The secondary flight control systems, are operating auxiliary with the basic flight control systems and give the pilot the ability to have a better and easier control of flying the aircraft. In contrast to the basic systems, we will not see all secondary flight control systems in every airplane, as they are not elementary for the complete control of the aircraft. The most popular of these is the trim elevator, which helps maintain a constant angle of climb or descent, so it helps the pilot not to constantly move the elevator back - forward. There are also aileron trim and rudder trim and commonly are found on large aircrafts. Other secondary systems are the flaps, the slats and the Air Brakes / Spoilers.
Elevator Trim
Elevator trim balances the aerodynamic downforce applied to the tail of the airplane. So suitably adjusting the trim elevator, we can have a constant angle of tilt of the airplane to maintain the desired angle of attack without having to constantly move our rudder elevator.
In some cases, when the airflow changes over the tail, we may need to readjust the trim elevator to keep the desired angle of attack.
The use of trim elevator is important in various flight phases, especially when approaching the runway. Also it's used to maintain constant altitude in our final flight level.
Aileron & Rudder Trim
In many aircrafts, especially in larger ones, there are two other auxiliary flight control systems. The aileron trim and the rudder trim. By their names is obvious and their role. There are both help to balance the forces that changing the tilt of the airplane at the axes of roll and yaw.
Aileron trim is small surfaces on the wings of the aircraft, on the back of the aileron. It also works with the same philosophy as the aileron, so when the right getting up the left one getting down. One good reason for the pilot to use the aileron trim is to balance the airplane when it has weight difference in the fuel tanks of the wings.
Rudder trim is a surface located on the rudder, and is used for small corrections to the vertical axis.
Flaps
Flaps are located to the back of the wings of an airplane and are used to reduce the speed with which the airplane can fly safely. So when using the flaps, we can reduce the speed at which a stall occurs, resulting to have slower approach to the runway, and therefore a shorter distance for safe landing. In a similar way can reduce the distance on the runway during takeoff, as they allow the aircraft to fly at slower speed.
In some aircrafts, the use of flaps helps to reduce the angle of tilt of the longitudinal axis (pitch), aiding the pilot to have a better view of the runway. In some other cases, depending on the type of flaps and the position of the wing, their extension may increase the pitch of the aircraft.
There are several types of flaps, depending on the size, the complexity and the speed of the aircraft. The main objective is to increase the lift and drag of the wings. In most smaller airplanes, this is achieved by increasing the angle at the rear of the wing by a simple tilt of flaps in correct degrees (plain flaps). In larger airplanes, except the tilt of flaps, there is also the expansion of flaps, that increasing the surface of the wing and making bigger the lift and drag.
Slats
The slats are thin aerodynamic surfaces along the wings of the airplane over the leading edge and allows the aircraft to be able to move with a greater angle of attack. Using the slats, we gain lift of the wing, so their extension allows the aircraft to fly at lower speed.
The most common use of slats is during landing and takeoff of aircraft, when its speed is close to stall speed. However, slats are closed in normal flight to minimize drag.
When the airplane is moving at low speeds, the air passing from the upper part of the leading edge, is unable to follow the surface of the wing and to smoothly reach the trailing point, resulting turbulence formed at the top of the wing and so lift reducing dramatically. Withtheuseofslatswe decreasethisphenomenon.
Air Brakes/Spoilers
Air brakes / speed brakes are the control surfaces that we use on a airplane to increase the drag exerted on it, so to reduce its speed.
The air brakes differ from the spoilers in the fact that air brakes increase the drag and lift, while spoilers reduce lift and it requires greater angle of attack to maintain it. The spoilers are at the top of the wings and used in most jet as air brakes.
There are many types in different airplanes. For example, the air brakes of the Bombardier CRJ900 located at the end of the fuselage on the tail of the airplane, which is divided in half and opens outwards. Another type of air brakes is the parachute as in the case of the Boeing B-47. On propeller airplanes the propellers can be used as air brakes themselves by changing their turning step. In jet aircrafts, spoilers are used in combination with ailerons to control roll.
During landing and after touchdown, the full extent of the spoilers and air brakes, causing a dramatic loss of lift so that the weight of the airplane applied to the wheels and reducing the case of slipping. Furthermore, increasing the drag it helps to reduce the braking time.
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For FlightSimmer.GR
Giannis Evagelinos
