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Thread: Effect of wind on speed

  1. #1
    vebrown Guest

    Default Effect of wind on speed

    I read the Shortwing Air Race postings with great interest and was wondering what would be the true effect of the wind. If you had a crosswind both out and back, speed would be reduced because of the crab. But what about directly upwind for one leg and directly downwind for the other.

    For example, in the worst case of wind equal to your airspeed, you would really go fast downwind, but all of your gain would be cancelled on the other leg and you would never get back to the starting point. The effect must be there for all wind speeds, just less pronounced.

    Maybe we need a still day to really get the speed nailed down.

    My Pacer is broke right now but I used to get only about 120 MPH out of it. I think it was not rigged correctly. The right wing was heavy.


  2. #2
    Wayne Guest


    You are 100% right about that. Also, roughly 2/3 of the time we are flying in a head wind. A 90 degree cross wind is a head wind.

  3. #3
    JohnW Guest


    A graphic example of exactly what effect wind has can be seen by looking at the back of any E6B "slide rule" (this is what "digital" does for us...the first good example of which was when children suddenly "lost the ability" to tell time... they had to see it "spelled out" for them in numerals) (uh, Vern...this is NOT a personal attack!).

    Okay, I've thought about it. But, I'm having a hard time getting my head around the math explaining how the "headwind 2/3 of the time" claim can be valid??? Isn't there something of equal importance about a TAILWIND being from BEHIND us up to 90 degrees, as well? Doesn't the whole theoretical definition depend on EXACTLY 90 degrees to the longitudinal axis of the airplane flightpath? Either way..."added to the upwind side" must mean "subtracted from the downwind side" or 90 degrees would not be a valid number (as in: 90 + 90 = 180. It does NOT equal 240!)! That is...once the "crab angle" exceeds 90 degrees (to the FLIGHTPATH) the CROSSWIND EFFECT diminishes correspondingly as the angle becomes less than 90 degrees -although, with a "sign change" as well, when from "behind") to the loss/gain of "forward motion"? Doesn't this compute to "HALF the time we're flying" rather than 2/3 of the time, or is this simply statement in the category of how "when I was a Kid I walked to school every day -UPHILL both ways"? Somehow I'm seeing "vector angle" taking a(n) [inappropriate] role in this "2/3 claim". Simply put, once the headwind gets beyond 90 degrees TO THE INTENDED LINE OF FLIGHT, it ceases to be a "headwind". That line of thinking by default means that we are not only flying with a HEADWIND 2/3rds of the time...it means we are also flying with a TAILWIND 2/3 all the time, as well! How can that be?

    I'M only flying 100% of the time I am aloft...much as I could "get into" more hours in the day, I'm skeptical this isn't what's really happening (I DO know that the hours a person spends in flight are NOT subtracted from their life span!Fly more, Live longer!)

    I think the whole thing becomes "less philosphical" when you consider what Wolfgang Langeswitz (sp?) said about it: "An airplane flys within a mass of air. What that mass of air is doing at the time the airplane is flying through it has no meaningful effect on 'how fast the airplane is flying'. It can, and does, however have a meaningful effect on 'how fast the airplane is travelling over the ground, and in what direction'. It is easy to confuse the two separate issues, but they remain totally independent of each other, EXCEPT that the pilot has to learn how to NAVIGATE to get to where he is going." And THAT is why Uncle Sam came up with the infamous E6B computer. All of which works, of course, until the speed of the air mass over the ground exceeds the speed of the aircraft in flight INSIDE that airmass! Then things get " REALLY interesting" (I personally recommend STAYING HOME when that happens!). Think about landing a TriPacer on Mt. Washington in 200mph winds...(yipes!).

  4. #4
    Join Date
    Aug 2005
    Hurricane, UT


    Don't know about the rest of you, but I am flying in a headwind approximately 80% of the time and that has nothing to do with an E6B or wind triangles or any high end math, it's just a statistic.
    Andy Anderson

  5. #5
    metrallarider Guest


    That sounds like the story my Dad would tell us about trudging to high school; uphill both ways!

  6. #6
    Join Date
    Aug 2005
    Vero Beach, FL


    I never get lost, I just head into the wind and it takes me right to my destination!

  7. #7
    Wayne Guest


    LOL that sounds like me. But seriously, I will justify my statement that approximately 2/3 of the time we fly in a headwind. If you look at your E6B or use a wind triangle you will notice that a 90 degree cross wind has a substantial head wind factor. If you figure your ground speed both with no wind and a 30 KT cross wind at 90 degrees you will find that your ground speed will be higher with no wind. The wind will need to be from behind you by at least 20 degrees to cancel out the loss in ground speed by the cross wind. So you see, if you feel like you are flying in a head wind most of the time, YOU ARE. WAyne

  8. #8
    p_everette Guest


    And barefoot in the snow!

  9. #9
    CF-KZE Guest


    Quote Originally Posted by Geoff Newcombe View Post
    I never get lost, I just head into (you must mean WITH) the wind and it takes me right to my destination!

    Me too! Isn't that total freedom?


  10. #10
    CF-KZE Guest


    Altitude is most of the times a win-win. Not only the TAS increase of 1.75% per thousand feet, but very often, a head wind turns into a right crosswind, or that right crosswind turns into a tailwind.

    If I have 8,000 ft of play, I will most of the times benefit and save if I climb. Very rarely, I gain flying low but it happens.

    Another trick, for what it's worth; when flying under a broken overcast with sunny breaks, stick your back right at the base of clouds, push down, throttle back and watch the airspeed hitting hard in the red. Those updrafts are paying off on a long distance.

    It's a rough ride but it was rouhg anyways when lower.

    My two cents

    Last edited by CF-KZE; 09-17-2009 at 07:54 PM.

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