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Technical Interview Q & A PDF







What are the characteristics that keep solid and fluid different?

• When the force is applied tangentially on solid then it experiences a finite deformation and shear stress that is proportional to the deformation. Whereas, when the same shear stress is applied on the surface of fluid then it experiences continuous increasing deformation where, the shear stress is proportional to the rate of change of deformation.

• The fluid dynamic is dividend in three different areas. They are as follows: Hydrodynamics (flow of liquids), Gas dynamics (flow of gases) and Aerodynamics (flow of air). Whereas, the state of, solid doesn’t represent any of the stages.

What are the objectives of Aerodynamics?

Aerodynamics deals with the theory of flow of air and it has many practical applications in engineering. There are some objectives that are being used in aerodynamics and these are as follows:

• It is used to predict the forces, moments and heat transfer from the bodies that is moving through the liquid.

• It deals with the movement of wings or use of the wind force. This way it requires the calculations to be done for the aerodynamic heating of the flight vehicles and the hydrodynamic forces applied on the surface of the vehicle.

• It is used to determine the flows that are moving internally through ducts. This way it makes the calculations and measurement of the flow properties that is inside the rocket and jet engines.

What are the sources involved in aerodynamics?

There are two sources that are involved in the case of aerodynamics forces and moments that are on the body. These forces are as follows: • Pressure distribution: this is the distribution that is over the body surface

• Shear stress distribution: this is the distribution that is over the body surface These sources are for the body shapes and it doesn’t matter how complex they are. The mechanism that is being used to communicate with the bodies that is moving through a fluid. Both the pressure (p) and shear stress (?) having the dimension force per unit area. This helps the movement of the body through the fluid.

What are the conditions given for the two flows to be dynamically similar?

To measure the dynamicity of the two flows consider two different flow fields over two different bodies. This way the conditions that get generated are as follows:

• The streamlined pattern shouldn’t be geometrically similar.

• The distribution of the volume over change in volume (V/V8), pressure over change in pressure (p/p8), and time over change in time (T/T8). These changes take place throughout the flow of the field and they remain the same against the common non-dimensional coordinates

• The force coefficient remains the same.

• There is a similarity in both the flows like the solid boundaries are geometrically similar for both flows.

What are the differences between continuum flow and free molecule flow?

• The flow that is moving over the body i.e. in a circular cylinder of diameter d is the continuum flow, whereas the flow that consists of individual molecules moving in random motion is the free molecule flow.

• The mean free path (?) defines the mean distance between the collisions of the molecule and if this path (?) is smaller than the scale of the body measured (d) then the flow of the body is considered as continuum flow.

• The path (?) that is of same order as the body scale then the gas molecules then the body surface will have an impact of the molecules and this is known as free molecular flow.

What are the differences between inviscid and viscous flow?

• Viscous flow is the flow in which the molecule moves in random fashion and transfers their mass, momentum and energy from one place to another in fluid. Whereas, an inviscid flow is the flow in which there is no involvement of friction, thermal conduction or diffusion while the molecules are moving.

• Inviscid flow consists of the limited influence of friction, thermal conduction and diffusion that is limited to thin region that is limited to the body surface. Whereas, the viscous flows involve the flows that dominates the aerodynamics of the blunt bodies like cylinder. In this the flow expands around front face of cylinder and it separates from the rear surface of it.

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.

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