multi engine 2a - electrical, pneumatic, hydraulic, etc.

electrical, pneumatic, hydraulic, fuel, landing gear, ice control, and cabin oxygen systems

why do small multi-engine systems use direct current systems?

they are simpler and lighter than equivalent alternating current (ac) systems

alternators

produce alternating current, which is changed to direct current as it leaves the alternator

what advantages do alternators have over generators?

* lighter and smaller than generators of equivalent power output
* offer better performance and longer service life when operating at high altitude
* produce more power through a wider range of engine speeds

what storage batteries are used?

12- or 24-volt lead acid batteries

where are battery compartments often located?

the nose baggage compartment, behind the aft baggage compartment, or in one of the wings

what electrical systems do most small multi-engine airplanes use?

12 or 24-volt **direct current (dc)**

define **pneumatic pump**

a pump that uses pressurized air to power the %%**gyroscopic flight instruments**%% and possibly some %%**auxiliary systems**%% (wing deice boots or inflatable door seals)

what are gyroscopic flight instruments **drive n by?**

vacuum or pressure systems

why are vacuum systems more often used for instruments?

* they provide cleaner and cooler air than pressure systems
* the air is drawn in through a filter, through the flight instruments, and then discharged out the pump

how can pilots check on the pneumatic system inside the cockpit?

* typically use %%**pressure or vacuum gauges**%%
* some systems use %%**warning lights**%%

define **engine-driven hydraulic pump**

* supply hydraulic pressure in most multi-engine aircraft
* some smaller aircraft use pumps powered by electric motors

define **hydraulic actuators**

convert fluid pressure into mechanical force

* **hydraulic cylinders:** used in applications that require ^^linear motion^^
* **hydraulic motors:** used in applications for ^^rotary motion^^

define **hydraulic accumulator**

a device for storing hydraulic pressure and for absorbing the internal shocks that result from operating the hydraulic system

* typical accumulator has 2 chambers
* one pre-charged with nitrogen pressure that acts like a powerful spring on one side of a piston with hydraulic fluid on the other side
* applying hydraulic pressure causes the piston to compress the nitrogen

define **auxiliary fuel pumps**

supply fuel pressure fors tarting or when the engine-driven pumps fail

define **boost pumps**

generally operated continuously to maintain fuel pressure to the engine-driven pumps and to supply fuel to the engine if the engine-driven pumps fail

**cross feeding** is used to…

laterally balance the fuel load and ^^increase range^^ after an engine fails

* most often cannot cross feed fuel from the auxiliary tanks
* to maximize the fuel that is available for crossfeed, ensure the main tanks are as full as possible

define **electrohydraulically powered landing gear**

uses electric power to drive the hydraulic pump in the landing gear

* most systems have a reversible electric motor, allowing to power the hydraulic pump in either direction to retract or extend the gear

**landing gear safety switch** (aka **squat switch)**

prevents the landing gear from retracting when the aircraft is on the ground

define **inflatable deice boots**

rubber boots attached to the leading edges of the wings, horizontal stabilizer, and vertical stabilizer


1. when on, air from the engine-driven pneumatic pumps inflates the boots to break the ice
2. the slipstream airflow blows it away
3. after each inflation cycle, the pumps apply suction to deflate the boots and hold them tight to the contour of the airfoil surface
4. the cycle alternates between the protected surfaces to reduce load on the ice pumps and to keep the ice accumulations symmetrical on each side of the aircraft

define **ice-bridging**

in situations when pilots inflate the boots before sufficient ice has accumulated, the soft, thin ice is merely pushed away from the surface and **refreezes in a hard shell j**ust outside the reach of the boots