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A modern aircraft has multiple systems on board to operate the aircraft. These systems are complex and cannot be monitered with the human eye, but at the same time these systems need to be monitored for optimum evaluation of the flight of an aeroplane. One of the systems for monitoring the performance of operating parameters of an large aircraft is the ‘open’ and ‘closed’ loop systems. These systems are often referred to as Numerik Control Systems (CNC).

There are two types of CNC ( Computer Numerik Control) systems. these systems help moitor the efficacy of the aircraft in flight where its engines generally operate at a frequency of 400 hertz.

‘Open loop’ operating system means that the controller system and the motor have a one way interaction. However the output of the motors is monitored through a 'closed loop'. The closed loop corrects errors in position, velocity, and acceleration, thus giving a graphic feedback on the operating system and its efficacy.

Diagram of an Open Loop system

Diagram of a Closed Loop System

The engine starts from cold and when it achieves a rpm of 400 hertz, the system goes into ‘open loop’.

The system will stay in 'Open Loop' till the undermentioned conditions are achieved.

1. The Coolant Sensor has achieved a temperature of 40oC/104oF.

2. After starting the engine from cold a specified amount of time has elapsed.

3. The operating temperature has risen to the required level.

Temperature in an aircraft relates to the servo mechanism on board and air-conditioning along with the power electronics. These need thermal regulation and directly affect the open loop. Thermal management in an aircraft is through a two way hot loop.

The open and closed loop are pivotal in steering the aircraft accurately. When an aircraft is in flight an updated comparison between the actual and required direction is made. This allows for correction till he actual direction is achieved. This is closed loop system and forms the basis of all flight systems.

The mem-cal stores the different specifications of engines.Once the required condition is achieved the aircraft systems go into 'Closed Loop' operation. Closed loop systems work out costlier and are also more complex.They are harder to tune and the failure rate is more.