27 Asymmetric Flight

Question 1

Describe the ‘Wings Level’ method for correcting adverse yaw of a failed engine and give:

• Advantages
• Disadvantages

Answer 1

• To correct a yaw to the left (caused by a failed left engine) rudder to the right is applied
• The sideways component of force produced by the rudder counters the sideways component of thrust
• The AC effectively flys into the RAF at an angle
• Turn coordinator and slip ball remain centred

Advantages:
- Continue to fly straight so less disorientation

Disadvantages:

• Force generated by rudder increases drag and so reduces performance
• May have to set rudder at a high AOA so increased risk of stalling the rudder

Question 2

Describe the ‘Banking’ method for correcting adverse yaw of a failed engine and give:

• Advantages
• Disadvantages

Answer 2

• Dropping the wing of the active engine generates a sideways component of lift which opposes the yaw
• Must be limited to a 5 degree AOB, more can have an adverse effect
• Whilst the Turn coordinator does not indicate a turn, the Slip Ball will move towards the downward wing as the AC will begin to slip

Advantages:

• No additional drag so improves performance
• Greater rudder authority so less chance of a fin stall

Disadvantages:
- Disorientation can occur as the AC will be flying at a bank but will not be turning

Question 3

What is a Critical Engine?

Answer 3

A critical engine is the engine on a multi-engined AC which, if lost, would result in the biggest yawing moment

Question 4

Which engine is the critical engine on a multi-engine Jet AC?

Answer 4

• Since Jet AC don’t suffer from p-factor or slip stream effects, the critical engine is determined if there is a cross wind on the runway at take-off
• AC has a natural tendency (positive directional stability) to turn into the wind
• Therefore the critical engine is the in-to wind engine

Question 5

What is Vmc (Vmca) and what factors is it determined on?

Answer 5

• Vmc is the minimum control speed in the air
• i.e. The minimum speed required to maintain control following a critical engine failure after take-off

Factors:

• Max take-off thrust
• Max SL mass
• Most unfavourable CG position
• Trimmed for take-off
• Out of ground effect
• Critical configuration for take-off (gear up)
• If prop, windmilling or feathered but only if it has an auto feather

Question 6

What is Vml and what factors is it determined on?

Answer 6

• Vml is the minimum control speed for approach and landing
• i.e. It is the minimum speed required to maintain control if the critical engine is lost during the approach or landing

Factors:

• Go-around thrust
• Trimmed for landing
• Critical configuration for landing
• Most unfavourable mass
• Most unfavourable CG position
• Able to reach 20 degrees angle of bank in 5 sec

Question 7

What is Vmcg and what factors is it determined on?

Answer 7

• Vmcg is the minimum control speed on the ground
• i.e. The minimum speed required to maintain control following a critical engine failure on the ground
• Using Fin only, not front gear steering
• On ground AC rotates about the main gear, not the CG
• Therefore shorter arm between fin and point of rotation
• Vmcg > Vmc

Factors:

• Max take-off thrust
• Most unfavourable CG position
• Most unfavourable mass
• Most critical take-off configuration
• Trimmed for take-off
• Maintain control with no more deviation than 30ft from centre line

Question 8

What is the influence of Air Density and Altitude on minimum control speeds?

Answer 8

• Colder and lower altitudes will require faster minimum control speeds
• More thrust is available so more force required to counter the yaw moment
• Therefore higher speeds are required

Question 9

What is the maximum amount of force which can be applied to the rudder to maintain control for Vmc and Vmcl?

Answer 9

150 lbs