Assignment On Aircraft Power Systems Engineering Essay

In this assignment, I intend to supply a brief presentation about the rule of operation of the aircraft electrical power systems, specifically, Integrated Drive Generators ( IDG ) in a modern aircraft. I will compare and contrast the fluid and electrical methods of power coevals and give a brief on the safety safeguards to be followed when managing aircraft electrical power supplies and during a functional trial.

There are assorted sorts of power coevals on an aircraft, viz. electrical ( generators & A ; batteries ) , fluid ( fluid mechanicss & A ; pneumatics ) . Depending upon the application, the power beginnings may change.

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The chief map of any aircraft electrical system is to bring forth, modulate and administer the electrical power in the aircraft. Modern aircrafts use more electrical power as they are equipped with more Electronic Flight Instrument System ( EFIS ) . This is done so as to cut down pollution in the environment, for a clean and safe flight.

Electrical power is used to run:

Aircraft Flight Instrument- Electronic Centralized Aircraft Monitoring ( ECAM )

Essential Systems- Primary Flight Display ( PFD ) , Navigation Display ( ND )

Passenger Services- In-Flight Entertainment ( IFE )

Most of the aircraft systems use a power criterion of 115 VAC @ 400Hz ; 28VDC.

There are assorted electrical power beginnings on the aircraft:

Engine Driven AC Generators ( EDG )

Auxiliary Power Units ( APU )

Ram Air Turbine ( RAT )

Battery Supply

External/Ground Supply ( Spoor, 2012 )

Components in an electrical system include:

AC Generator/Alternator produces AC power.

Changeless Speed Drive Unit ( CSDU ) regulates the revolving velocity ( input ) to present a changeless end product from the engine to the generator.

Integrated Drive Generator ( IDG ) , Generator and CSDU connected either coaxially or side-by-side. Largely coaxal connexion.

Transformer Rectifier Unit ( TRU ) converts the AC power to DC power

Generator Control Unit ( GCU ) proctors and controls the generator end product.

Each engine powers up one or more generators. Airbus A380 has four engines and four generators. Whereas, Boeing 777 has two engines and two generators. The power produced by these generators is used to power up the full aircraft. ( Boeing, 2012 )

All the other power beginnings, except external supply, are used in instance of exigencies merely.

External power supply is used on land when the engines and the APU are non running. It is supplied via Ground Power Unit ( GPU ) . GPU can be portable or stationary and they provide AC power through the external stopper on the olfactory organ of the aircraft. They can be used to power up an full aircraft or a specific country in the aircraft. ( Spoor, 2012 )

Figure: Aircraft Electrical System ( Authoritative Jet Sims, 2012 )


The rule of a hydraulic system is to change over unstable power into mechanical power and so utilize it for assorted applications on the aircraft, such as extension/retraction of set downing cogwheels, flaps, and velocity and wheel brakes.

The power beginning here is the hydraulic fluid. The force per unit area for bring forthing the hydraulic power is supplied by the Engine Driven Pump ( EDP ) and the Electric Motor Driven Pump ( EMDP ) . They are both mounted on the engines.

Normally used hydraulic fluids on the aircraft are:

MIL-H-5606 ( Mineral Based Fluid )

MIL-H-83282 ( Synthetic Hydrocarbon Based Fluid )

MIL-H-87257 ( Same as MIL-H-83282, but it has been improved in its low temperature viscousness )

MIL-H-8446 ( Phosphate-Ester Based Fluid ) ( Wikipedia, 2012 )

Particular attention must be taken when managing the hydraulic fluid. Some of the hydraulic fluids are skin/eye thorn. Besides it is highly of import for the fluid to be free from any taint for flight safety.

Advantages of the hydraulic system as a power beginning includes:


Easy installing

Simplified Inspection

Minimal Care

Approximately 100 % system efficiency, with merely negligible loss due to clash. ( EAC, 2012 )

Figure: Basic Hydraulic System ( Free Online Private Pilot Ground School, 2006 )






Power is generated by the engine, by rotary motion of turbine shaft.

Power is generated by incompressible hydraulic fluid. Pressure for hydraulic propulsion is supplied by EMDP and EDP.

Similar to that of an electric circuit.

Components include: Generators/Alternators, Batteries, Switches, Bus bars, Fuses, Circuit Breakers, Voltage Regulators, Ammeters, and Wires. ( Free Online Private Pilot Ground School, 2006 )

Components include: Reservoir, Pump, Hydraulic Fluid, Accumulators, Actuators, Filters, Hydraulic Fuses, Tubing, Pipes, Valves, and Sealing waxs.


Lights, Radio Equipment, Indicators, Warning Systems, Heaters, Starting motor. ( FlightLearnings, 2012 )

Extension/retraction of set downing cogwheels, flaps, and velocity and wheel brakes.

Principle of Operation

Generate, Regulate and Distribute electrical power generated.

Work is done by traveling an incompressible fluid, Pascal ‘s Law. ( EAC, 2012 )


In instance of chief engine driven generator ( EDP ) failure, there are assorted methods to guarantee continued power supply for safe landing:

Auxiliary Power Unit ( APU )

Ram Air Turbine ( RAT )


When the chief engine generators fail, APU or RAT is deployed. When the secondary methods fail, batteries are used as the last resort for a safe landing and emptying.


Auxiliary Power Units ( APUs ) is a little gas turbine engine which provides electrical, hydraulic and pneumatic power ( depending on the design ) for land or in-flight operations. It is besides used as a backup beginning in exigency state of affairss. It is normally found on big aircrafts. It is normally located in the tail terminal of the aircraft. When started, it usually runs on 100 % velocity. It produces 115VAC @ 400Hz. Some can besides bring forth 28VDC.

The chief intent of the APU is to get down the engines in the aircraft. This is because the engine requires high rotational velocity for its self-sufficient operation. In this instance, APU is started by battery or hydraulic collector and so used to bring forth the necessary rotational velocity. It is besides used to run the equipment when the engines are shutdown. This is used for air conditioning for the riders prior to engine start. However, it can besides be connected to a hydraulic pump to power up hydraulic equipment ( flaps and flight controls ) . ( Wikipedia 2012 )


Ram Air Turbine is a little airflow driven turbine that is connected to either a hydraulic pump or an exigency alternator or a chief generator. In normal flight, it is stowed off in closed compartment in flying or fuselage. It is deployed merely when there is entire power loss due to engine failures. It provides adequate power to run the critical systems, such as, flight controls. The power generated by the RAT depends on the airspeed. More the velocity, more the power generated will be. Some aircrafts use RAT in normal operation. For illustration, in harvest dusting RAT is used to power up the chemical sprayer. ( Wikipedia, 2012 )


Aircraft batteries are used to get down the engines or the APU. But they are besides used in exigency state of affairss as a last resort for safe landing. There have been instances where it has been used to re-start the engines even after engine flame-out. They besides act as a buffer for the DC connexions. It regulates the electromotive force to guarantee the power quality for the equipment connected to it.

Two types of batteries are used in aircrafts today, Lead-acid and Nickel Cadmium ( Ni-Cd ) . Lead-acid batteries are either valve regulated or vented. They are used in visible radiation and general aircrafts. Ni-Cd batteries are used in larger aircrafts. Lead-acid batteries are by and large heavier and have less capacity than the Ni-Cd 1s. ( Dr. Thomas, 2010 )

Figure: Lead-Acid Battery ( Chief Aircraft, 2012 ) Figure 4: Nickel-Cadmium Battery (, 2012 )


From 1950s to early 1960s some propjet aircrafts used ‘frequency wild ‘ , now Variable Frequency ( VF ) system. Airbus A380 and Boeing 787 Dreamliner are some of the modern civil air power aircrafts that have adopted the VF system once more.

Figure: Simplified Frequency Wild System ( Scribd, 2012 )


As shown in Fig.4, the Variable Frequency Generator ( VFG ) is straight connected to the engine cogwheel box. ( Langlois, 2004 ) provinces: ‘VFG is a conventional lesion rotor synchronal alternator ‘ . There is no CSD or IDG in this system. This is done so as to better the dependability of the system and besides to cut down the weight of the aircraft. Airbus A380 uses aluminium overseas telegrams alternatively of Cu for weight decrease. The system is besides to the full computerized. Contactors and Surfs have been replaced by solid-state devices for increased dependability and public presentation ( Global Aircraft, 2012 ) .


Frequency Wild AC power can merely be supplied to the resistive circuits such as the electrical warmer, engine de-icing warmers, windshield warming, etc. as shown in Fig. 4. The AC power generated is sent to the TRU where the electromotive force is stepped down from 360Hz-760Hz ( Langlois, 2004 ) to 28V and so rectified to DC electromotive force. Then it is used by the DC constituents.


A traditional Changeless Frequency unit has merely a changeless frequence of 400Hz electromotive force supply. A changeless velocity thrust unit drives the generator. It is besides expensive and non easy to keep. A VFG is flexible as it can manage a scope of frequences instead than a changeless 1. In this unit, there is no CSD or IDG. It is more advantageous over Changeless Frequency Unit because:

It has low care

Long lifetime


Procedure temperature is controlled within VFG itself.

Equipment protection from extra torsion harm

The variable frequence generator ( VFG ) is used on applications with a high per centum of resistive AC or DC tonss and provides power to many of the following coevals aircraft. Hamilton Sundstrand ‘s variable frequence starting motor generator ( VFSG ) and motor accountant system provides chief engine start and control.

The electromotive force is controlled around the generator. This is done by commanding field strength of the AC generator by feedback signal from the electromotive force regulator, which keeps the electromotive force changeless irrespective of the velocity and burden fluctuations.

VFGs are preferred over DC systems because they were much less affected by hapless brush public presentation at higher heights and they had better power to burden ratio.


DC actuators are typically high-velocity reversible series-wound motors. Their end product is converted to driving torque utilizing step-down gear box. These motor actuators are self-contained units, as they combine both electrical and mechanical devices. They can exercise additive push over a short distance.





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