My apologies for all the questions, but point me towards the Terry Hendricks or MTB thread or URL that goes into the how the estimate was or is made, and I’d be grateful. (I’ve actually searched on Terry Hendricks, MTB, hydrofoil, etc. and there are a lot of threads - if you could just narrow it down a bit.)
Thanks.
Kevin
the lift requirements during the initial acceleration down the wave are be less, but once you are on the wave at constant speed, weight is weight, and your lift has to be equal to that weight. Interesting point about interaction with the bottom of the board though. Some thought has to be put into the board/foil interaction, especially for shallow foils. a concave leading into the space between the board and foil could lead to even lower pressures over the foil, similar to the foresail on a sailboat or a biplane wing. And one more thought, as to max blade width, it is a good saftey concern that it should be kept within the outline. Someone a while back made a peanut shaped board, that would increase the aspect ratio you could safely use. once I get done with my two exams tomorrow I’ll put some more thought into this, its really interesting. Much more interesting than a straight hydrofoil boat problem, since you aren’t dealing with level flight.
the lift requirements during the initial acceleration down the wave are be less, but once you are on the wave at constant speed, weight is weight, and your lift has to be equal to that weight.
Quote:No. … . although your lift in the vertical plane has to be equal to your weight if altitude is to be maintained, the difference when riding on a sloping wall is that the lift required is in a less than vertical direction and the force required is thus less . . . . . . an extreme example is surfing a nearly vertical face. . . . . the lift needed for ‘hydrofoiling’ is applied in a nearly horizontal direction (at right angles to the face). … . . which means that far less force is needed. . . . . my experience in the water has shown that this is correct.
BTW I drew my wingtips up the wrong way oops they were actually curved downwards .
I need a scholarship from FCS so I can finish the design and then they can tap into the bodyboard market. Thats unlikely but its more than likely they are one of the 3000.
Regards, Brett Curtis.
Here’s what I mean:
The point being that ‘hydrofoiling’ is the art of lifting in relation to the water surface, not the horizontal plane.
A simple vector diagram can be used to calculate how much less wing area it takes to lift above the water surface on a wave face with a 45 degree slope compred with a horizontal one. . . . . . . … . . . … and in fact it takes 0.707 times the force (and thus 0.707 times the wing area) to lift free of the water on a 45 degree sloping wall (excluding inertia)
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Interesting comment by you Tom, “BTW I drew my wingtips up the wrong way oops they were actually curved downwards” .
Regards Brett Curtis.
requirements during the initial acceleration down the wave are be less, but once you are on the wave at constant speed, weight is weight, and your lift has to be equal to that weight.
No. … . although your lift in the vertical plane has to be equal to your weight if altitude is to be maintained, the difference when riding on a sloping wall is that the lift required is in a less than vertical direction and the force required is thus less . . . . . . an extreme example is surfing a nearly vertical face. . . . . the lift needed for ‘hydrofoiling’ is applied in a nearly horizontal direction (at right angles to the face). … . . which means that far less force is needed. . . . . my experience in the water has shown that this is correct.
you’re right, drag from the foils will help to counter the weight as well in an inclined problem. I think the agle the board is lifted at is somewhere between perpendicular to the water surface and up though. A board will have one rail dug into the wave and one rail not even on it. That introduces another complexity of one tip being nearer the surface than the other tip. (I know you drew it as an extreme example). So yes, less lift would be needed, thank you for explaining.
Interesting comment by you Tom, “BTW I drew my wingtips up the wrong way oops they were actually curved downwards” .
Wingtips turned up are called winglets and curving them upwards as the airlines do is way more efficient (at controlling the vertical vortex generation and thus balancing the pressure differential at the wing-tip) than down, thats why they do it.
But yours are curved down…which is more of a surface tracking /planing style of foil technique like mine.
Quote:LOL I meant wrong as in not showing what I made rather than wrong as in wrong way to go. The idea at the time was that the downward curving tips would create more lift by preventing flow escaping from the tips. . . of course we have gone to the complete opposite extreme with the upwards curving wings which curve right into the deck (coffee tin/hoop/plumbing pipe/Vort-x/tunnel fin) so we must be right, right?
Roy, if youre there…I wonder if you remember wether you had planing or surface piercing or surface tracking foils back then?? Your science is a bit of this and a bit of that, but it may just be your recollection of the events.Did you take and keep notes?
Quote:Yes we took notes, all our foils remained submerged as far as I could tell
It does take 0.707 times the lifting force to lift out of the water on a 45 degree slope BTW (just wondering why you quoted that conversation again. :)
Roy,
Even at a 45 deg angle, doesn’t the foil need to lift the rider upwards (against gravity)? I think that requires a force equal to the rider’s and board’s weight to maintain ‘flight’. With the 45 deg angle, you would need a larger foil to have a vertical component equal to rider+board weight. For straight line riding, I mean. Of course, I am not taking into account the direction the water is moving onto the foil, this could completely invalidate my argument, as the water movement could be striking the 45 degree foil at a more advantageous angle to provide more lift in the direction against gravity (or up).
Brett, can you tell us how the concaves vs convex foils handle? Big or small difference? Ever played with sweep angle?
JSS
I think the angle the board is lifted at is somewhere between perpendicular to the water surface and up though.
Quote:yes that’s true, another point is that any vertical (in relation to the board) fin area or struts become horizontal area fins and lift in the vertical direction whenever the board is rolled away from the horizontal onto the rail. . … I use that principle a lot with my designs. . . . so when hanging high on the wall with the board rolled away from horizontal the previously vertical fin starts to act as a partially horizontal wing… . and the same thing happens in a bottom turn or cutback. it gets tricky to explain because everything becomes relative to the planes of reference, and when those planes of reference which we normally expect to stay together start moving apart then our language can become ambiguous .
Hi Max,
You are talking about maintaining altitude on the wave face, which is another matter (important though it is).
I was just isolating the force required to lift the board perpendicularly to the wave face.
What I did was use a big vertical fin/strut (about 50 square inches in area) which did some of the lifting against gravity when hanging on the wall rolled on the rail, while it did that the horizontal lifting foil would more easily ‘unstick’ the board from the face by acting perpendicularly to the wave face and thus more horizontally
An extreme way to visualise it is that a big singlefin becomes a horizontal aircraft wing while the ‘lifting’ foil now just shoves the board horizontally away from the vertical wave face
So somewhat weirdly the vertical and horizontal fin areas both do ‘lifting’ work against different planes of reference at different times.
got to go, attitude adjustment (liquid) required before I go into ‘OM’ mode
Cheers
Hi Maxmercy.
I think you have solved your question with your own thoughts.
Regards, Brett Curtis.
Roy,
Even at a 45 deg angle, doesn’t the foil need to lift the rider upwards (against gravity)? I think that requires a force equal to the rider’s and board’s weight to maintain ‘flight’. With the 45 deg angle, you would need a larger foil to have a vertical component equal to rider+board weight. For straight line riding, I mean. Of course, I am not taking into account the direction the water is moving onto the foil, this could completely invalidate my argument, as the water movement could be striking the 45 degree foil at a more advantageous angle to provide more lift in the direction against gravity (or up).
Brett, can you tell us how the concaves vs convex foils handle? Big or small difference? Ever played with sweep angle?
JSS
thanks Roy!
looks great! any photo’s or video’s of the board in action?
……In Dale’s post at the beginning there are a few pictures of the plywood hydrofoil paipo, and it looks like there no upward angle or a aeroplane like foil on the wing. Anybody knows more about this?
This board was designed by Gaylord Miller who was at Scripps Institution of Oceanography in 1960. Several were built (I built a copy when I arrived there in the fall of 1960). The board shown in the picture belongs to a friend of mine who was given it about 45 yrs ago by a graduate student who had built it.
The one I built in 1960 was my first wave-riding craft. The combined learning curve for both surfing and riding the board was a bit too much for me so I set it aside and started riding a conventional surfboard (Yater). In the late 60’s or early 70’s I gave the board to Stanley Pleskunas and Steve Lis to play with. Its present whereabouts is unknown.
To set the angle of attack, one tilted the whole board about the pitch axis. This process is exceedingly demanding on the rider (at typical speeds the rider is given only a fraction of a second to recognize any change in hull elevation and make the appropriate response in pitch angle), hence they were almost alwyas ridden with an excessive pitch angle and hence planed on the foil rather than the latter operating submerged.
mtb
Thanks for showing up Terry. You can field the questions better than I can . Regards, Brett.
Quote:……In Dale’s post at the beginning there are a few pictures of the plywood hydrofoil paipo, and it looks like there no upward angle or a aeroplane like foil on the wing. Anybody knows more about this?
Oh!! so now its 3097 views is it…? What the deuce do you think you are playing at,huh?If I was a lesser man I’d see you all off, but thankfully for you,there are limits.
3097 views… I want names!! …And now !!
@!! you all , you freakishly tall devils.!!!
spuuut wrote: Wingtips turned up are called winglets and curving them upwards as the airlines do is way more efficient (at controlling the vertical vortex generation and thus balancing the pressure differential at the wing-tip) than down, thats why they do it.
But yours are curved down…which is more of a surface tracking /planing style of foil technique like mine.
(The above pic is not of my foils nor bears any resemblance. its just an example of what not to do.)
Winglets work just as effectively on either the top side or bottom side of a foil/wing (and are similar in effect with regard to lift to just extending the wing to increase its aspect ratio) [Ref: Barnes W. McCormick - Aerodynamics, Aeronautics, and Flight Mechanics -John Wiley and Sons, 1979 ISBN 0-471-03032-5]. One reason they are on the top of the wing on airliners is to reduce the possibility of the winglet striking the ground during landing–especially in cross-wind landings. On a surfboard, one would presumably want them on the bottom side to decrease the probability of one of the winglets penetrating the sea surface due to the transverse (side-to-side) slope of the wave face relative to the board, and hence potentially leading to ventilation of the foil and a reduction in efficiency.
Your comment in regard to the pic is correct “…an example of what not to do.”… – but not because of the side of the foil the end plates are on, but rather that winglets should be of a high aspect ratio (McCormick again) vs. those shown in the pic.
Hi Smallwaves,
I don’t have any photos, we didn’t photograph our work in those days, we wanted to keep the whole idea quiet (which seems strange now) . . . . . looks like I will have to build another one, and photograph it. I remember that the foils were painstakingly finished . . . more than a dozen micro thin rollered coats of graphite/epoxy over kevlar.
We also did a big shield shaped wing (like the paipo ones, about 200 square inches or so) mounted way forward on the board. . . this one was unsurfable because it would just pop the nose up, the tail would stay low, and the board would stall. . . now I realise that all I probably needed was a foil on the tail as well . . . the big wing was made from edge glued balsa, perfectly foiled and again, glassed with kevlar and epoxy, it took about 2 months to build, and got stolen by some people who probably have no idea what it is !
Thanks for showing up Terry. You can field the questions better than I can . Regards, Brett
You’re doing fine. Our respective wave-friding craft were designed with different objectives, so it’s good to cover the spectrum.