In flight, an aircraft can rotate about any one or any combination of its three rotation axes. These axes are at right angles to each other and all pass through the aircraft’s center of gravity. Movement about the lateral axis is pitch. Movement about the longitudinal axis is roll and movement about the normal axis is yaw as shown in figure 01. This is achieved via a primary flying control system which in its most basic form consists of moveable control surfaces linked by a series of cables and rod to controls in the cockpit
The primary flight control surfaces are the elevators, ailerons and rudder which hinge at the trailing edges of the main surfaces and maneuver the aircraft about its three axes, producing both primary and secondary effects. During training, the aircrafts available will mostly have the old fashioned cables and rods flight control system which adds a very natural feels to the flight controls “figure 02”. More advanced aircrafts have “fly by wire” systems which consist of onboard computers that receive inputs from the pilots in the form of control arm movement. The computer then starts moving flight controls accordingly
As discussed above, the elevator helps the aircraft rotates about the lateral axis by changing the aircraft’s pitch. Regardless of the flight control system used in a specific aircraft the concept remains the same. Moving the control wheel forward causes the elevator to move downward. This produces aerodynamic force acting on the tail plane in an upward direction causing the aircraft to pitch nose-down and vise versa.
While training on aerial maneuvers, flight instructors spend a considerable amount of time helping students understand the effects of flight controls and how to utilize each control wheel movement to achieve the desired aircraft attitude. The elevator is one of the primary flight controls used throughout the flight to control pitch and during aerial maneuvers like stalls and slow flight.
The primary effect of the rudder is to provide yaw control about the normal axis, moving the left rudder pedal forward moves the rudder to the left. In flight, this produces an aerodynamic force on the fin and the aircraft yaws to the left and vise versa. To maintain coordinated flight at all times, constant rudder pressure must be applied to counteract turning tendencies produced by the aircraft engine. A rudder usually has a secondary effect of inducing a roll around the longitudinal axis.
The primary effect of ailerons is to provide roll control about the longitudinal axis by moving the control wheel to the right deflecting the right aileron upward and the left aileron downloads putting the aircraft in a roll to the right. Moving an aileron upwards causes an increase in the effective angle of attack and corresponding increase in lift, whilst an upward movement of the aileron causes a reduction in the effective angle of attack and a decrease in lift. The difference in lift between the two wings produces the necessary rolling action.
In addition to changes in lift, the deflection of the ailerons also causes variations in drag. Induced drag increases on the downward-deflected aileron, while the upward-deflected aileron produces more profile drag. At lower airspeeds, the increase in drag is greater on the downward-deflected due to induced drag increasing at lower speeds which in return induces a yaw moment in the opposite direction.
Combining primary control surfaces is part of some aircrafts’ designs to satisfy different needs. Delta winged aircrafts like the Concorde use elevons on the trailing edge of the wings. These perform the functions of both ailerons and elevators. Moving the control column backward or forward moves the elevons like elevators and they deflect by equal amounts in the same direction as shown in figure 03 below.
Every student pilot must learn to understand how primary flight controls work and how to use each one to rotate about its respective aspect. Understanding flight controls can be the difference between life and death in some situations where an aircraft is in an abnormality or an emergency. Most flight academies will show students how the entire flight control system operates in great detail using a plane in maintenance to help build a better understanding of the whole system inside a student’s head.