Vmc

Question 1

What is Vmc?

Answer 1

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.

Question 2

What must occur if engine fails before Vmc while still on the ground?

Answer 2

Aborted takeoff

Question 3

Is directional control possible if engine failure occurs below Vmc while airborne?

Answer 3

No it is not.

Question 4

What is the accelerate stop distance?

Answer 4

Runway length required to accelerate to a specific speed, experience engine failure, and come to a complete stop

Question 5

What is accelerate go distance?

Answer 5

Horizontal distance required to continue takeoff and climb to 50’ AGL, assuming engine failure occurs at Vr.

Question 6

What is rate of climb defined?

Answer 6

Altitude gain per unit of time

Question 7

What is climb gradient?

Answer 7

Actual measure of altitude gained per 100’ of horizontal travel, expressed as a %.

Ex: 15ft altitude gain per 100’ = 1.5% climb gradient

Question 8

Is climb gradient affected by wind?

Answer 8

Yes, it is. Unlike the rate of climb

Question 9

What are the type of twins called that have props that rotate in the same direction?

Answer 9

Conventional twins

Question 10

What are the motions that occur when an engine fails?

Answer 10

Yaw and Roll

Question 11

What is the critical engine?

Answer 11

The engine, that if it were to fail, would most adversely affect the performance or handling characteristics of the plane

Question 12

What factors determine a critical engine?

Answer 12

P-Factor
Accelerated Slipstream
Spiraling slipstream
Torque

Question 13

What does P-Factor have to do with making the left engine critical?

Answer 13

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.

Question 14

How does accelerated slipstream make the left engine critical?

Answer 14

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.

Question 15

How does Torque make the left engine critical?

Answer 15

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.

Question 16

What does Vmc deal with?

Answer 16

Directional control and not performance.

Question 17

What are the 4 warning signs that Vmc is occurring?

Answer 17

Loss of directional control
Stall warning horn
Buffeting before the stall
Rapid decay of control effectiveness

Question 18

What 2 actions must occur to recover from Vmc?

Answer 18

Reduce power on operating engine

Pitch the nose down

Question 19

What are the factors that affect Vmc?

Answer 19

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

Question 20

What are 2 causes that will allow Vmc to decrease?

Answer 20

Anything moving the CG forward, making rudder more effective

Anything allowing less rudder to be used, making more rudder available

Question 21

How does using power effect Vmc?

Answer 21

Increases, more rudder needed to stop resulting yaw

Question 22

How does increase in Density Altitude effect Vmc?

Answer 22

Decreases Vmc, output of engine thrust will decrease, making less rudder needed to oppose yaw

Question 23

How does CG location affect Vmc?

Answer 23

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

Question 24

What are effects of forward CG?

Answer 24

Stall speed - higher
Cruise - slower
Spin/Stall recovery - good
Flare - more difficult
Endurance - unchanged 
Range - worse

Question 25

How does the gear position effect Vmc?

Answer 25

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.

Question 26

How does the propeller windmilling effect Vmc?

Answer 26

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.

Question 27

How do flaps down effect Vmc?

Answer 27

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.

Question 28

How can the weight of the plane effect Vmc?

Answer 28

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

Question 29

How does a 5 degree bank into the operative engine effect Vmc?

Answer 29

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.

Question 30

What is the most desired condition to be in during Vmc?

Answer 30

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.

Question 31

How does being on ground effect effect Vmc?

Answer 31

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.

Question 32

Why is Vmc decreasing good?

Answer 32

It means more rudder is available to the pilot, and also means it is more effective so the plane is easier to control.