Primary Flight Controls Analysis Engineering Essay
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This report is about primary flight control. The main primary controls are the ailerons, rudder and elevators. Controls are altered during flight by the control column or yoke. In this report i will be reporting on how these controls affect flight, the primary and secondary effects such as roll, yaw and pitch flight. Also how these same controls manipulates the forces on a light aircraft like drag and lift as part of their natural mechanics to work. In addition, which control manoeuvre on the three planes or axis of movement, i.e. longitudinal, lateral and normal planes or axis .furthermore I will report on interfacing systems to work these controls and how it differs on larger aircrafts. I will also discuss modifications the controls, their advantages and disadvantages respectively.
Longitudinal, Lateral and Normal Axis.
The flight controls bend and manoeuvre around these three planes or axis. Longitudinal axis is through the aircraft from nose of the aircraft to the tail, movement around this axis is the roll. Lateral axis lies along both wings of the aircraft from the wingtip , through the wing root and fuselage to the wingtip. Movement around this axis is the pitch. And lastly the normal axis lies through the aircraft vertically, movement around this axis the yaw.
Figure 2: the three planes/axis of movement
Primary flight controls
Control column/Yoke:- The control yoke or column is used to control the aircrafts attitude in pitch and in roll. Left and right control the ailerons whereas a push and pull forward and backwards control the elevators. These manoeuvres using the control column or yoke is solely dependant on the pilots muscles because it adapts a pulley or Rod system to control the surfaces during pitch and roll. I will expand on this more on the interfacing section of this report.
Ailerons: Ailerons are on the trailing edge close to the wings tips controlled by the column or yoke . The move up and down vertically, alters the camber of the outboard trailing edge of the wings thus changing the amount of lift and drag ratio. The primary movement when the ailerons are used is the roll its secondary motion is a yaw. This is because during a roll the wing that descends has less drag and while the other wing has more induced drag causing the wing to not fly effectively through the air drop backwards during a roll. This eventually causes the 'skidding' away from the intended turn, eventually causing the tendency for yaw in the direction of the rising wing. This yaw is also know as 'Adverse Yaw'
Control during a roll is achieved by using Differential ailerons. This means when the control column is moved in any direction right or left, the up-going aileron moves through a greater angle of attack than the down-going aileron. Keeping a close ratio of induced drag on both wingtips.
Control during roll can also be achieved by the design of the ailerons. A typical example is the Frieze ailerons; these types of ailerons have lip extensions in the up-going aileron which disturbs the airflow increasing drag.
Figure 3:ailerons,differencial ailerons .
Figure 4:fries ailerons and lip extensions.
Rudder: The rudder sometimes called the Fin is located on vertically mounted aerofoil called the vertical stabiliser. These are controlled by pedals in the cockpit initiating movement of the aircraft in a horizontal rotation around its vertical or normal axis. During normal flight the symmetrical design of the vertical stabilisers and rudder/fins meets the relative airflow head on and no lift is produced. As the rudders or fins are initiated left or right, there is a deflection that meets the air relative airflow. Lift is then generated horizontally producing a 'YAW' which is the primary movement operating the rudder.
The secondary effect of a yaw movement is a roll. This can be caused general rudder usage but the roll effect is amplified by a motion of air from the propeller (common in single engine aircraft) called the slip stream.
Figure 6 slipstream
Figure 5: Aircraft yaw on a vertical or normal axis.
Elevator: The elevators provides the aircraft with the primary movement of pitch in the longitudinal axis of the aircraft. It is located on the rear of the horizontal stabilisers. The control of the elevators is through the control column which creates a camber in the horizontal stabilisers, thus changing altering lift produced. When the yoke is pushes forward the elevator takes a downward motion causing a change in camber which creates upwards lift, thus rotating the nose of the plane down and vice versa as the column is pushed back for a upwards pitch.
Figure 1: Pitching lateral axis.
Light and medium sized aircrafts powered by propellers uses pulley or rod system to interface between the control column and the surfaces to achieve roll, pitch and yaw. The pulley system is when a series of cable are connected from the column from the surface by cables. The rudder pedals also adopts the same system to initiate rudders.
Figure 7:Pulley system, Elevator ,aileron and rudder control
The pulley system depends on the pilots muscles to use, but in larger aircrafts the pilots strength alone is not enough to achieve movements on the control surfaces so it can use an electric motor system or a hydraulic system.
Control Modification Methods.
In light aircrafts which uses the pulley system it is imperative that during flight the pilot is able to use reasonable effort to achieve ever desirable maneuver he chooses. In addition the control also have to be reasonably light but not light but not too light to cause uncontrollable movement if a unintended force is applied. In these cases are modifications made to aid control, modifications such as mass balances, tab control systems and bob weights.
This modification method is when the aircraft designer will endeavor to balance the flying controls to ease control movement and progressive feel. The designer achieves this by adopting weights in a ratio of about:
Aileron 1 : Elevator 2 : rudder 4
This mass balance ratio is not ideal for all aircrafts it differs, the ratio is always put together to achieve a harmonization known as a pilots machine. It also has its disadvantages because it is often necessary to provide some sorts of assistance to the pilot to motion each respective control balanced with a mass.
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