Asymmetric Thrust Flashcards
Multi engine prop - engine failure
More lift on running engine wing, more drag on failed engine. Combination causes a yaw and roll towards failed enigne.
Consequences of Asymmetric flight.
Yaw
Roll
Loss of thrust
Reduces climb performance
reduced ceiling
slower max speed
increased drag: failed engine and rudder deflection.
Failure to stop the yaw
Continue to roll and yaw, spiral turn.
What affects how strong the yaw is?
Distance between thrust line and CG, longer = more yaw.
Windmilling or feathered,
Windmilling=more yaw
Which engine failed,
critical engine = more yaw
Amount of thrust,
more thrust = more yaw
Critical engine
If this engine fails, worse handling situation. The asymmetric blade affect is the cause of there being a critical engine.
Clockwise prop: Thrust is most at the right side of prop, so if left engine fails for left yaw as bigger distance between thrust line and CG. So left engine is critical.
4 anticlockwise props: Most thrust is left side of prop, yaw is right, if right engine fails even more right yaw. Because far right has big arm for left yaw, so when that gets taken more right yaw so far right prop is critical.
Smaller arm = less yaw
Why is it better to have inward rotating props?
Shorts arms, so during engine failure less yaw. Also, no critical engine due to the both props being exact same but opposites.
Contra rotating Props
Preventing a critical engine. Two props on same shaft rotating in opposite directions.
Critical engine and Wind
Aircraft wants to yaw into wind, normally.
If the engine failure makes it yaw the same way, the overall effect will be worse.
The into wind engine is critical.
Controlling an engine failiure
Objective: Return to straight and level flight, This requires all moments and forces to balance out.
2 methods:
Wings level,
Wings banked
Wing level method
Natural yaw moment left, but we cancel it with right rudder.
So rudder force left and thrust straight gives total reaction up-left down the RAF.
Aircraft flies sideways due to imbalanced rudder.
Advantages: Normal instrument indications
Disadvantages: Less effective rudder, greater chance of fin stall
Wings banked method
Aims to avoid the sideways motion by creating a force to balance the rudder out.
Achieved by banking the aircraft which tilts the lift so that it cancels out the rudder.
With right rudder, you would bank left so some lift cancels out the rudder force.
Now flying straight down the RAF.
Advantages: More effective rudder, flying in the direction you are pointing.
Disadvantages: Unusual instruments. Attitude indicator banked. Turn indicator, needle is middle, ball is half to the right.
Other facts: A heavier aircraft is better for this method, needs more effective rudder.
Bank angle should not be more than 5 degrees: due to increasing n,
Vmc gets faster, as AOB increase.
Minimum control speeds
The slowest speed at which it is possible for the pilot to control an engine failure on a multi-engine aircraft.
Vmg: Minimum control ground speed
Lowest speed at which you can maintain directional control on the runway with a critical engine failure:
-Using only rudder
-No nose wheel steering
-CG on aft limit (short arm)
- Full power on remaining engine
- maximum 30ft deviation from centre line.
Vmc(a): Minimum control airborne speed
Lowest speed at which the aircraft can maintain straight flight with a critical engine failure.
-Using 5 degree bank
-CG on aft limit
-Max power on remaining engine
-Max 20 degree variation in heading
-critical configuration but with gear up.
Vmcl: Minimum control landing speed
Same rules and definition as Vmc.
