AEROFORUM

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DRAG

Drag When an aircraft or any other body moves in atmosphere it experiences air resistance which retards its forward motion. This force is called drag. Drag occurs when an aircraft or any other object moves in air and it depends on the shape of the flying object. Aircrafts and other flying objects are designed in such a manner to reduce the drag, which increases the efficiency of the aircraft. Drag is experienced parallel to relative airflow. Drag is directly balanced by thrust produced by a propeller or an engine. Amount of thrust required to balance the drag depends of amount of drag, more thrust is required to balance a greater drag force produced. If the drag produced by an aircraft is low then the aircraft consumes less fuel and operating costs are also low. The total drag acting on an aircraft includes Profile drag Induced drag Inter

Aerodynamics of low and high cost bikes

Aerodynamics is field science of that studies about an object moving in air or behaviour of air inside a system. It is applied in various fields such as aeronautics, automotive, architecture etc. Generally Aerodynamic design of vehicles is used to reduce drag coefficient which is a major factor that affects fuel efficiency. Since low cost bikes are designed and developed for a budget market. Aerodynamics is used to improve fuel efficiency which reduces fuel consumption, which in turn improves the operating efficiency of the vehicle. In case of high cost bikes, performance of the vehicle plays a major role in design. Here aerodynamics is used to improve overall vehicle performance. On high speeds reducing the drag increases the vehicle movement in air. Most of the aerodynamically designed vehicles adopt tear drop model, which allows the air to pass through smooth surface of the design. In this type of design drag is considerably reduced which improves faster movement of the vehicle.

WING SHAPE AND ITS EFFECT ON LIFT

WING SHAPE AND ITS EFFECT ON LIFT The total Lift generated by an aircraft wing depends on three factors 1. Degree of Induced Downwash( Caused by wing tip vortices) 2. Chord wise Pressure Distribution 3. Plan form Shape of the wing Since the aircraft wing is similar on both sides it is appropriate to consider only the semi span of the wing to study about the effect of lift on wing shape. Let us consider three types of wings and its lifting ability, which depends on the angle of attack also. 1. Rectangular 2. Elliptical 3. Tapered The above figure illustrates the picture of how effective angle of attack varies with distance from aircrafts centre line. In case of rectangular wing the effective angle of attack Remains Constant - First 50 % of the semi span Quickly reduces to zero degrees - Next 50% of the semi span In case of Tapered wing the effective angle of attack Increases

Angle of Induced downwash

Angle of Induced downwash Downwash generated through vortex deflects the airflow from horizontal through an angle called as the angle of induced Downwash. This effect not only occurs behind the wing but also impacts the airflow approaching the wing by deflecting in upward from the horizontal through the same angle ( ʠ ). The resulting airflow is called effective relative airflow and the angle between effective relative airflow and the horizontal is called Ineffective angle of attack. The resultant lift force which acts perpendicular to the relative airflow is also deflected rear ward through the same angle ( ʠ i ). The angle of attack producing this Lift force is called effective angle of attack ( ʠ e ) which is the angle between chord line and effective relative airflow. A portion of lift tends to retard the forward motion of the aircraft is called Induced drag which acts horizontally rearwards. The amount of lift acting vertical

Three dimensional flow around Airfoil

Three dimensional flow around Airfoil When an aircraft is in flight, pressure is not only distributed in chord wise direction but also in span wise direction. Due to span wise distribution of pressure wingtip vortices are created. In atmospheric flight it is the tendency of fluid to move from high pressure area to low pressure area. The same scenario happens when an aircraft is in levelled flight. Pressure of air is lower than atmospheric pressure at upper surface of the wing and higher than atmospheric pressure at the lower surface of the wing. Beyond the wing tips the pressure is normal. This causes the span wise flow of air away from the fuselage on lower surface and an inward flow towards fuselage on upper surface. Now the airflow is on both chord wise and span wise direction. Both meet at trailing edge of the wing, which imparts a twisting motion to the air and series of vortices are formed on the trailing edge. These are known as trailing edge vortices. As the aircraft prop

Coefficient of Lift

Lift Coefficient: Coefficient of lift C L is defined as the lifting ability of the wing which depends on geometry of the airfoil. Coefficient of Lift Changes with change in angle of attack and it differs for symmetric and Assymetric airfoils. To Know about Coefficient of lift C L we plot the variation of lift with change in angle of attack. For asymmetric airfoil at 0 degree of angle of attack the lift generated is minimum and at 15-16 degrees its maximum which is called C L max . Angle of attack remains a straight line between 0 -12 Degrees. Above 12 Degrees rate of increase in lift reduces and forms a peak. The Peak formed denotes the maximum Angle Of attack C L max . At angles of attack beyond this point Coefficient of lift C L decreases which tends to reduce the lift. Now the Airfoil is stalled and it cannot produce further lift to maintain steady straight and levelled flight. The Angle at