Aero-Tips!

A good pilot is always learning -- how many times have you heard this old standard throughout your flying career? There is no truer statement in all of flying (well, with the possible exception of "there are no old, bold pilots.")

Aero-News has called upon the expertise of Thomas P. Turner, master CFI and all-around-good-guy, to bring our readers -- and us -- daily tips to improve our skills as aviators. Some of them, you may have heard before... but for each of us, there will also be something we might never have considered before, or something that didn't "stick" the way it should have the first time we memorized it for the practical test.

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Aero-Tips 12.25.06

Most airplanes have some sort of stall warning system. 

• Aerodynamic warning. As the wing nears the critical angle of attack, in most airplanes you'll begin to feel vibration, the "buffet". Depending on the airfoil design you may feel a strong, obvious buffet before the stall, or the wing may stall completely with little to no warning.
• Artificial stall warning devices. Not required until a few years after World War Two, artificial stall warning devices are designed to give the pilot advance warning of reaching the critical angle of attack. The first stall warning devices were visual, usually a red light in the pilot's field of view. Later the industry standardized on stall warning horns. In typical installation stall warning devices are rigged to activate when the indicated airspeed decreases to five to seven knots above indicated stalling speed.
• Some larger airplanes have "stick shaker" devices that artificially reproduce an aerodynamic stall warning, when the "real" aerodynamic feel does not give an adequate indication. In some airplanes this may be accompanied by an audible warning; advanced airplanes will actually "push" forward on the controls, reducing angle of attack and unloading the wing, if the pilot does not respond to the stick shaker.
• Modifications to the wing (intentional, like installation of vortex generators or Short Takeoff and Landing [STOL] wingtips, or unintentional, like attempted flight with frost or ice accumulation) may alter the warnings, and one or both wings may stall before the original stall warning devices sound or illuminate.
• Stall warnings may sound intermittently in turbulent air. In fact, if flying below the airplane's Turbulent Air Penetration Speed in moderate or greater turbulence, the wing is supposed to momentarily stall as you encounter gusts, to prevent overloading the wing and risking structural failure. It stands to reason that the stall warning horn may chirp in this occurrence.
• It's normal to hear the stall warning horn during your landing flare. If you do everything right, especially a short-field landing, you should penetrate this five-to-seven knot warning activation range as the airplane settles to the ground. Note: do NOT confuse this expected stall warning activation in the flare with a similar-sounding gear-up warning if flying a retractable gear airplane!

Aero-tip of the day: Anticipate when it's expected to hear the indications of an impending stall, and take action to return to a flying angle of attack at the first sign of an unexpected stall warning.

FMI: Aero-Tips