CENTER OF GRAVITY (CG) IN AEROMODELLING AIRCRAFT

Center of gravity or commonly known as CG in aeromodelling aircraft is a matter that must be considered before flying. CG itself is a center of gravity or center, where all the loads seem to be at that point, in other words, when we lift the object on its CG, the object will be balanced.
In aeromodelling aircraft, CG becomes the “fulcrum” and reference point of aircraft movements when doing rotational movements (pitch, roll, yaw) and translation (forward, up, down), so that CG will greatly determine the flight’s attitude, especially longitudinal (pitch) stability. CG can be arranged based on the laying of electronic components in the aircraft, such as shifting the position of the battery and others, batteries that are attached to non-permanent adhesives aim to increase the flexibility of regulating CG.
The following is how to view CG on aeromodelling planes. CG is the point where the location of the hand / finger that we use to lift the plane and plane is balanced as shown in the following figure:

In general, the location of CG from a monoplane trainer with a tail such as cessna, piper cub, spirfire etc. is located at 25-30{2530d6f9f361f4b7115c0b54e4f310320299c4537f29aebb7ff53c6a3142295d} or about a quarter of the chord (rear wing width) measured from the leading edge as shown above. When the CG is located at the position behind that point, or the rear weight, then the plane will tend to be more unstable and easily stalled, this condition is also called tail-heavy. Meanwhile, when the CG is located in the front position, or the front weight, then the plane will tend to swoop forward and difficult to control, this condition is called nose-heavy. Sometimes, tail-heavy conditions are often used for aerobatic aircraft, because an unbalanced plane means it’s easier to maneuver even though it’s difficult to control.
Then, on a flying wing type (without tails), the determination of the location of CG can be done using a calculator that is widely available online, such as at http://fwcg.3dzone.dk/, so we only need to input the size of our plane, and the location of the CG will appear as shown below:

the principle is, CG must be located a little ahead (about 5{2530d6f9f361f4b7115c0b54e4f310320299c4537f29aebb7ff53c6a3142295d} chord, also called static margin) from neutral point (NP). NP itself is the point where the plane will be in a neutral equilibrium condition, that is when the CG is at that point, there is no tendency for the aircraft to stabilize to its initial condition or to an unstable condition.

NP points are affected by wing and tail configuration and airfoil selection and can be calculated using moment equations.
Meanwhile, basically the location of the CG is based on the calculation of the longitudinal equilibrium of the plane, both because of the force and moments of the wings, tail and other components on the aircraft that produce the aerodynamic force as illustrated as follows:

Then, from the picture arrange the moment equation (force times distance) so that it can be seen when the moment = zero at the angle of attack (AOA) zero, and the moment graph towards AOA has neative peculiarity, then the plane is stable Calculations using the above method allow various types of wing, tail and airfoil configurations but it takes time and knowledge of physics and mathematics to determine CG in the above manner so that it is not discussed in detail in this article.

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