Some basic terms related to Aircraft Part-1

Now we will learn some basic terms related to aircraft.
1. Lift and Drag.

  • To fly an aeroplane, we must provide it with a lifting force at least equal to its weight.
We will try to understand this with a simple experiment.

  • Take a piece of stiff cardboard and push it through the air in such a way that it is inclined at a small angle to the direction in which you push it, the front (or leading edge) being slightly above the rear ( or trailing edge).
  • You will find that the result of pushing the cardboard through the air is to produce on it a force which tries to push it upwards and backwards.
  • The upward part of this force we call lift, the backward part we call drag.
  • The upward force will be sufficient to lift the cardboard, which will thus be suspended in the air.
  • That is how an aeroplane flies. The cardboard is, acting just like the wings of an aeroplane.

2. Thrust

  • To obtain lift we must constantly push the cardboard forward, and in the real aeroplane this is provided by the thrust.
  • The thrust is produced by power plant or engine of an aeroplane.
  • In RC Planes we use an electric motor or IC engine to produce thrust.

3. Air speed and Ground speed.

  • If we do the cardboard experiment outdoors and if the wind is blowing, it will only be necessary to hold the cardboard still in a similar position with it edge facing the wind.
  • We can feel the lift (upward force) and drag(backward force).
  • This is because, it is the same thing whether the cardboard is pushed through still air, or a stream of moving air moves past the cardboard.
  • The speed at which a body moves through the air, or at which the air moves past a body, is called the “air speed”.
  • The speed at which a body moves over the ground is called the “ground speed”.

4. Center of pressure (CP), Angle of Attack or Angle of Incidence.

  • If we push the cardboard through the air at a small angle – it is called the angle of attack or angle of incidence – we hold it at the center, then we shall feel lift and drag exerted upon it.
  • But you can see it will tend to rotate, its leading edge going over the top.
  • If we try to glide of its own accord, it will turn over and over.
  • This is because the effective or resultant force acting upon it is in front of the center line, whereas we are holding it on its center line, or its weight is acting downwards at the center.
  • If hold it further forward, or if we add weights to it so that its center of gravity is farther forward, we shall eventually find that it tends to turn the other way, the nose dipping downwards.
  • With a little practice we can find a position such that it does not tend to turn either way, and then we have found what is called the center of pressure (CP).

5. Center of gravity (CG).

  • Center of gravity is the point through which the weight of an aeroplane acts towards earth.

6. Stability and Instability.

  • When the CP and CG coincide, the plane is balanced, or is in equilibrium.
  • If the CP is in front of CG, it is said to be tail heavy condition.
  • If the CP is behind the CG it is said to be nose heavy condition.


Reference :- For the explanation of basics related to aeroplanes,  A ‘Without Formulae” Book, Flight Without Formulae (How and why an Aeroplane flies, explained in simple language) by A.C.Kermode, Author of “Mechanics of Flight” and “The Aeroplane Structure”, and co-other of “Hydrofoils”.
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