Forces Acting upon Aircraft During a Turn - Essay Example

Operating Systems Name: University: Tutor: Date: Forces acting upon aircraft during a turn An aircraft in motion will act just like any other object. They need a specific sideward push to make it turn. Shank and Hollister (1994) explain that if aircraft is viewed in a straight and level from its front and at the same time a push is acting on that particular aircraft is visible it will be realised that weight and lift is apparent; that is two forces. Lift does not act directly opposite to the weight of the craft if it were in a bank instead, it will tend to act in the direction of the bank. This basically means that when an aircraft banks then it becomes apparent that lifts tend to act in two distinct direction; upward as well as inward towards the center of that turn. Relating these aspects with Newton’s first law of motion as cited in Federal Aviation Administration (1991) states that when an object is at rest, it will resume that status unless acted upon by some external force(s). Therefore being any other object at rest, it will require specific sideway force to make it turn. Therefore when it has a normal turn (Kuchar, 1996) explains that such force will be made available by ensuring that the craft is banked so as to exert upward and lift inward forces. Beginning with the force of lift, it has two components which act at right angle to each other. Therefore vertical lift component will result from the opposing weight and the upward acting lift. At such point, there will be formation of horizontal lift component as a result of centrifugal force which tends to oppose horizontal acting lift. And since horizontal component of lift (centripetal force) do not act in equal and opposite direction the aircraft will be forced to turn from a straight fligthpath. Then we have centrifugal force which acts equal but in opposite direction to centripetal force. Apparently, centrifugal force comes as a result of inertia. According to Carpenter and Kuchar (1997), it is due to this force that a properly executed turn on an aircraft will make such aircraft to turn without necessarily relying on the supply from rudder. Conclusively, as aircraft expects to execute a turn, parts of vertical lift may act as horizontal component thus if aircraft fails to receive back pressure then it may lose altitude when executing such turn. Figure 1 below extracted from Aerodynamic Factors chapter two shows how these forces acts on an aircraft. Figure 1. Forces used while turning (Courtesy of Aerodynamics Factors; chapter two). Why an aircraft could collide with the ground during a turning maneuver Collision with ground during a turning maneuver may be as a result of mechanical, environmental or fault from the pilot. During turning maneuvers, airstrip may collide with the ground when buffeted with gusting wind. A typical example of such a situation relates to the pilot of the Cessna 182B Skylane (C182) as explained by ATSB. (2004) that this can be realised if it is characterised by strong downslope winds and lee waves. Another possible cause of collision when pilots try to execute turns is the presence of fluctuating airspeed. ATSB. (2005a) also reports that when pilots are unfamiliar with the airstrip they are using and unable to anticipate turbulence in the lee of that particular escarpment could be a possible cause of collision when executing turns. “A collision with ground might sometimes occur when the direction of the turn is not consistent with other conditions such as thick clouds or glaring sun” (Matthews, 2005 pp.58-9). Airstrip can also collide with the ground if the altitude at which it is operating cannot give it sufficient time to recover from a stall. Just like the case in C182 aircraft as reported by ATSB. (2005b), collision with ground can result when there is extreme angles of bank, sudden loss of lift due to turbulence or even when there is repeated retraction of flaps operated manually. Presence of mechanical turbulence is another reason why aircraft can collide with ground during a turn. Mechanical turbulence may not cause the collision directly but when such happens, the aircraft might strike trees or birdstrike if the wing flaps are found to have retracted position. Instruments available to the pilot to help him/her accurately turn the aircraft The instruments are: a. Rudder b. Elevator c. Ailerons d. Inclinometer e. Altimeter i) Ailerons and Rudder Pilots use turns to maneuver a change from and to a desired direction. This turn or maneuver involves using rudder, elevator and ailerons. To begin with ailerons for instance, when pilot wants to enter a turn, s/he will need to turn the control wheel which of course must be done simultaneously when entering a turn. This will be done when there is application of rudder pressure and aileron control pressure. Therefore the application of control pressure will be directly proportional to the speed at which the aircraft rolls into a bank. At such a point, the pilot will need to keep the rudder pressure enough so that the ball of the inclinometer (which is part of the turn coordinator) is centered. On the other hand, if the pilot needs to keep a constant altitude then s/he will need to apply enough back pressure which entails raising the nose of the aircraft which will ultimately increase the angle of attack. When such pressures are applied then there will be prevention of a descent. As the pilot decides on the best angle of the bank, rubber pressure and aileron pressures should be released. At such point, there will be no increase in bank because the aileron control surfaces will be at neutral point in their streamlined position. ii) Elevator Another important instrument is the elevator whose pressure should not be released but at some point be increased or kept constant so as to maintain altitude. It is also important to note that throughout the turn outside references should be cross-checked regularly and may be a check on the altimeter to determine if the pitch attitude is functioning. Checking pitch attitude is important because when losing or gaining altitude pitch, attitude may be adjusted in accordance with the horizon before rechecking on vertical speed indicator and altimeter to affirm that altitude is now being maintained. As the angle bank decreases, (Koczo 1996) explains that the elevator pressure at elevator should be smoothly released so as to maintain altitude. At this point though, it is important to note that when aircraft is no longer banked there will be increase in vertical component of the lift. As the pilot completes roll out, there should be attention to visual references from outside as well as to the indicator to ensure that the wings are at level and the turn is stopped. ATSB accident reports The first fatal accident reported by ATSB. (2006a) includes the pilot of Cessna 182B Skylane (C182) with one passenger who was on board. From the evidence as cited in Australian Bureau of Statistics. (2006a) the craft carried enough fuel for the flight. According to the eye witness the aircraft was seen turning left onto its final approach at about 50-80 ft AGL. Information added by the witness is that all turns that were made by the craft were at about450 angle of bank. To describe my first factor regarding the accident suffered by aircraft, the witness reported that the aircraft was buffeted by what is described in the report as “gusting winds”. Therefore I strongly suggest that key factor that caused the accident when it was trying to turn was the strong winds which was blustery. To further underscore the above cause, a Bureau of Meteorology assessment as cited in ATSB. (2006b) reports that there were gusty north-westerly winds. At its time of crash, it was observed to lose altitude, turned through 2950 before impacting the ground. Another case as reported by Bureau of Transport and Regional Economics. (2005) relates to the accident that C182 faced at low altitude while trying to approach Turalla. The report suggests that the main cause of this accident was its wings which were seen rocking from one side to another. The rocking of the wings was consistent with turbulence produced in the escarpment through the strong wind. According to the report, due to airspeed fluctuations, the approach became unstable within that turbulence. Therefore being unaware of the turbulence in that escarpment may have prompted the pilot to try right turn instead of climbing ahead which of course could have put the aircraft into increased turbulence. However, the report cites that the accidents might have also been triggered by memory of the pilot’s siblings. In addition to that, the aircraft was operating at altitude which was not having sufficient space to allow its recovery. It was also noticed that the accident occurred during the turn because there was either extreme angles of bank, rapid retraction of flaps which were manually operated or sudden loss of lift from turbulence. There was also strong indication that the aircraft might have stalled and slipped out of the turn because it was in a steep left turn. Such evidence was possible due to the nose down pitch attitude and steepness of the angle of its bank. On the accident, report suggests that because the aircraft did not rotate at the impact there was little time for the stall to develop into its spin. The report concluded that the aircraft might have stalled at a height where the pilot could not effect recovery. References ATSB. (2004). General aviation fatal accidents: How do they happen? (Aviation Research Paper No. B02004/0010). Canberra: Australian Transport Safety Bureau. ATSB. (2005a). 2005 annual review. Canberra: Australian Transport Safety Bureau. ATSB. (2005b). Aviation safety indicators: A report on safety indicators relating to aviation safety (Aviation Research Investigation Report No. B2005/0046). Canberra: Australian Transport Safety Bureau. ATSB. (2006a). Analysis of fatality trends involving civil aviation aircraft in Australian airspace between 1990 and 2005 (No. B2005/0388). Canberra: Australian Transport Safety Bureau. ATSB. (2006b). International fatality rates: A comparison of Australian civil aviation fatality rates with international data (No. B2006/0002). Canberra: Australian Transport Safety Bureau. Australian Bureau of Statistics. (2006a). 2006 Queensland at a glance (No. 1312.3). Canberra: Australian Bureau of Statistics. Bureau of Transport and Regional Economics. (2005). General Aviation: An industry overview (No. 111). Canberra: BTRE. Carpenter, B. D., and J. K. Kuchar, (1997). A Probability-Based Alerting Logic for Aircraft on Parallel Approach", NASA Contractor Report 201685, Hampton, VA, April. Federal Aviation Administration, (1991). Precision Runway Monitor Demonstration Report, Document DOT/FAA/RD-91/5, Washington, D.C., February. Koczo, S., (1996). Coordinated Parallel Runway Approaches, NASA Contractor Report, NAS1- 19704 - Task 11, Hampton, VA, May. Kuchar, J. K., (1996). Methodology for Alerting-System Performance Evaluation, AIAA Journal of Guidance. Control, and Dynamics. Vol. 19, No. 2, March-April. Matthews, S. (2005). The changing face of aviation safety. Paper presented by the President and CEO of the Flight Safety Foundation at the Safety in Action Conference in Melbourne, 21 March pp.58-9. Shank, E. M., and K. M. Hollister, (1994). Precision Runway Monitor", Lincoln Laboratory Journal, Vol. 7, No. 2, MTT Lexington, MA. SCA1125D – Operating Systems Assignment Marking Guide Name: ____________________­­­_______ Student ID:______________ Turning – 55 marks POOR SAT GOOD VERY GOOD Forces acting on the aircraft in a turn (20 marks) Factors in terrain collision (20 marks) Instruments for pilot guidance during a turn(15 marks) Examples from Industry – 30 marks POOR SAT GOOD VERY GOOD Description of the accidents (10 marks) Factors leading to aircraft crashing while turning (20 marks) Presentation – 15 marks POOR SAT GOOD VERY GOOD Expression (3 marks) Mechanics (spelling, Grammar, etc) (4 marks) Referencing (4 marks) Structure (format and logical sequence) (4 marks) Not following Submission Requirements: - 10 marks Overall Comments and Result: ________________________________________________________________ ________________________________________________________________ ________________________________________________________________ ________________________________________________________________ Read More