The SUP style of foiling

dllee · Joined: 03 Jul 2009 Posts: 5329 Location: East Bay

Some companies like Starboard have a much longer fuselage for pitch stability. Won US. Nationals.

ittiandro · Joined: 22 Nov 2009 Posts: 294

dllee · Joined: 03 Jul 2009 Posts: 5329 Location: East Bay

You must want to live a a virtual reality world.
What breaks the finbox is NOT the normal loading of a perfectly trimmed and controlled ride.
What breaks the box is a sudden loading, from a crash or a collision with another object.
Gotta prepare for the worse, and hope for the best.
I'd suggest you DO your projects, but test them in a safe venue. Sailing home without a fin is no big deal, up, across, or downwind.

dmilovich · Joined: 19 Jul 2009 Posts: 99

One thing to remember is that the small aft wing on a foil is generating lift downwards, not upwards. Like the horizontal stabilizer on an airplane, (that small wing on the tail), it helps counterbalance the weight of the rider, rig, and board which are all centered somewhat in front of the main wing of the foil, which is generating the big lift upwards that gets you out of the water. This arrangement, on both airplanes and boards, makes the whole thing easier to control. Going to one only wing makes it very much harder to balance everything.

ittiandro · Joined: 22 Nov 2009 Posts: 294

DLEE may be right in saying that what breaks the finbox is NOT the normal loading of a perfectly trimmed and controlled ride, but a a sudden loading, from a crash or a collision with another object.

Although rare, because of my style of windsurfing, this can be a real possibility and I’ll keep it in mind.

This warning is however of less concern to me than the warnings expressed by many other people’s that hydro-foiling on my self-made contraption ( a wing attached to the rear fin), can rip off the U.S. fin box , allegedly because of the natural hydrodynamic forces acting on the wing either when subplaning or, perhaps even more, when planing off the water.

At first I couldn’t believe that sub-planing or even planing , almost flying …, 1 m above the water on those carbon hydrofoils like those shown in the YouTube videos, could generate hydrodynamic forces strong enough to break the fin box, or even the hydrofoil wing, unless carbon-made, especially at the relatively low subplaning speeds .
This was my contention throughout my posts !

I started however to realize that these warnings may be justified , when I decided to look at this issue in the light of physics, more specifically by looking at the principles of hydro-or aero-dynamics, the theory of lift force, the Bernoulli forces, density, the lift coefficient, the angle of attack of the wing, etc .

I had to inch my way through very slowly because, not being trained in physics, this was uncharted terrain for me..

I believe though that I grasped the essential principles and I can work through some of the basic equations.

In particular, according to the lift equation : L=(1/2 D) x V2 X A X Cl , at the velocity of only 10 kmh, the force acting on the hydrofoil wing as lift ( L) is 4,650,125 N=474 kg.

A 474 kg lift is enough to push the 110 kg of board, rig and my own weight( 85 kg) off the water, but, unfortunately, I realize it now, it is also more than enough to break wing and finbox, as other people have been saying. .

I won’t explain here the host of other concept implied in this formula, because somebody trained in physics will know them already, while most people will not be interested

I’ll only say that In the above formula, D is the density of water( =1000) , V is the velocity of the fluid ( or the board ) in m/s for 10 kmh), A is the area of the wing in cm2 ( by hypothesis , 60 cm x 20cm= 1200 cm2 ) and Cl is the lift coefficient ( not to be confused with L, Lift)= 1.005215.
I t won’t be necessary to explain here how I calculated it. Perhaps it is wrong, but it seems to be very close to the CL shown in some Tables, in function of the angle of attack of the wing, which I set, in my case at around 10°, because it produces the smallest drag.

I may be wrong in my calculations, also because didn't consider the effect of the hydrostatic force, which may compound or even increase the lift .
If so, I’d certainly appreciate if somebody could correct me!

Thanks
Ittiandro

dllee · Joined: 03 Jul 2009 Posts: 5329 Location: East Bay

Talking FRP, the tail seems planing on the water fulltime, and the extra drag of the lifting fin should limit top speed, a possible self regulating formula. Kept on a sub 34cm fin, it mighr be fine for it's intended purpose of sailng around underpowered but going at a decent speed.

ittiandro · Joined: 22 Nov 2009 Posts: 294

dllee · Joined: 03 Jul 2009 Posts: 5329 Location: East Bay

FRP horizontal wings are half the size of foil's front wing, so you don't fully lift the tail clear of the water. To get full clearance, you'd need a horizontal foil the same size as foils, and you'd get the problem of balancing between front and rear foot pressure.
With the short vertical mast, you don't have resistance to downwind drift, so you lose early planing.
That nether world between foil and big fin might not be worth pursuit.

ittiandro · Joined: 22 Nov 2009 Posts: 294

U2U2U2 · Posted: Thu Mar 22, 2018 11:12 am Post subject:

There is a reason that USBox fins dont come very long, and why Powerbox and tuttle do.
In the box, a certain amount of flex is going to occur. This would be increased with the addition of a wing attached .

Its not feasible to turn a pig into a race horse, but you can turn a pig into a fast pig. Now is it possible to fly a BIC Windsup .. the difference in theory and fact is one works and one is a supposition

Using MATH to calculate windsurf equations , this is the one that works.

Board $2000
Sail $500
Mast $400
Boom $300
= $3200