It will probably get a lot crazier, here is grok description of Dynamic Soaring by radio controlled (RC) planes - “When RC gliders soar behind ridges in fast circles, it’s called dynamic soaring. This technique uses the wind gradient—differences in wind speed and direction between the air masses on either side of a ridge—to gain energy and achieve high speeds. Pilots fly tight, circular patterns, exploiting the wind shear to accelerate the glider by repeatedly crossing between the fast-moving air above the ridge and the slower or still air in the lee (sheltered side). This creates a continuous loop of energy gain, allowing the glider to reach impressive speeds, often exceeding 500 mph in extreme cases.”
Here is video or RC pilot going 548mph just from “taking” energy from ridge wind updraft high velocity air and behind ridge low velocity air
This has applications to downwind SUP as you gain energy and speed going across a wave face and then use that energy to climb up and over the next wave face usually aided by pumping, though one would not theoretically have to pump. This is the same way Albatrosses extract energy while soaring low over the waves in the open ocean. This video explains it very well.
Foil designers take note!! The albatross wing airfoil section is uniquely suited to the high speed and low speed flight. This image shows the different airfoil sections of different birds and the Eppler, a modern manmade airfoil shown as a comparison to the bird airfoils.
This graph shows the Life/Drag ratio of the different airfoils over different angle of attack.
The Lift/Drag ratio corresponds to many performance aspects, most easily understandable is the ability to glide, if a L/D ratio if 5 then one could glide say 100 feet and if the L/D ratio was 10 then one could glide 200 feet all else being equal. The reason the chart is plotted over the angle of attack is that the angle of attack is the same as the speed one is flying, although it is an inverse relationship, so 16 degrees is very very slow, think slogging behind a boat going 5 mph being pulled with your wing 2,000 cm2 wing at a super high (16 degree) angle of attack, then 8 degrees is a doubling though lift goes up the the square of velocity so the speed goes up only as the square root of the doubling of the angle of attack or sqr(2) = 1.41 so 16 deg and 5mph becomes 8 deg and 7.1mph, then again 4 deg becomes 7.1x1.41 = 10mph, then again 2 deg becomes 14mph, then again 1 deg becomes 20mph and 0.5 deg becomes 28 mph. When you drop down to your 1,000 cm2 wing you need to be getting twice as much lift per cm2 of your wing so again life is velocity squared so you would need to be going 1.41x faster than on your 2,000 cm2 wing. This means 16 deg = 7.1 mph, 8 deg = 10 mph, 4 deg = 14 mph, 2 deg = 20 mph, 1 deg = 28mph and 0.5 deg = 40 mph so one can see to do dynamic soaring while SUP foiling one would need to have a good glide ability which means to have a high L/D over a large speed range and this means a over a large angle of attack range from like 0.5 deg to 8 degrees. Looking back at the L/D vs angle of attack chart one can see that only the Albatross wing airfoil section has a high L/D ratio at both high speed and low speed and its also quite thick which is counter to some brands of very thin foils on the market today. Especially at 0.5 and 1 and 2 deg the albatross airfoil is almost 2X the L/D of the other airfoils. One feature all of the bird airfoil sections have that many modern foils have today is a deep and pronounced concave or reflex section on the rear lower surface, although one can see on the albatross airfoil this concave section is very smooth, long and more shallow then deep, and goes from the trailing edge all the way up to about 80% toward the leading edge.
Here is a link to the open source paper where the images were taken from:
https://doi.org/10.5028/jatm.v12.1182
