Axis surge vs uni Evolution

1

Rider 90KG, surf foil with foildrive (beginner / inter)

Setup 1: surge 890, Crazy Short, progression 375 tail, 0,5 + Shim (Black)

Setup 2: evo 155, Short fuse, afterburner 14.5, 1,0 plus shim (red)

I flew both wings in the same conditions (waist-high waves).

Axis Mast on both setups.

I feel like the Surge can be flown at a much lower speed and gives me a lot more lift – even though it’s clearly smaller than the Evolution 155. With the Surge, it’s much, much easier for me to maintain height.

The Evolution 155 feels like it needs more speed, even though it’s significantly bigger. In smaller waves I’m constantly using the motor and can barely maintain good height. Always low on the Mast After one turn.

Does anyone have any tips? Is it maybe the AB 14,5 backwing? (to Small?!)

I actually really like the Evolution, but I have the feeling that a similarly sized Surge (maybe 950) would have noticeably better low-end performance and still more speed.

2

More shim, a longer fuse, or a larger tail should help. I had the same issues you describe on the same setup and the first two both worked for me independently. I would like to try the 15.5 AB but they are sold out.

1 Like
3

I find the AB tail doesn’t have much low end and is more of a neutral carve tail. That axis tail seems to have more chord so you could try a chopped uni prog tail with the evo?

1 Like
4

Perhaps a little off topic, but I’m curious how tails help with low end at all. Don’t they push down to counteract the pitch moment in the wing? I’d imagine this just changes the neutral angle of attack of the foil, which you could also compensate for simply by adjusting your stance and or front to back pressure. Otherwise, I believe the tail is largely for control tuning not low end. Is that the right way to think about it? Technically, I’d assume a bigger tail decreases low end if it adds drag.

5

I dont know the physics but you can feel it while dockstarting:

bigger stabelizer or more (+)shim = you need less speed at the start.

6

Thanks! I believe it and have heard others say the same. Again just trying to understand by stating my assumption in case someone knows more and can correct me:

I would assume a bigger tail feels like it adds low end but technically does not increase system lift or decrease drag because:

a. It gives something else to push against without pushing through the water column when pumping

b. It can increase the angle of attack of the front wing subtly which adds more lift with less intentional and nuanced weight shifting which could easily lead to a stall if overdone at lower speeds.

Trying to reason through it because I’m struggling with the flat water paddle up and trying to convince myself which of my tails will help without having the skills to get up yet and confirm my theory :).

7

I think you are right. But bigger is helpful because for pumping, it gives you more leeway for error, and that seems to outweigh the increase in drag.

Here is a half finished response:

Have a look here some thoughts on trim, with a nice explanation of lift vs stab effort

I would suggest ignoring pitching moment initially, it’s only a thing when accelerating I’ve found, obviously it is there, but in steady flight I think it’s useful to skip it for a basic understanding.

Here is my “theory”:

I like to think of a tail (when considering lift, not turning, “feels” etc) as a “stabiliser” for a system that doesn’t strictly need it.

  1. The front wing has enough lift to lift you without the stab, but only if you stand in the right place
  2. The right place is right above the centre of lift, and that is quite specific.
  3. If you stand anywhere else, the system is very unbalanced
  4. The tail “stab” stabilises the system allowing you to stand much further forward of the centre of lift (and maybe a bit backwards of it), also reduces instability as it’s balancing your weight, (which I think would be “rotational inertia” or something)

So the stab is allowing you to stand forward of the “optimal” spot, but because all that lift comes with drag, you go slightly slower.

You could get lots of lift with minimal drag with a high aspect tail, but these are unforgiving and stall suddenly. If you are good, you can work with that, but a beginner needs lots of lift, AND lots of forgiving, so they go big, which comes with a drag penalty.

The lower aspect the tail, the more drag per lifting force you get, but it won’t stall, and is easier.

And the drag is small relative to the front wing, and the stable steady lift is comforting, and you can stand further forward too, which feels stable.

So on to your question: Low end.

Low end is two things that get confused

  1. how slow can I go, absolute speed
  2. how stable / pumpable / recoverable is the platform when slowing down

Max of 1 is achieved with the highest aspect foils possible, AR 18 race foils with knife tails can go slowest (correct me if I’m wrong), but they require very careful finesse to go slow, and absolutely cannot be ridden or pumped slow by beginners as they lack finesse.

2 is what most people mean when they say low end. How much can I stomp like a gorilla on it when it goes slow and still recover. This is helped by having a big stab. It’s not pretty, it’s not optimal, but it helps.

So I think you’re right, in as much as it’s adding more drag, which decreases low end, but what it comes with is stability, impossible to stall, etc, and that is more helpful than the small loss in glide.

Yes this is true, what I’ve found is that this is more a quirk of high lift foils

unlikely to make too much of a difference, but bigger easier as it gives you more scope for standing too far forward.