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Airplane Flying Handbook
Transition to Multiengine Airplanes
OPERATION OF SYSTEMS

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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

As just described, a loss of oil pressure from the propeller
governor allows the counterweights, spring
and/or dome charge to drive the blades to feather.
Logically then, the propeller blades should feather
every time an engine is shut down as oil pressure falls
to zero. Yet, this does not occur. Preventing this is a
small pin in the pitch changing mechanism of the
propeller hub that will not allow the propeller blades
to feather once r.p.m. drops below approximately
800. The pin senses a lack of centrifugal force from
propeller rotation and falls into place, preventing the
blades from feathering. Therefore, if a propeller is to
be feathered, it must be done before engine r.p.m.
decays below approximately 800. On one popular
model of turboprop engine, the propeller blades do,
in fact, feather with each shutdown. This propeller is
not equipped with such centrifugally-operated pins,
due to a unique engine design.

An unfeathering accumulator is an optional device that
permits starting a feathered engine in flight without the
use of the electric starter. An accumulator is any device
that stores a reserve of high pressure. On multiengine
airplanes, the unfeathering accumulator stores a small
reserve of engine oil under pressure from compressed
air or nitrogen. To start a feathered engine in flight,
the pilot moves the propeller control out of the
feather position to release the accumulator pressure.
The oil flows under pressure to the propeller hub and
drives the blades toward the high r.p.m., low pitch
position, whereupon the propeller will usually begin
to windmill. (On some airplanes, an assist from the
electric starter may be necessary to initiate rotation
and completely unfeather the propeller.) If fuel and
ignition are present, the engine will start and run.
For airplanes used in training, this saves much electric
starter and battery wear. High oil pressure from
the propeller governor recharges the accumulator
just moments after engine rotation begins.

PROPELLER SYNCHRONIZATION
Many multiengine airplanes have a propeller synchronizer
(prop sync) installed to eliminate the annoying
"drumming" or "beat" of propellers whose r.p.m. are
close, but not precisely the same. To use prop sync, the
propeller r.p.m. are coarsely matched by the pilot and
the system is engaged. The prop sync adjusts the r.p.m.
of the "slave" engine to precisely match the r.p.m. of
the "master" engine, and then maintains that relationship.
The prop sync should be disengaged when the
pilot selects a new propeller r.p.m., then re-engaged
after the new r.p.m. is set. The prop sync should always
be off for takeoff, landing, and single-engine operation.
The AFM/POH should be consulted for system
description and limitations.

A variation on the propeller synchronizer is the propeller
synchrophaser. Prop sychrophase acts much
like a synchronizer to precisely match r.p.m., but the
synchrophaser goes one step further. It not only
matches r.p.m. but actually compares and adjusts the
positions of the individual blades of the propellers in
their arcs. There can be significant propeller noise and
vibration reductions with a propeller synchrophaser.
From the pilot's perspective, operation of a propeller
synchronizer and a propeller syncrophaser are very
similar. A synchrophaser is also commonly referred to
as prop sync, although that is not entirely correct
nomenclature from a technical standpoint.

As a pilot aid to manually synchronizing the
propellers, some twins have a small gauge mounted
in or by the tachometer(s) with a propeller symbol
on a disk that spins. The pilot manually fine tunes
the engine r.p.m. so as to stop disk rotation, thereby
synchronizing the propellers. This is a useful backup
to synchronizing engine r.p.m. using the audible
propeller beat. This gauge is also found installed
with most propeller synchronizer and synchrophase
systems. Some synchrophase systems use a knob for
the pilot to control the phase angle.

FUEL CROSSFEED
Fuel crossfeed systems are also unique to multiengine
airplanes. Using crossfeed, an engine can draw fuel
from a fuel tank located in the opposite wing.

On most multiengine airplanes, operation in the crossfeed
mode is an emergency procedure used to extend
airplane range and endurance in OEI flight. There are
a few models that permit crossfeed as a normal, fuel
balancing technique in normal operation, but these are
not common. The AFM/POH will describe crossfeed
limitations and procedures, which vary significantly
among multiengine airplanes.

Checking crossfeed operation on the ground with a
quick repositioning of the fuel selectors does nothing
more than ensure freedom of motion of the handle. To
actually check crossfeed operation, a complete, functional
crossfeed system check should be accomplished.
To do this, each engine should be operated from its
crossfeed position during the runup. The engines
should be checked individually, and allowed to run at
moderate power (1,500 r.p.m. minimum) for at least 1
minute to ensure that fuel flow can be established from
the crossfeed source. Upon completion of the check,
each engine should be operated for at least 1 minute at
moderate power from the main (takeoff) fuel tanks to
reconfirm fuel flow prior to takeoff.

 

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