Project Cedrus - Hollow Carbon Masts

[jondrums]

I have been thinking for a while that there is a key difference between wind powered and wave powered foiling with respect to mast design.  For wave powered, I don't think that torsional stiffness is all that important and I expect very little angle of attack of the mast profile through the water.  For wind powered (wing or kite) I expect that the mast is used as a keel against the wind loads and therefore could have a lot of torsional loading as well as significant angle of attack through the water.  Those applications call for very different profiles.

[PonoBill]

The Axis aluminum masts are fundamentally a box section core with leading and trailing edges added to the box. That's not, of course, how they are made--they're extruded in one piece--but that's more or less how the structure works. The fuselage attaches to the box. The base plate surrounds the entire mast structure so there's a little bit of gain in stiffness there, but the fuselage does not. The carbon Axis mast inserts into the fuselage with an extension like a Tuttle, but even the newer fuselage, when used with the aluminum mast, connects only to the box section through the appropriately named Doodad.

I really don't know much about structural analysis but I do a lot of fabrication in thin aluminum, and when I design high strength, lightweight parts the first thing I do is figure out how I'm going to box it. I momentarily considered making a built-up aluminum mast with the same design as Kyles, including non-structural leading and trailing edges of cast urethane. I even bought all the stuff to cast the urethane bits, but I came to my senses.

The parts I make always have substantial bends to stiffen the main structure, and then for any stretch of flat aluminum, I add flanges, beads, and countersunk holes to add rigidity. I rarely use a thicker material to add strength. I violated my general principles in making the support brackets for my goofy PV installation on my motorhome project, opting for a shallow bend and had to add lateral support brackets as you can see in the forwardmost bracket. I hate to even look at these brackets--stupid.


It generally looks like I'm being decorative, but really it's all to make a floppy bit of aluminum into something stiff that can support a few hundred pounds. Like this shelf bracket made from 30 gauge aluminum (0.0120" thick).


First, some steps to stiffen the center of the flat areas and beads to stiffen the edges.


Then 90 degree bends to stiffen the main structure. In later iterations I used a counterpunch die to put a reverse countersink on the holes to further strengthen the middle which is where the bracket folded in my destructive testing. This bracket failed at a little over 260 pounds. One of the weights landed on my toes. Amateur fabrication is a dangerous sport.

Kayle probably doesn't remember me contacting him, I was thrilled to find someone else who had come to the same conclusions I had about the best way to build masts, and I'm sure I babbled like an idiot. I also think the same method could build some interesting wings though the shapes might be a bit limited. I was under the impression that you were in Oakland Kyle, but your website says you build the masts in the Gorge. Are you using the fab guys in Bingen?

[Phils]

I have been thinking for a while that there is a key difference between wind powered and wave powered foiling with respect to mast design.  For wave powered, I don't think that torsional stiffness is all that important and I expect very little angle of attack of the mast profile through the water.  For wind powered (wing or kite) I expect that the mast is used as a keel against the wind loads and therefore could have a lot of torsional loading as well as significant angle of attack through the water.  Those applications call for very different profiles.

Interesting, had not really thought about it this way. Of course, many of us use wind power to get onto waves.

[PonoBill]

There are huge differences in the forces applied in the various kinds of foiling, so much so that its a surprise that this stuff works at all. In wingfoiling we go from applying the force to shove us forward about nine feet above the foil (feathering the wing over your head) to six feet (reaching) to directly applied to the foil (riding in a wave or swell with the wing drifting). And it all works. Weird.

[BayAreaKite]

I'm sorry I'm out of town this weekend and can't weigh the exact setup you'd like me to give a number for, but most component weights are on my website and my estimate based on them is about 1.6kg for the mast + axis adapter + lightweight plate.

Project Cedrus is designed like any other airplane wing. Wings typically have a front and rear spar, sandwiched by upper and lower wingskins. These create the primary loadpath in all box structures. Foil masts don't need ribs, and in airplane wings they are there to support fuel loads and prevent the skins from buckling. But they are considered secondary structure, as if one fails it is not catastrophic. Even on large commercial jets, leading/trailing edges are non-structural. They serve aerodynamic purposes, creating high lift for takeoff and landing (slats + flaps) or controls (ailerons). The primary structural box has been the basic premise for wing design since the earliest aircraft.

There might be subtle differences between a mast designed for surf/sup vs. wind-powered, but I wouldn't say significant. The wind powered masts definitely see higher speeds and angles of attack in the water and therefore must have a more refined shape. As a kiter heals over and heads up wind, the mast actually becomes a lifting body. It is critical that flow separation (stalling) does not occur and also that the shape not be prone to ventilation. If any of you remember the original orange LF mast, that had a tendency to ventilate under an aggressive rider. Based on my experience and feedback, the surf/wing/SUP riders actually put higher loads into the mast due to wider boards, pumping, and quick changes of direction. They also don't go as fast as the kiters/windsurfers, and typically ride bigger wings, so one could argue drag is much less critical. I designed Project Cedrus for all activities, and feel that it is a good balance. Unfortunately the market is not big enough to offer custom tapered lengths or profiles for specific sports. I have yet to pay off my one set of production molds for one design, but if someone would like to commission molds for their perfect mast I'd be happy to quote the project;)

[PonoBill]

Damn, you've got me thinking about a built-up aluminum mast again. It would be relatively easy to do a prototype tapered mast in aluminum. Fortunately, I'm neck-deep in projects, and my aluminum forming equipment is a bit sketchy for holding dimensions on heavy gauge aluminum, but it's tempting.

Oh, crap, I just realized there's a good way to do this with minimal bending--actually just a bit of rolling. I could mill the front and back "bends" and the fingers to hold the aero bits out of bar stock, roll the aluminum skin and then tig the plates to the bars. I'd need something inside the bends anyway to hold the threads. It wouldn't be too hard to add some internal bracing too. Shit, that sounds pretty easy. Of course it won't be, I'll get wrapped around the axle doing this, but it would be fun.

I made some aero struts to replace the tubular ones on my Radical race car in a somewhat similar way. They worked fine until I scrubbed one off on the turn 12 wall at Portland International Raceway.

[Fishman]

There are huge differences in the forces applied in the various kinds of foiling, so much so that its a surprise that this stuff works at all. In wingfoiling we go from applying the force to shove us forward about nine feet above the foil (feathering the wing over your head) to six feet (reaching) to directly applied to the foil (riding in a wave or swell with the wing drifting). And it all works. Weird.

Definitely weird. It still seems strange to me that we attach the mast at the the rear of the board ( behind our body which is relaying and controlling the forces) 90 degrees to the board. The way we do it now seems like riding a unicycle, but moving the seat 12" in front of the pole. Sure it works but just can't help but think centering the forces transfer point directly under our body would give easier control. One day i want to try Angled foil mast to understand why that mast never caught on.

 

[Admin]

I'm sorry I'm out of town this weekend and can't weigh the exact setup you'd like me to give a number for, but most component weights are on my website and my estimate based on them is about 1.6kg for the mast + axis adapter + lightweight plate.

Kyle, I am super impressed by what you have accomplished.  1.6 kg (3.5 lbs) is amazing for any mast assembly, let alone on that is this stiff and strong.  Awesome.

[Califoilia]

One day i want to try Angled foil mast to understand why that mast never caught on.

Let me know whenever you're in South OC, CA and I'll hook you up with a ride on one. He just did another version with a carbon mast, and different set of wings that works even better...was on it two days ago behind the boat, and had an absolute blast!!

[PonoBill]

There are huge differences in the forces applied in the various kinds of foiling, so much so that its a surprise that this stuff works at all. In wingfoiling we go from applying the force to shove us forward about nine feet above the foil (feathering the wing over your head) to six feet (reaching) to directly applied to the foil (riding in a wave or swell with the wing drifting). And it all works. Weird.

Definitely weird. It still seems strange to me that we attach the mast at the the rear of the board ( behind our body which is relaying and controlling the forces) 90 degrees to the board. The way we do it now seems like riding a unicycle, but moving the seat 12" in front of the pole. Sure it works but just can't help but think centering the forces transfer point directly under our body would give easier control. One day i want to try Angled foil mast to understand why that mast never caught on.

Actually the position of the center of lift of the front wing is generally directly under your center of mass if your back foot is over the mast and your front foot is roughtly 20 inches from the back foot.