What is Vmc?
Minimum control speed with critical engine inoperative.
Marked with a red radial line on most airspeed indicators.
Only about directional control. No requirement the aircraft be capable of climbing at this airspeed.
What must occur if engine fails before Vmc while still on the ground?
Aborted takeoff
Is directional control possible if engine failure occurs below Vmc while airborne?
No it is not.
What is the accelerate stop distance?
Runway length required to accelerate to a specific speed, experience engine failure, and come to a complete stop
What is accelerate go distance?
Horizontal distance required to continue takeoff and climb to 50’ AGL, assuming engine failure occurs at Vr.
What is rate of climb defined?
Altitude gain per unit of time
What is climb gradient?
Actual measure of altitude gained per 100’ of horizontal travel, expressed as a %.
Ex: 15ft altitude gain per 100’ = 1.5% climb gradient
Is climb gradient affected by wind?
Yes, it is. Unlike the rate of climb
What are the type of twins called that have props that rotate in the same direction?
Conventional twins
What are the motions that occur when an engine fails?
Yaw and Roll
What is the critical engine?
The engine, that if it were to fail, would most adversely affect the performance or handling characteristics of the plane
What factors determine a critical engine?
P-Factor
Accelerated Slipstream
Spiraling slipstream
Torque
What does P-Factor have to do with making the left engine critical?
The arm of the descending blade on the right engine is further away than the arm of the left descending blade, making it where the aircraft will yaw to the left more than if the right engine failed.
How does accelerated slipstream make the left engine critical?
If the left engine fails, the arm of the right engine is further away making the rolling action stronger than if the right engine failed.
How does Torque make the left engine critical?
Newton’s 3rd Law.
The props are spinning to the right, providing a force to the left from Newton’s law. If the left engine fails, the torque from the engine and from Newton’s law will make the aircraft yaw more than if the right engine failed since the left engine would have torque yawing the engine to the left along with Newton’s law pushing to the left to oppose the force of yawing to the right.
What does Vmc deal with?
Directional control and not performance.
What are the 4 warning signs that Vmc is occurring?
Loss of directional control
Stall warning horn
Buffeting before the stall
Rapid decay of control effectiveness
What 2 actions must occur to recover from Vmc?
Reduce power on operating engine
Pitch the nose down
What are the factors that affect Vmc?
Standard atmosphere Max power on operating engine Aft CG Critical engine windmilling Flaps up/gear up Up to 5 degrees of bank Most unfavorable weight
What are 2 causes that will allow Vmc to decrease?
Anything moving the CG forward, making rudder more effective
Anything allowing less rudder to be used, making more rudder available
How does using power effect Vmc?
Increases, more rudder needed to stop resulting yaw
How does increase in Density Altitude effect Vmc?
Decreases Vmc, output of engine thrust will decrease, making less rudder needed to oppose yaw
How does CG location affect Vmc?
The CG changes the length of the arm to the rudder. The longer the arm, the more effective. The shorter the arm, the less effective.
As CG moves forward, Vmc decreases
As CG moves aft, Vmc increases
What are effects of forward CG?
Stall speed - higher Cruise - slower Spin/Stall recovery - good Flare - more difficult Endurance - unchanged Range - worse
How does the gear position effect Vmc?
The CG moves in the direction of the travel the nose gear. Based off CG changes, it could be better or worse.
If the gear is down, it also had Keel Effect, making it stabilize into the wind. This prevents a turn, lowering Vmc.
How does the propeller windmilling effect Vmc?
It creates more drag than a feathered propeller. The extra drag adds to the yawing of the failed engine, making the yaw worse. It requires more rudder usage, therefore increasing Vmc. When the prop is feathered, it lowers drag, lowering Vmc.
How do flaps down effect Vmc?
If they are down, they create more lift than if they are up. The operating engine side has more lift than the inoperative engine due to accelerated airflow over the wing. This drag from accelerated airflow will cause the the plane to yaw in that direction towards the operative engine, opposing the yaw from the dead engine, making rudder more available to the pilot and lowering Vmc.
The more lift will cause a rolling action, to stop the rolling action you will input aileron. The ailerons will produce adverse yaw, making the plane yaw into the direction of the inoperative engine.
How can the weight of the plane effect Vmc?
The weight determines the amount of total lift required by the plane to maintain lift. When a plane turns, it uses horizontal and vertical lift.
The heavier the plane, the more horizontal component of lift, the more yaw to help oppose the yaw of the inoperative engine. Using horizontal lift along with rudder will decrease the amount of rudder use required to prevent the yaw, therefore decreasing Vmc.
Weight increase - Vmc Decrease
How does a 5 degree bank into the operative engine effect Vmc?
It uses the concept of horizontal lift to oppose the yaw from the inoperative engine. It reduces the amount of rudder required to maintain heading, allowing more rudder available for use, decreasing Vmc.
What is the most desired condition to be in during Vmc?
Zero side slip. It exists when relative wind is directly parallel to longitudinal axis of the plane. Results in minimal amount of drag possible with failed engine. This lowers Vmc.
How does being on ground effect effect Vmc?
Less drag is created on the wings, therefore more thrust is available, making it to where the operative engine has more power and will have more of a rolling action and yawing action. This increases Vmc.
Why is Vmc decreasing good?
It means more rudder is available to the pilot, and also means it is more effective so the plane is easier to control.
