DLE Section : Learning The Principles of Flight

Lets’ explore the wonders of flying.

Counterweight made from fishing lead sinkers

C.O.G (Center of Gravity) location is one of the most crucial parameter provided by the model’s manufacturer. The proper C.O.G location enables easy and stable flight. However, some pilot prefer different C.O.G location; deviating from the factory setting in order to obtain unique flight characteristics. They can be nose heavy or tail heavy. In most cases, battery mount location is adjusted to obtain the desired C.O.G.

There are some cases where the desired C.O.G is failed to be achieved, for example when using a much larger and heavier battery or smaller and lighter battery. This might also occur when using FPV models without mounting any FPV gears (just for flying the model). Additional weights called counterweights are used to solve this issue. There are many ways to find additional weight to be used as a counterweight (coins, stones, etc). Solid lead sinkers for casting/fishing are another option.

Fishing lead sinkers

They come in a variety of sizes and weights. You might directly use and load them to your model, or you might want to merge a couple of them into a single shape.

Firstly, the required weight is to be measured or you could try loading some of the lead sinkers to the model until the desired C.O.G location is achieved.


Secondly, construct the mold / die using wooden materials to a desired shape. Cover the internal part of the mold / die with thin aluminium sheet.


                                      Alu sheet

Finally, the lead sinkers are to be heated until they reach melting point and formed into liquid state. Immediately pour in the liquid lead to the mold / die.


Notes : Consult a professional for heating and melting process as the gas fumes from lead is extremely hazardous to human health.


                                Weight loss

“Don’t confuse symmetry with balance.”   ― Tom Robbins, Even Cowgirls Get the Blues

Basic Flight Aerodynamics

Forces of Flight

There are forces which are experienced during flight.

  1. Thrust – The forward propulsion force produced by the propeller or aircraft’s propulsion system.
  2. Drag – The air resistance which opposes the thrust force.
  3. Lift – The upward force which is required for the plane to fly.
  4. Weight – The aircraft’s weight which is caused by the gravity and opposes the lift.

Forces of Flight Rev1





The lift force is generated by the wing.  At a certain angle of attack, the shape of the wing’s airfoil creates a particular shape (refer to the picture below) in the airflow, a curved streamlines which generates pressure changes which produce the lift. Lower pressure on the wing’s upper surface and higher pressure on the lower surface causes this pressure difference, and therefore the lift force.

Notes: this hypothesis is taken from a research by University of Cambridge (25 Jan 2012).

Link: http://www.cam.ac.uk/research/news/how-wings-really-work


Angle of Attack

Lift airflow




The distribution of lift

The lift around the wing’s surface is not distributed evenly and it is explained by referring to the pressure distribution on airfoil. At a certain angle of attack, the top surface produces more lift than the bottom surface. The maximum lift, pulling and pushing forces combined, is located at the most curved surface; approximately 1/3 of chord length from the wing’s leading edge (front edge).

Pressure difference on airfoil

Pressure distribution on airfoil, picture by UK Open University. Link: http://firstflight.open.ac.uk/aerodynamics/index.html




Thrust and Drag

The Lift which is required for the flight, cannot be generated without the airflow on the wing surface. Thrust is the propulsion force which drives the aircraft forward, thus producing the airflow. One of the examples of the aircraft propulsion system is the propeller which is coupled with a rotating engine to spin the propeller to produce the thrust.

prop definitions

Drag is the thrust resistance and it should be reduced to a minimum amount to optimize the flight efficiency. The drag is generated from the shape of the aircraft. Landing gears, wing strut bar, the wing, tail, the fuselage, and other parts which experience the airflow should be designed to produce streamline airflow; starting by eliminating as many protruding external parts as possible. If it is the fundamental parts, remove them during flight, such as retracting landing gears during flight.

Drag on object shape

3 Planes of Movements

Planes of Movements Rev0

When the aircraft moves in one plane, it rotates about an axis. During flight, it can rotate about one, two or all 3 axes at once. There are 3 maneuvers on these axes:

  1. Maneuver about its longitudinal axis will cause the aircraft to pitch.
  2. Maneuver about its lateral axis will cause the aircraft to roll.
  3. Maneuver about its normal axis will cause the aircraft to yaw.





3 Basic Control Surfaces


Control surfaces Rev0

The aircraft needs 3 basic control surfaces in order to conduct the 3 maneuvers as explained previously:

  1. The ailerons are for rolling maneuver. To roll right, the right aileron needs to move up and the left aileron moves down. This causes the right wing to go down and left wing to go up, thus rolling the aircraft to the right.
  2. The elevator is for pitching maneuver. To pitch up, the elevator needs to move up. This causes the aircraft’s tail to move down and aircraft’s nose to move up; increasing the flight’s altitude.
  3. The rudder is for yawing maneuver. To yaw right, the rudder needs to tilt to the right. This causes the aircraft’s tail to tilt to the left and the aircraft’s nose to tilt to the right.






Learn from A Paper Plane Glider

The basic principles of flight can be studied and learned from many references; textbooks, articles, forums, etc. Those info are only theoretical and a practical proof will definitely provide a quick understanding of the flight principles.  That can be applied to a paper plane glider.

Constructing a paper plane glider is much faster than constructing the model aviation. The parts’ template are printed on a paper and cut according to the shapes.

Notes: the scale of this paper plane glider does not have to be big for easy and quick construction (approximately 200 mm of wing span).


Paper glider 06 Rev0

Paper glider 02 Rev0

Once all the parts have been assembled and glued together, various experiments can be conducted so as to learn the flight aerodynamics; the effect of control surface, the effect of C.O.G location, the wing’s dihedral / polyhedral /anhedral angle, the effect of winglets, flaps, slats and many more.

Paper glider 05 Rev0

Paper glider 03 Rev0

The control surface, such as ailerons, elevators, rudders, canards, flaps, etc, can be adjusted by simply folding the paper. The position of the control surfaces determines the aircraft maneuver when thrown into the air. Adjusting the optimal C.O.G location can be a challenge by adding / removing small weight ( applying tape to the nose or tail ) incrementally until the paper plane can glide smoothly through the air. The thin airfoil may also be shaped to a curved-shape for generating more lift at slower flight speed. Each and every adjustment made will give different flight characteristics.

Paper glider 01 Rev0

Paper glider 04 Rev0

Prioritise the fun and the learning will come.

“ Tell me and I forget, teach me and I may remember, involve me and I learn.”

                   – Benjamin Franklin