Check out Pritish Kumar Halder’s “List of Topics to Prepare” for Aeronautical Engineering Interview.
1. 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 implement the parts together. There are three types of strain:
- Tensile strain
- Compressive strain and
- Shear strain
2. What are the different types of modulus involved in mechanics?
Modulus of elasticity is given by Hooke’s law which 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 modules 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 changed in volume not in shape.
3. What are the mechanical properties required to know before performing maintenance?
The mechanical properties provide the definition of the behaviour of the material that is being put under the action of external forces. This is an important aspect of aeronautical engineering that is also used to gain knowledge for applications developed for aircraft. This provides an overall view of the structure of the aircraft and its maintenance aspect of it. The properties used are as follows:
- Specific strength and stiffness,
- Malleability and elasticity
4. Explain in brief 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 to the material. The loads that are given must be in the elastic range.
- Proof stress: defines the tensile stress
- Ultimate tensile stress (UTS): defines a material that is given by a relationship or its maximum load.
- Specific strength: defines the light and strength of a material that is used in aircraft making. This is done to maximize the payload and meet 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.
5. What is the purpose of load extension graphs?
Load extension graphs are used to show the result of mechanical tests done on the material to know their certain properties for example finding out the heat treatment of the material. These graphs show certain phases of a material when it is being tested for the destruction of the properties like elastic range, the 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 an elastic stage and plastic stage.
6. 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 set up 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.
7. What is the main function of propulsive thrust?
Propulsive thrust is used in an aircraft system, when an aircraft is travelling through the air in a 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 thrust 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 engines then the high-velocity exhaust gas is produced.
8. Why is the study of gyroscopes motion required to learn aircraft applications?
Gyroscopic motion is considered an important study for aircraft application for the inertia and momentum of the body that is used in a 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. A gyroscope is a 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 the property of rigidity as the gyroscope acts as a reference point in space.
9. What are the laws of gyro-dynamics?
Gyro-dynamics deals with a gyroscopic motion that is used for creating aircraft applications 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 of 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 centre of mass, then the spin axis that is used will remain fixed in inertial space without displacing any of the frames.
- 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.
10. What is being expressed by Sperry’s rule of precession?
Sperry’s rule of precession describes 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 to 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 the gyro-wheel. If the torque is applied and is perpendicular to the spin axis then it can be transferred as a force.
11. 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 the highest to the lowest point of the motion from the central position.
12. What are the different lift augmentation devices present?
Lift augmentation devices provide flaps that are moving wing sections that increase wing camber and provide an angle 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 a slower speed. Flaps provide a way to slow down the aircraft. There are two categories and they are as follows:
Trailing edge flaps include different flaps like
- A plain flap is used to retract the complete section of the trailing edge and it is used downward.
- A split flap gets formed by the hinged lower part of the trailing edge and the lowered top surface remains unchanged and it eliminating the airflow that occurs over the top of the surface of the plain flap.
- Leading-edge flaps: are used to augment the low-speed lift that is swept on the wing aircraft. They help increase the camber and allow the coupling to operate together with the trailing edge flaps.
13. What are the steps required to solve the problems of aircraft flying high and at very large speeds?
There are various steps required to solve the problems of aircraft flying high and at very large speeds 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.
- The use of one inboard pair that can be used to operate at high speeds, this will have a 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 downgoing wing by interrupting the airflow over the top surface.
14. What are the functions performed by the rudder?
The rudder is involved in providing the movement to the ports that give a lift force to the starboard. This will allow the aircraft to turn and uses the ailerons effectively to bank the aircraft by minimum use of the rudder. The functions performed by the 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 a spin to reduce the roll rate of the aircraft and there are some applications that provide low speeds and high angles to allow the raising of the wings.
15. What 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 are:
- 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 which is a horizontal stabilizer used to provide the stability to the aircraft.