Flattened coffee tins .
…
LOL!
Stewart’s Coffee
Unconventional–every time!
Check your grocer’s shelf for the can that gives you lift and drive!
Funny stuff Janklow ! Like the ‘lord of ring’ pic,excellent!
Yeah, you got me with the old B & W photo of the boat. Regards, Brett Curtis.
Quote:
LOL!
Stewart’s Coffee
Unconventional–every time!
Check your grocer’s shelf for the can that gives you lift and drive!
This discussion is SO inspiring, so thanks lads. Keep it coming!
I just read the last posting of Roy and there was some in it about the angles of attack and it got me wondering: i thought that when you use a foiled wing (like an aeroplane wing) you don’t need an angle of attack (or a very slight angle) is that true? It seems to me that an angles wing causes loads of drag.
Let me know what you guys think.
Yes a cambered foil would prodice more lift, but at the cost of more drag when you weren’t looking for that lift (when paddling). The ideal would then be a trimmable foil, with a flap (flaps effectively increase the camber of the foil). The method for trimming it could either be a wand(adjusting flap based on height out of the water) or some other method. This would allow you to keep the foils under water, as cavitation can quickly drop you back down if you rise too high. Roys figure for the area seems a little low to me, even with high aspect wings, the moths have about 5 times that foil area judging by the pictures, and they only weigh about twice as much as a surfboard. Maybe I am just underestimating the speed of the water’s flow relative to the foils. Also you would loose some efficiency having a straight wing across the bottom, as the flow is not actually parallel to the board ( think thruster toe in). Maybe a foil attached to some rotating mechanism like blakestah’s fins.
i just heard that a guy named Chris White is experimenting with a hydrofoil on a bodyboard. Looks amazing:
Roy, can you please post some pictures of your hydrofoil boards?
Good point lasersailor.
Regards, Brett Curtis.
Brett,
No, not all of us know this stuff. I have had ideas for a while, but am landlocked and have zero time now. Keep the info coming, this is great stuff. One question. Does how far beneath the board the foil is placed determine how much angle of bank (lean) you can turn with? How do you overcome the shallowness of the foils limiting your angles of bank? Or do they stick out of the sides of the board outline for this?
Thanks,
JSS
The depth the foils run will limit your bank angle, as you will loose lift on a foil if it breaks the surface, and that loss of lift coupled with suddenly having disproportionate drag will cause you to spin out into your turn as the outside of the board relevels. The depth the foil runs at is adjusted by a wand that tracks the surface in some hydrofoil set ups. Its connected to a flap so that the lift from the hydrofoil is constantly adjusted. if you are not foiling, the wand is parallel to the surface, and the flap is deflected to give you maximum lift for takeoff. At the other extreme, you are completely out of the water, the wand is hanging straight down, the linkages translate this to a flaps either centered or up to give less lift and make sure that the foils don’t break the surface. if the wand is in between parallel and perpendicular to the water, you get some deflection in between. I don’t know if that description made any sense, so here is a photo, you can see the wand hanging down from the bow. I think a combination of this system for adjusting ride height and blakestahs pivoting fin system to keep the foils properly in line with the flow would work great, alltough implementation would be more difficult than another system.
You make a good point about the upward component of the wave's velocity giving the foil some angle of attack, and I do think that a symmetrical foil mounted at 0 degrees is the way to go for that, the flaps would just be an added feature to keep your ride height in the area between board in the water and cavitation. Blakestahs rotating fin as a foil base would align the foils with the horizontal component of the flow up the wave face.
I’m curious, are you using the same treatment as outlined in say,
http://www.me.dal.ca/~dp_04_5/hydrofoil-foils-theory.htm
to estimate your foil area requirements?
Also, if possible, could you work up a rough summary of angle of attack versus where you are on a waveface? See figures, case 1 and case 2. Please feel free to add more positions and angles. Please consider using terms like pitch, roll and yaw, to discribe the respective orientation of the foilcraft at the various angles of attack, but any terms you like would be fine, if defined.
Also, if you’re inclined, please consider discussing stalling during a ride, that is ‘loss of lift’ and when it happens during a ride. And then possibly, what you have to do to get it back, lift that is.
Thanks,
Kevin
Case 1,
And case 2,
Hi Maxmercy, good to see you came back for part 2 !
Regards, Brett Curtis.
Quote:
Brett,
No, not all of us know this stuff. I have had ideas for a while, but am landlocked and have zero time now. Keep the info coming, this is great stuff. One question. Does how far beneath the board the foil is placed determine how much angle of bank (lean) you can turn with? Or do they stick out of the sides of the board outline for this?
Thanks,
JSS
The front foil is only 3 inches from the bottom, the rear one is wider than the board, both foils operate at the same lift angle.
This board worked well in a variety of conditions, was easy and stable to surf, and turned nicely.
Please, Brett, let us have a look-see at current set-up?
And hear about riding the current set-up?
Quote:
The vertical distance doesnt determine how much angle you can turn with, you can lean as far in as you want, but the inside rail can and does periodically contact the water and probably because theres not enough foil lift,(re lasersailor), but its momentary and inconsequential. I’m sure I needed the extra lift anyway !
Quote:Yes, that’s the principle we were working on… . in fact we intended that the surfboard bottom and rails would provide some of the lift during the ride (depending upon speed and bank angle). . . . this worked very well, the board handled well at lower, transitional and higher speeds. . whenever an underwater foil is providing lift, it reduces the load on the bottom and can reduce drag, even if the bottom is still contacting the water (provided that the foil is at a low angle of attack in relation to the surfboard bottom to prevent the foil from stalling) .
It is important when estimating lift ‘requirements’ to remember that when a surfboard is riding at a glide angle below the horizontal (i.e pointing downwards) less lift is required to lift the board above the wave face than when riding on a horizontal water surface.
The main reason why most boat hulls experience a lot of drag prior to becoming airborne (followed by a big drag reduction once airborne) is that the foils are cranked up to a large lift angle in relation to the bottom. . . … this means that the bottom and the foils fight each other until the foil wins. . . . . . what I do is to keep the lift angle very close to that of the surfboard bottom. . . . this means that the surfboard bottom and foils work together. . . . and the board thus gains a drag reduction at lower and transitional speeds as well as when airborne. . . . the angle of climb out of the water is gentler, and descent is also gentler. . . . there is no ‘hump’ to overcome, just a smooth ride at all times.
It’s fun and useful to become airborne, however this should not (In my opinion) be seen as the sole use of horizontal foils. . . . lift can be useful in any quantity . . . . . because of the inherently better lift/drag ratio of foils when compared with planing hulls.
.
Hi Kevin, I 'm not sure what info you want…
Regards, Brett.
I’m curious, are you using the same treatment as outlined in say,
http://www.me.dal.ca/~dp_04_5/hydrofoil-foils-theory.htm
to estimate your foil area requirements?
Also, if possible, could you work up a rough summary of angle of attack versus where you are on a waveface? See figures, case 1 and case 2. Please feel free to add more positions and angles. Please consider using terms like pitch, roll and yaw, to discribe the respective orientation of the foilcraft at the various angles of attack, but any terms you like would be fine, if defined.
Also, if you’re inclined, please consider discussing stalling during a ride, that is ‘loss of lift’ and when it happens during a ride. And then possibly, what you have to do to get it back, lift that is.
Thanks,
Kevin
Case 1,
And case 2,
Brett,
Great info, especially the safety tip of not letting the foil get bigger than the outline. I’m pretty sure that would not have entered my mind and I would’ve gotten the lacerations of experience that it looks like you’ve got. Another question: you have mentioned concave vs convex foils. Which do you find are more stable/ride better? From your previous posts, you seemed to prefer concaves for your foils. Can you give us an idea how they are different from one another, and possibly why? Would you still attach concaves from the wingtips, for safety, or from the center, for other reasons?
I likened the concave and convex to dihedral and anhedral in an earlier post. Definitions: dihedral is a wing shaped like a v, center of wing at bottom. Anhedral, think upside down v, wing tips down.
Roy, did you ever play with the same type thing? How did it work?
Great stuff,
JSS
FYI - found a great website concerning aerodynamics and stability
Hi Maxmercy,
Our flat plane wings (if you look closely at the drawing) have downwardly curved bulb tips ( effectively anhedral) they give a tad more lift and a tad less drag, however our current Vort-X foils have extreme dihedral, which gives zero foil based stability… .the stability being provided by vertical fins which project below the wings, and by the board, which (in the case of the vort-x tunnel always touches the water, even if only lightly)
So dihedral will give less stability . . . . . stability is gained by foils which are at right angles to the axis of roll of the board, and instability (i.e zero foil based rail to rail resistance) is maintained by foils which are in line with the axis of rotation (as a centrally mounted tunnel is)
If you want to fly without touching the water at all, then foils with rail to rail resistance (for stability without hull intervention) are needed, so I suggest if that’s what you are after then go easy on the dihedral, and the wider the wings are, the more stability you will get. . .
is that what you have found Spuuut?
BTW a wider than the board foil (at least at the tail) is no problem as long as it is nice and smooth, to avoid cuts.