OEI/Vmc Flight Principles Flashcards
What are the 4 Factors concerning the Critical Engine?
(PAST) P-Factor Accelerated Slipstream Spiraling Slipstream Torque
Explain P-Factor. How does this make the LEFT engine critical?
- The principle that the descending prop blade (on the right) is producing more Thrust than the ascending prop blade (on the left)
- This asymmetry creates a shift in the Center of Thrust to the right of each engine, making the ARM between the Center of Thrust of the Right engine and the Longitudinal Axis of the a/c is greater
- Increased Thrust on the Right creates a/c YAWing reaction to the Left
Explain Accelerated Slipstream. How does this make the LEFT engine critical?
- With more Thrust being produced on the Right side of each engine, there is consequently more LIFT being produced on the Right side of each engine, acting back over the wing.
- There is a greater ARM between the Excess Lift felt on the Right Wing and the Vertical Axis of the a/c
- This asymmetry creates a ROLLing reaction to the Left.
Explain Spiraling Slipstream. How does this make the LEFT engine critical?
- With both engines Operative, the spiraling slipstream produced by the Left Prop strikes the Rudder/Vertical Stabilator encouraging YAW to the left, however the slipstream produced by the Right Prop does not strike the Rudder, thus having no real affect on the a/c’s Yawing tendency
- If the Right Engine were to quit, the Left Props slipstream would still be striking the Rudder and opposing a/c Yaw into the INOP engine. If the Left Engine quits, the Right Props slipstream does not provide the same opposition.
Explain Torque. How does this make the LEFT engine critical?
- Newton #3: For each action there is an equal and opposite reaction
- In a traditional twin engine, both propellers rotate clockwise as seen from the pilot’s seat, thus creating a Rolling action in a Counter-Clockwise direction about each Engine
- Thinking bigger picture, the entire a/c now feels ROLLing in the Counter-Clockwise direction, and if the Left engine fails, the Right engine’s prop rotation will continue to “encourage” Rolling to the Left/Into the dead engine
What is Vmc?
The Sea Level CAS at which, when the critical engine is suddenly made inoperative, it is possible to maintian control and maintain straight/level flight at the same speed with bank angle no more than 5 degrees
- NOT a fixed airspeed in reality
Where can you find information about Minimum Control Speed in the FARAIM?
23.149 - discussed during TO and also approach and landing!
What are you gonna use your acronym MFu4 SMAC 5G for?
To remember the conditions at which an a/c must be under for the manufacturer to determine Vmc…these are also the 11 factors that most adversely affect Vmc!
What are the FAA published standards for a/c manufacturers to use when determining Vmc/factors most adversely affecting Vmc? (13 items)
23.149 - MFu SMAC 5G 150/20
Most unfavorable Weight (lightest)
Flaps Up, Gear Up, Cowl flaps TO, Trimmed for TO
Standard day/atmospheric conditions
Max Takeoff Power
Aft CG (most unfavorable)
Critical Engine out/windmilling
5 deg of bank max
Ground affect negligible/airborne
150lbs of pressure on rudder (do not exceed)
20 deg loss of heading (do not exceed)
Will the FAA published standards described in 23.149 be the same for every aircraft?
No, this is a formula! It will be different depending on the operating characteristics of each aircraft.
Most Unfavorable Weight
Vmc Increases.
Lighter a/c are more easily displaced. Need MORE rudder to maintain DC, meaning DC will be lost SOONER.
Flaps Up, Gear Up, Cowl flaps TO position, Trimmed for Takeoff
Vmc Increases.
Flaps Up/Gear Up = NO Keel Effect resisting YAW into inoperative engine.
Additionally, no excess DRAG countering THRUST from operative engine, creating more YAW into the inoperative engine.
Need MORE rudder to main DC, meaning DC will be lost SOONER.
Standard day/atmospheric conditions
Vmc Increases.
With piston engines, a lower Density Altitude causes P-Factor and engine Thrust output increases.
This creates more asymmetrical thrust/lift, creating more YAW/roll into the inoperative engine.
Need more rudder to maintain DC, meaning DC will be lost SOONER.
Max TO power on each engine
Vmc Increases.
More power on Operative Engine increases P-Factor and engine Thrust output.
This creates more asymmetrical thrust, creating more YAW into the inoperative engine.
Need more rudder to maintain DC, meaning DC will be lost SOONER.
Aft/Away CG
Vmc Increases.
Aft CG has SHORTEST ARM with Rudder.
This decreases rudder effectiveness.
Aft CG has LONGEST ARM with Center of THRUST.
This has the most adverse affect on YAW.
Need more rudder to maintain DC, meaning DC will be lost SOONER.
