Duotone Wing & Foiling Tech Talks - Foil Position, Trim & Shims

[@ph5888]

Great that you are doing this tech talk. I really appreciate all the infos about your equipment!

[@scoty7392]

This is one of the best videos I’ve seen explaining tail shimming and tuning. The only thing I feel is missing is the effects of shimming on feel, pitch sensitivity, turning, and speed. Negative shimming may turn better and be faster but also pitch sensitive and harder to ride, etc.

[@duotone.wingfoiling]

Thanks, happy that it helps you! You're right, it's a fine line between lower drag and being too pitch sensitive when reducing angle on the stabilizer. You can be faster with more angle / a more draggy system because of better control and the ability to push harder. Of course it also depends on your riding level what's best for you personally. Better riders can get away with a more nervous setup and enjoy the extra turning it offers them. Lower level riders will be better off with a more stable system to unlock their best. Cheers, Klaas

[@franpinyol8500]

Hi again, If the stab plays a negative force (down) compared to the front wing (up).... then, a large stab increases lift but does not increase glide nor speed, as a larger stab increases drag and does not add lift... am I right ?

[@duotone.wingfoiling]

Hi Fran, Jerome had some issues to answer your post here for some reason, did not work - lift yes a bigger stab will create more downward pressure, but this can also then lead to the front wing coming up/but makes more drag and can actually make the foil perform worse if too large. Glide can be better normally/but the pump speed/efficiency is mostly worse, as it is then slower to pump. Slower for sure, unless the back stab was too small to start with. Ride weight and experience level can however then vary a lot, as some will prefer the bigger back stab to stay up longer, whilst others want a smaller stab for a higher pump action speed. Generally we try to hit the middle/sweet spot with our foil sets, most of the time no need to change anything.

[@duotone.wingfoiling]

Hi Fran, Jerome sent me this to add to my comment, as you can see, it's not always that simple...:-) Yes, you are right, except for "a large stab increases lift". Not in all cases. Let me explain: During low speed take off, when your fuselage has a positive angle of attack, higher than say 5 degrees, then your stab is momentarily also having a positive angle of attack and it is generating lift in the same direction as the front wing. In that case, a larger stab increases the overall lift of your system. Once you start to accelerate and you reach cruising speed with your fuselage closer to 0 degrees, then your stabiliser is pushing in the opposite direction as your front wing and thus is removing lift from your front wing, making your setup less efficient for a fixed speed and fixed angle of attack (close to 0 degrees). In summary it is a little more complicated when we start looking at various speeds and various angle of attack of your fuselage, sometimes the bigger stab helps, sometimes it doesn't. You might tell me: "well that is weird because I definitely feel more lift at cruising speed with a bigger stab, and here you are telling me that a bigger stab makes my setup less lifty" What you are feeling is not more lift from your system, you are feeling the center of pressure of your system moving further forward and applying more force into your front foot than your rear foot. I hope that I was clear enough and have answered your question.

[@franpinyol8500]

I think you should explain the difference and relationship between "front foot pressure" and "lift". Also, the difference between lift at low speed (before on foil) and lift while fliying at high speed. Are both affected by shimming ?

[@duotone.wingfoiling]

yes, people tend to mix things up a bit here, even ourselves during test reports between different people. So front foot pressure is whilst you are up on the foil already, this is how relating to how much pressure you feel from the front wing pushing upwards under your front foot - many people would call this then lift, as it feels light it is lifting. Actual lift should be the way the foil lifts from getting the board released from the water to a foiling position. Foils with a lot of "lift" in this case, tend to often have a lot or good front foot pressure, but this can be too excessive, if you are looking for speed/manouevers or an inexperienced rider will not know how to use his/her body weight to keep the foil down. Lift at low speed can be good, to get up onto the foil, this can be adjusted by shimming, yes by adding positive tail shims. Or by moving the mast further forward, which is generally the better way to get the "right" amount of front foot pressure. Lift while flying at high speeds is then a different story, as you want the foil to feel as neutral as possible, here I would revert to "front foot pressure" as a guide, to feel comfortable having just enough of it, to be able to push against, without the foil coming up too much. Here negative shims can help to reduce too much "lift" or front foot pressure. But Jerome can give a much better explanation as a designer, this is more from myself as an end user, using terminology/logic from testing/discussing with people on the beach. That is quite different from the sometimes quite technical discussions that some people have/use/prefer. :-)

[@franpinyol8500]

@@duotone.wingfoiling thanks so much !!

[@chriscumming5232]

I’m not sure I understand the front foot pressure concept. Doesn’t this just depend on where I’m standing? All foils generate more lift as speed increases. If I find the front foot pressure increasing too much doesn’t that just mean I’m standing too far back or the mast is too far forward?

[@BonieuxJerome]

All front wings will generate more lift as speed increases IF the fuselage stay at exactly the same angle of attack. Remember that we have not only the front wing generating lift upwards but also the stabiliser which is generating an opposite force and thus subtracting lift from the front wing as speed increases. We explain that in more details in our other video "foil basics" kzbin.info/www/bejne/mJDFfWWhqNqSoaM

[@jmunkki]

Remember that this advice applies to stabilizers mounted on the board side of the fuselage. The effect would be reversed for a brand where the stabilizer is mounted on the opposite side.

[@BonieuxJerome]

Good point! We should have specified that in the video ;)

[@BullroarerTook]

Hi Jerome - Could you please tell me how much shim I should use to make the 216C feel like the older 215 from the Windsurf foil set? (To me the 216 looks and feels much flatter/pitchier.) Thanks. (I can 3D print any angle shim.)

[@BonieuxJerome]

Hi, the 216 stab has about -2.0deg AoA in the center, compared to -2.3deg AoA on the 215 stab. You should thus use a 0.3deg shim on the 216 stab to make it similar to the 215. The thick part of the shim should be on the trailing edge side.

[@franpinyol8500]

At 3:50 , instead of "as you accelerate" did you mean "when you are riding at high speed" ?

[@duotone.wingfoiling]

If your front foot pressure doesn't stay similar if you change speeds (accelerate), but pushes your front foot up more and more and you have to bring your weight forward the faster you go, then you might want to try decreasing your angle of your stab with the use of a negative shim to keep it more balanced throughout the different speeds you're riding. Some riders prefer to have the "safety" of the front foot pressure building up, as it's usually more controlled at high speeds to have a bit of front foot pressure to push into. Play around to see what's actually faster for you and your level of riding. Hope this helps!

[@valentinopucci9879]

Great work guys! My question is : What effects does a negative Shims have while riding a wave? Example: if I ride a one meter wave without thickness and the foil tends to come out of the water, if I insert (negative) shim while riding the same wave will the foil tend to stay in the water longer? If so, will this happen at the expense of delayed flight departure? I hope I was clear

[@BonieuxJerome]

Hi, yes a negative shim could help you in that case, definitely worth trying it and check if it solves the problem you are having. One adverse effect from using a negative shim though, could be that your setup becomes too pitch sensitive. If that is the case, you might want to try a smaller size stabilizer without any shims. Lastly it could also be that the foil you are using is too big and generating too much lift once on a wave. If you give me you exact setup description and your weight, I might be able to have a more accurate tuning solution to your problem.

[@valentinopucci9879]

@@BonieuxJerome Thank you in advance for your availability but I just needed to understand how the shims work in the waves. Sometimes I find myself in the situation I described above and moving the mast is an increasingly delicate operation.