Flight Basics

  Streamline Streamlines are the ones that drawn such that their tangents at every point along the streamline are in the same directions as the velocity vectors at that point and forms a powerful tool in understanding flows. This definition leads to the equation of streamline as follows : Streakline A line created by particles in a flow that have previously passed through a common point in the flow field. It is obtained by a simple and efficient integration of particle pathlines within the flow solver as the unsteady flowfield is computed.   Pathline The line traced by a given particle when it flows from one point to another in a flow field. In unsteady flow, the pathlines for different fluid elements passing through same point are not the same.                                          

  Circulation  The Circulation C about a closed curve in a flow field is defined as the negative of the line integral of velocity around that closed curve. It is denoted by the symbol, Γ (Uppercase Gamma). This definition makes it a Scalar Quantity.  It is a kinematic property depending on the velocity of the field and the choice of the curve C. The word 'Circulation' generally means movement in a circle or circuit but in aerodynamics circulation has a very precise technical meaning as per the equation above. It does not necessarily means that fluid elements are moving around in circles in this fluid field rather when circulation exists in a flow it simply means that the line integral taken above is finite. For example, if the airfoil is generating lift, the circulation taken around a closed curve enclosing the airfoil will be finite, although the fluid elements are by no means executing circles around the airfoil. Vorticity Vorticity is mathematically defined as the curl...

  When an Object moves through fluid, velocity varies on the surface of the object which creates a pressure difference around the object which is greatest near the leading edge. All the distributed forces due to pressure were replaced by a single resultant force, this single force would act less than halfway back along the chord. The position on the chord at which this resultant force acts is called the Centre of Pressure. The idea of center of pressure as average location of pressure variation is very similar to the center of gravity as the average location of weight. The center of pressure moves along the chord line when angle of attack is altered. At normal cruising speeds, the center of pressure is positioned on the chord line near the center of the airfoil. When angle of attack increases center of pressure shifts towards the leading edge and the magnitude of total resultant force increases.

Camber is defined as the convexity of the curvature of an Aerofoil from leading edge to the trailing edge. It is the fundamental component of Aerofoil design which varies with the volitional speed, strength and purpose of the Aerofoil. The Greater the camber of the center line (line equidistant from leading and trailing edge) the more convex will be the upper surface. When upper and lower surfaces are mirror images, that leads to the mean camber line to be coincident with chord line then, airfoil is called as uncambered airfoil or airfoil of zero camber.  Uncambered Airfoils are also known as Symmetric Airfoils as mean camber line coincides with the chord line. Camber creates a pressure difference between the upper and lower surfaces of the airfoil even at zero angle of attack, as air flows at a higher velocity on the upper surface compared to lower surface which creates a low pressure at upper surface and high pressure at lower surface, due to which there is a generation of lift ...

  Is your Aircraft stable? Let's see what defines stability for an aircraft over time. Stability Stability is the ability of an aircraft to encounter with the disturbances produced by turbulence, wind gust and flight control inputs to continue with a placid and safe motion. A stable aircraft is said to have equilibrium in flight. The stability of an aircraft is judged on the basis of two phenomena known as static an dynamic stability. Static Stability   Static stability is the initial tendency of an aircraft to return to its equilibrium position. Let's say if an aircraft is disturbed by a wind gust and tends to reach its previous equilibrium then, its said to be statically stable.    Dynamic Stability Dynamic stability is the time history of an aircraft's motion after it initially responds to static stability. Being statically stable doesn't guarantee an airplane the dynamic stability because   after reacting to the disturbance it might go away from the neutra...

Aircrafts can be classified into various types depending on the mode of classification like no. of powerplants, position of wing, speed, tail configuration, size, Utility (Military, Civil), etc. Broadly they can be classified at air as a parameter which gives  1. Lighter than Air Aircraft (also known as Aerostats ) 2. Heavier than air Aircraft (also known as Aerodynes ) Lighter than Air        Any aircraft kept skywards by a gas, lighter than air contained by the craft is known as an aerostat. Examples of Aerostat are:- Airships Kite Balloons                                                                                                                          ...