# Aeronautical Engineering interview questions and answers - part 2

## Aeronautical Engineering interview questions and answers - part 2

### Part 1   Part 2   Part 3   Part 4   Part 5   Part 6 ## What are the differences between incompressible and compressible flows? • Incompressible flows are the flows that have a constant density (?). Whereas, the compressible flows are those that consists of variable densities. • The flows that exist are compressible in nature. Whereas, incompressible flows, doesn't exist in nature or are very rare. • Incompressible flows are used to model aerodynamic problems without loosing any detrimental accuracy i.e. most problems that exist in hydrodynamics considers the density (?) = constant. Whereas, compressible flow is hardly used as a mathematical model to, represent the hydrodynamics. • High speed flows are and must be treated as compressible, whereas incompressible flows are not considered for high speed flows. ## What are the different speed types of flows used in identifying Mach number? There are four types of flows that consist of different speeds and can be identified using Mach number: • Subsonic flow where M<1 everywhere, this is a field that is defined as subsonic if it matches the Mach number that is less than 1 at every point. These are displayed by smooth streamlines that consists of no discontinuity in slope. The flow velocity is everywhere less than the speed of sound and the disturbances are all around the flow field. • Transonic flow, where mixed regions exist and M<1 or M>1, this is a flow field that defines that the M8 is increased just above the unity and it is formed in front of the body. These are the mixed subsonic and supersonic flows that are influenced by both the flows. • Supersonic flow where M>1 everywhere, this type is defined when Mach number is greater than 1 at every point. They are represented by the presence of shock waves across which the flow properties and streamlines changes discontinuously. • Hypersonic flow where the speed is greater than supersonic, this is defined when the shock waves moves closer to the body surface and the strength of the shockwave increases leading to higher temperatures between the shock and body surface. ## What are the major sectors involved in aircraft maintenance? There are two major sectors involved in aircraft maintenance and these are handled by certifying technician in the field of support and maintenance. These are divided into two sectors as: • Category B1 (mechanical): these are the maintenance technicians that have good knowledge regarding the working of airframe, engine, electrical power systems and equipment. It also requires additional knowledge of aircraft structures and materials. • Category B2 (avionic): this deals with the integrated knowledge of aircraft equipments, electrical, instrument and radar related systems. They undergo proper training to handle the aircraft equipments and gain practical experience to deal with day to day activities. ## What are the operations performed by Category B technicians? Category B consists of two sectors in the field of maintenance and they are divided in B1 and B2 with certain roles. The operations performed by Category B technicians are as follows: • Activities related to scheduled on field inspections for aircraft maintenance. • Activities of complex rectification • Fault diagnosis on aircraft systems and their equipments. • Modification and performing special instruction to monitor and manage the system • Repairing of airframe and other aircrafts • Activities performed like removal of aircraft components and fitting the required parts. • Use of BITE (built-in test equipment) and diagnostic equipments to perform repair tasks. • Supervising and certifying the work of other technicians involved in it. ## What is the main source of power in aircraft? The main source of power is the hydraulic motor that is provided by the scheduled service and involves operations that allow technicians to solve complex system problems. This setup required certifying the technician to operate all the system the same way as it is been done with one system. The hydraulic motor needs to be operated the same way and maintained in a proper way. The alignment need to in synchronization with the aircraft auxiliary power unity (APU) before anything is done with the aircraft positioning. A standard need to, be followed to maintain the aircrafts and its parts equipped and working. ## What are the differences in the job performed by line maintenance certifying staff and base maintenance certifying staff? The difference that exists between the two is that line maintenance certifying staff has the responsibility to inspect, rectify and perform the related or associated maintenance activities on the aircraft on the airfield. Whereas, the base maintenance certifying staff, perform the maintenance activities away from the live aircraft areas. The maintenance that is being performed by the line maintenance staff is restricted to use limited tools, and equipments that are present on the site to perform the first line diagnostic maintenance. Whereas, Base maintenance certifying staff is associated with the line maintenance staff as it requires inspecting and performing complex modification in the aircraft carriers. ## What is the role performed by Category C personnel in maintenance of aircraft? Category C personnel are responsible for maintaining the management role of controlling the progress of the base maintenance inspections and seeing the work that is getting performed. These handle the category B and category A staff and monitor their work. They are responsible for ensuring the good work that will be carried out by providing the certification of maintenance. Category C personnel upon the completion of the maintenance job done by the base maintenance staff provides the certificate to allow the servicing of the aircraft to proceed. This way the people working in the staff become eligible to perform and provide services for flight. 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