GLOBAL POSITIONING SYSTEM (GPS)

GLOBAL POSITIONING SYSTEM GPS (Global Positioning System) is the only system today able to show you where your exactly position on the earth at anytime and any weather condition. 24 satellites are all orbit around the earth at 11,000 nautical miles or approximately 20,200 kms. above the earth. The satellites are placed into six different orbital planes and 55 degree inclination. They are continuously monitored by ground stations located worldwide. GPS ELEMENTS We can divide GPS system into three segments. SPACE SEGMENT USER SEGMENT CONTROL SEGMENT SPACE SEGMENT The space segment comprises a network of satellites . The complete GPS space system includes 24 satellites, 11,000 nautical miles above the earth, take 12 hours each to go around the earth once or one orbit. They are orbit in six different planes and 55 degrees inclination. These positions of satellites, we can receive signals from six of them nearly of the time at any point on earth. Satellites are equipped with very precise clocks that keep accurate time to within three nanoseconds ( 0.000000003 of a second or 3e-9) This precision timing is important because the receiver must determine exactly how long it takes for signals to travel from each GPS satellite to receiver. Each satellite contains a supply of fuel and small servo engines so that it can be moved in orbit to correct for positioning errors. Each satellite contains four atomic clocks. These clocks are accurate to a nanosecond . Each satellite emits two seperate signals , one for military purposes and one for civilian use. SOME SPECIFICATION OF SATELLITE Weight 930 kg.(in orbit) Size 5.1 m. Travel Velocity 4 km/sec Transmit Signals 1575.42 MHz and 1227.60 MHz Receive at 1783.74 MHz Clocks 2 Cesium and 2 Rubidium Design life 7.5 year (later model BlockIIR 10 years) USER SEGMENT As the pilot fly , the GPS receiver continuously caculates the current position and display the correct position / heading.The GPS unit listen to the satellite's signal and measure the time between the satellites transmission and receipt of the signal. By the process of triangulation among the several satellites being received, the unit computes the location of the GPS receiver. GPS receiver has to see at least four satellites to compute a three dimensional position (it can compute position with only three satellites if know altitude). Not only latitude and Longitude , but altitude as well. There are numerous forms of display among the various manufacturer. No frequency tuning is required , as the frequency of the satellite transmissions are already known by the receiver. CONTROL SEGMENT The control Segment of GPS consist of: Master Control Station ( one station ): The master control station is responsible for overall managment of the remote monitoring and transmission sites. As the center for support operations , It calculates any position or clock errors for each individual satellite from monitor stations and then order the appropriate corrective information back to that satellite. Monitor Stations ( four stations ): Each of monitor stations checks the exact altitude , position , speed , and overall of the orbiting of satellites. A station can track up to 11 satellites at a time. This check-up is performed twice a day by each station as the satellites go around the earth. OPERATION The principle of GPS is the measurement of distance between the receiver and the satellites. The satellites also tell us exactly where they are in their orbit above the earth . The receiver knows our exact distance from satellite , knows the distance between satellites. GPS receivers have mathematical method by computer to compute exactly where the GPS receiver could be located.

AUTOMATIC DIRECTION FINDER

	AUTOMATIC DIRECTION FINDER ADF (Automatic Direction Finder) is the radio signals in the low to medium frequency band of 190 Khz. to 1750 Khz. It was widely used today. It has the major advantage over VOR navigation in the reception is not limited to line of sight distance. The ADF signals follow the curvature of the earth. The maximum of distance is depend on the power of the beacon. The ADF can receives on both AM radio station and NDB (Non-Directional Beacon). Commercial AM radio stations broadcast on 540 to 1620 Khz. Non-Directional Beacon operate in the frequency band of 190 to 535 Khz. ADF COMPONENTS ADF Receiver : pilot can tune the station desired and to select the mode of operation. The signal is received, amplified, and converted to audible voice or morse code transmission and powers the bearing indicator. Control Box (Digital Readout Type) : Most modern aircraft has this type of control in the cockpit . In this equipment the frequency tuned is displayed as digital readout. ADF automatically determines bearing to selected station and it on the RMI. Antenna : The aircraft consist of two antennas. The two antennas are called LOOP antenna and SENSE antenna. The ADF receives signals on both loop and sense antennas. The loop antenna in common use today is a small flat antenna without moving parts. Within the antenna are several coils spaced at various angles. The loop antenna sense the direction of the station by the strength of the signal on each coil but cannot determine whether the bearing is TO or FROM the station. The sense antenna provides this latter information. Bearing Indicator : displays the bearing to station relative to the nose of the aircraft. Relative Bearing is the angle formed by the line drawn through the center line of the aircraft and a line drawn from the aircraft to the radio station. Magnetic Bearing is the angle formed by a line drawn from aircraft to the radio station and a line drawn from the aircraft to magnetic north (Bearing to station). Magnetic Bearing = Magnetic Heading + Relative Bearing. TYPE OF ADF INDICATOR Four types of ADF indicators are in use today. In every case, the needle points to the navigation beacon.Those four types are: Fixed Compass Card : It is fixed to the face of instrument and cannot rotate. 0 degree is always straight up as the nose of aircraft. The relationship of the aircraft to the station is refered to as " bearing to the station " MB or aircraft to magnetic north. This type of indicator, pilot must calculate for the bearing by formular MB = RB + MH Rotatable Compass Card : The dial face of the instrument can be rotated by a knob. By rotating the card such that the Magnetic Heading (MH) of the aircraft is adjusted to be under the pointer at the top of the card. The bearing to station (MB) can be read directly from the compass card without calculation and make it easy for pilot. Today , they designed automatically rotate the compass card of the instrument to agree with the magnetic heading (MH) of the aircraft . Thus MB to station can be read at any time without manually rotating the compass card on the ADF face. Single-Needle Radio Magnetic Indicator : Radio Magnetic Indicator is an instrument that combines radio and magnetic information to provide continuous heading , bearing , and radial information. The face of the single needle RMI is similar to that of the rotatable card ADF. Dual-Needle Radio Magnetic Indicator : The dual needle RMI is similar to single needle RMI except that it has a second needle. The first needle indicated just like single needle. inthe picture , the yellow needle is a single which indicate the Magnetic Bearing to the NDB station . The second needle is the green needle in the picture. The second needle (green) is point to VOR station .The dual needle indicator is useful in locate the location of an aircraft. OPERATION ADF operate in the low and medium frequency bands. By tuning to NDB station or commercial AM radio stations. NDB frequency and identification information may be obtained from aeronautical charts and Airport Facility Directory. The ADF has automatic direction seeking qualities which result in the bearing indicator always pointing to the station to which it is tuned. The easiest and perhaps the most common method of using ADF , is to " home " to the station . Since the ADF pointer always points to the station , the pilot can simply head the airplane so that the pointer is on the 0 (zero) degree or nose position when using a fixed card ADF . The station will be directly ahead of the airplane. Since there is almost always some wind at altitude and you will be allowing for drif, meaning that your heading will be different from your track. Off track , if the aircraft is left of track, the head of the needle will point right of the nose. If the aircraft is right of track , the head of the needle will point left of the nose. For fixed compass card , if you are not fly Homing and you want to fly heading at some degrees. You must use the formular MB = MH + RB to find out what degree the ADF pointer should be on. Today , the fixed card indicator is very unsatisfactory for every day use which can still be found on aircraft panels but not many planes that pilot actually uses it due to it has easier type of indicator. For rotatable compass card, it was a big step over the fixed card indicator. The pilot can rotate the compass card with the heading knob to display the aircraft MH " straight up " . Then the ADF needle will directly indicate the magnetic bearing to the NDB station. For Single needle Radio Magnetic Indicator , the compasscard is a directional gyro and it rotates automatically as the aircraft turns and provide continuous heading . It is accurately indicates the magnetic heading and the magnetic bearing to the beacon. This instrument is a " hands off " instrument. For dual needle Radio Magnetic Indicator, it is give the pilot information the same as the single needle such as aircraft heading and magnetic bearing to the NDB . The seacond indicator will point to VOR station . This help pilot to check the location of the aircraft at that time .

AIRCRAFT NAVIGATION SYSTEM (VOR)

	VERY HIGH FREQUENCY OMNI-RANGE VOR (VHF Omni-Range) is the basic Electronic navigation that in use today . This VHF Omni-Range navigation method relies on the ground based transmitters which emitted signals to VOR receiver. The VOR system operates in the VHF frequency band , from 108.0 to 117.95 MHz. The reception of VHF signals is a line of sight situation . You must be on the minimum altitude of 1000 feet (AGL) above ground level in order to pick up an Omni signals service range. VOR Range VOR Class= Low Altitude 1,000-18,000 feet Range 40 nautical miles VOR Class=High Altitude 1,000-14,500 feet Range 40 nautical miles VOR Class=High Altitude 14,500-60,000 feet Range 100 nautical miles VOR Class=High Altitude 18,000-45,000 feet Range 130 nautical miles OPERATION The VOR facility at ground base transmits two signals at the same time. One signal is constant in all directions as a reference phase. Another signal, it is variable-phase signal and it rotates through 360 degrees, like the beam from the lighthouse. Both signals are in phase when the variable signal passes 360 degrees (reference to magnetic north) and they are 180 degrees out of phase when the rotating signal passes 180 degrees The aircraft equipment receives both signals. The receiver will calculate the difference between the two signals, and interprets the result as a radial from the station to pilots on the aircraft. RADIALS: The two signals from VOR transmitter generate 360 lines like spokes in a wheel . Each line is called a Radial . VOR navigation equipment on the airplane will determine which of those 360 radials the airplane is on. VOR INDICATOR A : Rotating Course Card is calibrated from 0 to 360 degrees, which indicates the VOR bearing chosen as the reference to fly by pilot. B : Omni Bearing Selector or OBS knob , used to manually rotate the course card to where the point to fly to. C : TO-FROM indicator . The triangle arrow will point UP when flying to the VOR station. The arrow will point DOWN when flying away from the VOR station. A red flag replaces these TO-FROM arrows when the VOR is beyond reception range or the station is out. D : Course Deviation Indicator (CDI). This needle moves left or right indicating the direction to turn the aircraft to return to course. DOT : The horizontal dots at center are represent the aircraft away from the course . Each dot represent 2 degrees deviate from desired course. How It Works The followings are just the typical, some aircraft may be vary in details . The pilot can set VOR receiver to selected ground station or another word is to select a radial to define a magnetic course toward or away from VOR station on receiver. The Radial of the VOR receiver is divided into 360 degrees, at the point 360 is representing Magnetic North . When we called out , we called in three digits such as 090 that means on the East and 270 means on the West . The proper time to tune navigation receivers is while the aircraft is on the ground because the pilot has to do the flight planned and known where to go. After takeoff, usually start from altutude of 1000 feet minimum above ground level, the VOR receiver will get signals from transmitter and the flag will show arrow FROM (left picture). When the aircraft has gone half way or close to next VOR station and VOR receiver got that signals from next station . The arrow flag will change from FROM to TO arrow (from right picture) . At this time, pilot should select OBS to Radial of next VOR station. CDI on the indicator shown off center by four dots and that means eight degrees off the course, the pilot must correct the heading of aircraft. If the aircraft out of transmitter range or VOR station not operates, the VOR receiver will show red flag or indication to tell pilot that don't misunderstand because CDI needle will stay at center all the time.

AIRCRAFT NAVIGATION SYSTEM

	NAVIGATION INTRODUCTION Finding the way from one place to another is called NAVIGATION. Moving of an aircraft from one point to another is the most important part for any kind of mission. Plotting on the paper or on the map a course towards a specific area of the earth , in the passed, used to be a task assigned to a specialised member of the aircraft's crew such a navigator. Such a task was quite complicated and not always accurate. Since it depended on the observation , using simple maps and geometrical instruments for calculations. Today, aerial navigation has become an art which nears to perfection. Both external Navaids (Navigational Aids) and on-board systems help navigate any aircraft over thousand of miles with such accuracy that could only be imagined a few decades ago. The Method of Navigation There are three main methods of air navigation. There are: 1. Pilotage , 2. Dead Reckoning , 3. Radio. Pilotage or Piloting is the most common method of air navigation. This method, the pilot keeps on course by following a series of landmarks on the ground. Usually before take-off, pilot will making pre-flight planning , the pilot will draws a line on the aeronautical map to indicate the desired course. Pilot will nots various landmarks , such as highways , railroad tracks, rivers , bridges . As the pilot flies over each of landmark , pilot will checks it off on the chart or map. If the plane does not pass directly over thelandmark , the pilot will know that he has to correct the course. Dead Reckoning is the primary navigation method used in the early days of flying. It is the method on which Lindberg relied on his first trans-Atlantic flight. A pilot used this method when flying over large bodies of water, forest, deserts. It demands more skill and experience than pilotage does. It is based on time, distance, and direction only. The pilot must know the distance from one point to the next, the magnetic heading to be flown. Pilot works on the pre-flight plan chart , pilot plan a route in advance. Pilot calculate the time to know exactly to reach the distination while flying at constant speed. In the air, the pilot uses compass to keep the plane heading in the right direction. Dead reckoning is not always a successful method of navigation because of changing wind direction. It is the fundamental of VFR flight. Radio Navigation is used by almost all pilots. Pilots can find out from an aeronautical chart what radio station they should tune to in a particular area. They can then tune their radio navigation equipment to a signal from this station. A needle on the navigation equipment tells the pilot where they are flying to or from station, on course or not . see sample of aeronautical chart , preflight plan chart : click here Pilots have various navigation aids that help them takeoff,fly, and land safely. One of the most important aids is a series of air route traffic control , operated throughout the world. Most of the traffic control uses a radar screen to make sure all the planes in its vicinity are flying in their assigned airways. Airliners carry a special type of radar receiver and transmitter called a transponder. It receives a radar signal from control center and immediately bounces it back. When the signal got to the ground, it makes the plane show up on the radar screen. Pilots have special methods for navigating across oceans. Three commonly used methods are: 1. Inertial GuidanceThis system has computer and other special devices that tell pilots where are the plane located. 2.LORAN Long Range Navigation The plane has equipment for receiving special radio signals sent out continuous from transmitter stations. The signals will indicate the plane location 3.GPS Global Positioning System. is the only system today able to show your exact position on the earth any time, anywhere, and any weather. The system receiver on the aircraft will receives the signals from sattelites around the globe. TERMINOLOGY ADF Automatic Direction Finder. An aircraft radio navigation which senses and indicates the direction to a Low/Medium Frequency non-directional radio beacon (NDB) ground transmitter. DME Distance Measuring Equipment. Ground and aircraft equipment which provide distance information and primary serve operational needs of en-route or terminal area navigation. EAT Estimated Approach Time EFIS Electronic Flight Instrument System , in which multi-function CRT displays replace traditional instruments for providing flight, navigation and aircraft system information, forming a so-called " glass cockpit ". ETA Estimated Time of Arrival GPS Global Positioning System . A navigation system based on the transmission of signals from satellites provided and maintained by the United States of America and available to civil aviation users. HDG Heading. The direction in which an aircraft's nose points in flight in the horizontal plane, expressed in compass degrees (eg. 000 or 360 is North, 090 is East) HSI Horizontal Situation Indicator. A cockpit navigation display, usually part of a flight-director system, which combines navigation and heading. IFR Instrument Flight Rule . prescribed for the operation of aircraft in instrument meteorological condition. ILS Instrument Landing System . consists of the localizer, the glideslope and marker radio beacons (outer, middle, inner). It provides horizontal and vertical guidance for the approach. INS Inertial Navigation System. It uses gyroscopes and other electronic tracking systems to detect acceleration and deceleration, and computes an aircraft's position in latitude and longitude. Its accuracy, however, declines on long flights. Also called IRS, or Inertial Reference System. KNOT (kt) Standard Unit of speed in aviation and marine transportation, equivalent to one nautical mile per hour. One knot is equal to 1.1515 mph., and one nautical mile equals to 6,080 feet or 1.1515 miles. One knot is equal to one nautical mile per one hour. LORAN C Long Range Navigation is a Long-Range low frequency Radio Navigation. Its range is about 1,200 nm by day to 2,300 nm. by night. MAGNETIC COURSE Horizontal direction, measured in degrees clockwise from the magnetic north. MACH NUMBER Ratio of true airspeed to the speed of sound. Mach 1 is the speed of sound at sea level. Its values is approximately 760 mph. NDB Non-Directional Beacon. A medium frequency navigational aid which transmits non-directional signals , superimposed with a Morse code identifier and received by an aircraft's ADF. RMI Radio Magnetic Indicator. A navigation aid which combines DI ,VOR and /or ADF display and will indicate bearings to stations, together with aircraft heading. RNAV Area Navigation. A system of radio navigation which permits direct point-to-point off-airways navigation by means of an on-board computer creating phantom VOR/DME transmitters termed waypoints. TACAN TACtical Air Navigation. Combines VOR and DME and used by military aircraft only.System which uses UHF frequencies , providing information about the bearing and distance from the ground station we have tuned into. TCAS Traffic Alert and Collision Avoidance System. Radar based airborne collision avoidance system operating independently of ground-based equipment. TCAS-I generates traffic advisories only. TCAS-II provides advisories and collision avoidance instructions in the vertical plane. TRANSPONDER Airborne receiver / transmitter which receives the interrogation signal from the ground and automatically replies according to mode and code selected. Mode A and B wre used for identification, using a four digit number allocated by air traffic control. Mode C gives automatic altitude readout from an encoding altimeter. VFR Visual Flight Rules. Rules applicable to flights in visual meteorological conditions. VHF Very High Frequency. Radio frequency in the 30-300 Mhz band, used for most civil air to ground communication. VOR Very High Frequency Omnidirectional Range. A radio navigation aid operating in the 108-118 Mhz band. A VOR groun station transmits a two- phase directional signal through 360 degrees. The aircraft's VOR receiver enables a pilot to identify his radial or bearing From/To the ground station . VOR is the most commonly used radio navigation aid in private flying. VORTAC A special VOR which combines VOR and DME for civil and military used . System provides information about the bearing and distance from the ground station we have tuned into.

AIRCRAFT PROPELLER CONTROL AND OPERATION (3)

AIRCRAFT PROPELLER CONTROL AND OPERATION Control and Operation (page 3) Hydromatic Propellers Basic Operation Principles : The pitch changing mechanism of hydromatic propeller is a mechanical-hydraulic system in which hydraulic forces acting upon a piston are transformed into mechanical forces acting upon the blades. Piston movement causes rotation of cam which incorporates a bevel gear (Hamilton Standard Propeller) . The oil forces which act upon the piston are controled by the governor Single Acting Propeller: The governor directs its pump output against the inboard side of piston only, A single acting propeller uses a single acting governor. This type of propeller makes use of three forces during constant speed operation , the blades centrifugal twisting moment and this force tends at all times to move the blades toward low pitch , oil at engine pressure applied against the outboard side of the propeller piston and this force to supplement the centrifugal twisting moment toward the low pitch during constant speed operation., and oil from governor pressure applied against the inboard side of the piston . The oil pressure from governor was boosted from the engine oil supply by governor pump and the force is controlled by metering the high pressure oil to or draining it from the inboard side of the propeller piston which balances centrifugal twisting moment and oil at the engine pressure. Double Acting Propeller: The governor directs its output either side of the piston as the operating condition required. Double acting propeller uses double acting governor. This type of propeller , the governor pump output oil is directed by the governor to either side of the propeller piston. Principle Operation of Double Acting : Overspeed Condition : When the engine speed increases above the r.p.m. for which the governor is set . Oil supply is boosted in pressure by thr engine driven propeller governor , is directed against the inboard side of the propeller piston. The piston and the attached rollers move outboard. As the piston moves outboard , cam and rollers move the propeller blades toward a higher angle , which inturn, decreases the engine r.p.m. Underspeed Condition : When the engine speed drops below the r.p.m. for which the governor is set. Force at flyweight is decrease and permit speeder spring to lower pilot valve, thereby open the oil passage allow the oil from inboard side of piston to drain through the governor. As the oil from inboard side is drained , engine oil from engine flows through the propeller shaft into the outboard piston end. With the aid of blade centrifugal twisting moment, The engine oil from outboard moves the piston inboard. The piston motion is transmitted through the cam and rollers . Thus, the blades move to lower angle The Feathering System Feathering : For some basic model consists of a feathering pump, reservoir, a feathering time-delay switch, and a propeller feathering light. The propeller is feathered by moving the control in the cockpit against the low speed stop. This causes the pilot vave lift rod in the governor to hold the pilot valve in the decrease r.p.m. position regardless of the action of the governor flyweights. This causes the propeller blades to rotate through high pitch to the feathering position. Some model is initiated by depressing the feathering button. This action, auxiliary pump, feather solinoid, which positions the feathering valve to tranfer oil to feathering the propeller. When the propeller has been fully feathered, oil pressure will buildup and operate a pressure cutout switch which will cause the auxiliary pump stop. Feathering may be also be accomplished by pulling the engine emergency shutdown handle or switch to the shutdown position. Unfeathering : Some model is accomblished by holding the feathering buttn switch in the out position for about 2 second . This creates an artificial underspeed condition at the governor and causes high-pressure oil from the feathering pump to be directed to the rear of the propeller piston. As soon as the piston has moved inward a short distance, the blades will have sufficient angle to start rotation of the engine. When this occurs , the un-feathering switch can be released and the governor will resume control of the propeller.

AIRCRAFT PROPELLER CONTROL AND OPERATION (2)

AIRCRAFT PROPELLER CONTROL AND OPERATION Control and Operation (page 2) Governor Operation Condition On-Speed Condition The on-speed condition exists when the propeller operation speed are constant . In this condition, the force of the flyweight (5) at the governor just balances the speeder spring (3) force on the pilot valve (10) and shutoff completely the line (13) connecting to the propeller , thus preventing the flow of oil to or from the propeller. The pressure oil from the pump is relieved through the relief valve (6). Because the propeller counterweight (15) force toward high pitch is balanced by the oil force from cylinder (14) is prevented from moving, and the propeller does not chang pitch Under-Speed Condition The under-speed condition is the result of change in engine r.p.m. or propeller r.p.m.which the r.p.m. is tend to lower than setting or governor control movement toward a high r.p.m. Since the force of the flyweight (5) is less than the speeder spring (3) force , the pilot valve (10) is forced down. Oil from the booster pump flows through the line (13) to the propeller. This forces the cylinder (14) move outward , and the blades (16) turn to lower pitch, less power is required to turn the propeller which inturn increase the engine r.p.m. As the speed is increased, the flyweight force is increased also and becomes equal to the speeder spring force. The pilot valve is move up, and the governor resumes its on-speed condition which keep the engine r.p.m. constant. Over-Speed Condition The over-speed condition which occurs when the aircraft altitude change or engine power is increased or engine r.p.m. is tend to increase and the governor control is moved towards a lower r.p.m. In this condition, the force of the flyweight (5) overcomes the speeder spring (3) force and raise the pilot valve (10) open the propeller line (13) to drain the oil from the cylinder (14). The counterweight (15) force in the propeller to turn the blades towards a higher pitch. With a higher pitch, more power is required to turn the propeller which inturn slow down the engine r.p.m. As the speed is reduced, the flyweight force is reduced also and becomes equal to the speeder spring force. The pilot valve is lowered, and the governor resumes its on-speed condition which keep the engine r.p.m. constant. Flight Operation This is just only guide line for understanding . The engine or aircraft manufacturers' operating manual should be consulted for each particular aircrat. Takeoff : Placing the governor control in the full forward position . This position is setting the propeller blades to low pitch angle Engine r.p.m. will increase until it reaches the takeoff r.p.m. for which the governor has been set. From this setting , the r.p.m. will be held constant by the governor, which means that full power is available during takeoff and climb. Cruising : Once the crusing r.p.m. has been set , it will be held constant by the governor. All changes in attitude of the aircraft, altitude, and the engine power can be made without affecting the r.p.m. as long as the blades do not contact the pitch limit stop. Power Descent : As the airspeed increase during descent, the governor will move the propeller blades to a higher pitch inorder to hold the r.p.m. at the desired value. Approach and Landing : Set the governor to its maximum cruising r.p.m. position during approach. During landing, the governor control should be set in the high r.p.m. position and this move the blades to full low pitch angle.

AIRCRAFT PROPELLER CONTROL AND OPERATION (1)

AIRCRAFT PROPELLER CONTROL AND OPERATION Control and Operation (page 1) Propeller Control basic requirement: For flight operation, an engine is demanded to deliver power within a relatively narrow band of operating rotation speeds. During flight, the speed-sensitive governor of the propeller automatically controls the blade angle as required to maintain a constant r.p.m. of the engine. Three factors tend to vary the r.p.m. of the engine during operation. These factors are power, airspeed, and air density. If the r.p.m. is to maintain constant, the blade angle must vary directly with power, directly with airspeed, and inversely with air density. The speed-sensitive governor provides the means by which the propeller can adjust itself automatically to varying power and flight conditions while converting the power to thrust. Fundamental Forces : Three fundamental forces are used to control blade angle . These forces are: 1. Centrifugal twisting moment, centrifugal force acting on a rotating blade which tends at all times to move the blade into low pitch. 2. Oil at engine pressure on the outboard piston side, which supplements the centrifugal twisting moment toward low pitch. 3. Propeller Governor oil on the inboard piston side, which balances the first two forces and move the blades toward high pitch Counterweight assembly (this is only for counterweight propeller) which attached to the blades , the centrifugal forces of the counterweight will move the blades to high pitch setting Constant Speed, Counterweight Propellers The Counterweight type propeller may be used to operate either as a controllable or constant speed propeller. The hydraulic counterweight propeller consists of a hub assembly, blade assembly, cylinder assembly, and counterweight assembly. The counterweight assembly on the propeller is attached to the blades and moves with them. The centrifugal forces obtained from rotating counterweights move the blades to high angle setting. The centrifugal force of the counterweight assembly is depended on the rotational speed of the propellers r.p.m. The propeller blades have a definite range of angular motion by an adjusting for high and low angle on the counterweight brackets. Controllable : the operator will select either low blade angle or high blade angle by two-way valve which permits engine oil to flow into or drain from the propeller. Constant Speed : If an engine driven governor is used, the propeller will operate as a constant speed. The propeller and engine speed will be maintained constant at any r.p.m. setting within the operating range of the propeller. Governor Operation (Constant speed with counterweight ) the Governor supplies and controls the flow of oil to and from the propeller. The engine driven governor receives oil from the engine lubricating system and boost its pressure to that required to operate the pitch-changing mechanism. It consists essentially of : 1. A gear pump to increase the pressure of the engine oil to the pressure required for propeller operation. 2. A relief valve system which regulates the operating pressure in the governor. 3. A pilot valve actuated by flyweights which control the flow of oil through the governor 4. The speeder spring provides a mean by which the initial load on the pilot valve can be changed through the rack and pulley arrangement which controlled by pilot. The governor maintains the required balance between all three control forces by metering to, or drain from, the inboard side of the propeller piston to maintain the propeller blade angle for constant speed operation. The governor operates by means of flyweights which control the position of a pilot valve. When the propeller r.p.m. is below that for which the governor is set through the speeder spring by pilot , the governor flyweight move inward due to less centrifugal force act on flyweight than compression of speeder spring. If the propeller r.p.m. is higher than setting , the flyweight will move outward due to flyweight has more centrifugal force than compression of speeder spring . During the flyweight moving inward or outward , the pilot valve will move and directs engine oil pressure to the propeller cylinder through the engine propeller shaft. Principles of Operation (Constant Speed with Counterweight Propellers) The changes in the blades angle of a typical constant speed with counterweight propellers are accomplished by the action of two forces, one is hydraulic and the other is mechanical. 1. The cylinder is moved by oil flowing into it and opposed by centrifugal force of counterweight. This action moves the counterweight and the blades to rotate toward the low angle positon. 2. When the oil allowed to drain from the cylinder , the centrifugal force of counterweights take effect and the blades are turned toward the high angle position. 3. The constant speed control of the propeller is an engine driven governor of the flyweight type.

Type of propellers

TYPE OF AIRCRAFT PROPELLERS Type of propellers In designing propellers, the maximum performance of the airplane for all condition of operation from takeoff, climb, cruising, and high speed. The propellers may be classified under eight general types as follows: 1. Fixed pitch: The propeller is made in one piece. Only one pitch setting is possible and is usually two blades propeller and is often made of wood or metal. Wooden Propellers : Wooden propellers were used almost exclusively on personal and business aircraft prior to World War II .A wood propeller is not cut from a solid block but is built up of a number of seperate layers of carefully selected .any types of wood have been used in making propellers, but the most satisfactory are yellow birch, sugar mable, black cherry, and black walnut. The use of lamination of wood will reduce the tendency for propeller to warp. For standard one-piece wood propellers, from five to nine seperate wood laminations about 3/4 in. thick are used. Metal Propellers : During 1940 , solid steel propellers were made for military use. Modern propellers are fabricated from high-strength , heat-treated,aluminum alloy by forging a single bar of aluminum alloy to the required shape. Metal propellers is now extensively used in the construction of propellers for all type of aircraft. The general appearance of the metal propeller is similar to the wood propeller, except that the sections are generally thinner. 2. Ground adjustable pitch: The pitch setting can be adjusted only with tools on the ground before the engine is running. This type of propellers usually has a split hub. The blade angle is specified by the aircraft specifications. The adjustable - pitch feature permits compensation for the location of the flying field at various altitudes and also for variations in the characteristics of airplanes using the same engine. Setting the blade angles by loosened the clamps and the blade is rotated to the desired angle and then tighten the clamps. 3. Two-position : A propeller which can have its pitch changed from one position to one other angle by the pilot while in flight. 4. Controllable pitch: The pilot can change the pitch of the propeller in flight or while operating the engine by mean of a pitch changing mechanism that may be operated by hydraulically. 5. Constant speed : The constant speed propeller utilizes a hydraulically or electrically operated pitch changing mechanism which is controlled by governor. The setting of the governor is adjusted by the pilot with the rpm lever in the cockpit. During operation, the constant speed propeller will automatically changs its blade angle to maintain a constant engine speed. If engine power is increase, the blade angle is increased to make the propeller absorb the additional power while the rpm remain constant. At the other position, if the engine power is decreased, the blade angle will decrease to make the blades take less bite of air to keep engine rpm remain constant. The pilot select the engine speed required for any particular type of operation. 6. Full Feathering : A constant speed propeller which has the ability to turn edge to the wind and thereby eliminate drag and windmilling in the event of engine failure. The term Feathering refers to the operation of rotating the blades of the propeller to the wind position for the purpose of stopping the rotation of the propeller to reduce drag. Therefore , a Feathered blade is in an approximate in-line-of-flight position , streamlined with the line of flight (turned the blades to a very high pitch). Feathering is necessary when the engine fails or when it is desirable to shutoff an engine in flight. 7. Reversing : A constant speed propeller which has the ability to assume a negative blade angle and produce a reversing thrust. When propellers are reversed, their blades are rotated below their positive angle , that is, through flat pitch, until a negative blade angle is obtained in order to produce a thrust acting in the opposite direction to the forward thrust . Reverse propeller thrust is used where a large aircraft is landed, in reducing the length of landing run. 8. Beta Control : A propeller which allows the manual repositioning of the propeller blade angle beyond the normal low pitch stop. Used most often in taxiing, where thrust is manually controlled by adjusting blade angle with the power lever.