| Re: Viper lifting foils
[Re: taipanfc]
#245038 03/01/12 04:55 PM 03/01/12 04:55 PM |
Joined: Jan 2005 Posts: 6,049 Sebring, Florida. Timbo
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Posts: 6,049 Sebring, Florida. | You could hinge it off the front beam, so you could retract it for launching/retrieving, then flip it down once in deep water. Might have to figure a way to work it around the spin pole, or have it pull up tight to the underside of the snuffer bag when up.
Blade F16 #777
| | | Re: Viper lifting foils
[Re: Timbo]
#245041 03/01/12 05:46 PM 03/01/12 05:46 PM |
Joined: Jun 2001 Posts: 9,582 North-West Europe Wouter
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Posts: 9,582 North-West Europe | Timbo is on the right track here
Hinge it off the mainbeam with a retainer line of the spi pole. This line will allow the AoA to be set. Place the foil at the tip of a round alu tube and make a loose sitting fairing from foam that youbslide ove the tube. This fairing will weathervane around the tube and thus not act as a daggerboard. As a result this appendage will not be loaded up much in the sideways direction. Two dyneema line may be run from the mainbeam just inside the hulls to the tube just above the waterlevel and thus make for a low cost hinge mechanism and sideways support.
When traversing the surf and landing just pull the foil horinzontal towards the spi pole and clear of the water.
The T- foil may be made of a single 300 by 100 mm piece of multiplex shaped by hand and glassed over. Fit it to the end of the support tube in such a way that it can rotate freely downwards with its trailing edge but never upward past the horizontal. That way the foil can never pull you down. The hinge needs to relatively closevto the leading egde for this. About 25% - 30% down the foil.
A simple rubber end stop will suffice to prevent rotation upward.
At relatively slow speed you pull the assembly a little forward thus maximizing AoA, with increasing speed you relax the line progressively thus reducing AoA and preventing excessive drag and pranching. Fiddle about with a bungee in parallel with the retaining line and get an automated AoA sytem, one that also recognizes pranching by the excessive drag that is associated with it and adjusts the AoA accordingly.
Hell, this may actually work !
Note how even a small diameter tube will be able to withstand the 30-60 kg buckling load. And how a single foil in the middle off the boat with twice the area will have exactly the same overall behaviour with respecttomrighting moments etc as two foils half the size at the tips of the daggerboards.
Last edited by Wouter; 03/01/12 05:46 PM.
Wouter Hijink Formula 16 NED 243 (one-off; homebuild) The Netherlands
| | | Re: Viper lifting foils
[Re: Wouter]
#245042 03/01/12 05:50 PM 03/01/12 05:50 PM |
Joined: Jun 2001 Posts: 9,582 North-West Europe Wouter
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Posts: 9,582 North-West Europe | With respect to foil area.
The total area of boat daggerboards will carry about 120 kg that is the sideways loading of the sails.
However it is best to start with relatively small assymetric foils.
Wouter Hijink Formula 16 NED 243 (one-off; homebuild) The Netherlands
| | | Re: Viper lifting foils
[Re: taipanfc]
#245052 03/01/12 09:23 PM 03/01/12 09:23 PM | Scarecrow
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Unregistered | Ummmmm.......
Central mounted foil is a really bad idea. Any lift from it is going to act as negative righting moment against the leward hull so you have added a heap of drag and you have to depower sooner.. if it is tall enough to get both hulls out of the water, you have still almost halved your available righting moment and there for will need to carry much less power. | | | Re: Viper lifting foils
[Re: taipanfc]
#245067 03/02/12 04:33 AM 03/02/12 04:33 AM |
Joined: Jun 2001 Posts: 9,582 North-West Europe Wouter
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Posts: 9,582 North-West Europe | I'm figuring that the difference between full foiling a 30 + 70 kg moth and a partially lifted 107+ 140 kg F16 (for only < 30%) may be an important difference. The F16 will still be carried by the leeward hull for 70% and thus be stabilized. This is basically what the nacra20c and A-cats are doing as well.
Additionally what is the difference between the righting moment of a viper with both L- foils in the water and a single foil in the middle of the viper ? When it comes to righting moment both setups will result in the same overall moment.
Personally, I don't believe that foils are much of a performance gain in most conditions. Hwever the reason I'm interested in them is improved stability of my taipan under spi in big waves especially during long distance racing. For me it is either T-foil rudders or this. This is easier for me to make and try.
Apart from that I'm looking at th following calcs
170 kg crew on my 120 kg Taipan F16 45 kg lift of centrally placed foil Combined weight carried by bouyancy will then be 245 kg or 110 kg + 135 kg crew. New rightingmoment will be transformed from 170*3.5+120*2.5*0.5 = 745 kgm Into 745-45 = 700 kgm = 157*3.5 + 120*2.5*0.5
basically by adding the central foil I expect to get a boat that will partially lift its bows at speed then without thus reduce the dependence of bouyancy to carry to sail loads and wave action.
Secondly I expect to get a boat that thinks that it sailed by a 45 kg lighter crew with the righting moment of a crew that is only 13 kg lighter. The reduction in overall weight ( by 15%) is more then the reduction in righting moment by ( by 6 %).
However, I still don't expect much if any perormance gain except for what is th result if increases stability under spi in waves/ chop
Last edited by Wouter; 03/02/12 04:34 AM.
Wouter Hijink Formula 16 NED 243 (one-off; homebuild) The Netherlands
| | | Re: Viper lifting foils
[Re: taipanfc]
#245093 03/02/12 10:01 AM 03/02/12 10:01 AM |
Joined: Jun 2001 Posts: 9,582 North-West Europe Wouter
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Posts: 9,582 North-West Europe | Doesn't work or doesn't work as well ... ?
I feel flying moths have very little daggerboard in the water and dependent on the Veal-heel canting of the lifting foil to compensate for that.
Doesn't seem the partially lifted cats have the same issues (nacra 20c, A-cats, New Viper)
Last edited by Wouter; 03/02/12 10:04 AM.
Wouter Hijink Formula 16 NED 243 (one-off; homebuild) The Netherlands
| | | Re: Viper lifting foils
[Re: taipanfc]
#245190 03/03/12 12:39 PM 03/03/12 12:39 PM |
Joined: Nov 2002 Posts: 465 FL sail7seas
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Posts: 465 FL | ...... But as for leeward heel being bad, the foils will lift you in the direction of the heel. So if you are heeled to leeward, then when you start foiling they lift more to leeward and on the moth no amount of hiking can counteract this as the foil forces are too high. ...... From above assuming partial lift, an upside down 'Y' appears better than a 'T' ? Then again assuming partial lift, V or U from the inside shear of each hull at the main beam? | | | Re: Viper lifting foils
[Re: taipanfc]
#245220 03/05/12 10:34 AM 03/05/12 10:34 AM |
Joined: Jan 2005 Posts: 6,049 Sebring, Florida. Timbo
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Posts: 6,049 Sebring, Florida. | I think the bigger question we need to address is;
1. Do we want to sail in the traditional sense, ie. no foiling, no lifing boards, etc.? (call it Old School)
2. Or do we want to go down the path of full foiling?
(the C cats and Moths have already figured it out, Dave Carlson was foiling his A cat 20 years ago)
3. Or some half-way, in-between measure, ie. C-boards, L boards, J boards... or what have you?
Blade F16 #777
| | | Re: Viper lifting foils
[Re: taipanfc]
#245223 03/05/12 11:24 AM 03/05/12 11:24 AM |
Joined: Jan 2005 Posts: 6,049 Sebring, Florida. Timbo
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Posts: 6,049 Sebring, Florida. | Just to be clear, I prefer Option 1 from my above post, and fully agree with Mini's last paragraph above.
Blade F16 #777
| | | Re: Viper lifting foils
[Re: Timbo]
#245234 03/05/12 01:04 PM 03/05/12 01:04 PM |
Joined: Jun 2001 Posts: 9,582 North-West Europe Wouter
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Posts: 9,582 North-West Europe | haven't we already answered that in our class rules ?
Wouter Hijink Formula 16 NED 243 (one-off; homebuild) The Netherlands
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