T Foils

[ross_burkin]

Phil do you have twisty grip adjustment on Primal as well as "push rod" adjustment?

[simon_jones]

Hi guys, we received our T/foil today. Only it looks like some fool has bashed it in transit. BUGGER! It has cracked on the front edge of the join and there is some degree of flex/movement. I don't imagine this would be much fun at mach 10. Although it might be spectacular to watch if it gave up altogether, never mind I'll have to get in touch with Aardvark and get it sorted.

[Will_Lee]

That's a pity!

Hope it's all sorted out soon. Have you been sailing yet?

Will

[simon_jones]

Hi Will,
   Not yet but we are planning to go to Draycote on sunday if the blast is still on. We can't go on sat as my Little boy is 4 , and I think my wife might go madder than a cherub with a broken T/foil if I don't make the party. It does all depend a bit on the weather as well.

[ross_burkin]

Hi Will,
   Not yet but we are planning to go to Draycote on sunday if the blast is still on. We can't go on sat as my Little boy is 4 , and I think my wife might go madder than a cherub with a broken T/foil if I don't make the party. It does all depend a bit on the weather as well.

Blast weekend this weekend?

[simon_jones]

Hi Ross,
Tim N has sorted it out . This weekend at Draycote. Are you going to be there? I think Hoppy is looking for a crew for Atum.

[ross_burkin]

BAH! I leave for a weeks skiing in Switzerland on Saturday  . Skiing or Cherub blast weekend? Tough call. If the ski trip hadn't already been paid for I would be there.

[ross_burkin]

Pressure recovery? Can any one explain this one or should I just wait until the dinghy show for a chat?

[Ben Howett]

Energy recovery from T foils... The quick answer is that with the foil mounted closer to the free surface (a la I14 as opposed to the current cherub trend of mounting at the tip of the rudder) the low pressure above the foil has the effect of flattening the stern wave and you end up with  the effect of a longer boat.

[Neil C.]

Phil Alderson wrote:
For fore and aft position of the blade I am thinking as far forward as possible as this lifts the boat more than rotating it to a bow down trim
[/quote]

OK, here's a question from a T-foil virgin which will doubtless seem daft to foiling experts, but...
I've never understood why the foil goes on the rudder. If the idea is to use a smallish foil to reduce the displacement of the boat (as opposed to making the thing fly completely like a Moth), and instead carry a lot of the crew weight on the more hydrodynamically efficient T-foil, why not put it really far forward, i.e. on the end of the daggerboard? What's the point of putting the "apparent" centre of buoyancy way out the back of the boat?

N.

[ross_burkin]

A boat without a T-foil pitches around the hulls centre of floatation. A t-foil rudder moves it much further back in the boat, almost round the foil its self. This makes the boat behave like it’s much longer which helps in a small boat with a tall rig. This is the main reason for having it on the rudder, I think. If you we're to have a foil on the dagger board you could get upwind lift like the moths do (you always see them healed to windward). But this would call for different hull shapes for effective use. A foil on the dagger board would mean that the boat would pitch around it and make it very see-saw like. It's much easier to control the pitch of the boat from one end, where as if it was in the middle it would be a very difficult balancing act. If you read Kevin Elways T-foil article in the members section it makes the whole t-foil thing very clear.

Unless someone would like to add to or correct my thinking...
I have other thoughts but I don't know how to word them. 

A 49er with a foil on the dagger board.

[Will_Lee]

There's a whole variety of reasons for the T foil being on the rudder than on the board. Here are two.

1) Self trimming: The feathers are on the back of an arrow or dart: When the arrow does not fly straight there is lift (and extra drag) made by the feathers at the back. This pushes the arrow back to flying straight. Now try that with the feathers on the front of the arrow - works fine until there is a tiny error in direction and then the feathers make those errors worse and it ceases to work! Now imagine a foil on the centre board (with no wand system) and it is the same. Everything is fine for approx one second until a wave/gust/comes and disturbs the system, then it is all over. (In fact, you don't have to dream, all you have to do is ask Fliptop how his uncontrolled foiling system worked on his Indian Takeaway. He sent some pics of the boat on the grass with foils in but oddly none of the boat in flight).

Similarly, if you overdo the T foil, the bow goes down, which unloads the T foil, so you are OK. Try that with a foil on the board!

Again similarly, you can load up the T foil by moving back, and unload it by moving forwards.

2) Pitching moment: Pitching about the back of the boat allows the whole boat to act as 'front', stabilising the rig for a certain sea state etc. . Also means you can get the people further back which relatively unloads the front of the boat, meaning less ploughing and more 
contouring.

[Phil Alderson]

Phil do you have twisty grip adjustment on Primal as well as "push rod" adjustment?

Just the push rod lead out to the sides. If I ever get around to building a rudder with a moveable foil then I would use a twist grip but with a fixed blade I think the tradeoffs are not worth it.

[simon_jones]

As our T/foil was damaged in transit and has to go back for repair. Is it worth asking for the T to be moved from the bottom of the foil to " A BIT" (technical term) further up. If so how far up the foil should the T be?
I know Will was talking about the pressures being equallised. Any thoughts ?

[Phil Alderson]

You are geting into very complicated fluid dynamics here so I doubt that there is a solid answer. there are advantages and disadvantages to the end and the middle

The Only hard rule I would say is make sure that the tips will not break the surface of the water when heeled, or the rudder ventilates and lets go suddenly