Foiler Design

Thanks,Simon! Sure appreciate these pix..... I figured it out Simon,thanks!

[Tcubed]

It is quite an interesting development in near surface foil sections, at least to me, i' ve never seen anything quite like it and it would be very interesting to see some polars for it with some numbers, L/D and so on.

[fishwics]

Note the leading edge is on the right in each picture.

Somewhere on this forum are some sketches from Jon Howes and discussion posted about 18 months ago. (Sorry cannot be more precise than that)

Simon

Here,post 105: Oh Lordy (Doug)

Originally Posted by fishwics

Note the leading edge is on the right in each picture.


Simon

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Simon, what does the rudder foil look like? Looks very small-is it a similar section?
The main foil looks like the aft edge is not sharp-but squared off-is that right?

[Tcubed]

Originally Posted by Jon Howes

I have attached three files. The first, "Basic Foil", is simply the output of my 2D design programme, this gives the pressure face and the zero pressure, bubble surface which continues into the wake, there is a pressure face bubble surface with a zero pressure differential also continuing from the trailing edge aft, this is not shown as it is a very boring, slowly curving line disappearing off to infinity! In reality it will close back in again but hydrostatic pressure, which drives this, is so low compared to dynamic pressure that it was not included in the calculation so the wake in this calculation shows a diverging bubble.

The second, "Practical foil", shows the trailing edge cut-off on the upper surface via a sharp chine. This would seem to be destructive of low speed performance, however, the amount of foil with this section is tiny (0.6 sq feet) and the foil above this has much greater area for low speed and acceleration, this low speed foil is lifted out of the water as the speed builds via a secondary planing surface just above the high speed section. The pitch control on the boat is used to trim the running angle of this planing surface.

The third file gives the coordinates of the practical version of the foil if anyone wants to play with it. Design lift coefficient is 0.2. The datum incidence as plotted gives this CL in 2D flow, obviously the 3D case suffers from downwash but this angular correction can be found by the usual, well known means from wing theory.

Jon.

It seems to me that this foil is quite different actually. Follows the second image as referred to in the above quote from Jon. The Tomahawk foil looks like it is designed to have a reattaching flow at certain regimes. Hopefully Jon can shine some light on these speculations.

[tspeer]

Originally Posted by Karl Wittnebel

Tom where is that tutorial? I looked on his website but didn't find mention of optimizing two foils in relation to each other.

This isn't Matveev's material, but I just ran across NACA-RM-L52L11, which has test data for the waves behind a hydrofoil. This should help you locate the aft foil in the upwash from the forward foil.

[fishwics]

Originally Posted by Doug Lord

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Simon, what does the rudder foil look like? Looks very small-is it a similar section?

Short chord, but fairly wide span. I suspect it had been borrowed off a Bladerider. (Sorry - didn't pay too much attention to it!)

Remember this boat is a pre-production model. Production boats are not expected until the middle of the year.

Originally Posted by Doug Lord

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The main foil looks like the aft edge is not sharp-but squared off-is that right?

It's probably as sharp as you can sensibly get it in what looked like a moulded foil. About 1mm thick or somewhat less. About the same size as the steps on the upper surface.


Simon

[sigurd]

I thought out this leeboard/foil arrangement, for putting under the vaka/ single aka joint of a proa. For my purposes, I wanted pitch moments to be resolved in the air mostly anyway, so it makes more sense to me than two foils, one at each end of vaka. If you were using a rig with a large yaw and pitch moment, then it would not make sense.
With a kite, those moments can be small, and even automatically changed by towpoint movements.
With a masted rig, they could be minimized by ama shifting back and forth, and balanced by extra aero surfaces.

By Bill Beaver:
http://www.moth-sailing.org/download/CSYSPaperFeb09.pdf

[sigurd]

Super interesting paper. The drag figures from the hull and tramps makes me wonder why the moths are not doing these things:
1)Lower freeboard
2)netting and not fabric tramp
3)jibing the daggerboard so the hull can point straight into the wind (makes for funny landings at 20kt I guess)
4)International Canoe style seat instead of tramp (with windward heel the lee tramp is the draggiest one I assume)
5) if the tramp sail is removed as in 2 and 4 then it may start to make sense to make gunwales more rounded.
???

Sigurd, I think an IC type sliding seat is against the Moth rules. But new foilers may well take advantage of sliding seats in various forms.

[ancient kayaker]

[quote=sigurd;265016] ...
3)jibing the daggerboard so the hull can point straight into the wind (makes for funny landings at 20kt I guess)
... /QUOTE]

I was looking at this idea as an offshoot of my sailing kayak experiments, and have a test lined up for the summer. It might be worthwhile on slower boats but I doubt much would be gained on a foiler.

Once a boat is planing, and definitely if it is flying, it is sailing so close to the apparent wind that the hull drag is already close to optimum. A foil-shaped slab-sided hull would be good under these conditions which may justify the typical moth shape.

[sigurd]

I think I disagree. The hull/tramp (aero) drag is, according to the paper, a good bit of the overall drag at 20kt, and if you look at the drag reduction when heeled to windward, I come to a different conclusion than the author - the tramps look like they may not give less drag, but the hull allows air to go under it easier. Either way, the drag must be less if it is all pointed into the wind. I don't see how this would benefit a lowrider (not flying boat) since the hull would be out of alignment with the water. In fact in a lowrider, the opposite might be beneficial - jibing the board into the wind, to align the hull to the water. This might be what you are planning?

From Alan Smith: http://dougculnane.blogspot.com/2009...ions-from.html