The purpose of this experiment was to find the normal force and the lift curve slope by measuring the static pressure distribution around a symmetrical aerofoil.The experiment involved studying the distribution of pressure for different angles of attack

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Pressure Distribution Around A Symmetrical Aerofoil

Introduction

The purpose of this experiment was to find the normal force and the lift curve slope by measuring the static pressure distribution around a symmetrical aerofoil.

The experiment involved studying the distribution of pressure for different angles of attack. There were five different angles of attack in the experiment - -4, 1,6,11 and 16 degrees.

To discuss about the experiment it is needed to understand some phrases. And they are as follows:

  1. Aerofoil
  2. Lift
  3. Angle of Attack
  4. Lift Coefficient
  5. Drag
  6. Stagnation point

Aerofoil

An aerofoil or airfoil section is a two-dimensional object, the shape of the cross-section of the wing, with the function of producing a controllable aerodynamic force by its motion through the atmosphere. To be useful this aerodynamic force must have a lifting component which is much greater than the drag component. In a powered aircraft the motion through the air is provided by the thrust so, in effect, the aerofoil is a device that converts thrust into lift.
Normally the aerofoil is incorporated into a wing with upper and lower surfaces enclosing the load bearing structure. The aerofoil diagrams are in figure 2 and 3.

Lift

When the aircraft is cruising in straight and level flight, at low altitudes, the wings are set at a small angle, 2 to 5 degrees, to the line of flight. The sum of dynamic pressure of the airflow over the wings and the function loads produce an aerodynamic force with the resultant vector quantity being directed upwards and backwards. Aerodynamicists have found it convenient to divide that resultant into two components that part acting backward along the flight path is the wing drag and that acting perpendicular to the flight path is the lift.

The amount of lift, and drag, generated by the wings is dependent on:
 (a) the angle at which the wings meet the airflow or flight path,
  (b) the shape of the wings particularly in cross section – the aerofoil,
  (c) the density (i.e. mass per unit volume) of the air,
  (d) the velocity of the airflow,
  (e) and the wing plan-form surface area.
There is a standard formula for calculation of lift from the wings:

Lift =  Newton

Where

 a dimensionless quantity – the lift coefficient – which relates mostly to item a, but also to item b.

ρ = the density of the air, item c, in kg/m³

V² = the aircraft velocity, item d, in metres per second squared

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S = the wing area, item e, in square metres

The diagrams are in figure 4 and 5.

Angle of Attack

The angle of attack of an aerofoil is the angle α between the aerofoil and the relative wind. Ideally, the direction of the wind is measured in the free stream, i.e. far enough away that it is undisturbed by the aerofoil. the angle α is measured relative to some reference on the aerofoil, and common choices of reference include

  1. The direction that produces zero lift, or
  2. The chord line of the aerofoil.

The diagrams are in ...

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