Aerospace Engineering

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:

► Strength,

► Stiffness,

► Specific strength and stiffness,

► Ductility,

► Toughness,

► Malleability and elasticity.

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.

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.

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.

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.

► 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.

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.

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.

► 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.

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.

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.

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.

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.

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.