After listening to a few podcasts I started to think of a few key performance dimensions, especially regarding Erik’s developments.
Obviously this is nearly entirely subjective and possibly inflammatory, but I wondered from those of you who have used all of them have mental recordings of their relative performance? (i mean I know everyone does)
(Reedin is entirely speculative based on what KDMaui seems to like from a foil, and it being a mid aspect - and the fact that I’m frothing to try one…!!)
Here is a first attempt
what of these would you agree with on the dimension front? ie is there a better dimension for “pump ease”
Are there 5 better dimensions to measure a surf foil?
Are there better “combination” features than the ones listed in the second image?
I love this Matt! It’s exactly how I think about foils. Something I would add is glide which isn’t exactly speed or pump. It’s kind of like Umami. Hard to describe but you know it when you feel it. Glide was one of the objectives for the Uni we’re doing. Absolutely frothing to share it! First 2 sizes are done
Cheers thanks @Erik, yeah glide makes a lot of sense… I wonder if I should replace “pump ease” with glide, but stoked to hear it resonated, and that you are doing well on the uni project.
I was thinking, what is the simplest trade-off dimension with a surf foil, and I guess it boils down to glide and turn (manoeuvrability)?
Comparing to surfboards:
Glide is like board length - where a longer board is more likely to let you get past flat sections on a wave, glide is similar
Turn is like board outline - rounder outline allows for a more dynamic turn, straighter is faster
Maybe the other dimension to add is speed (slow is like a rockered shortboard, great for in the pocket powerful waves, fast is like a flatter board, better for flatter waves).
This is great! I’m still trying to wrap my head around the different feels of the foils, which I like better and why. Having a good mental model of the tradeoffs helps. Here’s a rough sketch of the kind of mapping I’m trying to understand, but I don’t know nearly enough to actually fill it out. But it still helps to give me a sense whether I should be tuning, changing parts, or changing systems to get the feels I’m looking for.
Whenever anyone talks about how well a foil turns, I’m not sure how to interpret it. I feel like there are different aspects to turning. How easy it is to initiate a turn is one factor, and how hard it is to adjust or exit a turn once it’s started (how locked into the turn you are) is another. With some foils the roll resistance remains fairly constant, whether the resistance is high or low, but some really resist any changes to roll axis once a turn is initiated. I think I’ve heard it referred to as a pivot turn vs a carving turn and I guess it’s personal preference which people prefer.
Very interesting this thread!!! But can we deduct that a larger wingspan for same cm2 will always turn wider? Can we always deduct that a higher AR will overfoil sooner vs a lower AR for same CM2?
Can we always deduct that higher AR will glide better for same CM2(I guess thickness must be taken into account?)
I really liked the way that @TooMuchEpoxy described his taste for a foil. I like the foil that is having that amount of wingspan. I prefer to keep the same width and change the AR instead to have the same feel.
Is probably too simpliste, but:
let say I’m super confy on big waves(big wave for me is not really big waves) with a 78 wing span at 6.5 ar, I do fill it’s not over foiling it carves great, I do have a shortboard feeling instead of glide and trim surfboard…that I have with my higher AR foil…but I would love to have a bit more glide however.
So let pretend the foil I have is 950 and to have a higher AR with more glide and wish to have the same surf feeling, i would go to something like 750 for 78cm.
What are the other characteristics I need to take into account to know that new purchase will not overfoil sooner and hopefully turn and surf similar…and not having that glide and trim feeling of my higher bigger foil?
The magic sauce for designers is the roll/glide ratio. A better foil section will make an equal sized wing more efficient, allowing you to reduce the span slightly. Playing with anhedral, twist, sweep, configuration etc has potential to make a wider span wing turn better too.
The mast, fuse, and tail drag add up to a significant portion of the foil’s drag. Changing one or 2 of these things will also make an equal sized wing more efficient.
I think a lot of our future advancement will come from decreasing drag, freeing designers to play with other factors of the foil design with less consequence. the feeling of glide, acceleration, and “drive” in a foil are the best indicators of low drag. Things like pump can be hugely affected by tuning and ergonomics.
Stiffness is also super important. In my experience a foil cannot be too stiff, only too stiff for an existing foil design. A stiffer foil opens up new avenues in wing design that will end up in more control in the end.
We still have a ways to go as far as bringing all these factors together in a way that is close to optimal. The future is exciting! (And expensive)
@KDW Thanks for that! I’m excited to see some performance gains there. I think immediately we could see some gains from your shop on the rear wing attachment. I like the wings being flat mount because thats the more expensive part and we need that compatability but there’s definately drag drawbacks to that connection. Maybe take the most common wing fuse combos and 3d print some shims that do double duty of fairing in that rear wing to the fuse - think a shim that also runs forward of the wing and wraps around the LE a little to really blend it into the fuse. I do this with epoxy filler and release agent so it comes out as a seperate part - looks 3d printable.
Talking about front wings alone though i find the simple view of span being roll vs glide and area being speed range mostly holds in modern wings. I say modern wings because i think the thickness:chord has been established and that thickness is a big driver of that drag equation.
@KDW i need help understanding the mostly. Some wings seem to break this dynamic through artifically low stall speed, lower than their area would indicate. Looking at lift and drag vs speed drag increases dramatically with speed so getting that artifically lower stall speed is a dramatic boost. Kujiras do this - bumps limiting spanwise flow reducing tip vorticies, also maybe changing pressure stopping stall. What else in wing design reduces stall speed (without changing area)? Is it Camber? I understand camber presents other challenges(diving at speed?) and dealing with that is a big part of the foil design game right now.
