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I've heard three methods you should use in a multi-engine aircraft when engine-out, each recommending a different amount of bank:

  1. Wings level, hold aileron to maintain roll and correct using rudder.
  2. Ball centred, ailerons flush and correct using rudder.
  3. 5 degrees bank angle, hold aileron to maintain roll and correct using rudder.

Which one of these will result in the highest climb rate, and are there any advantages to other methods which don't give the best climb rate?

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    $\begingroup$ Gut says #3. If I get a chance to shut one down in flight tomorrow I'll test it out. $\endgroup$ – Steve V. Feb 15 '14 at 6:07
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I tested this out in the Seminole today. My (extremely nonscientific) results are as follows:

  1. Wings level, hold aileron to maintain roll and correct using rudder: 200 FPM

  2. Ball centred, ailerons flush and correct using rudder: 0 FPM

  3. 5 degrees bank angle, hold aileron to maintain roll and correct using rudder: 100 FPM

  4. 2.5 degrees bank angle, hold aileron to maintain roll and correct using rudder: 200-250 FPM

At least under today's conditions*, wings level was better than 5 degrees of bank, but approximately 3 degrees of bank was slightly better than both.


Today's conditions, for the interested:

  • 6000 MSL
  • -7 C
  • Engine shut down and feathered
  • About 1/4-1/2 ball deflection on all except #2
  • Probably about half tanks
  • No idea what the altimeter setting was
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  • $\begingroup$ So it's probably a better idea to err on the side of less bank unless you need it for directional control (i.e. near VMCA). Thanks! $\endgroup$ – Qantas 94 Heavy Feb 16 '14 at 2:09
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This will vary from plane to plane depending on design, and the best method to use for a particular airplane would be listed in the engine out procedures in the POH/AFM.

When the manufacturers are flight testing the airplanes they try various combinations and tell you the absolute best one so that you can get the best performance out of the airplane in a potentially dangerous situation. Fly your particular airplane by the book to ensure that the airplane does what the POH says that it will do.


Examples:

The Seminole POH says:

Trim the aircraft as required and maintain a 3° to 5° bank toward the operating engine. The balI wiII be 1/2 to 3/4 out for minimum drag.

The Diamond Twin Star POH says:

Establish minimum / zero sideslip condition (approx. half ball towards good engine; 3° to 5° bank).

The Cessna 441 POH says:

The one engine inoperative best rate-of-climb speed at various altitudes is shown in Section 5. Best single-engine climb is attained with the wings banked approximately 3° to 4° and with a 2/3 to 3/4 ball slip into the operative engine when the airplane is at low airspeed and heavy weight. As airspeed increases and/or airplane weight is significantly reduced, the 2/3 to 3/4 ball slip becomes less important.

I'm seeing a trend here among the light twins. :-)

On the other hand, in the jets that I have flown, we are taught to remain wings level and center the ball with the rudder:

Here is what the Lear 60 AFM says:

Use rudder pedal force as necessary to maintain slip/skid indicator centered.

The Falcon 50 AFM doesn't mention it at all.

This isn't the case for all jets though. The A320 Flight Crew Training Manual says:

ENGINE FAILURE

In flight, if an engine failure occurs, and no input is applied on the sidestick, lateral normal law controls the natural tendency of the aircraft to roll and yaw. If no input is applied on the sidestick, the aircraft will reach an approximate 5 ˚ constant bank angle, a constant sideslip, and a slowly-diverging heading rate. The lateral behavior of aircraft is safe.

However, the PF is best suited to adapt the lateral trimming technique, when necessary. From a performance standpoint, the most effective flying technique, in the event of an engine failure at takeoff, is to fly a constant heading with roll surfaces retracted. This technique dictates the amount of rudder that is required, and the resulting residual sideslip.

As a result, to indicate the amount of rudder that is required to correctly fly with an engine-out at takeoff, the measured sideslip index is shifted on the PFD by the computed, residual-sideslip value. This index appears in blue, instead of in yellow, and is referred to as the beta target. If the rudder pedal is pressed to center the beta target index, the PF will fly with the residual slip, as required by the engine-out condition. Therefore, the aircraft will fly at a constant heading with ailerons and spoilers close to neutral position.

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I'll add a physical explanation (based on the excellent How It Flies):

The thrust asymmetry generates a torque that will tend to turn the aircraft. To avoid turning, you counter this torque with rudder. The moment of the rudder will balance the moment of the thrust, but the force generated by the rudder will not be balanced and will cause some slip itself and slip increases drag. So you need to balance the force by adding a bit of sideways lift by banking into the live engine ("raise the dead").

The amount of bank depends on the relative magnitude of the moments and forces involved. If the engines are further apart, the moment of thrust will be larger so rudder will have to produce larger force to counter it and the bank will have to be higher to counter the rudder force. The further aft the rudder is, the less force it needs to produce to yield the same moment and therefore less bank will be needed.

It follows that the correct bank angle is different for each aircraft. See Lnafziger's answer for examples.

Note that the slip-skid ball will no longer correspond to slip directly. The ball shows the direction of total weight (gravity plus centrifugal force). Normally it is centred when the weight is correctly balanced by lift, but here the lift is additionally balancing the rudder force, so the ball will be slightly off centre as the weight is directly to the ground when flying straight, but the aircraft is slightly banked.

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3-5 degrees bank angle ("raise the dead"). Use the rudder to keep the skid/slip about half a ball off. That's the standard operating procedure for best performance.

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