Aircraft Systems - Report Example

Aircraft systems Introduction Aircraft systems are very complex systems. In many cases they are broken down into simpler unit systems either in the design stage, flight stage or in the maintenance stage which carry out homogeneous functions. Most aircrafts come up with manuals both for pilot use and technician maintenance use. These systems include electrical, hydraulics, fuel consumption, oxygen, propulsion, navigation, antiicing and deicing protection, flight controls and cooling systems. Task 1 Explain how an aircraft 3 phase electrical generator works, including the following In three phase generators, three single phase generators each having a primary wounding on one leg are symmetrically wound. Each winding is connected one wire of a three-phase system. The three cores are 120o apart making the empty legs of the three single phase generators to be in contact hence forming a center leg. This center leg carries the total sum of the three flux manufactured by the three phase currents Three-phase supplies distribution can either be connected using the star-connected distribution system or the delta connection distribution system. In a star-connected three phase distribution system the AC generator is connected to a three phase load resistances which will have to be identical for them to be balanced. The phasor diagram below shows the relative direction of each alternating phase voltages (VP) and the voltages among the lines (VL). All the three voltage lines should be 120o apart and the lines lead the voltage phase at 30 o. Overcurrent protection against faults in three phase distribution systems requires the placing of a phase protection between phases or from individual phases. In three phase distribution systems, phase protection (Merz price circuit) is placed on each phase. CT1 monitors the current output from the generator while CT2 monitors the distribution system. The efficiency of the operations of aircraft electrical equipment which require D.C. is reliant of the voltage regulator which controls the generators’ voltage output within specified tolerance. In three phase electrical distribution systems the voltage regulator consists of two windings assembled on each core. Task 2 Explain with the aid of a diagram how an integrated drive generator works. Also known as constant speed drive, the integrated drive generator (IDG) is an electromechanical device, which is installed to each unit of the engine and is used to regulate the generator speed. It can be mounted in two ways that is co-axially or side by side. In the engine, the input shaft is connected to the gearbox and the output shaft connected to the generator. The IDG relies on the variable ratio drive which employs a series of differential gears and hydraulic pumps. Using the clutch, the integrated direct generator can be disconnected from the engine either manually or automatically but reconnection can only be done when the aircraft is grounded. Most large modern aircrafts use brushless AC generators combined with the IDG. At normal speeds of between 4500/9000 and 12000 revolutions per minute, the IDG produces a 115/120 volts at 400HZ three phase with an output of 90mKVA. The IGD is oil-cooled in most commercial aircrafts (Tooley & Wyatt, 133). Task 3 Explain how a transformer rectifier unit works. A transformer rectifier unit converts alternating current in to direct current. It is mostly used to charge batteries. From the diagram above, the TRU is connected to the three phase 115/200 volts at 400HZ input which is further connected to a star wound primary winds of a transformer. Then the dual secondary winds that emerge from this connection are wound in both delta and star configurations. The output of the two secondary winding connections are rectified and further connected to the principal output terminals. From here a series of resistors (shunt) are used to derive the total current output of the TRU (Moir & Seabridge, 117 ). Task 4 With the aid of a diagram, explain the split bus electrical power architecture. The split bus system is a completely isolated generation system with two generators that are not synchronized. It is also called the non-parallel system which is mostly used on two engine aircrafts. The system’s primary power is based on the two AC generators which are integrated to the system. In case the integrated drive generator (IDG) (typically 40KVA) fails, an APU generator normally of 40KVA is used as a back-up. Since the APU can power the system at constant speeds, the IDG not required at this time. The major advantage of the split bus system is the two generators do not have to be worked at the same frequency and they can be run completely out of phase with each other. Though, the systems’ requirements of secondary power are derived from the step down transformers which provide 26 volts (alternating current) AC. A transformer rectifier unit, TRU, which provides 28V direct current, DC, is required to charge battery and power the DC bus bars. The left and right generators supply their own bus bars which are connected to specific loads via transfer relays. In case one generator fails, the remaining generator feeds the principle loads. Task 5 With the aid of a diagram, explain the parallel bus electrical power architecture. Parallel load distribution system APB – APU breaker XPC – External power contractor BTB – Bus tie breaker GCB – Generator control beaker GEN – Generator SSB – Split system breaker The electrical distribution system on passenger aircrafts with three to four engines is based on a parallel load distribution system. Each generator has its own distribution bus and AC load bus. The four generators are synchronized when all the four BTBs and GCBs are closed and connected to the distribution bar. When one generator fails, its GCB is opened hence isolating the generator from its own load bus bar. The bus bar is then connected and powered by the remaining generators. If a bus bar is overloaded the GCB is subsequently opened and the BTB isolated from the distribution system. When more than two generators fail, a load-shedding system is introduced to balance the system. In addition to the APU, the parallel load distribution system has an external power connection which is made available by one or two power supply units. These can be connected to the distribution bus. The parallel bus system has primary power supply features such as an IDG engine. The right and left sides of distribution are linked using a split system breaker link and ensures that any generator can supply any load bus bar and any combination of generators operate in parallel. The advantages of this system are that it delivers a parallel power system and maintains isolation especially when it’s needed. Works Cited Moir, I., and A. G. Seabridge. Aircraft systems mechanical, electrical, and avionics subsystems integration. 2nd ed. Bury St Edmunds: Professional Engineering, 2001. Print. Tooley, Michael H., and David Wyatt. Aircraft electrical and electronic systems: principles, operation and maintenance. Amsterdam: Butterworth-Heinemann, 2009. Print. Read More