flying grandpa wrote:Peter_Frank wrote:Again, if it is race wings with "faster" profiles and less camber, the pitching moment is much lower (typically named Cm in tables), and you can use a shorter fuselage without having a bigger rear wing, thus even less total drag.
Whereas more cambered freeride front wings, has much more pitching moment (= torque force trying to turn the opposite way so "instability"), and requires a longer fuselage, a bigger rear wing, or a better rider if you want to go fast with low stabilizer drag
I think it may be a bit more complicated.
First, we can play with CofG to counterreact Cm.
In real world, when you go fast with i.e. Sword, you need to move forward your front foot to countereact the foil tendency to go up. It is the stabilizer action responsible for this tendency.
The more cambered profiles of front foil counterreact this action naturally with the reduction of AoA (with increase of your speed), when its growing pitching moment incraeses. Above will give you less foil tendency to go up at speed when you have more camber, providing other parameters we will keep the same.
Whereas the longevity of the fuselage will determine the "quickness" of your setup.
The shorter the fuselage, the more lively your foil will be under your feet.
Tadeusz
Correct Tedeus
It is actually way more complicated.
The Cm will have a forward pitching reaction, true. Bigger the bigger wing or more camber.
Thus, a bigger stabilizer is needed (but often not used) for stability.
You could make a really self stable (but not auto "elevation" stable) foil, if having a low AoA on the stabilizer (negative lift), and then moving the CoG (your feet) forward.
Why dont we want that (for experienced riders) then ?
Because it is only stable at one constant speed.
At higher speeds eventhough the Cm and Cl counteract (squared with the speed), it will still go "up" because of the stabilizer negative AoA.
So I think the aim is to have a balanced trim, but less stable at one single speed (like on planes).
Meaning, the CoG a bit more aft (feet), and the stabilizer at a higher AoA so it is slightly lifting up, but close to neutral.
This way you can find a much better equilibrium where you can go faster without having to change CoG.
This is how my Zeeko foils work - I dont need to put weight forward (nor rearward) to go faster, it is in perfect balance
With more cambered foils, my experience is, that this equilibrium is not as easy obtainable in the same way, and the lift of the wing will change elevation in the water faster than the Cm will counteract the balance through the pitching and stabilizer, thus you will get a less stable "fast track" compared to a lower cambered wing
I havent any tests nor calculations of this, but just my experience from foils, and "hunch" from airplanes too.
Of course the AoA of the stabilizer could be changed so you ride with lower Cl at almost neutral AoA, and then it would be almost the same one could think, but not quite - as you still got a higher Cm eventhough having the same Cl, which means a different CoG (and also more drag).
Another parameter is the stabilizer AoA, that has to be different with different fuselage length (all others being the same), because the Cm (wing flow) gives a downwash so the AoA on the stabilizer is changing (being less negative if not neutral) the further away from the front wing you get.
Many interacting parameters, and this is just in one "plane" out of 3
Just some thoughts and experiences
Peter
