I recently had a wonderful social media conversation about foil wings for WWF versus Wing Foiling. I thought it would be helpful to share it with everyone. Here it is:
Friend 1: Have you tried any recently released wings with low camber foil sections? I find that foils that do not rely on camber to generate lift (rather generate it from angle of attack) have a much better top end. For example the Lift 150 hax (980cm2) has a lower camber than the 120 ha (775cm2) and both of these foils have a similar top end - the 150 is much harder to stall while pumping out of the hole. Granted, I find both of these to pump exceptionally well due to their minimal drag.
I think tuning your stabilizer angle could mitigate some these issues, but draggy front wings will always have problems with speed. It seems in general wind surfers seek out foils with more stability (longer fuze and larger tail). I do not have expience on a windsurfer, but I find that very thin wings which produce less drag allow the use of much smaller stabilizers (with less angle of attack relative to the fuze) which do not build up front foot pressure as the speed increases. This is because they do not need to overcome the downwards pitching moment caused by rapidly increasing front wing drag as speed increases.
Not that this is a discussion about flat water pumping: but for what it's worth surface area is mostly irrelevant for determining how a foil pumps. Efficiency matters much more here. Small fast foils take less energy to keep moving given they have less drag than larger wings.
I think tuning your stabilizer angle could mitigate some these issues, but draggy front wings will always have problems with speed. It seems in general wind surfers seek out foils with more stability (longer fuze and larger tail). I do not have expience on a windsurfer, but I find that very thin wings which produce less drag allow the use of much smaller stabilizers (with less angle of attack relative to the fuze) which do not build up front foot pressure as the speed increases. This is because they do not need to overcome the downwards pitching moment caused by rapidly increasing front wing drag as speed increases.
Not that this is a discussion about flat water pumping: but for what it's worth surface area is mostly irrelevant for determining how a foil pumps. Efficiency matters much more here. Small fast foils take less energy to keep moving given they have less drag than larger wings.
Me: spot on dude! It's amazing how differently these foils work for windfoiling versus kite/wing foiling. The difference is that the weight of the sail near the nose of the board provides a ton of downward pressure on the foil, while the kite/wing does the exact opposite and provides upward lift. It changes everything. You're totally right about the stab angle. We have to use a lot more stab angle with our sail attached to the nose of the board than kite/wing riders use. That stable angle balances the weight of the sail. The flatter and higher aspect front foils definitely do not over-foil, but these wings yaw, slip and slide for the same reason I just mentioned...sail weight. They glide great for WWF, but they totally suck for carving. We generally use them for downwinders. As far as pumping, you are the master in that area. I think you're right on.
Friend1: Interesting.. low camber does not necessarily mean high aspect as this describes the wings cross section (foil section). I wonder if the yaw and slide you describe is actually the roll stability of larger wingspans. These generally need to be counter-steered into a turn by yawing them which then causes a roll in the opposite direction (similar to initiating a turn on a motorcycle). Stabs with winglets will increase yaw stability but on large high aspects will make initiating turns slower.
Not that it applicable to windfoiling, but my favorite foils are >10AR with moderate wingspan -> which means small surface area. Based on what you are saying the sail weight makes your gear choices limited? I cant imagine being able to pump a foilboard with a sail attached.
Foils are awesome!
Not that it applicable to windfoiling, but my favorite foils are >10AR with moderate wingspan -> which means small surface area. Based on what you are saying the sail weight makes your gear choices limited? I cant imagine being able to pump a foilboard with a sail attached.
Foils are awesome!
Me: Yeah, it's a super interesting discussion. Love your input. There are so many nuances. First, there's the distinction between windfoiling and WWF. They are actually two totally different sports. Windfoiling is more like windsurfing, while WWF is more like surfing. For example, if I use a foil >10AR (even greater than 8AR) with low camber and thin profiles, it turns WWF back into windsurfing. It's back to big cumbersome sails, lots of harness use, rear footed stance, and speed. With the opposite approach (lower aspect, more camber, thicker profiles, very small sails) it turns the gear into surfing machines with a front footed surfer stance, out of the harness, wave slayer experience. The middle ground is fun to explore though, like using the RS1300 and EZ1600. I use both of them, but not nearly as often. They're just not as surfy. The glide is better which is the main reason I use them for certain situations. You can ride a wave forever, but you can't slay it. The sail makes the sport so different from wing/kite foiling. You can pump ok if you time a little downward boom pressure from your hands with the drive/float/climb/load of the foil pump, but we rarely pump because it's so easy to engage the sail a tiny bit when a little power is needed. I have definitely found that WWF is a niche sport. No one makes gear for it. We use kids sails because manufacturers have no idea what we really want. We use older foil models because newer ones don't perform as well. Custom designed boards because no manufacturers build what we want. Sounds crazy, right? It's just a small group of WWF riders on the Great Lakes, and a few scattered throughout the country. So much freakin fun though!!!!
Friend1: Interesting! I'm sure its different, but from my experience winging I don't agree with the points you made about small foils. I don't ever ride anything larger than 980cm^2 and use a 4m wing down to 12kts. To do this a long skinny downwind style board is key as it lets you get water speed less powered up. When I'm surf foiling or wing dinging downwind I much prefer to be on a foil that can easily outrun the waves - this allows you to be much more agile with the lines you take rather than be confined to only riding at the speed of the wave.
Me: I totally agree with you for winging, prone foiling and SUP foiling (and freestyle windfoiling in the waves). I think you're exactly right. It's different for WWF. We don't want all that speed. With anything much smaller than 1300cm^2 it becomes more speed oriented and rear footed windsurfing instead of front footed surfing. You can still have fun, but we lose the surfing experience. The sail is attached to the board and counter rotation of the sail plays a big role. Once the sail is flagged, then with every cutback, you experience counter rotation from the sail. This counter rotation induces roll in the foil. The rider compensates by tipping the sail in different directions which helps drive through the turns and control roll. But once you're in switch stance the body can only bend so much before you can't control or even reach the sail. So the slash and slay we experience is different than the slash and slay in other foiling sports. We want much less speed through cutbacks and more drive and grip. Too much speed while turning makes the sail uncontrollable. It's a much, much slower approach than other foil sports. Freestyle windfoilers go out in the waves with gear similar to what you are using, but they are windfoiling in the waves instead of surfing in the waves. It's all so much fun!
Me: To expand on the great discussion above with Brendon, here is an article from Windfoil Zone that distinguishes between the 4 types of windfoiling (actually 5 types as of 2023 if you include what the Slighshot pros are doing at the Columbia River gorge with large foils and small sails). https://windfoilzone.com/4-different-windfoiling-types/
Friend2: I read all your discussion points with interest. As a former hang glider pilot for many years I have a pretty good understanding of basic aerodynamics which I believe are similar in many ways to the hydrodynamic principles effecting how our foil wings fly through the water. In particular, Brendon you wrote; "I wonder if the yaw and slide you describe is actually the roll stability of larger wingspans. These generally need to be counter-steered into a turn by yawing them which then causes a roll in the opposite direction (similar to initiating a turn on a motorcycle). Stabs with winglets will increase yaw stability but on large high aspects will make initiating turns slower." Perhaps what is happening to cause the higher aspect and flatter wings in particular to yaw and slide around is "Adverse Yaw". The basic principle as I understand it is that in an aircraft you generally initiate a turn to right or left by activating the ailerons first. Lets say you are turning to the left. When you move the stick or yoke left the right wing aileron goes down and left wing aileron goes up. The downward aileron on the right wing increases camber and initiates more lift on that wing and the wing rises causing the plane to roll to the left. Then as the turn is initiated the apparent airspeed over the right wing increases because the wing has a greater arc to travel through the turn than the inside wing . This in turn increases lift even more since it is now flying faster than the inside wing but it also increases DRAG. This increased drag then can cause the nose of the plane to yaw to the right as the increased right wing drag actually tends to pull the nose in that direction. To correct and counter this in a plane the pilot usually applies some left or right rudder to reduce or prevent the adverse yaw. However, in wind and wing foiling we don't have a moveable rudder on our tail wing stabilizer. Using toe and heel pressure we initiate wing roll like a plane uses its ailerons. We control our pitch to dive or climb by front and rear leg pressure, but I can't think of any way we really have the ability to apply an adverse yaw corrective force to our foil wing in the way a plane rudder does. Anyway, this is a long explanation as to why I think what Eric describes as his wing yawing, slipping and sliding around is a function of adverse yaw at work. What do you guys think?
Me: From what I've read over the years, I think that's exactly right. Thanks so much for bringing that up. You guys are smart dudes. Everything Brendon says is exactly right in my opinion. What is so interesting to me is how it applies differently to foiling with a sail as opposed to foiling with a hand-wing. When foiling with a sail, changes to the foil will quickly change the sport from windsurf wave foiling to high speed wind foiling (by definition) with some hybrid sports on the spectrum in between. I think that happens for 3 reasons: One, because of the weight of the sail near the nose of the board, as opposed to a hand-wing lifting the board. Two, because of counter-rotation from the sail during cutbacks. And, three, because when we shift from low aspect/larger foils to higher aspect/smaller foils, resulting in larger sails used, we must change our entire stance on the board to accommodate. The entire stance shifts from front-footed surfy to back-footed windsurf stance. I carefully watch video of pros in all categories of foiling with a sail, and the stance shift is opposite at the ends of the spectrum. Complicated stuff, but these conversations make a huge difference in my understanding. Thanks guys!
Friend1: Interesting take! Not that I fly but as you describe - with an aircraft a turn is induced using the aileron, and than the rutter is used to correct for the yaw.
On a foil (because the center of mass is above the wings and you do not have flaps) I find that when I turn hard, I yaw the foil to the outside of the turn which induces a roll. So sort of the opposite order as in a plane I think. It's similar to countersteering a bike because you are balancing on something below you.
On a foil (because the center of mass is above the wings and you do not have flaps) I find that when I turn hard, I yaw the foil to the outside of the turn which induces a roll. So sort of the opposite order as in a plane I think. It's similar to countersteering a bike because you are balancing on something below you.
Addition: (Here are some additional thoughts that were not included in the conversation above.) The RS1300 (high aspect foil wing) is difficult to over-foil because of its high aspect nature, flat design, and thin profile compared to the Iwa and Maliko. The glide is incredible, however, the trade off is that the RS1300 has terrible grip and does not carve for WWF. It yaws, slides and slips through turns instead of carve. It's a lot of fun when you want incredible glide, but offers a very different riding style. These type of front foils are geared more toward wing foiling where the rider's feet are close to the centerline of the board. With the feet near the centerline the rider wants that very sensitive roll of the front foil (like the RS1300) because the winger's foot position has little leverage against the foil wing. But with WWF we ride boards with 30 inch width to accommodate the sail dynamics, and we put our feet at the rails of the board to turn. The heel of the front foot is at the upwind rail and the toes of the rear foot are at the downwind rail. We can carve like crazy on a front foil like the Iwa with all that leverage, but the roll sensitivity of the RS1300 makes it a poor choice for hard carving.
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