Author Topic: T Foils  (Read 44307 times)

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Offline Will_Lee

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T Foils
« on: August 13, 2007, 07:19:20 PM »
The place to discuss T foils.

Atum Boms T foil is 900mm x 150mm x 15mm with a section created from ellipses and straight lines, with the widest point 30% back from the front. It is made on 200 kg/cubic metre foam with a layer of 200g weave over everything, and under there a 1/2 layer of 200g unis, and a 3/4 layer of 200g unis. This was vac bagged at the December 2005 Sticky weekend.

The measurements were decided upon simply because we wanted to build it using the same techniques as we made the rudder, and we wanted one like Aqua Marina's, but a bit bigger. It was only the prototype but when we made a thinner one with a huge span of 1.4m, thinking it would provide huge medium wind advantage with costs at low and high speed (although the plan is to still cut it down to 900mm), it was v draggy and unimpressive. We then got the old one back in service pronto.

Offline tim_unerman

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Re: T Foils
« Reply #1 on: August 16, 2007, 06:52:16 PM »
Will, would you go for a symmetrical foil again or an asymmetrical foil if you had an option?

Offline Will_Lee

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Re: T Foils
« Reply #2 on: January 13, 2008, 06:05:04 PM »
Hi Tim,

Sorry for delay in answering. An asymmetric foil means less drag (for a certain lift) when the T foil is working, but more drag when the T foil is not working (ie feathered for min drag). A symmetric foil is easier to make, and easier to make right, but (if it is done right), an assy one is probably better.

Our next one will be assy I think, unless I change my mind!

W

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Re: T Foils
« Reply #3 on: January 13, 2008, 06:24:10 PM »
Will, What size rudder blade did you have on Atum? and was it too big, too small?

I am thinking that with the T on the bottom it gives a good endplate for the rudder, however at the point where you need more area (slow and pulling hard) I doubt if the end plate makes a difference
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Offline Will_Lee

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Re: T Foils
« Reply #4 on: January 18, 2008, 09:52:01 PM »
The blade I think is 740mm from the bottom of the stock downwards.

T-foil positions:

I think the 14's keep them high because the rising water near the surface is so marked. We have loads less of this, so I think lower is better.

That said, there is recovery of energy to be made, and a T foil on the bottom has to be very strongly built because of interference between the high pressure side of the rudder and the top of the T foil causing a huge twisty load on the join. If the T foil is moved up about 300mm from the bottom then the twisting disappears.

I do not know about fore-and-aft positioning of the T foil.

Will

Offline phil_kirk

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Re: T Foils
« Reply #5 on: January 25, 2008, 10:04:56 AM »
Obviously the T foil changes the handling and performance of the boat but

should different hull forms be fitted with different T foils.

ie. does a low rocker boat such as a DOG need a bit more downforce off wind to keep the bow up than a more rockery boat.

Offline Will_Lee

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Re: T Foils
« Reply #6 on: January 25, 2008, 12:31:02 PM »
Hmmmm possibly, but the thing about a t foil (unlike many things) is that even one which is not so good is loads better than not having one.

The optimal section of the T foil is dictated by the speed you go upwind (more=thinner), how heavy you are (more=fatter), and how far you can get back (more=fatter). The fatter you go, the