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Wind Speed Gradient and Fly Aways

Discussion in 'Phantom 2 Vision + Discussion' started by wharfbanger, May 7, 2014.

  1. wharfbanger

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    Given all the problems people are having I thought this warranted its own thread.

    After reading all the recent fly away stories, and suggestions by some that wind could be to blame, I did a little research.

    It turns out (and this will not be a surprise to experienced pilots) that wind speed does increase dramatically with height. The image below illustrates this point.

    To summarize this illustration, in areas with buildings, trees, or uneven surface, wind can more than double over the first hundred feet (30m). Then it can double again between 100 and 900 feet (270m).

    So, if your Phantom has a top speed of 34 MPH(15 m/s), and the wind is 20 MPH at ground level, you could experience a "fly-away" at 100 feet altitude.

    Or, if the wind is 10MPH at ground level, you could experience a "fly-away" at 900 feet.

    The wind speed gradient will be less of an issue over flat, un-forested ground or water.
     

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  2. Mal_PV2_Ireland

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    +1

    I'd say wind and inexperience causes at least 75% of "flyaways"
     
  3. Cocoa Beach Kiter

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    The graph you are looking at is a table demonstrating the reduction effect the land mass has on wind. It is showing what the reduction would be at intervals as the level approaches ground level. In this example the winds at 1500' are 100mph reducing to 31 at 200'. It is very rare (unless your in a tropical storm or hurricane, or live in the open plains) to have a wind that high at 1500'. If you want a better idea of winds in your local area look at the winds aloft forecast from a FAA pilot weather briefing or local weather service if you are outside the US.

    To give you an idea, here is a portion of the forecast from https://aviationweather.gov/

    Forecast Winds and Temps Aloft (MIA)
    Low High FB Winds Map
    1400z 2100z 0600z 1800z

    (Extracted from FBUS31 KWNO 071402)
    FD1US1
    DATA BASED ON 071200Z
    VALID 071800Z FOR USE 1400-2100Z. TEMPS NEG ABV 24000

    FT 3000 6000 9000 12000 18000 24000 30000 34000 39000
    EYW 1115 1218+15 1215+09 1313+02 3015-08 3235-18 316134 317442 319753
    JAX 1812 1919+15 2018+08 2011+02 2210-12 2910-24 313540 315548 308455
    MIA 1213 1318+14 1324+08 1326+01 9900-10 3322-21 324736 317444 811652

    The last line (blolded) shows the winds at 3000, 6000, 9000, etc above Miami Fl.. Decoding it reads the winds at 3000' are 120 degrees at 13kts, 6000' 130 at 18, 9000' 130 at 24.

    As you can see, wind is not increasing at a extreme increase (which is generally the case)
     
  4. jodaddy23

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  5. panhygrous pantler

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  6. mra1228

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    Interesting conversation -- I am a pilot so I'm very familiar with the inconsistency with wind.

    A rule of thumb I follow when flying phantom, first sailing an unfamiliar boat, paddle boarding, and kayaking is "always go upwind first".

    That way you can test the winds and effect and have the wind as your friend helping you get back to your starting position.

    So if at all possible check the winds and choose your launch site so your target area is upwind for first leg.
     
  7. wharfbanger

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    I think the important point is that wind speed increases very quickly up until about 1000 ft altitude, and then increases more gradually after that. Because most of us are flying below 1000 ft this is important.

    Do the "winds aloft forecast" include altitudes lower than 1000 ft? That would also be useful.

    I appreciate the 100MPH shown in the example may be unusual for Florida, but Florida is probably less windy than many other parts of the world (unless you have a hurricane). As you get to higher latitudes wind speed increases (in the southern hemisphere we have roaring 40's, furious 50's and screaming 60's).