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Thread: Formation Takeoff with Cross wind >5kts

  1. #1
    76th vFS Pilot Stryker's Avatar
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    Formation Takeoff with Cross wind >5kts

    Hi Guys,

    I had a question for the procedure in 476TTp3-3.A10C:
    "When crosswind component exceed 5 knots, wingman on the upwind side of the runway."

    What is the rationale for this? Understanding the big picture or the physics also helps me remember stuff like this, and possibly apply to other scenarios.

    I tried searching for discussion and answers on this and found some info, but I don't think my specific question is answered in that thread.
    http://www.476vfightergroup.com/show...wind+formation

    My intuition is that if the lead, being slightly ahead of the wingman, takes the downwind side of the runway, then the crosswind force vector will push equally on both the lead and wingman, since the affected surface area being acted on by the crosswind is equal, and thus pushing both in the direction of the crosswind equally and helping to avoid a collision. (Example A)

    Whereas, if lead takes the upwind side of the runway, then the lead blocks the crosswind for the wingman, and the lead is pushed into the wingman's plane, while the wingman's plane is less affected by the crosswind force vector, and does not move as much as the lead (due to the lead blocking wind in the path to the wingman). (Example B)

    I think the main point for lead taking the downwind side (wingman takes the upwind side) is to help avoid collision due to unequal crosswind force in the "B" example? Can someone confirm and correct my musings?

    crosswind-formation-takeoff.jpg

  2. #2
    76th vFS Pilot IronHog's Avatar
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    Quote Originally Posted by Stryker View Post
    Hi Guys,

    I had a question for the procedure in 476TTp3-3.A10C:
    "When crosswind component exceed 5 knots, wingman on the upwind side of the runway."

    What is the rationale for this? Understanding the big picture or the physics also helps me remember stuff like this, and possibly apply to other scenarios.

    I tried searching for discussion and answers on this and found some info, but I don't think my specific question is answered in that thread.
    http://www.476vfightergroup.com/show...wind+formation

    My intuition is that if the lead, being slightly ahead of the wingman, takes the downwind side of the runway, then the crosswind force vector will push equally on both the lead and wingman, since the affected surface area being acted on by the crosswind is equal, and thus pushing both in the direction of the crosswind equally and helping to avoid a collision. (Example A)

    Whereas, if lead takes the upwind side of the runway, then the lead blocks the crosswind for the wingman, and the lead is pushed into the wingman's plane, while the wingman's plane is less affected by the crosswind force vector, and does not move as much as the lead (due to the lead blocking wind in the path to the wingman). (Example B)

    I think the main point for lead taking the downwind side (wingman takes the upwind side) is to help avoid collision due to unequal crosswind force in the "B" example? Can someone confirm and correct my musings?

    crosswind-formation-takeoff.jpg
    Hi Stryker,

    When rolling with the crosswind component plane will tend to turn into the wind (due to weathervaning effect). So if crosswind exceeds 5 knots wingman is put on the downwind cause he is less experienced than the lead. If not enough rudder is applied then wingman will be pushed out of the runway which is far better than collision of 2 planes. At least this how I understand it.
    [SIGPIC][/SIGPIC]

  3. #3
    76th vFS Pilot Stryker's Avatar
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    Quote Originally Posted by IronHog View Post
    Hi Stryker,

    When rolling with the crosswind component plane will tend to turn into the wind (due to weathervaning effect). So if crosswind exceeds 5 knots wingman is put on the downwind cause he is less experienced than the lead. If not enough rudder is applied then wingman will be pushed out of the runway which is far better than collision of 2 planes. At least this how I understand it.

    Hi IronHog,

    Thanks for your response!
    Point of clarification - the procedure states that "wingman on the upwind side of the runway", but you said that wingman should be on the downwind side of the runway.

    Did you mean to say downwind?

    Also, I tried poking around the web for some docs on weathervaning with respect to formation takeoffs but came up empty. Are you quoting from some published material you read on the topic? If so I'd appreciate a link or maybe a doc-name to read further (if not no worries)?

    PS, welcome back from one of the FNGs!

  4. #4
    I posed this question to some formation-rated folks I know and the consensus seems to be "Upwind Side" so that lead's propwash / exhaust is blown away from the wingman.

    The onus is on Lead to know to go to the downwind side so there's no confusion on where the wingman has to be. Wingman just has to "go to the other side" per usual.
    Last edited by Emmy; 28Jun18 at 04:46.

  5. #5
    76th vFS Pilot IronHog's Avatar
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    Quote Originally Posted by Stryker View Post
    Hi IronHog,

    Thanks for your response!
    Point of clarification - the procedure states that "wingman on the upwind side of the runway", but you said that wingman should be on the downwind side of the runway.

    Did you mean to say downwind?

    Also, I tried poking around the web for some docs on weathervaning with respect to formation takeoffs but came up empty. Are you quoting from some published material you read on the topic? If so I'd appreciate a link or maybe a doc-name to read further (if not no worries)?

    PS, welcome back from one of the FNGs!
    Yeah - I meant upwind (as procedure states). I am not quoting any published material - I was just logically trying to think why we have such procedure, but from what Emmy wrote it seems that the reasoning behind it might be different.

    Thanks for the welcome!
    [SIGPIC][/SIGPIC]

  6. #6
    76th vFS Pilot Stryker's Avatar
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    Quote Originally Posted by Emmy View Post
    ...the consensus seems to be "Upwind Side" so that lead's propwash / exhaust is blown away from the wingman.
    The onus is on Lead to know to go to the downwind side so there's no confusion on where the wingman has to be. Wingman just has to "go to the other side" per usual.
    Emmy: It's good to have friends in ... "high places"! <har-har> Yes, the lead takes the downwind slot and wingman slides in adjacent, but I'm sure it's still good habit for the wingman to know the procedure and perform the crosswind calc, so that he can check that the lead's position is correct (and also catch a math mistake), and also good habit formed for when wingman is a lead on other flights/ops.

    Is this cross-wind check actually done in preflight check by folks here? Or is it added for realism (and usually skipped)?
    Last edited by Stryker; 28Jun18 at 16:21. Reason: correct : leads' --> lead's

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    Member Frodo's Avatar
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    I use the current weather wind direction and speed to determine the lineup for departure.

  8. #8
    Quote Originally Posted by Stryker View Post
    Emmy: It's good to have friends in ... "high places"! <har-har> Yes, the lead takes the downwind slot and wingman slides in adjacent, but I'm sure it's still good habit for the wingman to know the procedure and perform the crosswind calc, so that he can check that the lead's position is correct (and also catch a math mistake), and also good habit formed for when wingman is a lead on other flights/ops.

    Is this cross-wind check actually done in preflight check by folks here? Or is it added for realism (and usually skipped)?
    From my RL flying experience, a windsock check Vs ATIS Vs which way was traffic flowing was a part of my pre-flight walk around.

  9. #9
    76th vFS Pilot Stryker's Avatar
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    Quote Originally Posted by Frodo View Post
    I use the current weather wind direction and speed to determine the lineup for departure.
    Hey Frodo,

    476TTp3-3.A10C:
    "When crosswind component exceed 5 knots, wingman on the upwind side of the runway."

    My point is that to determine the "crosswind-component" you must do some math...

    crosswind_component = sine(wind_angle_off_runway_heading) x wind_speed


    Note that a 25 knot wind at 10 deg off runway heading only produces 4.34 knots of crosswind-component, which is under the 5 knot crosswind-component limit, and therefore either side of the runway could be occupied by the lead ship.

    Additional examples:
    When 6 knot wind direction is 90 deg off runway heading (beam to runway) exceeds the 5 knot and therefore the lead must take the downwind side as specified in the TTP. When wind direction is 90deg to runway heading (beam to runway), crosswind_component = wind_speed

    When 6 knot wind direction is 45 deg off runway heading, crosswind_component is 4.24 knot and therefore less than the limit, and no factor.

    Crosswind-component - Although not specifically defined in the TTP, I interpret this to be the calculated wind vector component (using my formula above) that is 90 deg to the runway heading.

    At least that's how I interpret the TTP. I could be wrong, of course.

    Are people doing the calculation above to determine the crosswind-component in preflight?
    Last edited by Stryker; 28Jun18 at 17:31. Reason: clarify - 90deg to runway heading (beam to runway)

  10. #10

    Condom


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    I know, i'm lazy... I use an app, full of GA tools, which includes a crosswind component calculator
    http://www.476vfightergroup.com/signaturepics/sigpic1750_22.gif

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