Vector Carbon Canefire 40 cm

Side note, if there is such a thing as Heavy Ground Effect under a windsurf board, has anybody ever tried watersking with a windsurf board, if the HGE Hypothesis is correct it should be possible get True Flight. No?

Kinda like a Hoverboard? Except they don't work on water (unless you've got power)

....................

Naa Barn, waterskiing's never gonna hover it.....
'cos you haven't got the lift from the sail !

If you look on the pic.of West Kirby,you see that the board in front looks
against the wind. Maybe 10°. I worked a 22cm fin so,that she is in front
on the right side of the tuttle base.
The end of the fin is on the left side of the tuttle base. angle is 7°.The fin do
the work. How always,but the board looks to the finish.We need right and left fins.
It works good. I reduce a little the brake of the board. Wolfgang

Putting it on the roof won't have the HGE.

A board is just over 1m2 in area, there is a limit to the amount of lift it can generate in free air.

This is a Shaka in 30knots, half way around your body weight is committed to the sail, and the nose of the board is pointing directly into wind, starting at a small angle, then an extreme angle, and then back down again.. I can guarantee there is not crazy lift from the board in free air, it's very controllable (the sail, less so).

Ian K said...
ie about 30 kg of lift all up.

You can also estimate this from a simple free body diagram made from a picture... both methods provide a similar result. So I agree thats about the right figure. ~1/3

Ian K said...
the Cd for bluff bodies is usually around 1.

errr why do you think its a bluff body? I dont think so.

Assuming its a streamlined body, with only a slight camber, at 5 deg AOA its likely to have fully attached flow and a Cl in the 0.5 range...

30kts speed, at 90deg to the wind of 20kts = 18.5m/s apparent wind speed.
Area = 1.2m^2 (~2m in the air on a 70cm wide board- average width of 60 over that length)
L = Cl.p.V^2.A/2 = 0.5*1.2*(18.5^2)*1.2/2 = 123N ~= 12.5kg.

ANd now to the curly one of ground effect... consider that in our case the board is sitting over the water at a small fraction of the chord- considering the apparent wind angle- we are talking a few %. Thats going to have a huge impact on the lift coefficient.
http://www.ghdstudios.com/radacraft/fig1.html
www.se-technology.com/wig/html/main.php?open=aero

My guess is it will be at least double.

Ian K said...
The previously referenced article

www.dsto.defence.gov.au/publications/2058/DSTO-GD-0201.pdf

gives a clue but is not definitive

"WIG craft have been championed on the basis that they are more efficient than
equivalent aircraft and quicker than equivalent marine vessels. The efficiency argument
is somewhat speculative. While theoretically an improvement in efficiency is gained by
flying in ground effect, this efficiency is reduced by design compromises required of the
WIG craft. Such compromises include strengthened hull structures, reduced aspect
ratios and larger control forces. The degree to which total efficiency is improved can
only be determined by the direct comparison of optimised designs of equivalent WIG
and aircraft. Only through such a comparison would the value of the improved
efficiency and the cost of gaining this efficiency be determined."

not to mention the height/chord has to be pretty big to avoid crashing into waves, so ground effect is limited for these types of vessels. Comparing apples and oranges.

Te Hau said...

Way too many pies!

Hey, I resemble that

Very interesting (and intellectual) thread too.

This conversation is complete double dutch to me.

Not one sentence can i make head nor tail of.

All i know is,if you sheet in,in the gusts,you go faster or you go over the handle bars.

Ian K said...
The second reference you gave has the Cl increasing from 0.8 to 1.1 at a clearance of 0.5 the chord - which might be about 50mm. Parts of the board near the nose where it has more clearance, will have less of a gain, those closer to the wet area... will be getting wet.

err more like 0.05 of chord (which is more like 1m )Sometimes two wrongs combine to get the right number... But then look at the area from the mast track back that is sitting at 1 or 2 cm off the water, with a chord of ~1m in the apparent wind direction... The first graph shows that things get funky under 5% of chord. Lift/drag goes thru the roof. I dont think thats just the drag disappearing.

yep mike- thats looking at it from the other angle... build it and see. The fastest boards from the last 5 or 6 years were designed to exploit aerodynamic nose lift.

Wineman said...

Te Hau said...

Yep, I reckon some of these boyos may be getting baffled by science.....

what I know is that my boards get up in the air in the bear offs and hover with the whole lot out of the water.The faster I go the more lift I get off the nose and I build my boards with varying nose areas just to use this effect.
I'm up to speedy #8 now and mostly playing with this effect.
The fastest runs I've done have been hover jobs and I don't feel the chop 'cos the board's not in the water.I call that sail lift and nose lift.
I've also (for other sailors) modified a number of older longer slalom boards for using as speed boards.
They all have the problem of too much nose lift in big gusts and by shortening the nose and reducing the area this problem comes totally under control so I guess that indicates that nose lift is real and it is a sizeable force.
No science, no theory just the real world , chop it up and see.

Well that's gone & done it!

How to destroy a perfectly good theorising, hocus pocus thread by being practical & actually building AND testing somefink.

What's poor Barn gonna fearorise or preach on now.
(Maybe go sailing )

Hey Wineman, where did I say any of this lift wasn't important?

I'm simply disputing the claim that 100% of the weight can be lifted by a windsurfer without any force going through the wetted area..

I was first told it can be taken from the sail. I debunked that. Then it turned into HGE and I was told that I would need to do a handstand on a board to keep it from taking off at 70k...

Now I'm just after a Figure of lift. The ballpark figure is from my 5kg to Slowies 25kg of lift from the board..

Extraordinary claims require extraordinary evidence.. So far it seems everybody has backed off their claims except me..


(And I can't go sailing, I'm injured)

^^ hahah I don't need encouragement!

After the 30knot scenario broad reaching in 25knots, I can move onto sailing deep downwind at 45knots in 45knots of wind at SP on a 40cm wide board, that'll get interesting..

If my injury doesn't heal by next year I may have to take up this leisurely sport of Speedsailing, then I won't be all talk..

mr love said...

You need evidence?

Sandy Point 2010.
Mr Love takes off from the East bank on the Luv Mus Small

Hold it, this sounds like a personal account, the most notorious form of evidence possible.. There was even a Church Of Speedsailing disciple there to witness this aqua miracle!!



Now, we have all been lifted out of the water, but usually that is just transfering forward speed into vertical lift, and doesn't last long. Sustained sailing 4 feet above the water would of course contradict the HGE hypothesis..

----

I note there is some Anti-Science factions forming, this usually happens in any Church when the Science contradicts Doctrine... I'll just note that whenever anybody is in a plane a few thousand feet in the air, that planes is up there thanks to Scientific theory.. It works..

Te Hau said...

petermac33 said...

This conversation is complete double dutch to me.

Not one sentence can i make head nor tail of.

All i know is,if you sheet in,in the gusts,you go faster or you go over the handle bars.

Yep, I reckon some of these boyos may be getting baffled by science.....

what I know is that my boards get up in the air in the bear offs and hover with the whole lot out of the water.The faster I go the more lift I get off the nose and I build my boards with varying nose areas just to use this effect.
I'm up to speedy #8 now and mostly playing with this effect.
The fastest runs I've done have been hover jobs and I don't feel the chop 'cos the board's not in the water.I call that sail lift and nose lift.
I've also (for other sailors) modified a number of older longer slalom boards for using as speed boards.
They all have the problem of too much nose lift in big gusts and by shortening the nose and reducing the area this problem comes totally under control so I guess that indicates that nose lift is real and it is a sizeable force.
No science, no theory just the real world , chop it up and see.

I'm not getting baffled by the science, I'm a scientist, in a previous life I used to design wind tunnels.

We're just using unfamiliar terminology that makes it seem more complicated than it really is. All you really need to be able to do is visualise pressure. Blow up a ballon a few times and get the hang of pressure.

Then if you can arrange for the pressure of air or water on one side of a solid object to be more than the other you get lift.

But one big constraint on all this is as a particle of fluid, air or water, moves into a region of higher pressure it must slow down. All a particle of fluid, say a 1cm by 1 cm by 1cm cube can see is its neighbours, if the one in front is pushing back with higher pressure than the one behind it'll slow down.

You've probably seen the equation F=ma the harder you push something the quicker it accelerates. This equation is called Newton's second law of motion. It's pretty intuitive, we all know you've got to push heavy things harder to get them up to speed.

The fluid dynamicists modified Newton's equation to allow for the flexible nature of fluids, the force becomes a pressure gradient, friction became viscosity, they still refer to it as the Navier-Stokes equation because that sounds more complex than "F=ma for fluids".

So in specially designed wings the air over the top speeds up a bit and the air below slows down a bit. But you can only speed air up by a small percentage, and slow the air down below by a small percentage, otherwise smooth flow becomes unfeasible. The more wind speed you have to start with the more you can slow the air down without upsetting smooth flow.

That's why the wing loadings for various aircraft are much higher for faster planes, you can afford to drop or raise the pressure further without correspondingly slowing or speeding the airstream up or down by more than a few percent.

The hang glider - wingloading 6.3 kg per square metre goes about 30 knots
Spitfire 158 kg per square metre 300 knots
A380 663 Kg per square metre even faster

So ground effect or not I have trouble seeing any wing of 1 square metre developing much more than 6.3 kg of lift efficiently in 30 knots. In attempting to generate 25 kg the air on the underside would be brought to a stand still or the air on the upper surface coaxed to do more than 50 knots, or a combination of both, unlikely, I can't visualise a flow pattern consistent with this.

So ground effect or not I have trouble seeing any wing of 1 square metre developing much more than 6.3 kg of lift efficiently in 30 knots. In attempting to generate 25 kg the air on the underside would be brought to a stand still or the air on the upper surface coaxed to do more than 50 knots, or a combination of both, unlikely, I can't visualise a flow pattern consistent with this.


6.3kg of lift would obviously never get the gear out of the water, so why does it happen and how do we hover it all for 1-300 metres at a time?

remember there are other forces involved than just the board creating the lift.

When the sail is raked back and the gap between the board and sail is closed the sail itself is generating significant lift which is pullign up thru the mast base.

The amount of lift needed from the board itself is probably failry minimal. on a lot of baords the biggest problem speed sailers have is actually keeping the boards to stay down and flat.

You also need to take into acount the amount of lift the fin is generating.

looking from where the force is applied by both sail and fin the sail would be doing most of the lifting and the fin only really lifts the last 25% of the board.
Getting this balance right would give the board the right angle of attack to generate the ground effect that makes it feel like its hovering.

Too much angle and the board will flap up and down - too little wont see enuf air getting in under the board to do the job and it will slam thru chop.