AERONAUTICAL LECTURING NOTES

What is fluid mechanics? It is a science that deals with movement of fluids (Liquids/gas) and its interaction with solid surface. 99% of the practical flow is wall bounded. What is meant by continuum?   All matters are made up of atoms, fluids too. Atoms have some gap in between them.   Now just consider the flow over a circular cylinder of diameter d. The mean distance that an atom travels between two successive collisions is called as Mean free path (λ).   When comparing λ and d, if λ is too small than d, we can assume that the flow over the cylinder as continuum. What is no- slip condition? Consider a fluid flow over a solid surface. The layer of fluid which is attached to the solid surface sticks to the solid surface and so it has zero relative velocity with the solid surface. This is what called as no-slip condition. Due to no slip phenomenon the layer of fluid attached with the surface has zero relative velocity and the next layers are moving with ...

Write down all type of power plants that are being used in aircrafts? Reciprocating engines Gas turbine engine Ramjet engine Scramjet engine What are the types of gas turbine engines? Turbo jet Turbo prop Tubo fan Turbo shaft Which gas turbine engine is fuel efficient? Turbo fan What are the components of Turbojet engine? Inlet Compressor Combustion chamber Tubine Nozzle Exhaust  Write the advantages of gas turbine power plants. The capital cost of plant is low. This can be quickly commissioned. It requires less space. Capacity to use wide variety of fuels Write the disadvantages of gas turbine power plants About two third of the power developed by the turbine is used to drive the compressor. Hence net output of plant is low. Low efficiency Needs special cooling arrangements Operating temperature is high of the order of 20000C.

What is Newtons second law and how it matches with Aircraft Engine? If some mass ‘M” is accelerated, then a force presents. Same way the mass of fuel air mixture is accelerated by a chemical reaction thus creates exhaust force. What is Newtons third law and how it matches with Aircraft Engine? For every action there is an equal but opposite reaction.  The exhaust force created is also having equal and opposite reaction called Thrust which is always in the direction of flight. What is a propeller? And how it functions? A propeller is simply a rotating aerofoil. It provides thrust in the same way as how an aerofoil mounted on wing generates lift. To know how a wing generates lift click here . When propeller rotates, the hub has to cover a least circular path whereas the tip has to travel a large circular path; in the same time. So propeller tip will be experiencing high speed than hub; that means from hub to tip speed is increasing. Suppose if we want to hav...

Define force The most commonly used type of input in mechanical system is force and it is the reason for moment, torque, stress to exist. When a force acts over a body; it gets imbalanced ; and moves in the direction of applied force. Define Work Work is the output made from the input; force. Mathematically Work = Force x Distance (N-m or Joule) Define torque Torque is described as force acting along a distance (Perpendicular distance). Torque creates twisting and makes rotation. Torque = Force × distance Define friction When a body moves or tends to move over other body, a force appears between the objects of interest. This force is called friction. Friction acts opposite to the direction of motion. Mathematically F  =   µ X R F- Friction; µ- Coefficient of friction; R- Normal force acting between surfaces Define power Power = (Force x Distance) / time      ((N-m)/s) Or  Watts

Define density or mass density. Density of a fluid is defined as the ratio of the mass of a fluid to its volume. Density, ρ = mass/volume (Kg/m3) ρ water = 1000 Kg/m3 Define specific weight or weight density. Specific weight or weight density of a fluid is defined as the ratio between the weight of a fluid to its volume. Specific weight, γ = weight/volume (N/m 3 ) γ = ρg γwater = 9810 N/m 3 Define specific volume. Specific volume of a fluid is defined as the volume of fluid occupied by an unit wt or unit mass of a fluid. Specific volume vs = volume/ wt = 1/γ = 1/ρg      ----- for liquids Specific volume vs = volume/ mass = 1/ρ   ----- for gases What is specific gravity? Specific Gravity = Weight of the substance/ Weight of an equal volume of   water OR Specific Gravity = Density of the substance/Density of water The same formulas are used to find the density of gases by substituting air for wat...

What is matter? Matter has following properties 1. occupies space  2. All things are made of because .  3. Matters have mass. What is mass? Mass is a measure of the quantity of matter in an object. Mass determines inertia of matter. To be more specific the mass depends purely on the intensity of atoms present in the object. Atoms have electrons,protons and Neutrons. What is weight? Whatever may be the intensity of mass (whether it is heavy or light), that mass will be attracted by bigger mass, Earth.Biggest mass in the universe is Sun. If you refer universal law of gravitation, you will find the physics behind it that is Bigger mass always attracts lesser mass. The attraction force depends upon the distance between objects in interest. When mass is attracted by some vector like gravitational force, it also becomes a vector and that vector is called as Weight.                     Weight = mass x accelera...

What is a beam? Beam is a structural member which primarily withstands vertical or inclined loads by creating shear force and bending moment. What are the different types of supports? Hinged support or pinned support Roller support Fixed support What are static equilibrium equations? ∑ F x =0   ( Summation of X direction forces zero) ∑ F y =0     (Summation of Y direction forces zero) ∑ M p =0 (Moment with respect to any point is zero) What are types of loading in beam? Point load Uniformly Distributed load Uniformly varying load Concentrated moment What are types of beam? Based on the supports beams are classified into Cantilever beam Simply Supported beam Fixed beam Overhanging beam Continuous beam

What is torque? Define moment? Torque is simply a moment of force. Moment of force is just the product of force and perpendicular distance. Unit “Nm”. What is Moment of Inertia? The moment of inertia measures the resistance to a change in rotation.  Change in rotation comes from torque. Moment of inertia I = mr 2 . Please note moment of inertia strictly depends upon the axis of rotation.

What are the layers of atmosphere? Troposphere- 0 to 10 Kms Stratosphere- 11 to 50 Kms Mesosphere-50 to 80 Kms Ionosphere-80 to 500 Kms Exosphere-500 to Infinity Kms What are the axes of an aircraft? Longitudinal Axis- Along the length of the fuselage Lateral axis- Along the length of wing span Normal axis- Mutually perpendicular to the above two axis What are the moments occuring with reference to those axes? Longitudinal axis- Rolling Lateral axis- Pitching moment Normal axis- yawing

What are the major parts of an aircraft? Main wing Tail wing Powerplant Fuselage Landing gear What is the reason for stall? Define critical angle of attack? If the angle of attack for an aerofoil increases from zero deg, you can watch the increase in lift and drag. If you keep on increasing the AOA, at some point sudden loss of aerodynamic forces will occur. Aerofoil can create aerodynamic forces in a large magnitude when attached flow of air occurs at aerofoil surface.  As the aerofoil gets increased AOA, the flow of air starts detaching from the aerofoil surface. If fully detached then no aerodynamic forces will be generated. That is what the reason for stall. The angle at which stalling starts is the critical angle of attack. What is stagnation point? Stagnation point is the point in the airflow where the velocity gets its zero magnitude because of the presence of object in airflow. The flow deviates/joins between upper and lower surface of the ...

What are the phases of flight? Takeoff Climb Cruise Descent Loiter Landing What is aerodynamic centre? Aerodynamic center is the point in the aerofoil where the pitching moment is constant even though if we change angle of attack. To solve flight dynamics problem it is the pivotal point. What is center of pressure? Centre of pressure is the point where the pitching moment is zero. When angle of attack varies cop varies. So it is tedious if we try to solve dynamics of flight by taking COP as reference.

What are the forces acting on flight? Aerodynamic forces- Lift, Drag and Side fore Propulsive force- Thrust Gravitational force- Weight Buoyancy force- Negligible When air flows over wing it creates resultant. We are solving that resultant in three mutually perpendicular axes. So we get Lift, Drag and Side force. Write down the equation for lift and drag? Lift=0.5*(density)* (square of velocity)*(Wing planform area)* (Coefficient of lift) Drag=0.5*(density)* (square of velocity)*(Wing planform area)*(Coefficient of drag) If lift increases, what will happen to drag? Since lift and drag are just the components of the single resultant force which is created because of the airflow over the aerofoil, drag increases if lift increases.

Add caption Fig 1 What is flight path? The curve which we attain by tracing  Center  of gravity( C.G.) of airplane at every second is known as Flight path. What is flight velocity? The tangent drawn to the flight path at any instant gives flight velocity. What is Relative Air flow? When aircraft moves, atmosphere stays rest. But in our dynamics approach in order to make analysis simple, we are considering aircraft to be stationary and the air as moving. So whatever the flight velocity with which we move, we will feel that much velocity against to that; that velocity is what Relative air flow velocity or free stream velocity. What is angle of attack? The angle between relative air flow and the chord line of aerofoil is the angle of attack. Fig 2 What is angle of incidence? The angle between fuselage reference line and average chord of wing is the angle of incidence. see fig. 1 for reference. you just draw chord line for th...

What is parafoil? A leading edge opened aerofoil is called as “Parafoil”. We know already that leading edge is facing into the wind for aerofoil. Since it has been opened, it just admits the air to flow inside the volume covered by the upper and lower surfaces. How aerofoil creates lift? What is bernouli's principle? How it suits to the aerofoil? Aerofoil has its upper surface curved, whereas bottom is moreover flat. Physically the curved portion accelerates the flow and so the top side airflow is getting increase in velocity. Lower surface is experiencing less velocity when comparing the upper surface. We know from Bernoulis law that for a fluid flow, if fluid velocity increases then pressure drops. In the upper we are feeling less pressure and in the bottom a high one. Bernoulis principle: Total energy of a steady flowing fluid system is constant. Ʃ E= k PE+KE= k mgh+0.5 mv 2 =k dividing both sides by volume ρgh+ 0.5ρv 2 =k High p...

What is aerodynamics? Aerodynamics is the study about the object moving in airflow. Here we will pay our attention to the airflow and also to the object immersed in the airflow. What is aerofoil? If you throw a pencil in air, you see, it flies and comes down instantly. So it is also having ability to fly. Technically speaking, every object is having some figures called Coefficient of lift, Coefficient of drag which governs its motion during flight. The shape which has more coefficient of lift and less coefficient of drag can stay in fly for more. Such a shape is what aerofoil. Aerofoil is having top surface (Upper camber) and lower surface (lower camber). Also it has leading edge and trailing edge where the two surfaces meet. Leading edge is facing to the wind. What is chord line? A line joining the leading edge of an aerofoil to the Trailing edge is known as Chord line. What is camber line? We know that aerofoil is having top surface (upper camber)and bot...