MULTI ENGINE OTHER FACTORS

Multi Engine Other Factors Lesson by wifiCFI


New Airspeeds

Vxse: Best Angle of Climb with a Single Engine

Vyse: Best Rate of Climb with a Single Engine/Least Rate of Descent

Vsse: Safe Single Engine speed

Vmc: Minimum controllable airspeed (more information later)

Definitions

Absolute Ceiling: The aircraft cannot climb any higher.

Service Ceiling: The aircraft can yield a 100 FPM climb.

Single Engine Service Ceiling: The aircraft cannot climb any higher on a single engine.

Single Engine Service Ceiling: The aircraft can yield a 50 FPM climb on a single engine.

Vyse

It is important to discuss Vyse when discussing multi-engine airplanes.

In multi-engine aerodynamics, Vyse can represent two things:

Best Rate of Climb on a Single Engine

Least Rate of Descent on a Single Engine

For an aircraft flying below it’s Single Engine Ceiling:

Vyse represents Best Rate of Climb 

For an aircraft flying above it’s Single Engine Ceiling:

Vyse represents Least Rate of Descent

Zero Sideslip

With a single-engine airplane or a multiengine airplane with both engines operative, sideslip is eliminated when the ball of the turn and bank instrument is centered.

This is a condition of zero sideslip, and the airplane is presenting its smallest possible profile to the relative wind. 

As a result, drag is at its minimum. 

Pilots know this as coordinated flight.

In a multiengine airplane with an inoperative engine, the centered ball is no longer the indicator of zero sideslip due to asymmetrical thrust. 

In fact, there is no instrument at all that directly tells the pilot the flight conditions for zero sideslip. In the absence of a yaw string, minimizing sideslip is a matter of placing the airplane at a predetermined bank angle and ball position.

There are two different control inputs that can be used to counteract the asymmetrical thrust of a failed engine:

Yaw from the rudder

The horizontal component of lift that results from bank with the ailerons.

Used individually, neither is correct.

Used together in the proper combination, zero sideslip and best climb performance are achieved.

Correct Procedure

Rudder and ailerons used together in the proper combination result in a bank of approximately 2° towards the operative engine.

The ball is displaced approximately one-third to one-half towards the operative engine.

The result is zero sideslip and maximum climb performance.

Power Loss vs Performance Loss

An engine failure will cause both a power loss, and performance loss to the aircraft.

The power lost will be 50%.

The performance loss will be between 80-90%. 

Why is the performance loss so great?

See depictions on wifiCFI.

Example:

A multi-engine airplane that is powered by two 180 horsepower engines.

This gives us a total of 360 available horsepower.

When one engine is suddenly made inoperative, the total available horsepower decreases from 360 to 180.

The aircraft in the example requires 160 horsepower to maintain level flight.

That means the aircraft with both engine operating has an additional 200 horsepower that can be used for climb performance.

However, the aircraft with one engine inoperative only has an additional 20 horsepower available for climb performance.

This results in a 90% loss of climb performance.

FAA Sources Used for This Lesson

Airplane Flying Handbook (AFH) Chapter 12


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