Aeronautical Engineering Interview Questions and Answers
1.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.
2.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.
3.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 § and shear stress (?) having the dimension force per unit area. This helps the movement of the body through the fluid.
4.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.
5.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.
6.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.
7.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.
8.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.
9.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.
10.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.
11.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.
12.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.
13.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.
14.What are the safety recommendations required while maintaining aircraft?
The safety recommendations are required while dealing with the accidents and the inquiry of the aircrafts. The recommendations needed are as follows:
CAA (Civil aviation authority) examines the applicability of self-certification of aircraft engineering and verifies the criticality of the tasks that need to be performed on the system. They also check the system for further services without doing any functional checks.
Review of the system takes place to interpret the single components of the aircraft that is vital in its design.
Reviewing of the quality assurance system and the reporting methods take place to encourage more better designs to be provided for the use.
Reviewing the need to, introduce a format of job description and grades that is being provided to the engineers and managers.
Providing a mechanism for an independent assessment to carry out the work audit and operations can be performed smoothly.
15.What are the different stress types present in aircraft operations?
Stress is a result that is caused when a solid e.g. metal bar is subjected to an external force. Stress is defined as force per unit area and the basic unit includes MN/m2, N/mm2 and Pa. There are basically three types of stress:
Tensile stress: it is the stress that is setup when the force tries to pull the material apart.
Compressive stress: it is the stress that is produced by the force that is trying to crush the material.
Shear stress: is the stress that results from the force that tends to cut through the material i.e. tend to put one material slide over another one.
16.Why is strain a major factor in aircraft engineering?
Strain is when a material is altered in shape, this happens due to the fact that the force is acting on the material. The body is strained internally as well as externally without having any differences of dimension but it just has the differences at the atomic level. It is the ratio of change in dimension over the original dimension. It is very important due to the fact that building an aircraft requires the knowledge of these factors and the formulas that are associated with it to successfully implementing the parts together. There are three types of strain:
Compressive strain and
17.What are the different types of modulus involved in mechanics?
Modulus of elasticity is given by the Hooke’s law that states that stress is directly proportional to strain, while the material remains elastic. The external forces that are acting on the material is just having the sufficient to stretch the atomic bonds this way the material can also return back to the original shape. The different types of modulus are as follows:
Modulus of rigidity: this defines the relationship between the shear stress (t ) and shear strain (? )
Bulk modulus: this defines that if a body volume v is subjected to an increase in an external pressure then the volume will be changed by dV, this deformation will be change in volume not in shape.
18.What are the mechanical properties required to know before performing maintenance?
The mechanical properties provide the definition of the behavior of the material that is being put under the action of external forces. This is an important aspect to aeronautical engineering that is also used to gain knowledge for applications developed for aircrafts. This provides an overall view of the structure of the aircraft and the maintenance aspect of it. The properties used are as follows:
Specific strength and stiffness,
Malleability and elasticity
19.Explain in brief about each property used in mechanics?
The properties of the mechanics are as follows:
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.
20.What is the purpose of load extension graphs?
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.
21.Why is torsion such an important feature in aircraft engines?
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.
22.What is the main function of propulsive thrust?
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.
23.Why is the study of gyroscopes motion required to learn aircraft applications?
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.
24.What are the laws of gyro-dynamics?
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 precession to provide the visible effects gyro-dynamics. These are as follows:
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.
25.What is being expressed by Sperry’s rule of precession?
Sperry’s rule of precession describes about the direction in which the precession takes place. This precession 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 precession 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.
26.What are the elements required to display oscillatory motion?
The elements required to display oscillatory motion are as follows:
Period: this is related to the time and it signifies the time that elapses in between the motion that will repeat itself after some time again. Oscillatory motions allow themselves to be repeated after equal intervals of time and this is called as periodic.
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.
27.What are the different lift augmentation devices present?
Lift augmentation devices provides flaps that are moving wing sections that increase wing camber and provide an angel of attack. Flaps have their own use like if an aircraft takes off and land in a short distance then the wings of it should produce sufficient lift at lower speed. Flaps provide a way to slow down the aircraft. There two categories and they are as follows:
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.
28.What are the steps required to solve the problems of aircraft flying high and at very large speed?
There are various steps required to solve the problems of aircraft flying high and at very large speed are as follows:
Build stiff wings that allow and provide the resistance to torsional diversion beyond the maximum speed of the aircraft.
Use two sets of ailerons and one outboard pair that can be operated at low speeds.
Use of one inboard pair that can be used to operate on high speeds, this will have less twisting impact when the ailerons are positioned outboard.
Use spoilers that can be positioned independently or can be paired with ailerons. These reduce the lift on the down going wing by interrupting the airflow over the top surface.
29.What are the functions performed by rudder?
The rudder is involved in providing the movement to the ports that gives a lift force to starboard. This will allow the aircraft to turn and uses the ailerons effectively to bank the aircraft by minimum use of rudder. The functions performed by rudder are as follows:
It is used with different applications that are involved in taking off and landing to keep aircraft straight.
Providing assistance that is, limited only for the aircraft to turn correctly.
Used in applications during spin to reduce the roll rate of the aircraft and there are some applications that provides low speeds and high angles to allow the raising of the wings.
30.What are the criteria need to be followed for an aircraft to be longitudinal statically stable?
The criteria that are required for an aircraft to be longitudinal statically stable, is:
To have a nose-down pitching disturbance that is used to produce the aerodynamics forces to give a nose-up restoring moment.
This restoring moment that is produced should be large enough to return the aircraft to its original position after the disturbance.
The requirements are met by using the tail-plain that is horizontal stabilizer used to provide the stability to the aircraft.