Aircraft Engineering Interview Preparation Guide

Download PDF

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.

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.

★ 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.

★ 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.

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.

★ 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.

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.

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.

★ 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.

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:
★ 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.
★ 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.

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.

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 shock-wave increases leading to higher temperatures between the shock and body surface.

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.

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.

★ Cycle:
It represents the completion of one period and it also signifies the motion that is completed in one period.
★ Frequency:
Defines the number of cycles completed in unit time.
★ Amplitude:
Defines the distance from one point to another or from highest to lowest point of the motion from the central position.

★ In-compressible 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, in-compressible flows, doesn't exist in nature or are very rare.
★ In-compressible 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 in-compressible flows are not considered for high speed flows.

★ Trailing edge flaps includes different flaps like.
★ Plain flap that is used to retract the complete section of trailing edge and it is used in downward.
★ Split flap gets formed by the hinged lower part of trailing edge and the lowered top surface remains unchanged and it eliminates the airflow that occurs over the top of the surface of the plain flap.
★ Leading edge flaps is used to augment the low speed lift that is swept on the wing aircraft. They help in increase the camber and allow the coupling to operate together with the trailing edge flaps.

Sperry's rule of procession describes about the direction in which the procession takes place. This procession is dependent on the direction of rotation for the mass and the axis of the torque that is applied on the material. It provides a guide to the direction of procession that allows easy finding of the direction of the applied torque. This also helps in finding out the direction of the rotation of gyro-wheel. If the torque is applied and is perpendicular to the spin axis then it can be transferred as a force.

★ If a rotating body is mounted and it is free to move about any axis that passes through the center of mass, then the spin axis that is used will remain fixed in inertial space without displacing any of the frame.
★ If a constant torque is applied to any direction such as about an axis, or perpendicular to the axis, then the spin axis will move about an axis that is mutually perpendicular to both the spin and the torque axis.

Gyroscopic motion is considered as an important study for aircraft application for the inertia and momentum of the body that is used in circular motion. The momentum is the product of the mass of a body and its velocity. This is a measure of the quantity of motion of a body. Inertia is the force that doesn't allow any change to happen in momentum. Gyroscope is the rotating mass that can be moved freely at right angles to its plane of rotation. This utilizes the gyro rotor or gyroscopic inertia to provide the motion unless it is compelled by an external force to change the state. This uses property of rigidity as gyroscope acts as a reference point in space.

Gyro-dynamics deals with gyroscopic motion that is used for creating aircraft application as it allows inertia and momentum of the body. These laws consist of the two properties of rigidity and procession to provide the visible effects gyro-dynamics.

Propulsive thrust is used in aircraft system, when an aircraft is traveling through air in straight or level flight then the engine produces a thrust that is equal to the air resistance or the drag force on the aircraft. If the engine thrust exceeds the drag then the aircraft will accelerate and if drag exceeds the engine thrusts then the aircraft system will slow down. The thrust force that is used for aircraft propulsion should always come from air or gas pressure. The forces that are external always act on the engine or propeller. This propeller can be driven either by a piston or a gas turbine engine. If there is a use of jet engine then the high velocity exhaust gas is produced.

Torsion is used to drive shafts for aircraft engine driven pumps and motors. They are also involved in having a force behind propeller shafts, pulley assemblies and rive couplings for machinery. The shear stress is setup within the shafts and it results from the torsional loads. The size and the nature of torsional loads and stresses need to be known while making the design or else premature failure can occur. The shafts are used as a component to transmit torsional loads and twisting moments or torque. They can be a cross section or a circular component as it is more suitable to transmit the torque for pumps and motors to supply the power to the aircraft system.

Load extension graphs are used to show the result of mechanical test done on the material to know their certain properties for example finding out the heat treatment of a material. These graphs shows certain phases of a material when it is being tested for destruction of the properties like elastic range, limit of proportionality, etc. The material needs to obey Hooke's law. The elastic limit needs to be at or very near to the limit of proportionality. If the limit is passed the material ceases to be proportional to the load. If the stress increases on the material then the waist reduces as the stress = force/area. This graph represents a curve that shows different stages like elastic stage, and plastic stage.

Strength:
This is the applied force on a material that can withstand prior to fracture. It is measured by the proof or yield stress of a material that is under action.

Working stress:
This is the stress that is being imposed on a material as a result of the load that is being subjected on the material. The loads that are given must be in the elastic range.

Proof stress:
Defines the tensile stress.

Ultimate tensile stress (UTS):
Defines of a material that is given by a relationship or its maximum load.

Specific strength:
Defines the light and strong of a material that is used in aircraft making. This is done to maximize the payload and meeting all the safety requirements.

Malleability:
Defines the ability to be rolled into sheets or get a shape under pressure. This includes examples of gold, copper and lead.

Elasticity:
Defines the ability of a material to return to its original shape when an external force is removed from the material.