Pros and Cons, Aluminum foil -vs- Carbon foil

[Laughingman]

Hi there

As far as light wind free riding is concerned is there any real advantage to carbon over aluminum?
I have been told that the aluminum is more durable and repairable, provides a more direct feel, is less expensive but heavier (the foil weighs 10lbs)
Carbon is lighter but disintegrates if you hit anything with it...

What am I missing?

Thanks
Pete

[Laughingman]

Okay, I know we have at least two manufactures of foils paying attention to this forum. I'm sure you guys can weigh in on this question instead of bashing in one case and outing on another case.
You guys are selling carbon fiber foils... Why what makes them better then the aluminum ones that at least one of you learned on.

[BWD]

The weight has got to be an issue at some point, but carbon foils are probably easier to sell and profit on than aluminum ones.
This is certainly the case with other sports gear at least.
Perhaps aluminum wings on a carbon strut would make sense to give a little more durability without as much weight as all metal foils??

[Johnny Rotten]

I'm not a foil expert but with experience in both a machine shop and a composites lab as well as some formal schooling on mechanical things. I should be able to answer this from practical and theoretical perspective

Here are a few of the pros and cons of working with these materials.

Aluminium,
disadvantages:
1) I can't imagine how you could build an aluminium foil with a decent aspect ratio orf foil profile to any level of tolerance without cnc ing this from a block of aluminium. The radius's look a little tight for sheet metal work... and if you wanna do those fancy winglets on the end you'd either have to bend it after machining (potential scrap costs) and then heat treat it to make it stiff while controlling any warping, machine it from a large block of aluminum.(high tooling, machine time costs as well as materials cost). Or weld em on and grind it pretty. (tig welders aren't cheap and grinding aluminum isn't much fun either)

Maybe someone is banging crude foils out of a sheet metal. but that's more of a plate than true foil. It'll work but limits the range of angle of attack before separation occurs.

2) As stated before the aluminium is likely going to be machined so it will be solid and a light weight foam or hollow core is not an option. (the center axis of a part in bending carries NO significant load)

3) Stiffness. (modulus of elasticity) You just can't get the same stiffness for a given thickness from aluminium that you can get from carbon. Meaning you could make a higher aspect carbon foil than you could an aluminum one without it turning into a noodle.



Advantages to aluminum: can't think of any....I think if you had a SOLID carbon foil of the same thickness as an aluminum one it would be a serious weapon and would not disintegrate on impact (think G10 fins) As to reparability, If the aluminum has any stiffness it's likely heat treated so you'd likely break it rather than bend it. then you're back talking to your tig welder. broken carbon bits can be fixed with a bit of cloth and glue. True a thin carbon wing is likely to splinter but if you have the pieces, Metal work actually requires much more skill. If reparability is of concern, a layer of Kevlar would act as a nice aramid basket to keep your broken carbon bits together and make them much more repairable.

If I were going to take the time to machine a big chunk of aluminium, I would use this machine time to make a mold, and then lay the part out of carbon. using a hollow/foam/honeycomb core to make it as light as possible where it is not heavily loaded.


As to "direct feel" this is utter horseshit, depends on the stiffness of the part not the material. With good design you can get whatever "FEEL" (stiffness) you want from a composite. Although there are often times trade-offs between weight and aspect ratio to achieve this. As stated before a solid carbon part will have a higher stiffness than a solid aluminum one. So the direct feel would go to an equivalent carbon part.

[Laughingman]

Thanks Bwd and Johnny

Here is the foil I am looking at.
http://skyski.com/store/ripper-foilboard.html

Johnny, could you take a minute and review what they are selling here? I can get a complete unit for $1300.
How do you think they are making these and at a weight of 10lbs do you think this would be cumbersome in the water?

FYI I did catch the spelling correction. Thanks

[BraCuru]

My short practical findings. Big disadvantage of heavy foils (including aluminium) for strapless riders is a fact they are much more difficult to launch it. And it was a mission impossible for me to launch it in a heavy breaking zone.
I experienced it a week ago when I tested a 5kg sinker. Ended up walking upwind a beach 30mins after 10 minutes trials to pass through the wild breaking Baltic waves and shore current.
Anything what sinks is causing a board works like a fishing float and it's really hard to put feet on the flat deck.
Don't remember when I had to complete "the walk of shame" last time

Then I swapped the foils to carbon Moses A-Wing (which is a floater of 2,5kg weight) with a strapless waveboard there was no problems to cross the same breaking zone!

Durability of Moses is positively surprising - I have to admit. It went through a hard test last 6 months and still in great shape

[Arcsrule]

Laughing man, A carafino is just a few dollars more than the the aluminum foil. Get a quote!

[Johnny Rotten]

Thanks Bwd and Johnny

Here is the foil I am looking at.
http://skyski.com/store/ripper-foilboard.html

Johnny, could you take a minute and review what they are selling here? I can get a complete unit for $1300.
How do you think they are making these and at a weight of 10lbs do you think this would be cumbersome in the water?

FYI I did catch the spelling correction. Thanks

The site indicated all components shaft wings and fusilage are NC machined from billet 6061 -T6 aluminium. It's definitely a wing..... not a plate.

6061 T6 actually has very comparable stiffness to carbon. Possibly better depending on the lay-up. The heat treated designation of T6 means it's pretty hard, and for the most part not recommended for forming or bending. So if you smoke this foil it's probably done... you won't likely be able to bend it back without it breaking. and any welding bits back together will screw up the initial heat treatment and stiffness of the part making it prone to noodle like behaviour or further failure.

The maker appears to have spared little expense and shows very serious pride in their work as evident by the mirrored polished finish......this is a beautiful piece....all that work...... they could've made some beautiful molds.......

My main concern for this part is not in it's build but the fact that you are using it outside of it's original intended application. That is for light wind kite boarding vs. being pulled by a boat.

When pulled by a boat, efficiency doesn't really matter, you can literally have a "boat load" of drag and the boats motor by definition will pull it. Ever tried a wake board behind your kite.....they are TOTAL power whores. But at 25 mph behind a boat they have the ability to carve hard and nice steep rocker lines for ramping off the wake and landing smoothly. Great boards, but utter rubbish for kiting....until you hit that nuking 6m day.....

Foils like wings are designed to work in certain speed ranges. As you get into lower speeds for light wind riding you may end up needing higher angles of attack to get the lift you need to ride "on foil," If it's outside of the design speed range of the wing, the angle of attack may be too high and the flow will separate and the foil won't ever lift you the way you want it to at the drag limited speed your kite is able to produce in light wind. It will be little more than a surfboard with a big anchor attached to it.

If you know someone who is using these successfully behind a kite in light wind then giverrr, but if you are blazing a new trail, I wouldn't bet 1300 bucks on it....best talk to the maker, ask em what speeds it works BEST at.

I can't comment on the weight and it's impact to it's ride as I don't ride foils..... 10lbs doesn't seem excessive, many production kite surfboards are approaching this weight. and are still ridable, (albeit a little turdlike in my opinion) but it's a lift generating device, weight should take care of itself whereas the presence of a big fin with a submerged aircraft in water will limit your ability to turn and huck the board around more than the weight anyway

The fish floater analogy someone used may be an issue in light wind. normally you can easily use the kite to pull you up onto a flat board, However if there's so little wind that you are going to be the only guy riding, (hence the desire for a foil) there may not be enough wind to easily yank you up.

[BraCuru]

The fish floater analogy someone used may be an issue in light wind. normally you can easily use the kite to pull you up onto a flat board,

It was the problem mainly in strong winds for me
To be pulled on a strapless board by a kite? Ofcourse possible but not a common, practical and easy thing to do especially in the breaking waves. More weight in a sinking foil - stronger fish floater effect. Wrong fett weight distribution during the pulling by kite and the board got strong tendency to spin in the wrong direction. That's my experience.
I did not like it at all. But maybe I need more practice.

[Laughingman]

Thanks guys for the input and Johnny thanks for your time. I truly appreciate your indepth knowledge of the manufacturing processes. I wish I had that understanding. At my work we use extruded aluminum daily but it is for the most part prefabricated for us "Octanorm" for example.

Here is a short video of people using this board. I think I will try to get in touch with them and talk with the manufacturer a bit more before I throw my hat into this ring.

https://www.facebook.com/photo.php?v=10 ... 944&type=3

It's flash so no apple iOS devices.....