CAT Aircraft Make Use of Weather Radar - Assignment Example

Assignment Brief CAT aircraft make use of weather radar. a) Provide a diagram and refer to it when explaining the principle behind Radar mark) Radar is used to detect an object that specifically uses radio waves. It is, therefore, used to determine or measure certain parameters like speed, altitude, direction, as well as the range of objects. Objects such as missiles, weather formations, ships, vehicles and aircraft among others, are some examples of such objects that are radar is used to detect. Radar can be said to be a dish or antenna used to transmit radio wave or microwave pulses. Such are the pulses that normally bounce off the objects that come in their path. There’s always a small part of the energy of the wave to the antenna that is normally placed at a similar site where the transmitter usually is placed. Clear-Air Turbulence (CAT): when air masses have a turbulent movement where there are no visual cues that look like the clouds. The meeting of the air actually is the cause if the turbulence and this air move widely at different speeds. It is not easy for the standard airplane radars to detect CAT. This because CAT should have some association with the clouds that normally show a movement of air that cannot be predicted. When with cloud covers, the Clear-air Turbulence normally appears differently. This makes it not to be visible for both the eye and again; it cannot be measured with the sensors. Research shows that a similar turbulence is likely to occur in the future several times or repeatedly because of a change in climate. As a normal happening, there’s an occurrence of wind shear along the stream of the jet. In this case, several layers of air that are extended normally move in a horizontal manner, going against one another and taking totally different speeds. It is proved that strong wind shear can also create breaking waves such as those waves found on water. Due to the breakages of such waves, there is normally the creation of vortices in the air or turbulence which are associated with clear air. When there are lights and ranging instruments that are installed in the aircraft, laser-based is the one responsible for detecting such. To determine the density of the air, there’s the use of the backscatter values that are measured for air molecules, nitrogen and oxygen. This is also enabled through the emission of UV short-wave radiations following the flight direction. The information on turbulence, mostly in distant areas, is then provided by the fact that there is a fluctuation in the density. This usually makes it just for the first time to be visible and very predictable. UV laser radiations are emitted by a lidar instrument that can be installed when one is on the aircraft, and this emits radiations in the direction of the flight. Again, as has been discussed, the backscatter value for air molecules, nitrogen and oxygen is responsible in finding the air density.. When this density begins to fluctuate, it is possible to know the turbulence information. b) Using the diagram in a), explain how the radar principle is used in airborne weather equipment in a CAT environment. (2 marks) To meet those limitations for weight, as well as those for strict space, airborne radar comes in very useful. Such are very necessary for all the equipment for airborne. Still the same, the radar sets of airborne are said to develop peak power that is similar to the peak power found with the sets of the shipboard and the shore-based. Airborne radar sets are also made in different many models that are similar to the shipboard radar, in order to attend to different purposes. As for these sets, some of them are normally attached to blisters, also known as domes and normally form part of the fuselage, while others are attached to the aircraft’s nose. The main purpose of radar in the fighter aircraft is so that it can act as an interceptor and destroy the enemy aircraft. However, for this to be done, the radar system of the aircraft should be tracking enabled. A part from the mentioned ones, airborne radar also has some other purposes including, use in bombing, control of missiles, navigation of the aircraft as well as early warnings of the airborne. c) Explain the weather radar display, relating relevant characteristics of the display (e.g. range, colours etc.) to the flight path of the aircraft and atmosphericConditions. (2 marks) Talking about weather radar display, it is responsible in sending directional microwave radiation pulses. This happens on the order that takes microsecond long and uses a cavity of magnetron or klystron tube. This tube is usually connected using a waveguide to the parabolic antenna. It is because of the Rayleigh scattering that occurs at certain frequencies that the wavelengths of 1-10 cm become almost equal to the diameter of the ice droplets or particles of interest. It only means that, back in the direction facing the radar station, there’s part of the energy of each pulse that will have to bounce off the named particles. Reflectivity on a Radar Display Colour and level are used to describe the returns of radar. Weak returns, for example, are normally described using colour range of blue to green. On the other hand, very strong returns are described using the colour range of red to magenta. The severity of the return normally shows the increase in the numbers in a verbal report. As an example, the National Doppler Radar sites of the U.S. use different scales for different reflectivity levels. Some of the scales include, yellow for 36 Dbz, red for 52 Dbz, green for 20 Dbz and magenta for 65 Dbz. A part from heavy rains being indicated by the strong returns symbolized by the red and magenta colours, strong winds, thunderstorms and hail can also be indicated by such. However, a careful interpretation is required for several reasons, some described below. d) Aircraft may fly through extremely unstable air, with multiple occurrences of, and build-ups of, cumulonimbus clouds. Describe likely conditions in flight in and around the cumulonimbus clouds (2 marks) Cumulonimbus can be regarded as the main source of danger in flight given the reason of turbulence and heavy precipitation. and explain the limitations of weather radar in these circumstances and (2 marks) Hail It is a major threat, because weather radar does not indicate the nature of returns. Only the knowledge of a Cumulonimbus’s structure and the observation of different clues can help. The presence of hail within a Cumulonimbus varies with altitude and wind. Below FL100, hail is very likely to be encountered under the storm, can be in the cloud or better still around it (up to 2NM) and between FL 100 and FL 200, 60% t of hail is encountered in the Cumulonimbus and 40 % is encountered outside the cloud, under the anvil, above FL200, hail is likely to be encountered inside the cloud. Indeed, moisture is driven upward by strong drafts. It then freezes and is transformed into hail, before being blown downwind. When possible, it is better to try to avoid a storm by flying on the upwind side of the) Cumulonimbus. It is however considered that less risk normally exists of hail in places which are of humid air than those of dry air. It is even considered that moisture sometimes act as a heat conductor, hence it helps to meet the hail. How, in daylight, could aircrew seek to avoid extremely turbulent conditions? (1 mark) Turbulence Turbulence caused as a result of Cumulonimbus should not only have a limit to the cloud. It is very important to take precautionary measures as weather radars are not able to detect turbulence in clean air. In order to reduce the possible risk of meeting a severe turbulence, a Cumulonimbus needs to be cleared by a minimum of 5 000 ft vertically and 20 NM laterally. Lightning is a very strong indicator of severe turbulence. The radar does detect rainfall, Wet hail and wet turbulence, ice crystals, dry hail and dry snow, though, these three elements give small reflections, as explained below. The radar does not detect clouds, fog or wind, when droplets are too small, or when no precipitation at all clear air turbulence (no precipitation). 2. CAT aircraft are designed and certified to operate within a range of climactic conditions. a) What are the reference parameters for atmospheric conditions? (2 marks) In order to maintain stability, the level flight aircraft normally rely on a constant air density. CAT can always occur where there is significance of air density due to the temperature gradient more so at the tropopause. A horizontal gradient of temperature can always be experienced especially when an aircraft goes through changing its position horizontally from within, to outside or vice versa. The change, of course, by the aircraft should not be resulted into by a change of position since the streams of jet normally meander. The aircraft can traverse an altitude of the tropopause that is not constant and encounter any associated CAT. It is important for the pilot to communicate the position of the aircraft including the velocity, of turbulence and the altitude to the air traffic control. This is to warn other aircraft that might be entering the region. Sudden accelerations that are not expected, or bumps from the turbulence may be experienced since the aircraft moves very quickly. b) Explain the conditions that can lead to ice formation on an aircraft in the air. (1 mark) The droplets of the super cooled liquid water that are contained in the air normally causes icing. This is normally characterized by the average sizes of the droplets, temperature of the air and the content of liquid water. Such factors normally affect the speed as well as the extent of ice formation on the aircraft. c) How is ice detected on an aircraft on the ground? (1 mark) Ice is detected on an aircraft on the ground using an instrument known as ice detector. This instrument is always referred to as an optical transducer probe available for aviation job. This does not have any moving part as it is entirely solid and uses the optical principle. The instrument uses un-collimated light to monitor the optical capacity and the refractive index of the object being probed. It should be desensitized in order to ignore a water film. d) Using a diagram of a suitable detector, explain how ice is detected on an aircraft when airborne. (2 marks) I. MAGNETOSTRICTIVE ICE DETECTOR - The frequency of the resonant may sometimes reduce due to accreting of the ice on the probe. - the ice signal is activated and the strut and probe are supposed to be de-iced and this is caused by a reduction of the probe frequency lower than a predetermined threshold. 2. Lucas Mk 3 Series Ice Detectors The Lucas system uses a cylindrical collecting head that rotates close to a stationary cutting edge. This system is designed for fixed wing aircraft The Lucas Mk 3 series ice detectors consist of a small electrically driven cylinder upon which ice may collect. Part of the cylinder is exposed to the super cooled icing airflow. A knife-edge cuter that operates close to the cylinder is used to detect the presence of ice. .The ice build-up initiates a shaving action which increases the torque on the electric motor that is driving the cylinder. The torque on the motor under non-icing conditions is negligible. The shaving action, however, causes the motor to rotate slightly within its mounting against a spring pressure. This movement of the motor operates a micro-switch, the signal from which may be used to light a warning lamp or other signal or to initiate the operation of a de-icing or anti-icing system. This unit is capable of continuous operation, or could be made to go off and on at the pilot’s discretion. The collecting head is self-cleaning and requires no heating. In flight ice detector for aircraft to provide an indication of the onset of icing conditions or to automatically initiate aircraft de-icing or ant icing systems. i. With the aid of a suitable diagram, describe a CAT aircraft airframe anti-icing system in a descent below FL 200. (2 marks) ii. With the aid of a suitable diagram, describe a CAT aircraft airframe de-icing system in a cruise at FL180. (2 marks) There are three purposes that are served by aircraft frame De-icing procedures. These include removal of any frozen and semi frozen moisture from the aircraft surfaces and protection of the aircraft surfaces from the effects of contaminants that can occur between treatment and becoming airborne. 3. Use diagrams to explain the function and operation of a basic CAT aircraft Pitot-static system down to component level. a) With the aid of a suitable diagram, explain the basic operation of the airspeed indicator (ASI) (2 marks) This is an instrument used in an aircraft to display the speed of the aircraft. It records the speed in Knots to the pilot. It also measures the difference in pressure found around the craft and when the pressure is increased by propulsion. The ASI also is considered as the pitot-static system of aviation instrument which operates through measuring pressure in the pitot as well as in the static circuits Figure of Airspeed indicator connection Figure of the Internal mechanism of an airspeed indicator b) Explain at least 2 of the errors affecting the accuracy of an ASI some of which may be corrected during the Pitot-static system design phase. (2 marks) Errors in Airspeed Indicator Errors and Abnormal Operation The most-pronounced problem with the Pitot-static is the situation of blockage of the Pitot tube, or the static ports or both together. The blockage of the static port of the pitot tube is considered to be the greatest and most dangerous error that can be found in association with the airspeed indicator. The pitot tube blockage makes the drain hole to remain clear and the airspeed to read zero. On the other hand, the pitot tube and pitot tube hole blockage causes the airspeed to act like an altimeter, hence recording higher speeds when the altitude goes higher. Another error of the ASI is that of the metal fatigue. This error usually deteriorates the elasticity of the diaphragms. This can also cause errors in static pressure measurements. This error is corrected through position error correction (PEC) and it varies in accordance with aircrafts and different aircraft speeds. c) With the aid of a diagram, explain the principle and operation of an altimeter.(2 marks) The altimeter is the kind of instrument which is used professionally by the metrologists and leisure sports people. It is hence very useful in finding out the height of buildings and structures. However, it is also used in kite flying and hiking. Principle of Operation Pressure altimeter is defined as an aneroid barometer used to measure atmospheric pressure at the location of the altimeter. It gives the reading of the altitude in feet. It uses the static pressure as a source of its operation. It is a fact that air is denser at sea level than it is at aloft. This follows the fact that, as pressure in the atmosphere decreases, the altitude increases. The continuous change in pressure at different levels is what causes the altimeter to indicate changes in altitude. The AL sometimes is used as a barometer as it is also supplied with static pressure from the ports that are static. d) With the aid of a diagram, explain the difference between a vertical speed indicator and an altimeter. (2 marks) I. Vertical speed indicator(VSI) Figure of a vertical speed indicator VSI is a covered diaphragm which is connected to the static port and a case of the surrounded instrument which is also sealed. It supplies static air pressure with a leak that is metered at the case’s back, and this measures more gradual changes in pressure. This shows clearly that, in case the plane continues to climb, the pressure might not be able to catch up to each other, thus allowing for the reading about the rate to be measured on the face of the instrument. The VSI dial will return to zero showing the level of the flight just immediately the aircraft will level off, the pressures that come from both the static pressure and the metered leak from the inside of the diaphragm will equalize. Principle of Operation VSI operates independently away from the static pressure. However, it is still known as a differential instrument for pressure. This has a diaphragm with a linkage that is connecting and gears to the pointer of the indicator that is found inside an airtight case. The static line of the pitot-static system is linked directly with the inside of the diaphragm. Within the instrument, which is the outer part of the diaphragm is again connected to the static line. However, this is done through a restricted orifice. II. An Altimeter On the other hand, an altimeter is defined as an instrument that measures the aircraft’s height which is above a particular pressure level. This instrument is the sole instrument that can indicate altitude. Hence, its one of the most very important instruments being installed in an aircraft. e) Explain the consequences, in terms of instrument readings only, of a blocked static source during the flight phase of climb. (2 marks) Blocked Pitot System In case the pitot tube remains open in either partial or complete blockage, it has an associated hole that remains clear. This bar rams air from entering the pitot system. The air in the system already usually vents through the drain hole. In that case, the remaining pressure usually drops up to the ambient air pressure. These effects make the ASI reading to drop to the zero level. This is because the ASI normal senses no difference between the ram and the static air pressures. ASI sometimes fails to operate since the pressure that is dynamic cannot get into the pitot tube opening. On the other hand, the static pressure has the ability Reference 1. EYERS, C.J., ADDLETON, D., ATKINSON, K., BROOMHEAD, M.J., CHRISTOU, R., ELLIFF, T., FALK, R., GEE, I., LEE, D.S., MARIZY, C., MICHOT, S., MIDDEL, J., NEWTON, P., NORMAN, P., PLOHR, M., RAPER, D., STANCIOU, R., 2005. AERO2K GLOBAL AVIATION EMISSIONS INVENTORIES FOR 2002 AND 2025.QINETIQ/04/0113. FARNBOROUGH, UK). 2. EYRING, V., KO¨HLER, H.W., VAN AARDENNE, J., LAUER, A., 2005. EMISSIONS FROM INTERNATIONAL SHIPPING: 1. THE LAST 50 YEARS. J. GEOPHYS. RES. 110, D17305. DOI:10.1029/ 2004JD005619 Read More