PRINCIPLES OF FLIGHT 9 WWW.GOFLY.ONLINE Y ONLI NE FLI GHT SCHOOL Airflow characteristics, from streamlined to turbulent While the wing is still producing lift the airflow remains laminar or streamlined, which means the airflow flows smoothly over the wing. As the wing nears the stall, approaching the critical angle of attack, the airflow starts to become turbulent towards the back of the wing. The part of the wing where the laminar airflow starts to separate and become turbulent, is called the separation point. Effectively, lift is reduced from the back of the wing first, and both the separation point and centre of pressure move forward as the wing approaches its critical angle of attack, normally around 16 degrees. Maximum lift is produced at, or just before, the critical angle of attack. As the critical angle of attack is passed, the centre of pressure moves drastically rearward, and at this point the air becomes very turbulent on top of the wing and lift is drastically and suddenly lost, and the wing is said to have stalled. Lift and drag As an aerofoil increases its angle of attack, the lift increases and so does the induced drag until the aircraft passes the critical angle of attack where lift is suddenly lost. Maximum angle of attack for lift generation The maximum angle of attack for lift generation on most light aircraft is just prior to the critical angle of attack. This is around 16 degrees angle of attack on most light aircraft. Most efficient angle of attack There is an angle of attack that represents the maximum lift for the least amount of drag for each aircraft. This is the most efficient angle of attack and offers the maximum lift for the least amount of drag. This angle is also known as ‘best lift to drag ratio’ and is used to determine the aircraft’s best glide ratio. Stall Speed Considerations The pilot operating handbook (POH) for your training aircraft will contain information on the stall speed for your aircraft type. Normally the POH will specify a clean stall speed, that is a stall speed with no flap deployed, and a stall speed with full flap.This published clean stall speed is a stall speed that’s been calculated in level flight at maximum weight and is a 1G stall. This is the speed at which the aircraft will stall while trying to maintain level flight by increasing the angle of attack past the critical angle of attack. As many light aircraft do not have an angle of attack indicator, using the published stall speed is a fairly accurate way to avoid the stall. On the airspeed indicator, the stall speed with zero flap is normally located at the bottom end of the green arc (normal operating speed) and the stall speeds with flap is normally located at the bottom of the white arc (flap operating range) Please consult your flight instructor or pilot operating handbook for more information. Best glide speed considerations The best glide speed for your aircraft type will be nominated in the pilot operating handbook (POH). The best glide speed for a light aircraft refers to the airspeed at which the aircraft achieves the maximum glide ratio, also known as the best glide ratio or L/D ratio (lift-to-drag ratio). The best glide speed is influenced by factors such as the aircraft’s weight, configuration, and aerodynamic characteristics. Stability and Control Factors affecting the Stability and Control of a 3 Axis Aircraft Longitudinal stability Longitudinal stability, also called pitch stability, refers to an aircraft’s stability when pitching up or down, that is, the rotation of the aircraft around its lateral axis. An aircraft with poor longitudinal stability will require the pilot to constantly monitor and correct pitch fluctuations. It is one of the major factors affecting the ease with which the aircraft’s pilot is able to maintain level flight. Changes in centre of gravity position Moving the Center of Gravity (CG) forward tends to increase longitudinal stability by increasing the static margin, which is the distance between the CG and the aerodynamic centre of the aircraft. This makes the aircraft more resistant to pitching
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