Sticky Weekend

[BenR]

longer and higher aspect, unless someone is going for a horizon job on the rest of us by building a foiler!

[phil_kirk]

Generally shorter cords similar length new sections.

The argument for longer foils is in simple terms more grip on the water therfore more power from the boat = more speed. Against this is more wetted area = more drag and a greater heeling moment due to the CLR being lower down.

Surface area of the foil creates drag and hence contributes to limiting the boats top speed limit.

So the new foils are going high aspect by reducing cord. This also means the foil thickness is reduced. There is a danger that in low speed manoeuvres that the skinnier foils may loose grip on the water.  If so there is a balance speed and control (skill level).

As foils get skinnier the section shape and planform will become more important.  As you probably know traditional dinghies with mostly flat foils have sufficient area that section shape is less important for control.   

[Torchy]

Sorry Neil...there has been a bit of double entendre going on

[Torchy]

Kirky...

Previously you mentioned that you might have to re-set the angle of your foil because of too much lift ie still +ve even when level. You also mentioned that the tips were bending. This sounds like a foil developing a lot of lift.

What's the section?

Might the solution to cut the middle section out of the foil to make it smaller and reduce the drag? If it really is developing lots of lift that's a net gain...

Any thoughts?

[phil_kirk]

The foil was made over 80 gm^2 foam wit a layer of glass roughly at the horizontal neutral axis. This was not of course for strength but to make it easier to handle the foam whilst routing.  The foil is higher aspect shorter cord of 100mm and longer 1m and thinner than my previous foil but used the same three layers of uni either side and a layer of weave. 

The bending is probably due to the change in shape not being compensated by the change in laminate.  I also don't know if the previous foil bent or not.  Does anyone else's?

The new foil included more camber than my first so much so that on the first sail it felt quite draggy and sensitive to angle of attack.  I filled in some of the concavity on the lower surface reducing the lift  but the foil felt less draggy.  The added camber means the foil needs to angled more neutral to generate zero lift or a downforce to point the bow up in waves.  I noticed that the pro built foils have the t foil angled downwards such that the rudder has to be angled forward to generate lift. 

I'm not sure when I will get round to this re-angling exercise. It's fine in flat water and light winds but less so in waves.

It was interesting to compare the effect of the older more conservative foil and the new one.  Perhaps I would have completed more races at the nationals with the older rudder which had a larger vertical foil. 

[Torchy]

Thanks Phil, didn't realise that angling down was common. Does anybody have any comments on the angle that professional foil builders set the T at? Loco's is level.

Can I make a request that people bring foils to the sticky so comparisons can be made?

[Clive Everest]

Angling the T foil down means that the rudder vertical has to be raked forward to give the correct AOA on the T.
This reduces the chances of air being sucked down the rudder as it would have to travel upstream.
Look at a PIC of a foiling Moth.

From my experience with SK I am trying to set up the new boat so that with the rocker line of the boat flat (stem and stern level) the T foil can be set over a range of 2 degrees pitched down relative to the zero lift line to 4 degrees pitched up.
When going upwind the Bow will be pitched up another 3 degrees giving a total of 7 degrees of lift. Above this the induced drag is likely to become too high.

On the foils attached to the Demon rudders the zero lift angle would appear to be when the foil is pitched down by 2 degrees due to the camber of the foil.

If you have crafted you own foil section and want to try and work out the zero lift angle the best free program is Java foil http://www.mh-aerotools.de/airfoils/javafoil.htm


Clive

[simon_jones]

Loco's foil was re angled twice by cutting through the rudder section. This was done as the original shape/angle was far to positive causing a lot of nosedives.

[Torchy]

Thanks guys

[Phil Alderson]

Pocket Rocket's last two foils have been angled down. It also brings the foil more under the boat reducing the nose down leaver arm from the foil.

[Hayley_Trim]

Just a reminder that you're all very welcome to stay chez Trim on Saturday if you'd prefer not to brave the workshop. You're also welcome to stay on the Friday night if it makes the Saturday morning a bit more civilised. There'll be food on Friday evening if you want it.

A vague idea of numbers would be handy but not essential; there's plenty of room for last minute extras as long as you bring your own bed.

[Tom Hole]

Hi

I'm planning on coming to the sticky so I can learn about how to repair bits and bobs.
I know Paul and Roland have talked about building a new t-foil, maybe I will use that as a practice project at a later date.
For now, i'm just dreaming of new ideas but not doing anything about it due to lack of skills and can't really complain about Subtle
Anyone willing to let me  have a look at their projects/learn/add an extra hand that would be much appreciated.

Tom

[Hayley_Trim]

Tom, you are more than welcome to come along, watch, join in, lend a hand (always useful), come for curry etc. Especially as the exams will be over (not that I mean to sound like your dad or anything  )

[Torchy]

Hi Hayley,

Sam and Nigel at Chez Trim please but not that triangular duvet if that's OK...

...seriously (so unlike me), we are bringing sleeping bags and camping mats

[roland_trim]

Roland talked about building a new t-foil, maybe I will use that as a practice project at a later date.

The weekend always works with no real format. People can just arrive or bring bits they would like to do. Spare hands will always find something to do.

I am very likely to be making a T- foil over the weekend and maybe also some parts of the rack supports. Please be gentlle with me over the weekend, I will be desperate to be working on the Evo2. On the bright side, the new boat will need a new foil .