Description of how a hydrofoil stabilizer works and how you can use this knowledge to get capture more energy from waves and feel more confident and in control when riding.
Thank you for the top video and the very didactic content. On French forums, the convention for the sign of the angle is reversed. They are referenced with respect to the plane of the front wing (= longitudinal v), placing a shim under the front screw (for a tail under the fuselage in navigation as yours) corresponds to increasing the angle difference between the tail and the front wing (= increasing the longitudinal v), and therefore we say that the angle of attack is positive. It can be confusing with all these conventions.
Hey Gwendal, really appreciate the kind words man. Omen uses that convention too, but mispoke in the video at one point and referred to it a negative angle. I agree positive should be in the direction of increasing downforce from the tail and negative should be decreasing downforce. When looking at the foil it's easy to mix it up though as more positive shim makes the stab point "down". Sorry for mixing that up and adding to the confusion!
I recently joined the church of negative shimming last winter. Reducing the angle of incidence for the stabilizer has really helped with weight distribution and reduced drag. It also makes the foil less pitch sensitive.
Hey Tai, stoked you're getting great results with your gear, messing around with tuning is the best way to learn more about your gear. Negative shimming relative to what though is the question. Every brand has a different angle built into their tails so a "negative shim" on one brand might bring your foil into perfect tune while the same with another brand could be going too far and make it super unstable.
@@omenfoils I wish more brands listed their built in angles. The current Kraken fuselages from SABFoil have 2.3 degrees baked in, which is increased from their older fuselages.
@@taiguy yeah, lots of angles at play so it get's complicated fast. They probably don't want to overwhelm beginners with too much info. Ultimately though, the actual angle doesn't matter if you do this procedure to dial in the amount of shim.
Thank you SO much! Best explaination I have heard so far. So much conflicting and inaccurate info based on random opinions and lack of experience out there. This is so helpful. Well done!
Thanks Philippe, stoked to it's helpful info. Recording this one I was a bit worried I'd gone too deep and too long (first time for everything). Didn't want to oversimply things though and I think for riders like me a deep understanding of the mechanics leads to better riding.
It does come at a cost though! You'll notice your foil is harder to pump/generate speed going slow due to the lack of stability and also have to fight the tendency to nosedive at high speed. Have fun playing with it!
@@omenfoils Understood. I'm thinking for low energy downwinding where you might want a bit of help to get up, are often flirting with the low end of the foil, and have a paddle to assist in generating forward speed a negative shim might be a net benefit. Will see!
@@solentfoiler5969 yeah, you are definitely correct - how far you can push it without losing stability is the real question :) Looking forward to hearing how your experiments go!
Great job, Greg! Super clear information. I love that even though I'm a pretty tall rider, the Omen 850 Operator/87 Stiffy/Ahi small without any shim feels pretty great out of the box. It's one of the few rigs that I'm not feeling the need for a lot of faffing, even though it's something I kind of enjoy. You can just hop on and know it's sorted from the first ride and rip!🤙
Believe it or not, your lift force always equals the weight of the system when cruising. (Basic aero/hydro dynamic knowledge) Lift and weight are said to be balanced. When the lift gets bigger (than the weight) you start climbing (and opposite). Ideally you do not want your system to climb or drop as the speed (e.g. due to wind speed change) alters. Usually the gear starts to raise the nose as the speed increases which you compensate by moving your body mass slightly forward. If your original trim reacts as described so far you may shim your tail foil to give it less down angle. This reduces the overall nose up climbing which in turn must be compensated by either moving your body to the back (or the mast to the front) If this is trim procedure of reducing the down angle of the tail foil is overdone the gear will start dropping (instead of climbing) the nose as the speed increases. There exists a sweet spot for the tail foil angle where a change in speed wont let the nose either rise or drop such that no corrective relocation of the body mass is needed. It is not desirable to reduce the tail foil down angle so much that the nose drops with increasing speed, better to stay slightly away form this trim point. Better let the nose climb slightly (but not to much) with increasing speed. It should be noted that reducing the tail foil down angle comes together with a necessary relocation of the mass to the back (or mast to the front). As the center of gravity moves to the back the dynamic stability of the system is reduced. many tiny mass relocations correction are needed to compensate for this. If your trim has a rather large down angle the mass must relocate closer to the front this increases the dynamic stability but unfortunately gets you a nose climbing setup as the speed increases.
Hi There, did you watch the full video? I don't think I implied (and if I did, certainly didn't mean to) that the total lifting force increases or decreases with changing the tail shim. Only that (as you state above) that it will vary the rotational moment of the system which must be compensated for by the rider shifting weight as speed changes (or with a great tail design with the perfect shim is balanced through the full speed range).
Also, I would add that most stabilizers are not perfectly designed for the exact setup people are riding so getting them to balance at one speed does not necessarily mean that balance will be maintained through the speed range. This is one of the reasons we have a tail dedicated to each front wing and a shim recommendation for each mast length.
On your last point regarding relocation of mass that's what I was trying to demonstrate showing how my hips moved forward at high speed with "too much" tail shim and backwards with "too little". Maybe an animation would be more helpful to show these concepts. Sounds like you have a great understanding of flight dynamics, I didn't want to get into static and dynamic stability as the video was already a lot longer than I intended but it's a great point and one I hope to tackle in the future :)
Thanks, really glad to hear the content is hitting the mark. Have to give credit to Dave who has been doing an awesome job editing the last couple videos which I think makes them easier to follow from an attention perspective.
Great detailed video! I will be for sure sharing with friends who don’t understand tail shimming. I really enjoyed the last bit about longer masts and tail size/shim relationship. I’ve been winging a system that allows fuse, mast, and tail/shim adjustments. Over the years I’ve come to think of rigging up my gear like I’m a chef or mad scientist. I like to mix things up based on the wind and swell size and I’ve made most of the same conclusions you outlined, but through trial and error, not intelligence. It really is a personal thing, as I know people who ride completely different settings with the same gear and seem perfectly happy. I hope to demo your foils sometime soon! Let me know if you plan any demos in the Mid Atlantic USA.
trial and error is at the core of all scientific knowledge my friend, nothing unintelligent about it! That and wild speculation is how all this stuff was figured out. Dave from theliftjournal is an ambassador in NJ, shoot me an email and I'll connect you guys, would love to get you on the gear Graham! greg@omenfoils.com
Hello Greg, great video! What do you think about shimming for Downwind? Considerations for easier takeoff? Also, Shimming considerations for big wave conditions vs small wave conditions winging? Or do you set the balance and never touch it
I don't SUP so this should be taken with a grain of salt! If you shim a bit less it will slightly increase lift during takeoff, but that being said it will decrease stability, in your low-mid range speed which would make it easier to blow a wave at the beggining as you are accelerating (I've felt this when under shimmed surf foiling). For big vs small wave surfing on our foils I don't change the tail shim, as you suggested it can be thought of as setting the balance of the system or tuning an instrument. To adjust for wave size/speed I do use a baseplate shim though and made a video on the topic a couple posts back. If the waves are too big for your foil even with the baseplate shim the next step is a smaller foil and similarly a bigger foil for smaller waves. All that being said though, this is assuming the the front wing and tail are designed together and the tail creates the right amount of downforce through the whole speed range. This is not the case with most foils though so I could definitely see the merit in changing the tail shim to suit the conditions (despite that it would be a lot to manage if you have a few foils). You could do the same exercise I showed in the video to determine the perfect shim for slow speed, mid speed, and high speed of your system and then use that shim for small, medium, and big conditions (relative to the size of the foil). Does that make sense?
I really appreciate your high quality content. I do have a question though. What is your perspective on when to make slight adjustments to the mast position (forward and back) versus when to begin to play with shims as outlined in this video? Regards!!
I think you may have answered this question in the previous video on "track position", although I am still a little confused about the relationship. Regards!!
@@WingedSturgeon happy to provide clarity if I can. The mast position changes the how the system responds when you unweight the board. Mast too far forward and the board with pitch nose up when you unweight and vice versa for mast too far back. Tail shims are similar in that they also control the pitch of the system but in relation to speed rather than weighting/unweighting. Dopes that help?
Great video! Weirdest combo I've ever used is a 1780 with a high aspect DW 157 tail. My question: On one of my foils when I put that specific DW 157 tail on (it's monoblock, no shimming allowed) the foil becomes incredibly difficult to get into the air. However, once in flight it is insanely fast and skatey which I like. I'm having a hard time understanding exactly why this makes it harder to take off, but so fun in the air. It doesn't have increased front foot pressure at speed, but it also doesn't have good takeoff, so I'm just a bit baffled as to if this tail is naturally sitting nose up? Down? Flat? Thanks!
Hey Bryan, that is a weird combo! I suspect the problem you are encountering is due to the tail being too small for the front wing as you can probably imagine. To explain what you are feeling thing about your take off with a larger tail. With the front wing at a high angle of attack you'll be getting positive lift from the tail which will decrease your stall speed. Also the larger tail (and also a more cambered planform) will produce significantly more downforce at low speed meaning it will be easy to balance. In your case your foil will be very hard to balance at slow speed but will get easier as you go faster and the high aspect tail starts to produce more and more downforce. Does this make sense? Ultimately it sounds like you know what you're doing, I would think a smaller foil with properly matched tail might actually be a better overall setup for you even in super light wind. Of course that is highly subjective though, curious to hear your weight and reasons for going to the 1780?
@@omenfoils well in the instance of the 1780 it was just for a test run to see if it would work, and it was fine! That was the first foil I ever paddled up. Never ride it anymore. For my recent issue it's actually on a 900 so I don't think the 157 DW tail is too small, but it seems like it has zero lift?
@@Bryan-Wouzel I get it now! I misunderstood and thought you were asking about the 1780. That is surprising the 157 doesn't create enough downforce for a 900. It would lead me to think it is very low camber section at a small angle of attack, however if that was the case it should provide good low end performance. Sorry Bryan, not sure I can help you on this one as I'm stumped as well!
Where did you learn all this knowledge? I have searched for literature on the hydrofoils we use but I have not found any. I have resorted to aerospace engineering, trying to extrapolate, but I make mistakes regularly.
Same way I learned about composites fabrics when starting out on what has become known as Aluula. Lots of hypothesis, thought experiments, trial and error, and ultimately trying to surround myself with people that are smarter than me!
@@omenfoils Thank you ! I was wondering about the size of the stabilizer. A long fuselage increases the stabilizer torque, so this means that if one has a long fuselage/small stabilizer, they have the same amount of torque as a small fuselage/large stabilizer. I have read and it seems logical to me that the induced drag from an increase in stabilizer size is greater than that associated with lengthening the fuselage. So why don't we see long fuselages and tiny stabs?
@@gwendal5620 great question, the answer comes down primarily to turning since the fuselage also affects the foil's turning radius and feel during a turn. For Omen we tried to choose the perfect fuselage length to hit the sweet spot between efficiency and turning performance. Also, the drag of the fuselage comes into play more when the foil is running at really high or low angles of attack so although a really long fuse and small tail may be more efficient when running at peak efficiency it would decrease the range of the foil in addition to affecting the turning performance as above.
great video, thanks. agreed on every thing you said and learned a few new ones, but there's something I didn't understand and would love a clarification about it. At minute 14 you start discussing what's wrong with too much angle of attack in the stab and you say "even though it might feel like more lift, it's only more front foot pressure, as there's actually less lift because the stab is creating more down force". I'm not sure what your definition of lift is, but if I "feel more lift" because of "more foot pressure", that's enough for me to call it... more lift! The stab is connected to the front foil via the fuse, so if the stab pushes down more, it makes the whole setup want to go up more and, again, that's what lift is in my world! And it's also compliant with one of my fundamental empirical observations I developed over years of experimenting: more lift always means more drag. So, why is it not more lift for you? Thanks!
great question gcgrammar, I didn't go into enough detail on this point as I was already aware the video was getting super long! The difference between "feeling" more lift as pressure on your front foot and more lift from the system is quite a big difference actually so important to understand. You are absolutely correct that generally more lift = more drag, however with the hydrofoil the front wing is lifting up (and creating drag) and the tail wing is "lifting" down (and creating drag). So this means if you add more "lift" to the tail by increasing it's angle of attack you get more drag, and also more front foot pressure since the tail is creating a rotational force which you need to counteract by shifting your weight forward. Nothing new there I'm sure but the next point is a key one! Every foil you have ever ridden is producing the same lift, if you think about it all it is lifting is itself, the board, and you - so whether it is a 2000cm front wing or 600cm front wing the "lift" is the same. The difference is what angle the foil is at to produce said lift through the speed range which corresponds to drag. So a large front wing will produce the same amount of lift as long as you can ride at the same speed, but the smaller wing will produce less drag (in general, as lots of other factors are at play). With this in mind, if you think about the tail producing more downforce, now the front wing has to produce more lift to counteract this downforce. This means the angle of attack of the front wing must increase slightly which also creates more drag. Does this make sense? Apologies for my complicated explanation, much easier to demonstrate with a white board or model!
@@omenfoils thanks a lot for putting that much effort in the explanation. I got your excellent point of any foil creating the same lift when it has to counteract the same weight (foil+board+rider), but with different drags depending on size and shape of the foil. That's why a 600 will always be faster than a 2000 if it's always me with my board riding it, I guess. But let's go back for a moment to the case you were presenting. If I increase the angle of attack of the stab and compare it to the same setup with less angle of attack, I now agree that at any same speed, the lift is the same. But doesn't adding more angle of attack to the tail also lowers the stall speed compared to less angle of attack? There'll be overall more drag, but if you have a steady pull from something (like a jet ski, for example), it should start flying a bit earlier than the same setup with less angle in the tail. That's my experience, at least, and that's why I call it (maybe technically incorrectly, I give you that) more lift. Thanks again!
@@gcammar happy to man, love chatting and thinking about this stuff. Often in explaining things it also sharpens my understanding or helps me to look at it from a new perspective. Most of what you are saying is 100% correct, with a jetski pulling you on a foil if you increase the angle of attack of the tail wing it will cause more drag and "feel" like more lift since you will get increasing front foot pressure as you speed up. The subtle thing you are missing though is when you take off the fuselage is not flying level, the whole foil is acting at a positive angle of attack. At this point the stabilizer actually provides additional lift since the angle of attack of the fuselage is so great. If you shim your tail for "more downforce" it actually reduces this angle and means you need more speed to take off. You will however get the feeling of stable flight starting at a slower speed, however as speed increases this will quickly go away and be replaced by too much front foot pressure.
@@omenfoils thank you, I love talking and understanding foils too. I understood the subtle thing you explained and yes, it opened up a new perspective for me. Here's the thing that makes me think it doesn't really apply to my case, though. I do four foiling disciplines (in order of preference): 1) Foil Drive (Plus, not gen2) assisted SUP foiling on waves, 2) Foil Drive assisted SUP foiling downwinders, 3) winging downwinders, 4) winging on waves. My Foil Drive board is 4.10x25x95L and my wing board is 5.0x26.5x90L, both custom and both with a perfectly straight rocker in the back half (if you really care, you can see them in this video: ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-pWp92_7AHPU.html) and that means that in all disciplines, I always take off by having the board plane first and then letting the foil come up out of mostly speed. In other words, I never really pump the board too hard when I take off and I keep the angle of attack of the board compared to the water surface always pretty small, no matter what foil I ride. So, in my particular case, it seems to me that in the pre-takeoff planing phase the fuse is always parallel to the water surface (because the board is still touching the water) and maybe that's why I experience the fact that a higher angle of attack of the stab makes the take off happen at a earlier moment/slower speed than with less angle of attack. Any thoughts now that I gave you more info? Thank you.
@@gcammar The board would still be at a positive angle of attack in order to plane but I do get your point that it is much less than stall so agree my point about getting positive lift from the shim is not relevant in your case. Perhaps you are shimming your tail to the same angle of attack as the board makes when planning which means the tail is at zero relative to your speed and giving the lowest possible drag meaning more energy can go into accelerating the front wing?
I was confused watching the video thinking that is opposite of what I feel with Armstrong. I guess with Armstrong you do the reverse? Start with no shim and then add shims until it feels balanced?
@@omenfoils you suggest that adding shims would make the nose of the stab point further down, but my shims are thicker towards the rear, so the nose of the stab points further up.
@@visskiss You have to think about it as changing the angle of attack of the tail wing. "Adding shims" is too general since the shim could increase or decrease the angle of attack.
@@Bravohi I believe Armstrong labels their shims the opposite of most brands and what I explain here. Start by shimming the front of the tail lower to get more downforce from the tail and then have the tail get "flatter" until you reach the sweet spot. Does that make sense?
It's confusing if "too much front foot pressure" should be solved by shimming or by a) displacing rider weigth to the front or b) changing the stance (moving front foot forward).
This video doesn’t show shimming as a way to deal with too much front foot pressure. It shows shimming as a way to counter “front foot pressure that increases with increasing speed.” Basically, you should be able to get a mast position and foot position that works for most speeds. If you find yourself needing to shift your stance to increase front foot pressure as speed increases, THAT’s when you need to try shimming the stabilizer.
@@griffinbrungraber9498 great explanation Griffin. Fran, all three of the things you describe can "solve" too much front foot pressure, but as Griffin points out only changing the shim can solve it though the speed range of the foil rather than just temporarily.
