Multi-engine Aerodynamics Flashcards

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Questions and Answers

What is the product of an engine failure in a multi-engine aircraft?

Asymmetric Thrust and Drag

How does the Lateral Axis respond to an engine failure?

Pitch Down

How does the Longitudinal Axis respond to an engine failure?

Roll Toward the Failed Engine

How does the Vertical Axis respond to an engine failure?

Yaw Toward the Failed Engine Signup and view all the answers

What are other terms used for 'failed engine'?

Dead engine Signup and view all the answers

How much of the AVAILABLE POWER is lost during an engine failure?

50% Signup and view all the answers

How much POWER LOSS results from an engine failure?

80% Signup and view all the answers

What is the Sideslip Condition?

UNFAVORABLE Signup and view all the answers

What is the Zero Sideslip Condition?

Best Performance Signup and view all the answers

What Four Factors affect Climb Performance?

Power Signup and view all the answers

What factors define a Critical Engine?

Accelerated Slipstream Signup and view all the answers

How is Vmc speed determined by aircraft manufacturers?

By the conditions set by the FAA under FAR Part 23.149. Signup and view all the answers

What does 'conventional twin' mean?

All engines spin in the same direction. Signup and view all the answers

What is Vmc speed?

Vmc = Minimum controllable airspeed Signup and view all the answers

Describe FAR 23.149 (SMACFUM).

Standard Day Conditions at Sea Level, Maximum power on the Operating Engine, Aft CG, Critical Engine Prop Windmilling, Flaps takeoff position, Gear up, Trimmed for Takeoff, Up to 5° of Bank into the Operating Engine, Most unfavorable Weight. Signup and view all the answers

What is S-Standard Day Conditions at Sea Level?(SMACFUM)

Sea level has the highest air density which allows the engine to produce maximum efficiency and thrust. Signup and view all the answers

What is M-Max Power?(SMACFUM)

When the operating engine produces max power, adverse yaw is increased towards the inoperative engine. Signup and view all the answers

What is A-Aft CG?(SMACFUM)

With an AFT CG, the ARM between the rudder and the CG is shortened. Signup and view all the answers

What is C-Critical Engine Inop & Windmilling?(SMACFUM)

Losing the critical engine will produce the most adverse conditions. Signup and view all the answers

What is F-Flaps Up, Gear Up, Trimmed for Takeoff?(SMACFUM)

This is the least stable configuration. Signup and view all the answers

What is U-Up to 5° of bank?(SMACFUM)

Banking into the operating engine creates a horizontal component of lift. Signup and view all the answers

What is M-Most Unfavorable Weight?(SMACFUM)

Light weight = unfavorable. Signup and view all the answers

Study Notes

Engine Failure Consequences

Engine failure in a multi-engine aircraft leads to asymmetric thrust and drag.
Yawing, rolling, and pitching tendencies result from lost power from the failed engine.

Lateral Axis Response

Loss of thrust leads to pitch down due to decreased lift from the horizontal stabilizer.
Additional back pressure is required to counteract the tail raising.
T-tail configurations, like in Seminole aircraft, are less affected due to their location above the engine's slipstream.

Longitudinal Axis Response

The aircraft rolls toward the failed engine as lift is reduced on that side.
Extra aileron input toward the operating engine is needed to maintain level flight.

Vertical Axis Response

Yaw occurs toward the failed engine due to lost thrust and increased drag from the windmilling propeller.
Extra rudder pressure on the operating engine is necessary to maintain control, encapsulated in the phrase "Dead foot, dead engine."

Terminology

Alternate terms for a failed engine: inoperative engine, dead engine.
In case of engine failure, approximately 50% of available power is lost, but the actual power loss can result in up to 80%.

Sideslip Conditions

Sideslip condition is considered unfavorable; applying rudder toward the operating engine misaligns the aircraft's axis with the relative wind, increasing drag.
The Zero Sideslip Condition is optimal, achieved by banking 2°-5° into the operating engine, improving performance by minimizing rudder deflection.

Factors Affecting Climb Performance

Key elements impacting climb performance include airspeed, drag, power output, and aircraft weight.

Critical Engine Definition

Factors defining a critical engine involve P-factor, accelerated slipstream effects, spiraling slipstream, and torque impact.

P-Factor in Conventional Twins

Under low speeds and high angles of attack, the descending blade of the right engine generates more thrust, impacting directional control more severely than the left engine.
The left engine is classified as the critical engine due to producing more yaw when it fails.

Accelerated Slipstream Effects

The critical engine's left side exhibits greater adverse roll losses due to the descending blade's thrust center being closer to the aircraft's center of gravity when it fails.

Spiraling Slipstream Contributions

The left engine's spiraling slipstream counteracts right engine yaw failures while the right engine's slipstream does not help when the left engine fails.
Thus, the left engine is deemed the critical engine.

Torque Effects

Torque from the operating engine creates rolling tendencies opposite to the engine's rotation—a critical engine is dictated by which engine failure increases the rolling tendency.

Vmc Speed Determination

Vmc is determined by FAA standards under FAR Part 23.149 (SMACFUM).

Definition of Conventional Twin

Conventional twins have engines that rotate in the same direction, usually clockwise relative to the cockpit.

Vmc Speed

Vmc represents the minimum controllable airspeed specifically noted as 57 knots indicated airspeed (kias) for the Seminole.

FAR 23.149 (SMACFUM) Overview

SMACFUM conditions for determining Vmc speed include: standard day conditions at sea level, maximum power on the operating engine, aft center of gravity (CG), critical engine windmilling, flaps up and gear up configuration, a bank angle into the operating engine, and most unfavorable weight.

Standard Day Conditions

Standard day conditions at sea level yield maximum engine power due to high air density, affecting engine performance and causing an increase in Vmc speed with altitude or temperature elevation.

Maximum Power Impact

Operating an engine at maximum power heightens adverse yaw toward the inoperative engine and increases Vmc speed.

Aft Center of Gravity

An aft CG diminishes rudder leverage, making directional control more difficult, which consequently increases Vmc speed.

Windmilling Effects

Losing the critical engine produces maximum adverse conditions, increasing drag and control inputs needed, which in turn raises Vmc speed.

Flaps and Gear Configuration

With flaps up, gear up, and trimmed for takeoff, the aircraft is in a least stable configuration which enhances stability and increases Vmc speed.

Banking Effects

Up to 5° of bank into the operating engine reduces rudder force needed for control and improves overall performance, decreasing Vmc speed by approximately 3 knots per degree of bank.

Weight Impact on Performance

Light aircraft weight is unfavorable since increased weight enhances the lift generated by the banked angle, improving stability, which serves to increase Vmc speed.

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Description

Test your knowledge on the effects of engine failure in multi-engine aircraft with these flashcards. Learn about asymmetric thrust and drag, as well as how the lateral axis responds during such failures. Perfect for aviation students and enthusiasts looking to enhance their understanding of aircraft dynamics.