Aircraft Electrical System 2

Md. Nur Alam Course/Batch: FENDA 09Page 19
Student ID: 33


Task: 01 (a)
Purpose of using configuration warning lights:
Aircraft warning lights are lighting devices used to make tall structures more visible to aircrafts, during both daytime and nighttime. These devices should have specific features, in terms of light intensity, beam pattern and light color defined by international regulations and national standards.
Aircraft warning lights (AWL) are lighting devices installed on any permanent or temporary structure which could pose a potential hazard to air navigation. Lighting systems, often called obstruction lights, are designed with different shapes, colors and light intensity to produce an acceptable level of safety: the final purpose is to prevent a risk of collision for aircraft flying near the structures.
Recommendations on obstruction lighting systems, technical standards and functional features, may vary according to terrain features, weather patterns, geographic locations and the overall layout of the structures that need to be lit.
In general there is no single standard defining minimum mandatory requirements governing design and installation of obstruction lighting; on the other hand the most common and widespread regulations are ICAO's (International Civil Aviation Organization, a specialized agency of the United Nations,) and FAA's (Federal Aviation Administration, an agency of the United States Department of Transportation). [1]
On aircraft
Aircraft use collision avoidance lighting systems to warn other aircraft of their presence. These lights include landing lights, red or white flashing beacons, wingtip strobes, and wingtip navigation lights. The wingtip navigation lights are required to consist of a red light on the left wingtip and a green light on the right wingtip. Landing lights are used during the descent and approach to landing, and at other times if deemed necessary by the flight crew or operator. [2]
http://lombardia.ati2000.it/media/docs/67-Lodolo_Menta_Calzavara.pdf
http://en.wikipedia.org/wiki/Aircraft_warning_lights
Task: 01 (b)
Electrical operation of bleed air overheat detection of F-28 Aircraft
This type of detector can be used in engine fire detection systems; alternatively it can be used in the bleed air overheat detection system. The detector can only sense fire overheat in a localized volume of the installation; it is more likely that multiple detectors are used to provide increased detection probability. A small gas turbine engine would typically be fitted with six of these detectors. The wing leading of a large aircraft could be fitted with over 20 overheat switches. The switches are connected in parallel as shown in Fig this forms a detection loop .If any one of the switches closes due to a fire or overheat being detected, the alarm circuit is activated thereby illuminating a system warning light. A simple test circuit allows some of the circuit to be tested from the flight compartment. Some aircraft are fitted with a dual loop of detectors to provide a back-up system in the event of loop failure, e.g. open circuit wiring. [3]

Figure: Overheat switches connected in parallel

Bleed air diction of F-28 Aircraft:



AIRCRAFT ELECTRICAL AND ELECTRONIC SYSTEM (page 222)
Task: 02 (a)
Landing lights:
Landing lights are lights used on aircraft to illuminate the terrain and runway ahead during takeoff and landing.
Almost all modern aircraft are equipped with landing lights if they are intended and approved for nighttime operations. Landing lights are usually of very high intensity because of the considerable distance that may separate an aircraft from terrain or obstacles; the landing lights of large aircraft can easily be seen by other aircraft over 100 miles away. [4]
http://en.wikipedia.org/wiki/Landing_lights
Anti-collision lights:
An aircraft anti-collision light system can use one or more rotating beacons and/or strobe lights, be colored either red or white, and have different (higher than minimum) intensities when compared to other aircraft. Many aircraft have both a rotating beacon and a strobe light system. Strobes and beacons are also considered anti-collision lights. [5]
Anti-collision lights should be used whenever the engine is running except when they interfere with ground operations. Strobes do not have to be used all the time if a beacon is on.
http://www.faa.gov/air_traffic/publications/atpubs/aim/aim0403.html#aim0403.html.23
Navigation lights:
Navigation light is a colored source of illumination on a waterborne vessel, aircraft and some spacecraft, used to signal a craft's position, heading, and status. Commonly, their placement is mandated by international or civil authorities.
Navigation lighting systems include:
Right-of-way lights — a red light is mounted on the left or port side of the craft and a green on the right or starboard side. In a situation where the paths of two watercraft or aircraft cross, these lights help each crew determine the other craft's direction and who has right-of-way. When two craft have crossing paths, each sees a red or green running light. The one on the port side of the other, which must yield right of way, sees red, while the one on the starboard side of the other, which has right of way, sees green.
Strobe lights — On aircraft primarily, strobe lights flash a high-intensity burst of white light, to help other pilots recognize the aircraft's position in low-visibility conditions.
Aircraft navigation lights are placed in a way similar to that of marine vessels, with a red navigation light located on the left wingtip leading edge and a green light on the right wingtip leading edge. A white navigation light is as far aft as possible on the tail or each wing tip. High-intensity strobe lights are located on the aircraft to aid in collision avoidance.
In civil aviation, pilots must keep navigation lights on from sunset to sunrise. High-intensity white strobe lights are part of the anti-collision light system, as well as the aviation red or white rotating beacon. [6]

Figure: 1) Navigation Lights 2) Aft Light 3) Anti-Collision Strobe lights 4)Logo Light
http://en.wikipedia.org/wiki/Navigation_light#Aviation_navigation_lights
Cabin, Cockpit and Cargo lights:
Main purposes of cockpit and cargo lights are to ensure the aircraft environment matches the exterior environment. This is done in preparation for a potential evacuation at dusk or at night. Going from a bright lit aircraft environment to one that's pitch black would require some time for our eyes to focus and see the evacuation slide. The main purpose is to produce a clear vision at dark. Since we need to have all the seconds on our side in the event of an emergency, blinking cockpit and cargo lights is one of many steps we take to ensure the safety of the aircraft.
Instrument lighting
Must illuminate each essential instrument and switch
Direct rays must be shielded from pilot's eyes
Must provide dimming control

Varies significantly by aircraft type and purpose
Usually overhead fluorescent lights
28 volts DC
Emergency lights
The main purposes of emergency lights is to try to draw others attention to help the aircraft. Mainly ATC and other surroundings to be alert of the emergency situation. This is also important to warn the passengers and crews.
Required by FAR 25.812
Must include exit marking signs, general cabin illumination, floor escape path lighting, and exterior emergency lighting
Must be battery powered and separate from main electrical system [7]
Pallett, E. H. J. Aircraft Electrical Systems. Longman Scientific & Technical. 1987.
Task: 02 (b)
Ice protection:
Two strategies are used for ice protection: de-icing and anti-icing. De-icing allows ice to form and then be removed on a periodic basis. The build-up of ice will have been investigated during type testing of the aircraft and the build-up removed before it poses a hazard. Anti-icing is when ice is not permitted to form at all. Three primary methods are used for both de-icing and anti-icing:

Fluid
Pneumatic
Thermal.

All three are controlled and operated by electrical systems; an aircraft can be fitted with any one method, or a combination of all three. Specific areas to be protected from ice formation are as follows:
Airframe
leading edges
control surfaces
lift augmentation devices
windscreen (or windshield)

Propulsion
Air intakes
Propellers

External components
pilot tubes
Temperature sensors
Angle of attack sensors
Water drains [8]

Figure: Ice and rain detector: ultrasonic sensor

Figure Ice detector: ultrasonic system

Figure Ice detector: ultrasonic system timer
Description about rain protection and rain repellent with Diagram:
Rain protection
Flying in rain condition poses a number of threats to the safe operation of the aircraft. Rain reduces visibility through the windscreen. To meet the correct in-flight visibility conditions required, the windshield is to be protected from rain. Some protection must be afforded when flying in heavy rain conditions in order to improve visibility through cockpit windshields. This job is accomplished by windshield wiper and rain repellent systems.
Windshield wiper
The windshield wiper system is based on 28 V DC variable speed motors; the rotary motion of the motor is changed by a gear mechanism in the converter to produce the sweeping motion of the wiper arm over the windshield. Normally two wipers are provided, one for the left (Captain) windshield panel one for the right (First officer) windshield panel.
A typical windshield wiper circuit is shown in a Figure. The normal arrangement is to have one wiper assembly per screen to ensure that at least on pilot can keep a clear screen in the event of failure. The motors are set by the control switch; typical wiper speeds are:
Low, 160 cycles per minute
High, 250 cycles per minute.
A parking switch in the motor/converter sets the wiper blade to the park position when the wiper is selected off. In the off position, the park switch in each motor/ converter closes; this causes the blades to position them at the bottom of each windshield. [9]

Figure: Windscreen wiper circuit
Rain repellent: This system is used to maintain a clear area on the windshield during take-off and landing. The rain repellent bottle is located inside the fuselage roof; this contains a pressure gauge, visual contents reservoir and a shut-off valve.
The control panel (normally combined with the wiper system) contains two switches to control the rain repellent system. Figure: 1.2illustrates a typical rain repellent system schematic. The repellent fluid is stored in a container; this is pressurized from an external air supply. Two electrically operated solenoid valves control the flow of repellent to the windscreens. Nozzles on the fuselage (forward of the windshield) direct the repellent spray onto the windscreens.
The rain repellent switches are momentary make type; pushing a switch once activates the respective solenoid valve. A time delay circuit in the valve controls the amount of repellent being released by closing the valve after a short time period, typically ½ second. A pressure gauge indicates when the container needs replacing. [10]

Figure: Rain repellent system schematic
Task: 02 (c)
Hydraulic servo activation, transfer valve and control surface actuation with diagram:
An electro hydraulic servo valve (EHSV) is an electrically operated valve that controls how hydraulic is ported to an actuator. Servo valves and servo-proportional valves are operated by transforming a changing analogue or digital input signal into a smooth set of movements in a hydraulic cylinder. Servo valves can provide precise control of position, velocity, pressure and force with good post movement damping characteristics.


Principles of Operation
An electric command signal (flow rate set point) is applied to the integrated position controller which drives the pilot stage. The thereby deflected nozzle flapper system produces a pressure difference across the drive areas of the spool and effects its movement. The position transducer (LVDT) which is excited via an oscillator measures the position of the spool (actual value, position voltage). This signal is then demodulated and fed back to the controller where it is compared with the command signal. The controller drives the pilot stage until the error between command signal and feedback signal will be zero. Thus the position of the spool is proportional to the electric command signal. [11]
Servo motors are used to drive servos, which are systems that control mechanical motion at a
location different than that of the primary controls. Servos typically operate through an electric or hydraulic connection to the control system. This means that an operator may position a control stick in one room, thereby transmitting a series of signals to a servo in a nearby room. The servo system will properly translate the signal from the control device and activate the servo motor accordingly, performing the movement indicated by the controller.
In essence, there is no specific difference between a servo motor and an ordinary motor. However, servo motors are generally smaller and designed for more dynamic performance and steady state accuracy. Generally, a servo motor also implies a link to a feedback control loop, as well as precise motion and high torque-to-inertia ratios. This motion should have the same degree of accuracy and torque in both rotational directions. Servo motors also imply high armature resistance, and more obviously, an electric powered device; hydraulic motors are sometimes used when larger power output is required. 
Like other electric motors, servo motors fall into two main categories: Alternating Current and Direct Current. DC servo motors are used for small and mid-level applications requiring moderate and low power output, while AC servo motors are used in more heavy-duty applications. Within these categories, there are further distinctions, such as brushless DC motors, split series motors, shunt control motors and permanent magnet motors. Each type has specific advantages and disadvantages, and should be chosen based on application and budget. For example, brushed DC motors are relatively inexpensive, but are more prone to maintenance concerns than brushless types. [12]
http://www.thomasnet.com/about/servo-motors-52773009.html
http://en.wikipedia.org/wiki/Electrohydraulic_servo_valve


Transfer valve
The transfer valve of conventional electro-hydraulic control systems receives electrical input signals from sensing devices and correspondingly controls the flow of pressure fluid to an actuator. The input signal in one type of transfer valve operates a torque motor whose armature displaces a flapper from a normal position relative to the fluid discharge nozzle of a chamber to create a pressure in the chamber proportional to the signal. This pressure acting on the end of a valve spool positions the valve spool to control the direction and extent of fluid flow to the actuator.
An object of the present invention is to provide a transfer valve with novel means for isolating the electrically operated means from the fluid pressure operated means.
Another object is to provide novel means for centering the signal of a transfer valve for a no-signal condition by fluid pressure.
The present invention contemplates a transfer valve having a member positioned relative to inlet and exhaust pressure fluid ports by differential pressure in response to electrical signals to control an actuator, the valve being provided with novel means for isolating the electrically operated portion which responds to the signals from the pressure fluid operated portion and also for centering the member which produces the differential pressure and also provided with novel means for centering the pressure operated portion for a no-signal condition by way of fluid pressure. [13]


http://www.google.nl/patents/US2835265
Control surface actuator
Aircraft control surface operating systems and apparatuses, and associated methods of use. In one embodiment, an aircraft system includes an actuator operable coupled to a control surface in one-to-one correspondence. The actuator can include at least a first fluid port and a second fluid port. A first fluid circuit can be configured to provide pressurized working fluid from a fluid source to the first fluid port on the actuator to retract the actuator. A second fluid circuit can be configured to similarly provide pressurized working fluid from the fluid source to the second fluid port on the actuator to extend the actuator. The aircraft system can further include an accumulator configured to store pressurized working fluid for actuator operation in the event of a pressure drop in the fluid source. [14]

http://www.freepatentsonline.com/7059563.html
http://www.google.com/patents/US4762205

Task: 03
Stall warning system:
What is a stall
When an aircraft exceeds its critical angle of attack, it enters a condition known as a stall, where one wing becomes inoperable and causes the aircraft's nose to yaw in the direction of the stalled wing. If the stall isn't recovered from, the aircraft begins to rotate in the direction of the yaw, entering an incipient spin. From there, the aircraft enters a stabilized spinning pattern where it plummets toward the ground in a near vertical position. While a spin can be recovered from, recovering from the stall that would cause it the best option for resuming safe flight.
What is a Stall Warning System
Technically, a stall warning system is a device that delivers an audible warning as an aircraft approaches stall speed. A staff warning horn, which has a pressure sensor that trips a switch that prompts the audible warning, is a simple example of a stall warning system. [15]
http://goarticles.com/article/What-are-Stall-Warning-Systems-and-how-do-they-Work/2577840/
Purpose of stall warning system
A system that warns the pilot when the angle of attack of the wing reaches a point that will likely produce a stall. Stall warning systems measure the angle of attack. Some systems use a small air-operated vane on the leading edge of the wing to detect the high angle of attack. Others use an angle of attack probe on the fuselage. A few of the smaller airplanes have a reed-type horn in the wing that changes its sound as the angle of attack changes. Some stall warning systems turn on a light or sound a warning horn when the angle of attack gets too near the angle that could cause a stall. Some of the more elaborate systems, called stick shakers, vibrate the control column, and stick pushers actually push the control column forward when a stall is approached. [16]
http://www.datwiki.net/page.php?id=7503&find=stall%20warning%20system%20(aircraft%20flight%20instrument)&searching=yes
Operations of three stall warning systems
Three stall warning devices and their function:
Reed Sensor
Vane Sensor
AoA Sensor
Function of Reed stall warning sensor:
Airflow is directed from a scoop in the wing leading edge and into a reed and horn assembly. In the pre-stall condition, the air pressure on the leading edge reduces (relative to cabin pressure) because the stagnation point has moved. This draws air through the reed, causing it to vibrate at an audible frequency (much like a musical instrument); this is amplified in an acoustic horn and the crew receives a tone.

Function of Vane stall warning sensor:
Vane sensor is an alternative device used at GA, located in the wing leading edge. The vane is held in a forward position by an internal spring and connected to a micro-switch. At normal angles of attack, the vane is held back by the airflow (against spring pressure) and the micro-switch is held in the open position. At higher angles of attack, airflow pressure on the switch is reduced and the vane eventually moves forward (by the spring force) thereby closing the micro-switch. This completes the warning circuit that activates a light and horn.
Function of AoA sensor:
This is the most important sensor located both sides of front fuselage (cockpit). An angle of attack (AoA) sensor vane aligns itself with the prevailing airstream; this rotates a shaft inside the housing. The vanes shaft is connected to a synchro that provides an electrical output proportional to the angle of attack. A viscous damper connected to the AoA vane stabilizes vane movements and reduces the effects of turbulence. The AoA sensor contains a heater that pro-vides continuous de-icing/anti-icing, prevents condensation and reduces changes in damper fluid viscosity. [17]
Task 04
Evaluation of centralized warning system to the overall safety of an aircraft:
Centralized warning system:
Centralized warning system is a warning unit which gives audible or visual warning of conditions in unrelated systems. it Includes items such as master warning or flight warning systems, central instrument warning, or caution and warning systems, tone generators, annunciators. A typical system shown below

Figure: A typical annuanciator system schematic
The increasing use of indicator lights throughout flight compartments develops the necessity of Centralized warning indication. It offers more easy way to detect the fault indications as well as the condition/position of operating components. Basically a typical system consists of an annunciator panel within the visual limit of pilot which contains centralized group of warning and indicator and a malfunctioning or advisory massage.
Warning annunciator
Warning annunciator system (WAS) monitors various parameters and triggers up appropriate warning and caution when certain combination of parameters exceeds the warning and caution thresholds. Both visual and oral alert used. This consists of three basic components,
Master warning
Master caution
Central warning panel


Master warning:
It contains red colored light which come on whenever triple chime or three lights comes on in the central warning panel due to aircraft system malfunction. The light will remain on until the fault is corrected. The master warning lights and triple chime alert can be turned off or reset by pressing either master warning button light, after resetting the system is rearmed will respond again to any subsequent malfunctioning.
Master caution:
This is colored amber. It comes on and single chime will comes whenever one or more of the amber caution light of the central panel comes on.
Central warning panel: Top half of the lights here red. Eight of this recorded by FDR. A illustrate figure given below [18]

Figure: central warning panel

Operation:
When a fault occurs lights are illuminated via "fault pulser" and SCR circuit arrangement. The identification of fault on annunciator panel indication system is cross checked by the overhead panel indication.
Its contribution to aircraft safety:
When fault arise due to malfunctioning overhead panel light for that system illuminates but it is not readily observed By the pilots , their attention drawn to the annuanciator and master caution and warning lights. As the whole system is just ahead to the pilots visual limiting it's more easy and reliable to take necessary step for them in case of any fault operation or malfunctioning.
The warning comes to the master warning and caution are verified twice before comes on. So here is no chance to fault indication.
As the lights not extinguished until the correction of subsequent fault line its more reliable then overhead panel.
it reduces the pilots visual fatigue. Instead of checking more lights on overhead panel they can easily shout out it on central panel.
The full system incorporates of two indication methods one is Lighting indication and another one is oral. Hence there is no chance to avoid the warning.
As its main behave recorded by the FDR (flight data recorder), it is helpful in time of investigation and operational checking. [18]











Bibliography
http://lombardia.ati2000.it/media/docs/67-Lodolo_Menta_Calzavara.pdf
http://en.wikipedia.org/wiki/Aircraft_warning_lights
AIRCRAFT ELECTRICAL AND ELECTRONIC SYSTEM (page 222)
http://en.wikipedia.org/wiki/Landing_lights
http://www.faa.gov/air_traffic/publications/atpubs/aim/aim0403.html#aim0403.html.23
http://en.wikipedia.org/wiki/Navigation_light#Aviation_navigation_lights
Pallett, E. H. J. Aircraft Electrical Systems. Longman Scientific & Technical. 1987.
AIRCRAFT ELECTRICAL AND ELECTRONIC SYSTEM page : 324
http://www.tc.gc.ca/media/documents/ontario-eng/wildlife-manual-eng.pdf
AIRCRAFT ELECTRICAL AND ELECTRONIC SYSTEM page : 324
http://www.thomasnet.com/about/servo-motors-52773009.html
http://en.wikipedia.org/wiki/Electrohydraulic_servo_valve
http://www.google.nl/patents/US2835265
http://www.freepatentsonline.com/7059563.html
http://www.google.com/patents/US4762205
http://goarticles.com/article/What-are-Stall-Warning-Systems-and-how-do-they-Work/2577840/
http://www.datwiki.net/page.php?id=7503&find=stall%20warning%20system%20(aircraft%20flight%20instrument)&searching=yes
AIRCRAFT ELECTRICAL AND ELECTRONIC SYSTEM page : 348
http://www.faa.gov/regulations_policies/handbooks_manuals/aircraft/amt_airframe_handbook/media/ama_Ch10.pdf





Unit title/no: Aircraft Electrical System [84]
Assignment title/no: Function and operation of airframe electrical system [02]

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