Line-pull ratios
  • After recording line-pull in all the Beauforts (up to 4+) with my 4 KAP kites I have come up with some line-pull ratios.

    Our wind strength forecasts come in knots in Australia so that's what I work on.
    The ratios are: line-pull (lb) to wind strength (kn)

    7ft Pirate Rok (with flexy fibreglass spars) 1:1
    ITW Levitation Delta (normal version) 1:2
    Peter Lynn 2m2 Pilot 2:5
    PFK Nighthawk 1:3

    For example, in 12kn the Rok pulls at 12lb, the Levi pulls at 6lb, the PL pilot pulls at 5lb and the PFK pulls at 4lb.
  • That's interesting to know. Thanks.

    Is the ratio relatively constant at different wind speeds?
  • Yes it is, at least for Bft 2 3 4.
  • As an aid to those of us - like me - who are not all that wind-literate, here is a general chart to help convert wind speeds often discussed. I am sure it appears elsewhere but a little repetition never hurts ...

    image
  • I tend to fly around Beaufort upper 2 in to lower 4. Knots wooosh over my head and MPH is my proffered scale.
  • Ha, that's something I really enjoy about this forum, and the Flickr group. Many different languages and units used. It adds flavour.
  • ;-) at the end of the day. its still the same language, but with accents.
  • Would love to know what ratio you'd find with a Fled. My guess is 1:1 at low wind speeds, but at 12 mph maybe stronger. I recall getting readings of 20 lb at less than 10 mph, but maybe that's just distorted parental memory.
  • Has anyone measured the pull of a 6' PFK in gales/force 8 or above yet??!!
  • The linearity is a little surprising to me, since air resistance tends to be proportional to the square of the speed. I guess the high flyers tend to just fly a little higher as the speed picks up. But I'd expect a low flyer like a flow form to show the square relationship. I'd be interested to see your raw data. My guess would be that the rok shows the most curvature, since it probably flies at the lowest angle of your four.
  • Wouldn't Pilot fly at lower angle than Rok?
  • Linearity? Probably not in reality, these are very very rough ballpark figures. Certainly not statistically rigorous, just a sense of the relative pull.
    Wind speed is too variable and so is the line-pull to get accurate data, you would need to continuously and simultaneously measure wind speed and line pull. I'll keep collecting data anyway and see what eventuates.

    I thought about measuring line angle too but that's for another day.
    Within their wind ranges Levitation Delta and PFK are always the highest, Rok next and PL 2m2 Pilot lowest
  • I'm guessing the 6' PFK in 60mph+ can pull over 30kg, i'm basing that on the effort i needed to tie it off and give my arm a rest by walking the rest down. after a gruelling 20 minute hand wind on a singing line.
  • I'm not so sure about 30kgs but it will likely remain an unknown since it is not an appealing test to carry out!!

    Day 29 of my aerial 365 mission beckons. Once the rain clears I have force 9 gusts to look forward to. Can't wait....
  • Kevin,

    BKT is a faithful fan of your mission, a great idea. Almost like a samurai trip. You need a lot of faith. '-)

    Sayonara!

    PS 8 kan = 30 kg = 66 lb
  • It's surprising how low the pull actually is, when you measure it. My guess is a PFK wouldn't get near 30kg pull before self destructing.
  • I can add 2 more kites to this list now

    7ft Pirate Rok (with flexy fibreglass spars) 1:1
    2m rokkaku with Skyshark P4x spars 1:1
    1.7m rokkaku with Skyshark P4x spars 3:4

    ITW Levitation Delta (normal version) 1:2
    Peter Lynn 2m2 Pilot 2:5
    PFK Nighthawk 1:3
  • Andrew, no measurement of dopero. ;o)
  • Very interesting. I would suspect that the ratio would be different (non-linear) in varying wind speed. In my littler experience, the Fled seems to pull much stronger when the wind picks up vs. the PFK Nighthawk which continues to be pleasant in stronger winds.
  • BKT I'm happy to oblige. Just post one over to me and you'll have your measurements. :-}
    Beautiful kites. They look a little too complex for me to tackle just now.
  • hqasem
    One thing I have learned by measuring these things is that the wind is very variable all the time. It's even difficult measuring kites consecutively because the wind speed will change between pulling one in and launching the other. I'd love access to a wind tunnel.
    Another factor is how different kites deform. As wind increases Roks get baggier and so produce more drag from shape alone while deltas flex and reduce surface area.

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