Directional Control of Multi-Engine Aircraft

Question 1

What are the two immediate effects that multi-engine aircraft suffer airborne when there is an engine failure?

Answer 1

1) Yaw towards the failed engine

2) Roll Towards the failed engine

Question 2

What is there an initial yaw towards the failed engine?

Answer 2

Due to:

• Position of failed engine
• Power on remaining engines
• Drag produced by failed engine or propeller
• Directional stability

Question 3

Why is there a roll towards the failed engine?

Answer 3

• Secondary effect of yaw

- Due to reduction in slipstream over the wing behind the failed engine

Question 4

What will happen if the engine fails and control responses are left unchecked?

Answer 4

Aircraft will enter spiral dive about the failed engine.

Question 5

What is the critical engine?

Answer 5

The critical engine is defined as the engine which, when failed, gives the greatest yawing moment.

Question 6

What 4 factors is the critical engine dependent on?

Answer 6

1) The distance from the CoG
2) Asymmetric blade effect (propeller aircraft)
3) Slipstream (prop effect)
4) Torque (prop aircraft)

Question 7

Define Vmca or Minimum Control Speed - Air?

Answer 7

The minimum calibrated airspeed at which, when the critical engine is suddenly made inoperative, it is possible to maintain control of the airplane with that engine inoperative and maintain straight flight with an AoB not more than 5 deg.

Question 8

If flown below Vmca, is there sufficient control deflection available to maintain directional control of the A/C?

Answer 8

No

Question 9

Although Vmca is defined as an airspeed, does the problem actually relate to power?

Answer 9

Yes, by reducing power, the asymmetry is reduced.

Question 10

What speed must Vmca not exceed? What conditions are applied to this?

Answer 10

• Vmca must not exceed 1.13 times the stall speed
• Maximum TO power or thrust on remaining engines
• The most unfavourable CoG
• Airplane trimmed for TO
• Max Seal level T/O weight
• Most critical T/O config
• Airborne and out of ground effect
• The propeller of the inoperative engine - windmilling, in most probable position, feathered

Question 11

Under the previous conditions, what should the force required to operate the rudder not exceed?

Answer 11

150 lbs.

Question 12

What is the definition of Vmcg?

Answer 12

The minimum calibrated airspeed during the T/O run at which, when the critical engine is suddenly made inoperative, it is possible to maintain directional control of the airplane using rudder alone.

Question 13

When calculating Vmcg, what conditions must aircraft designers apply?

Answer 13

• Maximum T/O power or thrust on remaining engines
• The most unfavourable CoG
• The aeroplane trimmed for T/O
• Most unfavourable T/O weight

Question 14

What is max displacement in feet on the runway for aircraft to regain control of centreline when critical engine fails?

Answer 14

30 ft

Question 15

Is directional stability enough to maintain control of the aircraft is an engine fails?

Answer 15

No, needs to be enhanced with either sideslip and/or rudder deflection as along this stability is insufficient to overcome the adverse yaw.

Question 16

What are the three flying techniques that can be used to create the restoring forces?

Answer 16

1) Bank Only Method - Rudder is fixed or free
2) Rudder Only Method - Wings level
3) Angle of Bank (AoB) and Rudder Method - Zero Sideslip

Question 17

What is generally the best option to create the restoring forces?

Answer 17

The Bank and Rudder technique as it removes issues with dangers of single control methods such as fin stall at angles of high sideslip.

Question 18

Describes the Rudder Only - Wings Level technique

Answer 18

• Most basic method for controlling the A/C required the ailerons to keep the wings level and rudder to counter the aw
• A/C flight path is a sideslip toward the failed engine with the aircraft in balance
• Disadvantages are increased drag by the sideslip and the large rudder forces required.

Question 19

Describe the small angle of bank method (AoB and rudder method)

Answer 19

• This method for controlling the A/C requires a small angle of bank toward the live engine and rudder to counter the yaw
• This method is the most efficient as the horizontal component of lift is used to counteract the sideslip without significant losses in performance
• Flight path of A/C is straight with a slip indicated towards live engine

Question 20

What is the Bank Method Only? (Large angle of bank)

Answer 20

• Requires a large angle of bank toward live engine
• Method best know when rudder is not available or full travel has been reached
• Flight path is a sideslip toward the live engine with significant slip indicated toward live engine
• Major disadvantage is reduction in lift caused by additional bank