to
turbocharger operation, therefore, is effective heat
management.

The pilot monitors the condition of a turbocharged
engine with manifold pressure gauge, tachometer,
exhaust gas temperature/turbine inlet temperature
gauge, and cylinder head temperature. The pilot
manages the "heat system" with the throttle, propeller
r.p.m., mixture, and cowl flaps. At any given cruise
power, the mixture is the most influential control over
the exhaust gas/turbine inlet temperature. The throttle
regulates total fuel flow, but the mixture governs the
fuel to air ratio. The mixture, therefore, controls
temperature.

 

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