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Airplane Flying Handbook
Transition to Multiengine Airplanes
ENGINE INOPERATIVE LOSS OF DIRECTIONAL CONTROL

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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

Forces created during single-engine operation.
Figure 12-19. Forces created during single-engine operation.

The AFM/POH-published Vmc is determined with the
"critical" engine inoperative. The critical engine is the
engine whose failure has the most adverse effect on
directional control. On twins with each engine rotating
in conventional, clockwise rotation as viewed from the
pilot's seat, the critical engine will be the left engine.

Multiengine airplanes are subject to P-factor just as
single-engine airplanes are. The descending propeller
blade of each engine will produce greater thrust than
the ascending blade when the airplane is operated
under power and at positive angles of attack. The
descending propeller blade of the right engine is also
a greater distance from the center of gravity, and
therefore has a longer moment arm than the descending
propeller blade of the left engine. As a result,
failure of the left engine will result in the most
asymmetrical thrust (adverse yaw) as the right
engine will be providing the remaining thrust.
[Figure 12-19]

Many twins are designed with a counter-rotating right
engine. With this design, the degree of asymmetrical
thrust is the same with either engine inoperative. No
engine is more critical than the other, and a VMC
demonstration may be performed with either engine
windmilling.

In aircraft certification, dynamic Vmc is determined
under the following conditions.

Maximum available takeoff power. Vmc
increases as power is increased on the operating
engine. With normally aspirated engines, Vmc is
highest at takeoff power and sea level, and
decreases with altitude. With turbocharged
engines, takeoff power, and therefore Vmc,
remains constant with increases in altitude up to
the engine's critical altitude (the altitude where

the engine can no longer maintain 100 percent
power). Above the critical altitude, Vmc
decreases just as it would with a normally aspirated
engine, whose critical altitude is sea level.
Vmc tests are conducted at a variety of altitudes.
The results of those tests are then extrapolated to
a single, sea level value.

Windmilling propeller. Vmc increases with
increased drag on the inoperative engine. VMC is
highest, therefore, when the critical engine propeller
is windmilling at the low pitch, high
r.p.m. blade angle. Vmc is determined with the
critical engine propeller windmilling in the
takeoff position, unless the engine is equipped
with an autofeather system.

Most unfavorable weight and center-of-gravity
position.
Vmc increases as the center of gravity
is moved aft. The moment arm of the rudder is
reduced, and therefore its effectivity is reduced,
as the center of gravity is moved aft. At the same
time, the moment arm of the propeller blade is
increased, aggravating asymmetrical thrust.
Invariably, the aft-most CG limit is the most
unfavorable CG position. Currently, 14 CFR
part 23 calls for Vmc to be determined at the
most unfavorable weight. For twins certificated
under CAR 3 or early 14 CFR part 23,
the weight at which VMC was determined was
not specified. Vmc increases as weight is
reduced. [Figure 12-20]

Landing gear retracted. Vmc increases when
the landing gear is retracted. Extended landing
gear aids directional stability, which tends to
decrease Vmc.

 

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