multi engine 2c - determining performance

define **unaccelerated flight**

where thrust equals drag

why is performance not doubled with a second engine?

* a twin must also carry the %%weight of an additional engine and propeller%% + airframe structure to support
* additional %%parasite drag%% of the two engine nacelles
* the vertical stabilizer and rudder are ^^usually larger^^ so the tail can control the yaw of a failed engine
* additional drag
* more fuel → increasing the %%fuel capacity%% to give reasonable range
* also means ^^more weight^^

what relationship dictates performance?

* the relationship between **power available** and **power required**
* %%excess horsepower%% leads to %%increased climb performance%%

define **thrust**

a force that overcomes drag, normally measured in pounds

define **power**

the rate at which work is done, so it is tied directly to **speed**

why is the **performance penalty** severe when there is engine failure in a multi-engine plane?

* the thrust line is not through the centreline of the airplane
* must use the rudder to maintain directional control
* the %%vertical stabilizer and rudder%% becomes a vertical airfoil generating sideways lift, generating drag
* the parasite drag of %%the engine nacelles and a feathered propelle%%r are not present in a single airplane

when is the performanced in the POH reliable?

the associated conditions displayed on the chart

V**ef**

speed at which the critical engine is assumed to fail during takeoff

V**lof**

lift-off speed

* often about 10% higher than V**mu (minimum unstick speed)**

V**mc**

minimum control speed with **critical engine inoperative**

V**r**

rotation speed

V**1**

* %%maximum speed during takeoff%% when the pilot must make the first action to **stop within the accelerate-stop distance**
* %%minimum speed following critical engine failure%% that pilot can **continue takeoff and** ^^**achieve the required height within the takeoff distance**^^

V**2**

* takeoff safety speed
* frequently a speed that allows for a safe climb out in the case of %%an engine failure%% or %%turbulence%%

V**so**

stalling speed or minimum steady flight speed in landing configuration

V**mca**

minimum control speed with critical engine inoperative **in air**

V**xse**

best angle of climb, single engine

V**yse**

best rate of climb, single engine

V**ref**

reference speed

* an airspeed for final approach, which adjusts the normal approach speed for factors like wind and gusts

V**sse**

intentional one-engine inoperative speed

define **accelerate-stop distance**

the runway length required to accelerate the airplane to %%**rotation or liftoff speed** (V**r** or V**lof**)%%, experience an engine failure, and ^^bring the airplane to a complete stop^^

what factors can affect accelerate-stop distance?

* **density altitude**
* **weight**
* **wind**

how does **increases in density altitude** affect accelerate-stop distance?

* **longer distance:** the engine produces less power and the propellers are less efficient
* **higher groundspeed** to become airborne → increases %%**accelerate and braking distance**%%

how does **weight** affect accelerate-stop distance?

* longer distance for **liftoff speed**
* longer distance to **stop it**

how does **wind** affect accelerate-stop distance?

* headwind
* decreases the accelerate-stop distance
* tailwind
* increases the accelerate-stop distance

define the **accelerate-go distance**

* the distance required to continue a takeoff and climb to 35 feet above the departure end of the runway following an engine failure at V**1**

define **climb gradient**

the altitude gained per horizontal distance, expressed as a percentage

* **ex:** 1.7% climb gradient → for every 1000 feet of horizontal distance, the airplane will climb 17 feet

define **single-engine absolute ceiling**

the density altitude that the airplane is capable of reaching and maintaining with the critical engine feathered and the other engine at maximum power

* if above this altitude when the engine fails, the plane will drift down

what factors affect the **rate of driftdown?**

* airspeed
* drag
* pilot technique

how to minimize the **sink rate of driftdown?**

* choose an airspeed that provides the **least difference** between %%**power available**%% and %%**power required**%%
* that is **best rate of climb, single engine (Vyse)**

define **single-engine service ceiling**

the maximum density altitude at which the airplane can climb at 50 feet per minute with one engine feathered

* varies with airplane weight