No, basic foils seem pretty simple, at least the first 90% as you wrote.
All my foils worked well enough and yours does look well designed.
I was trying to say, how it is really hard to attach the way a foil rides exactly to any one of its attributes, because they mostly influence each other.
Did you compare your foil to any other âknownâ foils?
From looking at your layup, I would expect the wing is not nearly rigid enough.
I stopped doing my own foils, when I noticed how even with 18 layers of uni directional carbon the wings were too soft to know if the instabilities in flight were due to my design or simply due to the layup.
Most brands did switch to ultra high modulus carbon layup, which is really hard to get your hand on.
In the beginning of mass market foils, many wings used winglets.
At this point, no company uses them anymore, as far as I know.
I only have one commercial beginner foil from waydoo that I can compare to. The rest is a bit too expensive at the moment.
I am surprised that my wing seems to be rigid enough up to now. The core itself (PLA+) is very stiff compared to foam. I have only a single layer of 160 g/m² glass + some carbon rovings. It is probably stiff enough because it is pretty small and has low AR and 9% thickness. The next wing I am making will have higher AR and will be laminated with 160 g/m² carbon. I will try to use vacuum bagging.
How would I notice that it is not stiff enough? It feels very good up to 35 km/h. I didnât try more at the moment.
If you have access rent a Fliteboard or Lift for an hour and try that. You will know what a good efoil - foil should feel like.
To me Waydoo has a reason why they are less expensive than these other brands who have been at it longer so perhaps their foils are not quite as good. I have never ridden any of these myself only Slingshot for a short while before I went with Gong so want to qualify my âguidanceâ
Guess it is hard to explain, if you do not have a reference.
Speed in a straight line will not be a problem.
If you turn hard or have some turbulent water, a soft foil will feel increasingly unreliable, making it pretty hard to turn in an efficient way.
Small size and low AR will help.
9% is less than most foils I measured.
F-One, Axis and Duotone all were in the range of 11-12% last I checked.
Probably also to get them strong enough. Many of the newer wings have like 100mm chord at 1000mm span and going from 9% to 12% get stiffness to 175%.
Thanks for the info. I think I will just buy a used sabfoil leviathan and make an adapter. Then I can compare and play around. Do these also work at approx 3 deg angle of incidence?
If you can get used Axis wings for a good price, that also might be a good option.
There has been a guy, who did a 3D printed fuselage for those (including 3D model), so it could be easy to adapt. But I did not try it.
I did some research and may have a lead for you to explore. My intuition about the fence changing the handling characteristics told me to think about the spanwise flow on the wing. After all, that is really what the tip controls. So if the span wise flow on the top vs bottom is affected, how could that change the performance?
From my preliminary research, it seems like the roll stability is coming from the vortex on the wing tip. Because water is so viscous and dense, a vortex which is âattachedâ to the wing tip will damp the roll rate significantly. Think about basically a balloon which is trying to move water out of its way as you roll the board, that is what the vortex can do.
Notice how on aircraft which prioritize efficiency, the tips are facing up? Upward pointing tips works to minimize the vortices much better. Reducing the size of the attached vortex allows for quicker roll rate.
In summary, the tips down creates much more span wise flow on the top of the wing and a larger induced vortex on the tip. This vortex is attached to the wing and becomes a factor in the roll rate or stability of the wing.
I would check the power efficiency of the wing with tips up vs down at a lower speed near stall where the AoA is high to validate this theory.
Fun topic, thanks for sharing! Great to see your creativity and motivation to test new ideas!
Experimenting is fun AF, hope you keep at it! I think of it as a car or bike on a banked track being similar to front wing tips down (or edges on a snowboard), and the inside tip grabs or digs in. Upward tips allow the wing to slide or slip and not bite into a turn (like soft rounded rails on a surfboard). I have found the opposite on the tail and upward winglets seems to lock in the feel more. Trying popular brand designs quickly adds to ones knowledge of what works, and I needed to reach a level or proficiency to really understand and feel what a foil is actually doing.
are you still looking for suggestions to try? you should be careful about choosing a RC-plane airfoil, they have much lower Re-Number as the foils we use, and therefore are much thinner.
You could get away with a thicker profile which would give you a wider range of speeds where the airfoil performs good. On the other hand a thinner profile will produce much less drag.
I am also quite surprised that your wings hold on, i had a wing failing on me despite it had 5 carbon layers, more about that here (in German). How many layers do you use in your wings?
I am working on a tool that predicts the drag of different wings, it is still not finish but it could help if you are planning a new wing.
here some results from comparing my Gong Sirus XXL to my Gong Xover, for my 100Kg of pumping setup (it ist just the Front wing drag):
It is pretty nice, but it also highlioghts some of the problems.
It is really hard to know what the actual parameters are, when using a foil the way we do.
Chnaging the NCRIT value completely changes which profiles work best.
Interesting, interesting, so much to read and tryâŚ! I now bought a Gong Veloce L and am looking forward to comparing it to my designs. Wing twist (washout, area and thickness all look very similar, really curious to see if it behaves completely different). Unfortunately, I am a Warmduscher, and I think itâs too cold already in Germany for testing
On my finished wing, I am using just a single layer of glass (approx. 160 g/m²), and a few very thin carbon rovings. I am a beginner, so the are no sudden changes in angle of attack that would stress the wing too much. But how is the wing centre designed in commercial wings? I attached a screen shot of my design. I have some thick carbon rods along the wing, some thick aluminium tubes that take the bolts, and an aluminium plate on the underside. Everything covered with an extra layer of 160 g/m² carbon. All this is embedded in 100% infill PLA+. It feels very stiff.
I do not agree about the Re being totally different in airplanes and wing foils. If you go 15x faster in air, then you have the same Re as in water (same wing chord). And I go 30 km/h on my foil, airplanes with a RG15 airfoil can easily go 300 km/h. AFAIK, differences in Re only matter when the order of magnitude is changed, this is not the case here.
RG-15 is, in some sources mentioned to be 1st choice for F3F model aircraft flight:
F3F model aircraft in dynamic soaring achieve speeds of 900 km/h (for me, this is still hard to believe for a small glider plane, but itâs true). http://rcspeeds.com/Aircraft?AirplaneType=BD
Note that top speeds are in mph, not km/h.
I did not know this software, seems to be interesting
I use xflr5 when I want to calculate something.
My tool is much more simple, it takes in account the Planform (Surface area, AR, e and thickness) and the conditions (total weight, water temperature, Laminar/Turbulent ) then it gives a drag prediction by interpolating in a database of xflr5 results.
It is for sure not perfectly accurate but it is definitely in the ballpark, I am looking at making it open to the public, we will see when it is availableâŚ
It depends of which wing we are talking about, the one I repaired, and something like a Xover (low aspect) are just a foamcore and a few layers of carbon/glas, if you go to something with a higher AR, like a Sirus, they have probably a few more layers and a stringer
Lots of interesting discussion on the wing shapes and drag here.
Just curious if any of you had any feedback on my theory for the roll stability vs wing tip direction. I have noticed that this effect also works across the entire wing, roll stable wings will have significant anhedral. Seems counter-intuitive given when in air anhedral makes roll less stable. Cheers.
I think I finally found an explanation for anhedral making hydrofoils more stable on roll:
If I want to turn left, I shift my centre of gravity (COG) to the left side of the board. This rolls the foil to the left. Because lift is always perpendicular to the wing, the lift vector now tilts to the left as well. A component of that lift becomes a side force, which makes the foil start to slip (drift) to the right relative to the water. In other words, the foil wants to keep moving straight ahead, but the tilted lift vector forces it into a curved path.
Once the foil is slipping sideways, the direction of the incoming flow changes: the water now arrives slightly from the right.
If the wing has anhedral, this sideways flow increases the effective angle of attack on the lower (left) wingtip in a left turn. The left wing therefore generates more lift and more drag.
The extra lift acts to level the foil (restoring roll stability).
The extra drag helps the system continue to yaw left, supporting the turn.
This behaviour mirrors what happens in aircraft. A dihedral wing allows an aeroplane to turn using rudder alone: deflecting the rudder left yaws the nose left and creates sideslip from the right. With positive dihedral, that sideslip increases the angle of attack on the right wing, rolling the aircraft into the turn. Roll and Yaw are therefore positively coupled for dihedral wings, and negatively coupled for anhedral wings (making anhedral wings stable on roll).
In the mean time, I made some more wings and stabs with proper vacuum bagging. This is really fun, and I am sooooo much looking forward to test them next summer.
i had in mind something flying 20-30 Km/hâŚ
