jakemoore wrote: ↑Thu Dec 17, 2020 9:47 pm
This flywheel hypothesis should be easy to test with the prior generation Ozone/Flysurfer kites where there was an option for regular or UL cloth.
It's easy to assume the UL stays aloft in less winds. I believe FS did a test also demonstrating faster turning with Deluxe. The Kitefinder guys did a back to back on Chrono Regular and Ultralight and liked the UL. But does the heavier kite provide a more powerful impulse to water start?
I would not say it is that easy to compare, because steering the kite and acceleration to higher flying speed is easier on UL kite if air volume=mass inside the kite is the same. Still air mass is the dominant factor, in earlier Soul18m approx 2/3 of total inertial mass.
But if you get both kites to fly exactly same speed in no wind (for simplicity 0m/s because wind does work on airfoil and add energy), the heavier kite has more Joules in kinetic energy. But just linearly as mass difference.. I estimated 0.7kg mass diff between UL and STD if on 18m Soul, maybe you have better figure?
"UL Soul18m" = 0.5 * 9.8kg * (10m/s)^2 => 490J
"STD Soul18m" = 0.5 * 10.5kg * (10m/s)^2 => 525J
but if you get "UL" to fly 11m/s (40km/h instead of 36km/h) due to quicker steering & acceleration due to lower kite mass it already has 593J as kinetic energy so it out 'performs' heavier sister on kinetic energy by over 10%.
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On airfoil lift equation both should be equal, so both needs to do work (delta energy) for rider 85kg with gear:
1) lifting up from water (no water resistance, just potential energy change maybe 1m of center of mass): 834J
2) accelerating to min. planing speed (min 3m/s or 11km/h ?): 383J
3) total work on energy changes rounding a bit up: 1220J
4) naturally 1220J is just get up and accelerate to planing speed but more work is needed to plane on TT or accelerate and engage hydrofoil. But used this example as getting out of water and accelerating board as "energy scale" like approx what kind of energies we are talking. If kite fails to produce this energy; get up from water and accelerate to planing, "wind is too low to ride".
So definitely wind has part on this but calculating lift force on anchored polar coordinates to lift up, then on moving coordinates and changing line angles is not "kiteforum simple".
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But let's say on Force-work (force x distance), center of mass moves 3m with 1220J => 1220J / 3m = 410N => 42kg roughly the pull needed by kite on average, sounds reasonable level of lift.
If you go to Nasa foilsim3 with 10m/s flying speed generic airfoil with 2.7% camber and AoA 5deg produces already 824N of lift, so goes nicely above of 3kg fabric mass + 42kg of pull required. 500N lift is achieved with 28km/h flight speed already, so a bit under 8m/s flight speed.
But we must go lower flying speeds and combine kinetic energy of kite which foilsim does not support on anchored kites, and anchor point ~90 degrees from flying vector. But airfoil kinetic speed vector is nicely same plane to airfoil drag vector. On foilsim3 drag with example parameters is 69N on lift 824N. If we evaluate drag with kite kinetic energy => kite (UL example above) kinetic energy is dissipated in drag after flying 490J / 69N = 7m. But naturally if new energy is not coming kite slows down because of pulling anchor and LIFT reduces and due to that drag reduces, so again we are not "kiteforum simple"-area but on integrating formulas area.
But maybe that describes a bit the idea behind flywheel theorem, why high inertial kite is IMO better at ultralow wind speeds. Like on my many times shared video I use 15M Speed4 to door-TT (lower water drag) when 16-17M LEI cannot even be turned/flown to zenith. Meaning S4 15m2 produces all work needed for me to plane and stay in plane, when LEI lift force cannot properly win even gravity. And I really doubt that I could have achieved that in Peak due to high L/D required on proper true 2-skin airfoil to do the trick. Now hydrofoil saves a lot because at HF flight as we know drag goes very low, so if you just get the impulse (force x time) or work (force x distance) done by kite to get on board & accelerate to HF flight speed.
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If you are better in real kite flight calculations, please complete the calculations. I've crossed some kite-electric-power thesis papers, formulas are there etc. I am too busy on other things trying to do calcs based on those.
Peter