27 WWW.GOFLY.ONLINE Y ONLI NE FLI GHT SCHOOL PRINCIPLES OF FLIGHT Sloppy controls As most inadvertent stalls happen at low airspeed, a common sign is controls that are becoming less responsive, or sloppy, as the airspeed starts to reduce. High angle of attack While a stall can happen at any speed, most inadvertent stalls happen at low speed and this normally corresponds with a higher than normal nose attitude. This is not always the case and can be hard to determine, for instance during a turn from base to final on approach to land. Low, diminishing airspeed For a low speed 1G stall, the airspeed will be low, and reducing as the stall approaches. Stall warning device Most aircraft are fitted with a stall warning device that warns the pilot of the imminent stall. The stall warning divide can be visual or aural and the stall warning normally is activated just prior to the stall. Elevator loss of effectivenessIn a low speed stall, there is often an obvious loss of elevator effectiveness, meaning the pilot can make large movements of the elevator with little to no change in pitch. Stick or control column position In most stall scenarios, the control stick or column is close to its maximum rear position. Stall buffet Just prior to the stall, as the airflow starts to separate from the wing, buffeting may occur throughout the entire airframe. Turbulent air coming off the wing and hitting the tail and/or fuselage contributes to the buffeting. The characteristics of a stall We have covered the symptoms of the approaching stall and while these symptoms may still be present during a stall, the main symptoms of a fully developed stall are described below. • Stall warning • Stall buffet • Stall break, where the aircraft nose suddenly pitches down • Increasing rate of descent • A low constant airspeed. Sometimes, it is not clearly obvious that the aircraft has stalled, as there may not be a clear stall break. However, a quick check of the Vertical Speed Indicate (VSI) and Indicated Airspeed (IAS) will confirm the fully developed stall. During a fully developed stall, indicated airspeed will be steady and low, and the vertical speed will be negative and increasing. Stall recovery procedure The recovery from either an approaching, or fully developed stall is achieved by: • Reducing the angle of attack by moving the control column forward. • Allowing airspeed to increase to a safe airspeed, above the stall speed. • Returning to a level attitude and applying full power. • Keeping wings level with rudder while recovering (no aileron) • Regaining height, by adopting climb altitude and airspeed, and when safe to do so, level off. The dangers of using aileron at the wing drop to recover a dropped wing A wing drop stall is where one wing stalls before the other. The wing that reaches the critical angle first will stall, losing lift and causing a roll at the stall. It is natural for the pilot to want to use aileron to pick up the down going wing during a wing drop stall, but this should be avoided at all costs. If the pilot uses an aileron to try and pick up the wing, the aileron will be deflected up on the up going wing, and this will suddenly decrease the lift available and potentially stall the upgoing wing. This can cause an abrupt wing stall reversal, where the other wing may stall violently and cause the aircraft to rapidly roll and yaw in the opposite direction.
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