Aircraft Maintenance Engineering (Coursework Sample)

AIRCRAFT MAINTENANCE ENGINEERING: AIRCRAFT HYDRAULIC SYSTEMS AND FLIGHT CONTROL
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SECTION A
Question 1
* Advantages of using variable displacement self-idling hydraulic pumps on a Modern Configuration Air Transport (CAT) aircraft.
They are versatile. This feature of versatility is one the greatest merits these pumps have. It is known to produce linear motions, as well. Moreover, it is quite effective in controlling force, torque, and the direction of speed. Variable displacement self-idling hydraulic pumps usually make sense when they tap into CAT aircraft hydraulic system for multiple functionality.
* The position of the pump Yoke (swashplate) when the engine is stationary and why it stays in such a position.
The swahplate is normally pivoted on a Yoke. The yoke is often positioned manually with the aid of a lever or a screw, which is responsible for positioning the pump yoke automatically to maintain a constant output pressure. When the engine is stationary the swashplate also becomes stationary in the housing CITATION Wil95 \l 1033 (Green, 1995). Since it is mounted on a yoke, the yoke is set at a perpendicular position to the cylinders, and there is no reciprocation by the piston; thus no oil is pumped.
* The purpose of the blocking valve in the pump.
The blocking valve is normally designed in a manner that allows it to remain open during the normal operations of the pump. It provides a route through which the fluid with high pressure is ported through the valve plate to the outlet pump.
* The function of the pump case drain
The pump case drain is responsible for the evaluation of the pump status without having to interfere with the normal operations of the pump. Thus, it best fits as the critical tool used for maintenance. In doing so, it takes note of the sudden changes in characteristics of the pump’s operation.
* The purpose of the depressurisation (on-off load) solenoid, and how it is actuated.
Depressurisation solenoid is used in to minimise the failure potential of the situation that may accrue in an aircraft like overheating due to fire. Often at times, the temperature of the metal may rise due to fire or exothermic reactions thus causing a rupture on the metal due to stress on the metal. Therefore, the depressurising solenoid aids in the reduction of internal stress by extending the lifespan of the metal at a certain temperature.
Question 2
* The purpose of the Quill drive and where it is used
A quill drive is generally used on locomotives. The main purpose of the drive is to protect and shear the engine when the generator seizes. Below is a diagram indicating the parts of an aircraft dc generator with the quill drive in position.
From the diagram, it is evident that the drive is mounted on a stationary hollow shaft that is that surrounds the driving-wheel axle. The entire wheel has pins on the armature mesh with spokes which enhance the transmission of motion to the wheels.
* How the hydraulic reservoir is pressurised and why.
The hydraulic reservoir is normally pressurized to 50psi. This pressure is also known to prevent the pumps from cavitations. The hydraulic system is not always pressurized, but what it does is to supply the so called head pressure. Air often originates from either the left engine compressor or the bleed of the right and left engines. The whole system has a set of manifold which is responsible of controlling the pressure supplied to the reservoirs.
Question 3
* The relevant ATA chapters I would use for-
¯ Servicing
ATA Chapter 12-00-00, which is Servicing Routine Maintenance.
¯ flight controls
ATA Chapter 27-00-00, which is Flight controls.
¯ hydraulic power
ATA Chapter 29-00-00, which is Hydraulic Power.
¯ Pneumatics
ATA Chapter 36-00-00, which is Pneumatic.
¯ Instruments
ATA Chapter 39-10-00, which is Instrument & Control Panels
¯ auto flight
ATA Chapter 22-00-00, which is Auto flight
¯ The publication I would use to identify spare parts
The publication I would use in identifying spare parts would be the ‘Civil Aviation Publication CAP 31 Aircraft Parts Authenticity’
SECTION C
* What a Frise Aileron is, and why it is used, an explanation of what differential aileron control is and why it is employed.
A frise Aileron is an aileron that has a nose like portion, which protrudes in front of the hinge line. It has several characteristics in the sense that it forms an extension of the surface of the wing when it is lowered. However, its nose normally projects below the wing when it is raised, thus increasing drag while at the same time reducing yaw. The name Frise came about due to the inventor of the frise aileron, a British engineer named Leslie George Frise.
It is mainly used due to its property of minimising the drag on the wing using the down aileron and the same time increasing drag on the wing using the up aileron. Differential aileron control is brought about by the difference in drag. This effect is known to counteract the effect of induced drag thus making a yawing motion that eventually stops the unfavourable yaw effect partially.
CITATION Joe01 \l 1033 (Yoon, 2001)
The figure above shows the various Frise ailerons. The differential drag is often accomplished by the Frise aileron through the maintenance of a smooth contour between the wing’s upper surface and the aileron. This ensures that very little drag is caused, whereas the bottom of the aileron surface juts downward to come up with a huge increase in drag.
* The purpose of Rudder limiter and why it is used.
The rudder limiter is mainly used to prevent the aircraft structure from over stressing at high speeds. Moreover, it reduces the maximum available angle of the rudder to fifteen degrees each. The rudder limiter is used in limiting certain travels at high speeds so that rudder overload can be prevented. It consists of an electric actuator which is responsible for the blockage of the rudder travel to the airspeed indicated. It also monitors the airspeed consistently from the air data computer CITATION Sys12 \l 1033 (Systems Notes, 2012).
* How elevator trim is provided on a fully powered flying control system, diagram illustration.
Every elevator is normally controlled by an independent control system. Elevator interconnection unit is the one responsible for the combination of the two. The elevator trim is provided on a fully powered flying control system through the servo tabs, which are normally deflected uniformly by the electric actuators.
CITATION Ame12 \l 1033 (American Flyers, 2012)
The figure shown above illustrates how the elevator trim is provided on a fully powered flying control system. The elevator down spring is used in producing a mechanical load on the elevator. This load makes it move towards a position known as the nose-down position. The elevator trim has the mandate of balancing the elevator down spring to put the elevator in a trimmed position. A situation may arise at times when the elevator trim does not function. This calls for the down spring to drive the elevator to a position referred to as nose-down position. Therefore, the nose of the airplane is lowered as its speed builds up and, as a result, a stall is prevented.
SECTION E
Question 1
* A list of the functions of the EBHA and what it refers to.
EBHA refers to the electric backup hydrostatic actuation. It is an actuator that is controlled electrically and is originally powered hydraulically by one of the G650’s two hydraulic systems. An electrical power is normally used as a backup. EBHAs play a very significant role as far as the operations of the aircraft is concerned. Some of its functions include the operation of the entire aircraft in case of certain failure circumstances. It has a special feature that enables it to function that way, which is being self-contained. This property enables it to function as a loner whenever there is an engine failure or the entire breakdown of the aircraft. Moreover, it improves the safety of the aircraft thus having a surety that everyone on board is safe. In addition, the EBHA proves to be very useful in providing the arena of controlling the entire flight since it has several power sources CITATION Ian11 \l 1033 (Moir & Seabridge, 2011).
* An explanation of what EHA is
EHA refers to electro-hydrostatic actuators. Most airplanes have so far developed the need to have accurate, compact and electric actuation for the turbine fuel. The EHA plays a significant role in ensuring that such an emerging industry trend is met. It does this by providing applications where the use of hydraulic power is the ultimate goal that would meet the high force requirements. The technology behind this is that it uses a bi-directional pump. The ports of the pump are normally connected every side of the linear actuator. The motor is responsible for driving the actuator in any direction, but whenever it is driven, the pump position’s it. However, the motor is often controlled by the servo controller just to ensure that the motor is functioning in the required manner. A sensor is also located at the actuator to provide the s...