Aircraft Electrical and Mechanical Systems - Case Study Example

Aircraft Electrical and Mechanical Systems: Aircraft Electrical Systems Aircraft Pitot-Systems Part 1: Pressure basics 1. The total pressure in a moving body of air This is also referred to as Wind load F = A × P × cd F - Represents force A – area P – Wind pressure Cd – drag coefficient Further modification of the formula developed by Electronic Industry Associations F = A × P × cd × Kz × Gh The new formula factors in Kz, which represents the exposure coefficient Kz= [z/33] ^ (2/7) z- Is the height from ground to center of the object Gh represents the gust response Gh = 0.65 + 0.60/ (h/33) ^ (1/7) h- Being the height of the object 2. Dynamic pressure in an inflow Pd = 1/2pv2 Where Pd – dynamic pressure (Pa) p – Density of fluid (Kg/m3) v- Velocity (m/s) Common densities used in the calculation Water – 00C– 1000kg/m3 320F – 62.4lbm/ft3 Air – 200C – 1.2 kg/m3 590F – 0.0765lb/ft3 Dynamic pressure can be explained as the kinetic energy that is contained in a unit volume of a fluid particle. In other words, dynamic pressure can be explained as the conservation of energy by a fluid that is in motion. The formulae are derived after first understanding that dynamic pressure is represented by the difference between static pressure and stagnation pressure[CITATION Cla75 \p 63 \l 1033 ]. 3. Static pressure Static pressure is a component of the Bernoulli’s equation. The Bernoulli equation is represented as Po = P + 1/2pv2 From the equation Po – total pressure along any streamline p – density of fluid v – flow velocity P – static pressure pv2 – dynamic pressure From this equation, we can therefore derive the static pressure equation Po = P + 1/2pv2 P = Po – 1/2pv2 = static pressure Static pressure can be defined differently depending on the setting such as fluid dynamics, design, and maneuver of aircrafts. However, it should be noted that static pressure is not a veritable pressure, as regular tools such as mercury column of aneroid cannot measure it quantitatively. This is why, the name static to distinguish it from other concepts such as dynamic and absolute pressure. 4. Variation of atmospheric pressure with altitude Atmospheric pressure reduces with height and vice versa. The main explanation for this phenomenon is that Air has weight, and it is this weight exerted on a unit area of a surface that is known as pressure. The atmospheric pressure can be defined as the total force or weight by an air column at a point or area. Moving up means the air column is reducing resulting into less weight due to less air. Therefore, the pressure becomes less, which explains why atmospheric pressure reduces with height. 5. Mathematical relationship between pressure and altitude Air presses on us more when at sea level that when on a mountaintop. This because at sea level the air pressure is approximately 14.7 lbs. /in2 and this value reduces as one goes up. Pressure varies significantly as one moves from the earth’s surface upwards to the top of the atmosphere. At higher altitudes, there is less air resulting less weight and consequently less pressure. Therefore, mathematically the density and pressure of air reduces with elevation. fraction of 1 atm average altitude (m) (ft) 1 0 0 1/2 5,486.3 18,000 1/3 8,375.8 27,480 1/10 16,131.9 52,926 1/100 30,900.9 101,381 1/1000 48,467.2 159,013 1/10000 69,463.6 227,899 1/100000 96,281.6 283,076 Fig 1.0 the table is compiled by NASA: it gives an estimate of air pressure across various altitudes. 6. Mathematical relationship between forward airspeed and pressure Airspeed refers to the speed of an aircraft comparative to the air. Airspeed is measured ordinarily on board an aircraft using an airspeed indicator that is connected to a pitot-static system. The relationship between pressure and airspeed is that the function of calibrated airspeed is part of the compressible impact pressure. It is also important to note that, at sea level pressure, the rate of equivalent airspeed is equal to calibrated airspeed. Part 2: Aircraft Pitot/Static measuring device 1. Description of types of basic pitot/static probes found on most 1st and 2nd generation aircraft 1st and 2nd generation aircrafts relied on non-compensating pitot tubes. These tubes were also associated with errors in static pressure measurements. 2. Description of types of pitot/static probes on 3rd generation aircrafts Modern aerodynamic pitot tubes have an ogival shape[CITATION Cla75 \p 97 \l 1033 ]. The shape is because of the formation of a quadratic polynomial profile. Example of this pitot tubes includes the S type and type L pitot tubes Part 3: Pitot/Static Instrument System 1. Mechanical air speed indicator An airspeed indicator displays the airspeed of the aircraft in knots, which is mostly read by the pilot. It works by measuring the difference in pressure that surrounds the aircraft and the rate of increase in pressure caused by propulsion. Fig. 1.1 Diagram showing the readings on a true mechanical airspeed indicator Fig. 1.2 Sketch showing all the parts of an airspeed indicator 1. Types of airspeed indications a. Indicated airspeed (AIS) b. Indicated airspeed (AIS) is the direct reading indicated by an aircrafts airspeed indicator before any corrections on the position, instruments, and other related errors. c. Calibrated airspeed (CAS) refers to the final airspeed shown on the airspeed indicator after major corrections have been made such as correction of position error that is caused by inappropriate pressure. Another adjustment is the correction of the instrument errors. d. Equivalent airspeed (EAS) is the airspeed measured at sea level marked by the International Standard Atmosphere. At this point, the measure dynamic pressure is equivalent to the altitude and true airspeed of the aircraft. d. True airspeed (TAS) it is also referred to as KTAS standing for knots true airspeed. True airspeed is the aircraft’s speed relative to its air mass in which the aircraft is flying. This information plays a substantial part in accurate triangulation of an aircraft 3. Mechanical altimeter an altimeter is an instrument mostly used in aircrafts to indicate elevation a good example is an aneroid barometer. It works by sensing pressure changes together with accompanying changes in altitude and indicating them on a scale for readability by the user e.g. pilot. Fig. 1.3 An aneroid barometer illustration showing how an altimeter works 4. Pressure altitude readings a. QNH – is the mean-sea-level (msl) pressure resulting from the barometric measured at the station by computing the weight of an unreal air column covering from the station to the sea level b. VFR – are a set of regulations that a pilot guide a pilot in operating an aircraft. c. QNE – can be described as the altitude readings on the altimeter when the aircraft touches down and the altimeter sub-scale set at 1013. Alternatively, in other terms it is the accepted ISA standard pressure set at 1013.2 hPa. 1. Operation of a basic electronic flight instrument system, including the air data computer, and the EFIS system The EFIS is a flight deck display system, which uses electronic technology rather than electromechanical[CITATION Cla75 \p 147 \l 1033 ]. A distinctive EFIS system consists of an Electronic Horizontal Situation Indicator (EHSI) and Electronic Attitude Direction Indicator (EADI); however, some designs integrate these two components. The EADI is attached direct to the autopilot with its display serving as a monitor that the pilot uses to observe the flight progress. The EADI additionally provides the necessary steering information that the pilot can follow. The EHSI is a single instrument that replaces several instruments that are preferably found on conventional aircrafts. The EHSI performs distinct functions including aeronautical map, weather information, heading flown, distance, time to go, and ground speed. Part 4: Jetstream 31 Pitot/Static System 1. Various components of the Jetstream 31 Pitot/Static system Fig. 1.4 Illustration of Jetstream 31 pitot-static system Part 4: Jetstream 31 Pitot/Static System 1. Various components of the Jetstream 31 Pitot/Static system 2. Operation of the Jetstream 31 pitot/static system a. Air data computer (ADC) – this is a pivotal avionics instrument, which is more of a computer found in the modern day glass cockpits. It is used to determine Mach number, altitude, calibrated airspeed, altitude trend using data from various aircraft instruments. b. Pitot tube – a pitot tube is used for measuring fluid flow velocity, it is a pressure measurement instrument c. ASI – the ASI measures and indicates the forward speed of an aircraft on the pitot system d. Altimeter – is used to determine the variations in air pressure that occur when there are changes in the aircraft’s altitude e. VSI – this instrument is used in the pitot system to indicate whether the aircraft is flying at a level flight or not f. The over-speed warning switch – this switch functions on the pitot system when the red lines in the airspeed/Mach are reached g. Cabin differential pressure gauge – is used as an indicator that displays the difference in between outside and inside pressure h. Drain trap – used to drain water that gets trapped and blocks the pitot system i. Static vents – these connect the altimeter to the static port j. Discharge valve – is used for regulating cabin pressure of an aircraft by means of differential valve 3. The pitot-static consists of equipment that measure various forces that are acting on the aircraft because of pressure, temperature, viscosity and density of the fluid in which it is operating. Using this information and properly working Pitot-static system helps the pilot determine altitude, Mach number, altitude trend, and airspeed. 4. When there are errors in the pitot-static system, it is very difficult to get readings, which is an extremely dangerous situation. Pitot-static system failure has been linked to individual airline disasters. Part 6: Compare and Contrast Pitot-static system 1. Main difference between lifeless and electrical pitot-static instruments system The mechanical system uses manual individual instruments to calculate and compare each component of data such as calculating the rate of climb, Mach number, and airspeed. The electrical system air data computer (ADC) to do all the calculation and comparison and finally display the final data on a central monitor. 2. State main differences in maintenance techniques between maintaining mechanical and electrical pitot-static instruments Maintenance of mechanical system are difficult and complex as compared to an electrical system. This is because, in a mechanical system, each component is on its own while that of an electrical system is centralized with component incorporated. 3. The main difference in the backup system of electrical and mechanical pitot-static system the backup system for the electrical system is simple and much preferred as compared to that of the mechanical system. Mechanical backup can become handy because, in case of technical failure, it is easy to recover on a mechanical system that an electrical system References CITATION Cla75 \p 63 \l 1033 : , (Clancy, 1975, p. 63), CITATION Cla75 \p 97 \l 1033 : , (Clancy, 1975, p. 97), CITATION Cla75 \p 147 \l 1033 : , (Clancy, 1975, p. 147), Read More