VMC & PAST Flashcards
1
Q
What is VMC?
A
- minimum controllable airspeed
- the speed at which the rudder no has authority to overcome the yaw caused by the critical engine being inop
- minimum flight speed at which the airplane is directionally controllable as determined in accordance with the FAA
- FAR 23.149
2
Q
What determines a critical engine?
A
- The failed engine that will have the most impact on performance & controllability
- The engine that will cause the most TROUBLE
- PAST
3
Q
Single engine vs multi-engine failure
A
- Single engine a/c failure the engine is located at the center, you would only lose thrust & lift
- Multi a/c there is an engine on each wing, if one fails all the forces. may act upon you
4
Q
PAST
A
- P-factor
- Accelerated slip stream
- Spiraling slip stream
- Torque effect
5
Q
P-factor (YAW)
A
- low speeds & high angles of attack the descending blade is producing more thrust than the ascending blade
- the effective thrust centerline shifts to the RIGHT
- right engine has a longer moment arm (leverage) than the left
- left engine failure will result in more asymmetrical thrust or yaw to the left
6
Q
Accelerated slip stream (ROLL)
A
- left engine is inoperative, the amount of greatest induced lift on the wing is further from the CG, which causes a greater rolling force than it does when the right engine is inoperative
- longer moment arm to the center of thrust of the right engine to the left
- the roll produced by the loss of the left engine will be greater than the roll produced by the loss of the right engine
7
Q
Spiraling slip stream (YAW)
A
- spinning prop produces a spiraling wind pattern that rotates in the same direction as the prop
- spiraling slip stream from the left engine strikes the vertical stabilizer from the left counteracting yaw from a right engine failure
- the right engines slip stream does not reach the vertical stabilizer, does not counter yaw from a left engine failure
8
Q
Torque (ROLL)
A
- For every action there is an opposite an equal reaction
- right engine fails, this left roll tendency will help us maintain control & resist the roll towards the right, inoperative engine, caused by asymmetric thrust
- If the left engine fails, the left roll tendency by torque will add to the left turning force caused by asymmetric thrust into the inoperative engine
- This makes it much more difficult to maintain directional control, making the left engine the critical engine
9
Q
SMACFUMA
A
- Standard @ sea level
- Max power on operating engine
- Aft CG
- Critical engine windmilling
- Flap, gear, & trim in T/O position
- Up to 5 degrees bank into good engine
- Most unfavorable weight (light)
- Airborne out of ground effect
10
Q
Standard Day @ sea level *BAD
A
- 15 C, 59 F, 29.92 Hg, 1013.2 mb
- engine performance decreases as density altitude increases
- When the operating engine has more performance, it will have more asymmetrical thrust into the inoperative engine
- This causes you to need more rudder input to counteract the yaw from that asymmetric thrust
- Resulting in an increase in airflow (airspeed) over the needed to maintain directional control
- As density altitude increases, performance will decrease and Vmc will decrease
- standard day at seal level be your worst case scenario where Vmc will be the highest
- Performance increases, controllability decreases, VMC increases
11
Q
Max power on operating engine *BAD
A
- The more power you have in your operating engine, will give you more performance in your operating engine causing more yaw into the inoperative engine
- require more rudder input to counteract that yaw
- We will need to have more airflow (airspeed) to have more effectiveness of the rudder
- with more power, we will both increase our engine performance and increase our Vmc speed
- Making max power our worst case scenario and Vmc will be at its highest
- Performance increases, controllability decreases, VMC increases
12
Q
Aft CG *BAD
A
- When you have an aft CG, the arm between the CG and the rudder is shorter, which means the rudder will be less effective
- A higher airspeed would be required to counteract the yaw into the inoperative engine
- So with an aft CG, the Vmc speed increases and a forward CG would decrease Vmc
- Performance increases, controllability decreases, VMC increases
13
Q
Critical engine windmilling *BAD
A
- When the critical engine is windmilling, it will create more drag than if it was feathered
- This will raise your Vmc speed
- In turn, once you feather that propeller, you decrease the Vmc
- Performance decreases, controllability decreases, VMC increases
14
Q
Flaps, Gear up Trim t/o position *BAD
A
- When flaps are out, they help stabilize the aircraft, which helps reduce Vmc
- we have less stabilization when flaps are up (in takeoff position), which increases our Vmc
- by lowering the gear we creating the “keel effect” which helps keep the aircraft straight
- the accelerated slipstream behind the engine at full power encounters the gear and creates excess drag and that drag helps to counter the turning tendency
- both flaps up and gear up will negatively affect your Vmc speed
- Performance increases, controllability decreases, VMC increases
15
Q
Up to five degrees of bank into operating engine *GOOD
A
- When one engine is failed and you have wings level with the ball centered, you will actually be in a mild side-slip because the failed engine is causing drag and a loss of lift
- turning to up to a 5 degree bank toward the operating engine, you will decrease the drag causing a better climb performance and improve performance, as well as decrease Vmc
- lifting the lift vector, the horizontal component of lift
- Performance increase, controllability increase, VMC decrease
16
Q
Most unfavorable weight (light) *BAD
A
- Unfavorable weight is light
- The heavier the airplane, the lower the aircraft’s Vmc
- The lighter the airplane, the higher the aircraft’s Vmc
- a heavy plane has more inertia versus a light plane which gives it a greater resistance to yaw
- lighter aircraft are easier to disrupt, less mass to overcome
- Performance increase, controllability decrease, VMC increase
17
Q
Airborne out of ground effect *BAD
A
- Vmc decreases in ground effect
- reduction in drag
- As the aircraft yaws and rolls toward the dead engine the dead engine’s wing would dip further into ground effect, reducing its drag as it became more efficient, thus reducing the yaw toward the dead engine
- out of ground effect it will have a negative impact on the a/c
- Performance increase, controllability decrease, VMC increase
18
Q
VMC Indications
A
- stall warning
- full rudder deflection
- HDG is “running away”
- any stall warning indication (horn, buffeting, unattested descent)
19
Q
Why do we position the ball half deflection when one engine is inoperative?
A
- we are positioning the a/c tail in the relative wind
