The first application of electricity in aircraft was in the form of the Engine Ignition System. This did not raise any power supply problems because self-contained magnetos supplied the current needed for ignition. For a long time there was no much use of electricity in aircraft, except that which was needed for simple lighting and communications. As and when the role of aircraft was broadly extended, the flying machine was improved in construction and in other aspects. Due to this, the need for a separate electrical system became inevitable in a modern aircraft.
For aircraft electrical system, the fundamental consideration was in determining the type and capacity of the system, the kind of generators and generator drives to be used based on the principle thing, which should be done electrically. The choice of the electrical system and its capacity is made on the following considerations:
(a) Aircraft role and environment.
(b) Type of apparatus existing in aircraft.
(c) Time scale.
(d) Available ground facilities.
(e) Aircraft safety requirements.
(f) Weight of installation.
(g) Total capacity of system.
Storage Batteries. Storage batteries serve the following functions as:
(a) To provide supply to starting accessories at the time of starting.
(b) It is used for aircraft starting (internal start) in case of external supply is not available.
(c) It is meant for standby source in case DC Generator fails in Air.
(d) It is used to provide supply to ignition coils in case engine RPM surged during flight. i.e., it is useful for relighting the aircraft engine in air.
Maintenance of Storage Batteries. The following checks are to be carried out to keep the batteries in fully serviceable conditions:
(a) Visual Examination. Container cover is to be opened and external damage, if any, are to be checked. The tightness of all nuts and connecting bus bar strips between cells are to be checked. The level of electrolyte as per the markings, the date of capacity test carried out and life expiry date are to be checked.
(b) Routine Charging. The batteries are to be sent for routine charging when any cell voltage falls below normal value.
(c) Capacity Test. This test is carried on the following occasions:
(i) At the time of initial build up.
(ii) When capacity falls below the normal value.