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2 Answers

Vg diagram…blue area?

Asked by: 2656 views Aerodynamics

Good day,

Wha is the blue area of a Vg diagram? Does it have a specific name? 

My guess is that it is the area of non-operations; that is the aircraft should/must not be flown in the blue area. The diagram doesn't label it but I am nervous my examiner will ask me about it.

Thanks for your time.



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2 Answers

  1. Chris Carlson on Jan 30, 2013

    My understanding, and someone more senior can correct me if I’m wrong, is that the blue area is not possible to operate in. In order to get there, you would have to pass the critical angle of attack without stalling (which is impossible) The positive G side is bound by the normal accelerated stall, and the negative by stalling the plane with a relative wind coming from above the cord line. My limited understanding unfortunately does not explain the reasons for the curved contact between the red and blue section sin the negative G, high airspeed corner of the graph.

    I look forward to a deeper response. Hope mine helped a little

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  2. Brian on Jan 30, 2013

    The linked diagram is confusing because the blue area shouldn’t exist on the bottom right side of the graph. The negative line should continue to the boundary of the diagram just as the positive line does. Chris has it right, the blue area is an area you cannot get to because you’ll have stalled the airplane.


    As for the funky layout in the negative area of this particular depiction, I can only speculate that the author of that diagram saw a V-n diagram that depicted gust loads. Gust loads can in some cases exceed limit load, resulting in the unusual line shape as seen in the negative area of your diagram. (It also occurs in the positive on a gust load V-n diagram)

    Most V-n diagrams will not depict that, the limit load line will simply be adjusted to the maximum gust load and made a straight line. In other words, the top half of that diagram is what you normally see, and the bottom half should mirror it.

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