====== Multi-Engine Aerodynamics ======

===== Zero Side-Slip =====


If both engines are operating, a centered ball is zero sideslip.

If one engine is out, a centered ball will NOT be zero sideslip due to aerodynamic forces applied by the rudder.

1/2 ball width TOWARD the WORKING engine will achieve zero sideslip in a C310.

Zero sideslip yields the best control and the best performance (less form drag)

<note important>When a light twin loses an engine, it loses 80% of its climb performance, due to the increased drag and decrease in excess power required for a climb.</note>

===== Critical Engine =====


The left engine is critical (typically) because...

...**P-Factor** -- Asymmetrical prop thrust on right (working) engine is further from centerline of the aircraft.

...**Accelerated Slipstream** -- The working engine pushes air across the wing behind it. Due to p-factor, the right engine creates more lift on the outboard section of the right wing than the inboard, therefore rolling the aircraft left. Additionally, less down-force is produced by the tail, making the aircraft pitch down.

...**Slipstream** -- the right engine's slipstream doesn't hit the tail (like the left engine's does), so it doesn't counteract any yawing moment. 

...**Torque** -- the engines turn to the right, rolling the aircraft to the left.


===== Vmc =====

Published Vmc is marked as a red line on the airspeed indicator.

Actual Vmc changes with different factors, while published Vmc remains the same.

Published Vmc is close to the worst case scenario, actual Vmc may be lower, especially after feathering the inoperative engine’s propeller. Don’t bet your life on that fact, Vmc may be higher than you assume it is.

Vmc, as defined by 23.149 must not exceed 1.2 Vs1.

Vsse is the Single engine safety speed. This speed is slightly higher than published Vmc and creates a safety buffer from Vmc for intentional engine out operations. We should never fly the airplane below Vmc or Vsse, if published, under single-engine operations.

Why is directional control affected by airspeed?
The faster the airspeed the more force the rudder can produce to resist the yawing tendency caused by asymmetrical thrust.

Vmc is the speed at which directional control can be maintained with one engine inoperative, under the following conditions...

  * Standard atmosphere. (FAR 23.45)
  * Most unfavorable CG and weight.
  * Out of ground effect.
  * Critical engine INOP
  * Bank no more than 5° towards operating engine.
  * Max available takeoff power on each engine initially
  * Trimmed for takeoff.
  * Wing flaps set to takeoff position.
  * Cowl flaps set to takeoff position.
  * Landing gear retracted.
  * All propeller controls in takeoff position. (INOP engine windmilling)
  * Rudder force required by the pilot to maintain control must not exceed 150 pounds.
  * It must be possible to maintain heading ±°20

===== FAR Part 23 Requirements =====


<note tip>There is nothing in 14 CFR part 23 that requires a multiengine airplane to maintain altitude while in the takeoff or landing configuration with OEI. (AFH Ch 12)</note>

The current 14 CFR part 23 single-engine climb performance requirements for reciprocating engine-powered multiengine airplanes are as follows.

**More than 6,000 pounds maximum weight and/or VSO more than 61 knots**: the single-engine rate of
climb in feet per minute (fpm) at 5,000 feet mean sea level (MSL) must be equal to at least .027 Vso 2.

For airplanes type certificated February 4, 1991, or thereafter, the climb requirement is expressed in terms
of a climb gradient, 1.5 percent. The climb gradient is not a direct equivalent of the .027 VSO 2 formula.
Do not confuse the date of type certification with the airplane’s model year. The type certification basis of
many multiengine airplanes dates back to the Civil Aviation Regulations (CAR) 3.

**6,000 pounds or less maximum weight and VSO 61 knots or less**: the single-engine rate of climb at
5,000 feet MSL must simply be determined. The rate of climb could be a negative number. There is no
requirement for a single-engine positive rate of climb at 5,000 feet or any other altitude. For light-twins
type certificated February 4, 1991, or thereafter, the single-engine climb gradient (positive or negative) is
simply determined.


===== FAR/CAR Regulations Applied to C310R =====


==== CAR Part 3 (1949) ====


§ 3.83 Stalling speed. **Vso at maximum weight shall not exceed 70 miles per hour (59.5kt)** for (1) single-engine airplanes and (2) **multiengine airplanes which do not have the rate of climb with critical engine inoperative specified in §3.85 (b)**.

(b) Climb with inoperative engine. All muliengine airplanes having a stalling speed Vso greater than 70 miles per hour or a maximum weight greater than 6,000 pounds shall have a **steady rate of climb of at least 0.02 Vso** in feet per minute at an altitude of 5,000 feet with the critical engine inoperative and:
  - The remaining engines operating at not more than maximum continuous power,
  - The inoperative propeller in the minimum drag position,
  - Landing gear retracted,
  - Wing flaps in the most favorable position,
  - Cowl flaps in the position used in cooling tests specified in §§ 3.581-3.596.

Vso = 72kt = 83mph -> Climb Required: 1.66fpm