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Question ID: 501237

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  • Question ID: 501237

    Large supercooled water drops, which freeze on impact on an aircraft, form:

    The answer is given as Clear Ice.

    To me this does not make sense, also the explanation contradicts the question

    "The droplet only partially freezes on impact, and the rest then freezes gradually as it flows back over the aircraft, giving a glass-like covering. "

  • #2
    Agree with you! Always fail that question because of that. When it freeze on impact is RIME ice!! Totally agree

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    • #3
      When supercooled droplets (SCDs) are LARGE, only a small amount of the droplet actually freezes on first impact with the leading edge. Some sources suggest that only 1/80th freezes on impact per degree C below zero. Therefore, there's lots of water remaining in liquid form that will flow back in the airflow over the wing surface, gradually freezing onto the sub-zero surface as it goes. Clear ice is formed. It's particularly serious if it flows so far back that it freezes in the hinges of the trailing edge flying controls, (which apparently happened on the BAe 146 from time to time).

      When SCDs are SMALL, most of the water can freeze on impact, or very shortly afterwards. The result is Rime Ice. A mixture of clear and rime icing is, of course, possible.

      More in ATPdigital Met Lesson 14

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