Effect of cooling/cowl flaps on speed

Discussion in 'Aviation' started by wuzak, Feb 14, 2015.

  1. wuzak

    wuzak Well-Known Member

    Jun 5, 2011
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    Hobart Tasmania
    I was just looking at this report and found an interesting table on the effect of cowl flap operation on speed.

    [td]Cowl Flap Position[/td][td]Cowl Flap Opening (in)[/td][td]True Speed (mph)[/td][td]Speed Loss (mph)[/td]
    [td]1/4 Open[/td][td]1-5/8[/td][td]278[/td][td]6[/td]
    [td]1/2 Open[/td][td]3-1/4[/td][td]264[/td][td]20[/td]
    [td]3/4 Open[/td][td]4-7/8[/td][td]249[/td][td]35[/td]
    [td]Wide Open[/td][td]6-1/2[/td][td]236[/td][td]48[/td]

    This is a significant drag rise for cooling purposes.

    I guess if the engine can stand extra temperatures for a few minutes that keeping the cowl flaps closed would help in trying to evade a pursuer, but not if it means the engine melting over enemy territory.

    Is there any data with regard to radiator flaps such as on the P-51, Spitfire or Mosquito?

    Later radial engine types used different systems, like the cowl ring, which provided the same function as the cowl flap but without sticking into the air stream.

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