Or you can do it based on the pressure of the water.
He originally seemed to do it with a pitot tube, but Page 121 of the pdf shows how he controls the rear flap with a diaphragm. To cope with different tacks would probably require two diaphragms mounted on the front wings.
In the video you can see a pod mounted on the lower front wing upper surface.
As this has "wandered" over here I thought that I should repost the images directly.
One of the main advantages of having a wand based control system is that the foil shape can be altered based on speed, this allows a lower overall drag setup, in certain circumstances, compared to a fixed foil where the section is restricted to what you chose at design time.
In other words, the foil has a much wider "working range".
Bruce, I'm very happy you've joined this forum.
The 45 degree ride misleads the wand about the real water level detected as "Too high".
Unless you consider it as the normal position, meaning the downwind reach is ridden very low compared to wandless systems, how would you sort that out ?
Edit: thanks Peter
Last edited by Europ2 on Mon Mar 31, 2014 2:15 pm, edited 4 times in total.
Nope, the AC72's weren't allowed to have any control surfaces on their foils. Oracle's advance was to make their adjustment system have a feedback system that allowed for very fine control. Originally they all had a button to adjust the AoA. Oracle's allowed for a very precise, push the button get a 1/2 degree angle change, system. This is part of what let them foil upwind where TNZ would pop out of the water trying to do the same thing.
The system on the kite boat is very similar to a moth. The flap follows the surface, moves a rod and alters the flap on the trailing edge of the foil to reduce and increase lift as necessary. As Bruce mentioned, Moths have advanced this a lot. They control wand length, gearing (how much affect the wand has on the flap), how quickly the wand snaps back, etc, etc's that I can't remember right now. It's interesting that the report about the Lister kite foil said that it was losing out downwind. This is my weak point in terms of ventilation/popping out the surface. There's a weird feedback loop when you head downwind too deeply going fast and as you start to drop off the foil you then point up to foil again but sometimes you get a pull from the kite which gives you way too much lift. There's a split second of sucking and then boom! The crashes from this are brutal. Sanding the foil to get rid of the shiny surface helped with this a lot. Being able to reduce lift as the foil started to breach seems like it's what I'm looking for, but maybe I'm wrong?
As a fairly experienced moth sailor and a wannabe kite foiler this thread is very interesting. The main concearn I have kite foiling is that I don't believe I can ever be as quick moving my weight to control foil AOA as a moth control system and the crashes are pretty brutal as a result. There is simply no way you can read the water surface at 30 knots+ to react fast enough.
This consists of a want to control the flap on the forward foil horizontal and a twisting tiller to control the fixed rudder horizontal. The main controls are a ride height adjuster (that simply gives you more or less ride height for a given wand position), a gearing adjuster (that controls how aggressive the flap is and allows you to be very aggressive in waves when control is paramount and less aggressive in flat water when a fast flap will adversely affect speed), wand length (which controls ride height and gearing indirectly and giving you more range) and wand elastic (which controls how fast the wand will move). We also sand the foils for the conditions with a polished finish in warm water and roughly sanded foils (using 80 grit!!) in cold water when you are skidding on the water and it feels like you are a bird coming out of the night club pissed on high heels.
The latest development in moth foils that Im aware of is having the flap mounted on hinges at the end of the horizontal rather than being attached via a flexible hinge. This closes to a tight fit when the foil is in neutral but as it moves to +ve or -ve AOA a gap opens up like on a 747 landing which gives you about 3 times more lift (or downforce if you are riding too high).
There are some major issues with doing this on a kiteboard principal of which is getting your kite lines caught on the wand but this makes a hell of a lot of sence to me. The main advantage of a kite foiler is a pull on the bar and flick backward on the kite will enable you to hopefully lift clear of trouble but on a moth if the foil leaves the water its pretty terminal. A kite takes a lot more of the vertical weight of the rider than does a moth.
I like the pitot tube with a diaphragm idea and I have often thought the off centre (and therefore always in the wrong place) wand solution is too crude.
I believe a moth will go upwind better than a kite foiler as the forces are much better aligned. Consider the 8m2 sail will take you form 7 knots wind when you start foiling, get you to double the wind speed in 12 knots of wind (as I did last sunday) and will take you up to 30 kotts wind speed and beyond if you have big enough cajhones but I would like to know if a moth has ever racked up against a kite foiler with riders/equipment of similar standards in their own field.
I am a beginner with the foilboard, perhaps 15 hours. But, to have a surface following control of the wing seems like no fun, and too complicated. It is difficult, but not too difficult, to control the board by weight shift.