Tiago1973 wrote: Peter_Frank wrote:
Just like an airplane is never symmetrical - it will never be very performing if it was
think some they are - those acrobatic airplanes that need to fly inverted
Peter_Frank wrote: The foils are not "plain straight" either - most have changing AOA out during the foil section (wash out), just like airplanes, for stability and agility.
from memory wash out main purpose is to control lif distribution across the span to reduce drag - the closer the lift distribution is to an elipse the lower induced drag you will have
for the same effect maybe it´s just easier to start with a wing with an eliptic shape platform, think spitfire, instead of choosing a different shape and then having to play with the AoA along the span (something that would require a CFD program to know what one would be doing..)
NACA has numerous foils optimized to operate at certain Reynolds (function of velocity and viscosity if I remenber right), but I do not know enough to just go there and pick 1 that would make sense for you guys
Think you need Spork jumping into this topic..
There are a huge number of additional aspects of this, than what most think.
But a symmetrical airfoil is only used in order to ride upside down, meaning it is bad both in normal flight and upside down, no matter what - a compromise you have to take on cost of performance.
Just like a TT, which can never reach the potential of directionals, because it is equally bad at both sides.
The faster you ride, the closer to a symmetrical foil you can have - but if fully symmetrical, it will never perform well
Washout has three purposes in fact.
The major is IMO to avoid tipstalling.
You can also use it to reduce induced drag, at low AR wings, yes.
And last but not least - if you have a swept wing, washout will add stability - and you could in fact ride without any tail wing if you wanted.
Not as performing though....
A spitfire with its elliptical wings is VERY prone to tipstalling, thus it was one of the first to use a lot of washout in order to avoid this.
But still a major problem in R/C model spitfires
Above is simple "aircraft" knowledge.
But when talking about a foil, you got a bigger number of situations:
When the foil reaches the surface, and is about to ventilate (stall), you can make this "easier to recover" by having a curved outline (negative dihedral) and washout, as the center might ventilate, but the tips are still in the water, and with lower AOA so they dont stall.
Just some thoughts, but many others present.
Regarding turning - the dynamics of a foilboard, there is a lot more aspects added too - a ballpark of its own, just like a kite and turning and the dynamics are not "simple" at all
I actually understand why foils are expensive, no wonder and makes sense !
The R&D for one.
And understand if Carafino is pissed because others are doing the same now, after a few has done all the basic work and testing and expenses.
On the other hand - if you dont have a firm patent, it is only natural that a good idea will evolve into many brands, and some will be able to discover new sides (like racing) and really get these aspects finetuned to perfection
This competition is a bonus for us as users
And nothing "odd" about this - the same goes for every other industry, windsurfers, surfers, cars, etc.
So I dont think badly about those making the same product, and reaching new performance borders !
Sorry, a bit of a detour maybe, just my thoughts