Effects of Controls – Other Aerofoil Controls

Flaperons are simply combining both aspects of flaps and ailerons.

They can be lowered to function much the same as a dedicated set of flaps.

Here a freight plane has been unloaded in the front first with the rear weight remaining with a large leverage

Principle of Moments

The moment of a force is a measure of its tendency to cause a body to rotate about a specific point or axis.

Consider the following system:

The magnitude of the moment of a force acting about a point or axis is directly proportional to the distance of the force from the point or axis. It is defined as the product of the force and the moment arm. The moment arm or lever arm is the perpendicular distance between the line of action of the force and the centre of moments.

Horizontal Stabiliser and its Turning Moment

Most airplanes are designed so that the wing’s centre of lift (CL) is to the rear of the centre of gravity.

Applying simple physics principles, it can be seen that if a bar was suspended at point L with a heavy weight hanging on it at the CG, it would take some downward pressure at point T to keep the ‘lever’ in balance. 

Turning Moment when forces are out of Balance

Turning Moment Balanced by the Tailplane

A small force with a large leverage effect adjusts continuously when the payload (eg passengers) moves about the cabin.

The Trim Tab is an adjustment to provide long-term relief from aerodynamic control forces. The Trim Tab introduces a force which holds the control surface in the desired position.

This removes the pressure from the control inputs that are required to be held. It is a labour saving device which reduces the fatigue on the Pilot.

A servomechanism (or just “servo”) is a device that allows an axel to be set to a specific angle.

Servos use small high-speed motors and a gearbox to achieve very large torqueing forces for their size. This is at the cost of taking a long time, relative to the speed of the motor, to turn.

Typically used to change the position of the control surfaces using a servo horn and actuator rod.