Critical Engine Flashcards
What is the definition of critical engine?
A critical engine is the engine which, if lost, will most adversely affect the performance and handling
characteristics of the aircraft
when are the effects of a critical engine most significant?
The effect of the critical engine is most significant when operating at low
airspeeds with a high power setting, thus producing more p-factor and torque.
Critical engine on conventional twins?
On conventional twins with the propellers rotating clockwise, the critical engine is the left engine
critical engine on counterrotating twins?
On aircraft with counter-rotating propellers, such as the Beechcraft Duchess or Piper Seminole, there is
no critical engine due to the turning tendencies cancelling each other out.
When else can an engine be termed critical?
An engine can also be termed as a critical engine if important systems are operated off that engine. (i.e.
landing gear, pressure system, etc.)
what four factors determine the critical engine?
P- P-factor
A- Accelerated Slipstream
S- Spiraling Slipstream
T- Torque
How does P factor help determine the critical engine?
P-factor- The descending propeller blade is producing more thrust than the ascending blade.
If the left engine fails, the p-factor being produced from the right engine is farther from the longitudinal
axis of the aircraft, creating more of a yawing moment.
How does accelerated slip stream help determine the critical engine?
Accelerated Slipstream- The air being forced over the wing by the operating engine creates extra lift.
This is basically the equal and opposite reaction of p-factor. If the left engine fails, the effect of the pfactor creates more induced flow farther away from the longintudinal axis of the aircraft creating a
rolling moment.
How does spiraling slip stream help determine the critical engine?
Spiraling Slipstream- The effect of the propeller being pulled through the air while rotating creates a
spiraling stream of air behind the propeller.
This spiraling air from the left propeller, due to its direction of spiral, hits the rudder creating more
airflow to make the rudder more effective. If the left engine fails, the spiraling slipstream from the right
engine spirals away from the rudder.
How does torque effect help determine the critical engine?
Torque- This is the opposite reaction to the action of the turning propeller
Torque tries to roll the airplane opposite of the propeller’s direction of rotation. If the left engine fails,
torque tries to roll the aircraft to the left, making it more difficult to raise the dead engine.
