Generally I eyeball the tail looking from the back along the line of the fuse, and tails that are factory set the trailing edge is almost to the very “top”(as when in use), so maybe 80-90% of what you see is the underside, with a sliver of the top surface showing. When mounting the kd race tail same as marlins, it shows more of the top, which squares with the description of it tuned for more speed.
So anyway I’m playing with my old 980 for foildrive, but I don’t have any stock tails with me, just kd tails, and since the hd to K1 fuse has a significant angle to it so it’s not perpendicular to the mast, my eyeball technique has no reference.
Using my phone’s level, I measured the difference btwn the angle of the flat sides of an afs front wing and tail: 2° difference less drag on tail, so I shimmed my kd race tail so it has that same difference from the 980. Now, it’s possible it was just too small for the weak waves and cold water, but even with a mid length board I couldn’t get it going.
So question, what is a good standard way to check that the tail is in the right ballpark?
PS: My advice is save your $
Go to a “test” friendly spot to setup gear (flat water, easy launch and land,take shims and tools to the waterline etc…).
Eyeball,ride,adjust,repeat…get it perfect, go ride anywhere.
Agreed. There’s no good way to measure angle that’s repeatable between tails besides feel. I usually put my mast where I want it and shim till it’s rideable
If you care about this topic, I strongly recommend you pull together a simple rig to accurately measure the angle of incidence of the tail versus the front wing. I’ve been doing this for 5 years every time I tune in a setup. Having the ability to get a setup the same is super valuable since conditions change so much session to session. Yes, it is all about how it feels and don’t just set it to numbers. But if you don’t know what the setup is, you can’t evaluate differences.
Here is a photo of the setup I made for this.
It is this level from Amazon combined with a couple pieces of wood cut to V-Blocks and with a piece of metal attached so the magnetic base of the level sticks to them.
If people are interested, I’ll post some better pictures of the setup. pretty easy to make.
To answer the question you haven’t asked - these days I am really like tails setup at 3.5-4deg angle of incidence to the front wing. That’s pushed a bit towards glide efficiency at the expense of a bit of pitch stability. For surfing waves where glide isn’t needed, I like 5deg. It seems to help make the foil a lot more stable in the low end.
Omen had a good video about this! Set mast to align front wing with board center of mass (previous video), then go riding and max out your foil speed and adjust stabilizer angle until it feels stable without creating too much front foot pressure at that speed.
So what are the two surfaces you are using for this? I’ve heard that approximate number before but my measurement of a factory stab as I said was 2°. And the phone level is as far as I’m going to go if I can’t just look at it, before feeling of course.
After looking it up it seems people find the line from leading to trailing edge. Doing that my 980 rig is at 4° difference when feeling the edges with my fingers so not exact by any means. When I eyeballed it I had put a 1° shim in there which made it right it seems. So maybe at 140cm it’s too small for this use.
Yeah but camber really throws that out the window. A camber vs flat vs symmetrical are going to measure radically different to achieve the same balance point
Typically a line from the center of the leading edge to center of trailing edge. This has traditionally been done in aviation with V-Block type fixture. That’s not perfect representation of the theoretical angle of incidence, but its good enough for a repeatable reference.
yes it I thought that too. All my front wings tail wing combinations shine at slightly different incidence angles. However, across several different pairs for the last few years I’ve not been unhappy when I start at 3.5deg and then try + and - in .5deg increments.
Years ago in the early days of big thick wings and hefty tails it was much more common to see 6-8deg tail angles built in. Super stable, but man did a lightbulb go on when I chopped the tails and took them all the way down to 4deg → the drag just evaporated.
Don’t worry much about actual front to rear wing angles. It could lead you down a very confusing path as changes in area, airfoil and other factors will change the degree angle required to achieve the same result.
The exceptions would be if your tail angle adjustment isn’t labeled or reliably repeatable, are checking to compare to simulation results, and a few other edge cases.
For example IQ windsurf class needs it because bad tolerances lead to a large variations in angle even with the same parts.
I have ridden foils at around -7 all the way to more than +1 between the wings that have the same balance, just different wing designs.
Interesting datapoint KD, good reminder not to zone in on a specific angle across all designs. My experience is more limited than yours obviously.
It takes experimentation to match up the right tail and the right incidence angle setup to get the feel right. In my opinion, having a way to measure the setup helps keep track of what works and makes it easier to dial in a setup. Maybe within a given brand’s system this isn’t necessary, but its a godsend when mixing and matching tails that don’t always fit up cleanly. I guess to each his own.
Thanks Kane, since they are your tails I’m working with and I’ve seen footage of you on the 980, I wondered if you specifically used the strangely angled HD to K1 fuse? Something seemed way off so I just want to get in the ballpark, and it seems like I might need a 3° shim or something.
Btw k1 front wings always had a completely different angle of incidence from other foils, which I think is why this fuse has its prong pointing upward like a……hmm I can’t think of anything……in order to make it closer to what seems normal, ie bottom surface roughly parallel to the fuse. For some reason they continued that angle for the rear end, but seem to have the tail cutout level so that should have fixed it. I wonder if, at low speeds, that fuse is going through the water so far from horizontal that it’s preventing acceleration, and I could overcome it when winging and prone sometimes but with fd it’s too much for it once I complete my j-turn. I hope there’s a fix because it seems like the ultimate fd foil.
I suspect the idea of the angled fuse is to align the fuse with the downwash from the main wing. It’s hard to say if that is effective or not, would require some careful side by side testing I guess
My 178 is up at camp, but I found an old heavily chopped 220. Compared to that, the kd race is 2° less drag, and on the tiny side. So next time I’ll try the chopped 220.
