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Why Va changes with weight?

Asked by: 5472 views Aerodynamics, Flight Instructor, Student Pilot

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2 Answers



  1. Dave Sandidge on Nov 01, 2016

    In short, the answer is: “In order to protect the aircraft from damage.” It all has to do with varying angles-of-attack at different cruise speeds, weights, g-loadings, and sudden gusts or maneuvering loads. But basically, you want the airplane to stall BEFORE it over-stresses itself to the breaking point. There are some very good Youtube videos on the subject.

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  2. Dave Sandidge on Nov 02, 2016

    A light, single-engine airplane at its minimum weight, flying (straight and level, unaccelerated flight) at 140 mph (quite fast), may have an angle of attack (AOA) of, let’s say, 2.5 degrees. If its wings stall at an AOA of 17 degrees , then it has to increase its AOA by 14.5 degrees to reach the stall. If the airplane encounters that 14.5 degrees increase suddenly (abrupt maneuvering, gusts…) the load factor increases (very abruptly), to a point where the airplane will break before it stalls. [Remember, if you double the lift, you double the load factor.] If you slow that same airplane down to its maneuvering speed, then the AOA will be greater at the outset (during straight and level, steady speed flight), before it encounters the sudden, abrupt loads, and will reach its stall AOA before anything breaks. Remember, the slower you fly, the greater the AOA, and the closer to the stalling AOA you are. A light, single-engine airplane flying (straight and level, unaccelerated flight) at its maximum gross weight already is flying at a much greater AOA to start with than when it’s not so heavy.

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