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QID 811230 - Effect of Wing Sweep

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  • QID 811230 - Effect of Wing Sweep

    The following message was originally sent by email to on June 3rd, 2018. I was requested to post this message on the ATP Forum.

    Dear Bristol Support,

    Regarding question 811230, Principles of Flight, the correct option is marked as "Delay - Higher". The explanation however does not seem to agree with the answer marked correct as it infers that the correct answer should be "Delay - Lower". It reads, quote, "when wings are swept [...] the formation of shock waves is delayed, along with the associated drag rise."

    I agree with the explanation given and would have thought "Delay - Lower" to be the correct answer to the question. I may be wrong as I am no expert in transonic aerodynamics.

    Kind regards,

  • #2
    This question has two distinct parts referring to two very different flight regions.

    1. With increasing speed, we encounter the transonic drag rise shortly after exceeding Mcrit and entering the transonic flight region. By sweeping the wings, we delay our entry into this region until we've reached a higher speed.

    2. The second part is asking about supersonic flight. We are not described as proceeding from the transonic to the supersonic region until we exceed a much higher speed - Mdet - which is around Mach 1.3.
    At these supersonic speeds, a swept wing will have a higher CD than an identical straight wing. The air takes a longer track from the leading edge to the trailing edge, increasing friction drag - and friction drag becomes very significant at these very high speeds.

    The explanation provided seems to cover the first part of the question only. I'll improve it.