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Thread: Formation Takeoff with Cross wind >5kts

  1. #11
    76th vFS Pilot Stryker's Avatar
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    This makes me think of another related topic... takeoff rotation speed... calculated based on weight and drag in the MDC.

    Does this takeoff rotation speed factor in the "headwind-component" of the prevailing wind conditions?

    headwind_component = cosine(wind_angle_off_runway_heading) x wind_speed

    If the headwind_component is not factored in to the rotation speed calculation, then we should be subtracting the headwind_component from rotation speed to get the effective-rotation-speed for takeoff?

    mdc_rotation_speed - headwind_component = effective_rotation_speed

    So for example, if wind conditions are 25 knot wind at 10 deg off runway heading, then headwind_component is 24.6 knots of wind coming towards you on the runway.

    Given that your rotation speed was calculated to be 130 knots, then
    130 - 24.6 = 105.4 knots (effective-rotation-speed)


    105 knots (effective-rotation-speed)

  2. #12

    TWOT


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    You don't have to do the math yourself, use one of these to guestimate the net crosswind:


  3. #13
    And according to my SME's, 10kts is the max allowable crosswind component for formation departures. Anything higher and you go single ship (both AF and USN)

  4. #14

    Condom


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    Quote Originally Posted by Stryker View Post
    This makes me think of another related topic... takeoff rotation speed... calculated based on weight and drag in the MDC.

    Does this takeoff rotation speed factor in the "headwind-component" of the prevailing wind conditions?

    headwind_component = cosine(wind_angle_off_runway_heading) x wind_speed

    If the headwind_component is not factored in to the rotation speed calculation, then we should be subtracting the headwind_component from rotation speed to get the effective-rotation-speed for takeoff?

    mdc_rotation_speed - headwind_component = effective_rotation_speed

    So for example, if wind conditions are 25 knot wind at 10 deg off runway heading, then headwind_component is 24.6 knots of wind coming towards you on the runway.

    Given that your rotation speed was calculated to be 130 knots, then
    130 - 24.6 = 105.4 knots (effective-rotation-speed)


    105 knots (effective-rotation-speed)
    You're taking off referencing indicated airspeed so the best thing that can happen is that you use less runway. Don't subtract anything from KIAS!
    http://www.476vfightergroup.com/signaturepics/sigpic1750_22.gif

  5. #15
    76th vFS Pilot Stryker's Avatar
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    Quote Originally Posted by Black View Post
    You're taking off referencing indicated airspeed so the best thing that can happen is that you use less runway. Don't subtract anything from KIAS!
    Great point, Black! Indicated Airspeed. Yup, nevermind on headwind rotation question.

  6. #16
    76th vFS Pilot Scaley's Avatar
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    So, my few pennies worth:

    Upwind/downwind side for formation takeoff's is (at least from when I was flying prop aircraft) for wake turbulence/prop(jet)wash avoidance. The lead's wash get blown away from the wingman. The same lineup is used for interval takeoff for the same reason.

    Wind check - I have a habit of old of setting the heading bug on the HSI to the wind direction from the brief. in RL if something changed my understanding of the wind I'd change the bug at that point. Since in DCS you can't see local wind effects the bug never changes. Regardless of crosswind component I always put the lead downwind for all takeoffs even if it's not required since there no advantage to doing it differently.

    I only actually check the component precisely if there a possibility it exceeds a limit or affects a performance number. If it's clearly within limits then it's the side that's important.

  7. The Following 2 Users Say Thank You to Scaley For This Useful Post:

    Emmy (29Jun18), Stryker (02Jul18)

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