Vmc

Question 1

What is the definition of a critical engine?

Answer 1

The engine whose failure would result in the most adverse effects on the aircraft’s handling and performance of a multi-engine aircraft.

Question 2

What factors determine the critical engine?

Answer 2

P - P-factor
A - Accelerated slipstream
S - Spiraling slipstream
T - Torque

Question 3

What causes P-factor?

Answer 3

With air moving horizontally across a vertically mounted propeller, the blade proceeding forward into the flow of air has a higher airspeed than the blade retreating with the airflow. Thus, the blade proceeding into the horizontal airflow is creating more lift, or thrust, moving the center of thrust toward that blade.

Question 4

What is accelerated slipstream?

Answer 4

One engine is producing thrust while the inop engine is creating massive drag with a windmilling prop. The thrust produced by the spinning prop accelerates the airflow over the wing producing more lift creating a rolling towards the inop engine.

Question 5

How does spiraling slipstream affect a critical engine?

Answer 5

A spiraling slipstream of air from the left engine strikes the vertical stabilizer from the left. This helps counteract the yaw caused by a failure of the right engine. The right engine’s slipstream does not hit the vertical stabilizer. If the left engine fails, the right engine’s slipstream will not counteract the yaw toward the inoperative engine.

Question 6

How does torque affect the critical engine?

Answer 6

For every action there is an equal and opposite reaction. On a multi-engine airplane with clockwise rotating propellers torque will: Increase the tendency to roll towards the inoperative engine (left engine failed) or counteract the tendency to roll towards the inoperative engine right engine failed).