The Aerodynamic Forces Acting upon an Aircraft During a Turn - Assignment Example

1. Discuss the aerodynamic forces acting upon an aircraft during a turn. Banking brings about the aircraft turning force due to the fact that when the aircraft banks the lift will act in the inward towards the center of the turn in addition to having a component which acts upwards. If an aircraft is in a straight and level flight it can be visualized that the lift and the weight of the plane will be the two forces acting on the plane. When the aircraft is banked the lift seizes to act in the direct opposite direction of weight and instead it will act in the direction of the bank. It is a basic principal that an object which is at rest or moving in a straight line remains will in its state unless there is an external acting on it. The plane being like any other object moving in a straight line must be supplied with sideward force so as to make it turn. Normally in aircraft the turning force of the aircraft will be provided by the banking. Banking will bring about a situation where the lift is exerted both inward and upward. During the turn there is a separation of lift into two components that act at right angles to each other. The component acting vertically opposite to the weight of the aircraft is called centripetal for or the vertical component of the lift. The horizontal component of lift makes the aircraft to be pulled away from a straight flightpath thus making it to turn. During turning centrifugal force which is the equal and opposite reaction to the change of the aircraft direction emerges. The centrifugal is equal and opposite of centripetal force. From this it is clear that in a situation where a turn is well executed, the force used in turning the plane is not supplied by the rudder. Unlike automobile and boats where steering is used to effect turning, in aircrafts turning can only be realized by banking because there is no any other available force. Conversely banking of a plane will automatically result in turning as long as there is no slipping in the inside of the turn. Good directional control of the aircraft is based on the fact that there will be turning attempt of the plane whenever there is banking. This therefore makes it important for this fact to be put in mind always especially when attempting to put the plane in a straight line. 2. Describe why an aircraft could collide with the ground during a turning manoeuvre. The first thing that need to be noted is that by banking an airplane to make it turn will not in any way bring an increase in the total amount of lift developed. But the lift is divided the vertical and the horizontal components. Because of this division there is reduction in the actual lift that is supposed to support the airplane’s weight and this will result into the lose of altitude by the plane unless there is creation of additional lift. This is usually by increasing the attacking angle up to the point the vertical component of the lift becomes equal to the weight of the aircraft. Due to the fact the vertical component of lift will reduce with the increase in the bank angle, there is need for the angle of attack to be increased progressively so as to produce sufficient vertical lift that is sufficient to support the weight of the plane For a given airspeed, the aircraft turning rate is dependant on the magnitude of the horizontal component of the lift. The horizontal component of the lift is proportional to the angle of bank as it increases or decreases with increase or decrease in the bank angle. This means that with increased bank angle there is an increase in the horizontal component of lift which increases the rate of turn. This means that at a given air speed the turning rate can be controlled through adjustment of the angle of bank. In order to have a vertical component of lift that is sufficient to keep altitude in a level turn there is need to have an increase in the angle of attack. But because the airfoil drag is proportional to the angle of attack, there will be increased drag with increased lift. This will in turn will cause reduction in airspeed that is proportional to the angle of bank; small reduction in airspeed will result where there is a small angle of bank and a large reduction in air speed will be caused by a large bank angle. There will be need to have additional power (thrust) to ensure that the airspeed does not reduce in level turns, where the additional power will be proportional to the angle of the bank. Suppose there is no increase in power the reduction in air speed will reduce the lift and thus the vertical component of lift will not be sufficient to balance the weight of the aircraft. This will therefore bring the plane down. The rate of turning will dictate the amount of power required to sustain it. If the plane makes a very sharp turn that it cannot provide the power to sustain it the plane will definitely loss altitude. 3. List and describe instruments that are available to the pilot to help him/her accurately turn the aircraft. Vertical speed indicator The vertical speed indicator is also known as a vertical velocity indicator (VVI). The instrument will indicate whether the aircraft in level flight, descending or climbing. The rate at which the aircraft is climbing or descending is given by the instrument in feet per minute. This instrument is important as it will give the pilot information if the aircraft is loosing height. The rate at which the plane is loosing height will help the pilot decide how much lift is required to keep the plane in level flight. This will be done by increasing the angle of attack of the aerofoil and increasing the power supply. If the plane keeps on descending it may mean that the pilot need to reduce the rate of turning as this is a clear indication that the plane is not able to negotiate the turn. The vertical speed indicator is a differential pressure instrument even though its operation is solely from static pressure. The instrument has a diaphragm that has linkage and gear system to indicator pointer which is in an airtight case. There is a direct connection of the inside of the diaphragm to the static line of the pitot-static system. There is also connection of the area outside the diaphragm that is within the instrument case but the connection is through a restricted orifice. The diaphragm and the case get air via the static line at the atmospheric pressure. In the case where the plane is in a level flight or on the ground the inside pressure of the diaphragm and the case of the instrument will remain the same with the pointer being at zero. When the plane descents or ascends there is a pressure differential which is indicated on the instrument needle either as a descent or a climb. The attitude indicator The attitude indicator is an indication of the attitude of the plane pictorially by use of miniature airplane and a horizontal bar. The miniature airplane and the horizontal bar relationship are the same as the relationship between the real aircraft and the horizon. This instrument will give the pilot an instantaneous indication of changes in attitude. This instrument will be very important for the pilot as it will indicate the banking of the plane and the altitude of the plane. Airspeed indicator This is an a differential gauge that is very sensitive that is capable to measure and promptly show the difference between pitot or impact pressure and the static pressure which is the undisturbed atmospheric pressure when the flight is level. When the aircraft is parked on the ground in a still air the two pressures will be equal. When there is movement of the aircraft in the air, the pressure on pitot line will be greater than the pressure in the static lines. The difference in pressure is indicated as on the face of the instrument by the airspeed pointer whose calibration may be in miles per hour, knots or some cases both. The pilot will find the knowledge of the airspeed of the aircraft to be very important when turning. This when turning the pilot will need to increase the power as discussed earlier. the increase in power will be sufficient if the airspeed is at the desired level. Suppose the pilot increases the power to the maximum and the airspeed is not being maintained at the level at which it was at the beginning of the turn, it will be a clear indication that the turn can not be maintained by the plane without loosing altitude. 4. Read the following ATSB accident reports (available from www.atsb.gov.au). Describe and discuss the factors that lead to the aircraft crashing while turning. Accident number 200506306 The accident involved a single-engine Cessna Aircraft Company 150G which at the time of accident the pilot was doing an aerial mustering operations. The aerial mustering operation involved flying a north to south pattern in a progressive pattern from the east to the west with the aim of directing the mustering personnel on the ground so as to locate the sheep. The evidence at the ground indicated that the plane was almost upright as it struck the ground as it indicated severe damage to the fuselage, nose section to the left wind. There was minimal damage to the vegetation in the vicinity of the initial ground impact which gave evidence that the impact of the aircraft with the ground was steep with a left angle bank ranging between 70 and 80 degrees. Also the damage to the wing and the position of the nose impact gave evidence that the aircraft the ground with its nose in a down attitude at a high speed. There was no evidence of the pre-impact defects on the aircraft. From this it was clear that the cause of the accident was due to excessive banking during the turns. Accident number 200204663 The aircraft involved was Cessna 182B Sky lane, it had one passenger on board and it was carrying sufficient fuel on board. The aircraft made a steep climb on its short final in a downwind position, making a turn to the right side using a 60-80 degrees banking angle. It this point it was observed to lose attitude rapidly. There was a turn of about 295 degrees before the aircraft impacting the ground. The aircraft hit the ground at an angle of 60-80 degrees nose down with the left wing low. This was evidence that excessive banking was cause of accident. Accident number 199701568 The aircraft involved was Cessna210 which was undertaking a geophysical survey west of Emerald. From the evidence it was found that the plane struck several trees while it was in an 85 -90 degrees angle of bank. There was no abnormality in the airframe and in the power plant that could have caused the accident. From the examination of the propeller it was clear it was functioning well at the time of impact. There was no any evidence that could indicate that the aircraft had a bird strike. From this evidence it was clear that the aircraft came down as a result of excessive banking. Reference U.S. Government materials (2009). Private pilot ground school..Aerodynamics in flight: flight principles applied to airplanes. Retrieved on 28th April 2011 from www.free-online-private-pilot-ground-school.com On 6 December 2005, the owner-pilot of a single-engine Cessna Aircraft Company 150G, registered VH_KPQ, was conducting aerial mustering operations on a family owned station, 156 km north of Broken Hill, NSW. At about 0835 Eastern Daylight-saving Time, the pilot was observed to circle some sheep at about 250 ft above ground level. Shortly after, ground mustering personnel noticed smoke nearby and found that the aircraft had impacted the ground and there was an intense fire. The pilot, who was the sole occupant of the aircraft, was fatally injured. The aircraft wreckage was found approximately 400 m to the south-east from where the pilot was circling. The aircraft was upright with evidence of severe impact damage to the left wing, nose section and rear fuselage. Examination of the aircraft, including the flight control systems and engine, did not reveal any evidence of pre-impact defects. Damage to the propeller indicated that the engine was operating at ground impact. The wing flaps were found in the retracted position. The steepness of the angle of bank and the nose-down pitch attitude at the aircraft's point of ground impact indicated that the aircraft was in a steep left turn at that time. Those indications and the minimal forward movement of the aircraft after ground contact were consistent with the aircraft having stalled and slipped out of the turn. The lack of aircraft rotation at impact indicated that there had been insufficient time for the stall to develop into a spin, consistent with it occurring at low level. The investigation concluded that the aircraft stalled at a height from which the pilot was unable to effect recovery Read More

This therefore makes it important for this fact to be put in mind always especially when attempting to put the plane in a straight line. 2. Describe why an aircraft could collide with the ground during a turning manoeuvre. The first thing that need to be noted is that by banking an airplane to make it turn will not in any way bring an increase in the total amount of lift developed. But the lift is divided the vertical and the horizontal components. Because of this division there is reduction in the actual lift that is supposed to support the airplane’s weight and this will result into the lose of altitude by the plane unless there is creation of additional lift.

This is usually by increasing the attacking angle up to the point the vertical component of the lift becomes equal to the weight of the aircraft. Due to the fact the vertical component of lift will reduce with the increase in the bank angle, there is need for the angle of attack to be increased progressively so as to produce sufficient vertical lift that is sufficient to support the weight of the plane For a given airspeed, the aircraft turning rate is dependant on the magnitude of the horizontal component of the lift.

The horizontal component of the lift is proportional to the angle of bank as it increases or decreases with increase or decrease in the bank angle. This means that with increased bank angle there is an increase in the horizontal component of lift which increases the rate of turn. This means that at a given air speed the turning rate can be controlled through adjustment of the angle of bank. In order to have a vertical component of lift that is sufficient to keep altitude in a level turn there is need to have an increase in the angle of attack.

But because the airfoil drag is proportional to the angle of attack, there will be increased drag with increased lift. This will in turn will cause reduction in airspeed that is proportional to the angle of bank; small reduction in airspeed will result where there is a small angle of bank and a large reduction in air speed will be caused by a large bank angle. There will be need to have additional power (thrust) to ensure that the airspeed does not reduce in level turns, where the additional power will be proportional to the angle of the bank.

Suppose there is no increase in power the reduction in air speed will reduce the lift and thus the vertical component of lift will not be sufficient to balance the weight of the aircraft. This will therefore bring the plane down. The rate of turning will dictate the amount of power required to sustain it. If the plane makes a very sharp turn that it cannot provide the power to sustain it the plane will definitely loss altitude. 3. List and describe instruments that are available to the pilot to help him/her accurately turn the aircraft.

Vertical speed indicator The vertical speed indicator is also known as a vertical velocity indicator (VVI). The instrument will indicate whether the aircraft in level flight, descending or climbing. The rate at which the aircraft is climbing or descending is given by the instrument in feet per minute. This instrument is important as it will give the pilot information if the aircraft is loosing height. The rate at which the plane is loosing height will help the pilot decide how much lift is required to keep the plane in level flight.

This will be done by increasing the angle of attack of the aerofoil and increasing the power supply. If the plane keeps on descending it may mean that the pilot need to reduce the rate of turning as this is a clear indication that the plane is not able to negotiate the turn. The vertical speed indicator is a differential pressure instrument even though its operation is solely from static pressure. The instrument has a diaphragm that has linkage and gear system to indicator pointer which is in an airtight case.

There is a direct connection of the inside of the diaphragm to the static line of the pitot-static system.

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