Downwind foil with assist

[KayakDoc]

Thanks. I may have to give him a shout. Anyone else have any Triton experience?

[KayakDoc]

Hanging out on South Padre Island for a few days. No wind. Drove over to Space X to take a look at the next Starship vehicles (launch is mid-November). Asked Elon for a factory second for my downwind foil assist project. Here we are loading it on the roof of my BMW X5. Space X is a lot less secure than I imagined. Lots of up close access. The space vehicles are really, really big and they look very utilitarian. It feels like a ‘not too much waste and get the job done’ kind of thing. I am beginning to think he might just get someone to Mars. I wish him the best of luck.

[KayakDoc]

Off topic…maybe. Space X received the OK to launch their Starship from Texas on Friday. 33 Raptor engines wrapped in a stainless steel tube. Heavy duty stuff. The link to foil with assist is in the choice of material. Stainless steel! It appears that Space X has moved away from carbon fiber booster bodies and is using steel instead. After visiting the launch site I was impressed by the size of the boosters, but also surprised by the choice of materials….until I thought about it. Giving up the “next best” for more traditional material that solves problems is pivot brilliance. I have long embraced carbon, kevlar, Nomex construction as cutting edge, yet always trying to build test foils from these materials is often a pain in the butt. I have built a ton of prototypes and there has to be an easier and cheaper way to do this. I have used cement moulds and styrofoam hot wire cuts for prototypes, but always make the test foils from carbon and glass. I wonder if hot-wiring PVC (Corecell) and bonding it to aluminum skins would super expedite the process. Any thoughts?

[smartang]

I find the lamination itself is the one of the more straight forward parts of the process. Even with the vacuum bagging prep, it's maybe 10% of the labor to build a board from scratch. And I'd have to guess PVC + Al has got to be fairly close wet lam carbon + eps in costs. Al doesn't allow for errors either, boding issues... Where's the stiffness coming from?

[KayakDoc]

Great questions. Thanks.

Just for building foils, not boards and really just the front foil. I have sanded a lot of wings, boards, moulds and I think an aluminum skinned front foil could be a fast build with little post finish. I have been using a lot of VHB tape in the last year and it should be OK for PVC core to aluminum. Bonding PVC cores, or many different cores for that matter, the resin interface is usually the fail point. There are some great epoxies for bonding aluminum to core materials, but not cheap. Stiffness vs weight has always been a problem although the first aluminum foil masts were superior to the initial carbon masts….mostly manufacturing issues. I do have some Nomex stashed somewhere. It would be fun to bond some aluminum skins to a shaped Nomex core and see what the result is. The stiffness comes from ensuring the compression layer and tension layer are in full contact via the Nomex. I built a 9.9 lb. Nomex/kevlar whitewater slalom boat that I raced at the ’77 Worlds in Spittal, Austria (man that was a long time ago). It was very stiff with close to zero swing weight. It turned with almost zero resistance, but it was very susceptible to any compression issues. It was really important not to hit anything with that boat (super denty). Regarding costs; thin aluminum sheet is fairly cheap and off cuts are usually available at local repair places. I have a lot of core cell so no worries there. I do have some VHB tape. It is expensive but I have enough to have some fun with. I am really just thinking about how to tinker older tech that might be repurposed, although having said that has anyone noticed the price increase from the Gen1 Foil Drive Assist Plus ($3174.00 US) to the Gen2 Foil Drive Assist Max ($5313.00 US)….HOOTCHY MAMA! The Houston kite guys I have been chatting with have said the Gen1 is no longer of interest and the first orders of the Gen2 are sold out. Man, these both seem expensive to me.

PS. Anyone else building gear with some repurposed material or tech? And I know that a few VI locals were building some efoils. Any DIY foil drive assists getting built out there. It would be great to hear about it.

[AJSpencer]

Hanging out on South Padre Island for a few days. No wind. Drove over to Space X to take a look at the next Starship vehicles (launch is mid-November). Asked Elon for a factory second for my downwind foil assist project. Here we are loading it on the roof of my BMW X5. Space X is a lot less secure than I imagined. Lots of up close access. The space vehicles are really, really big and they look very utilitarian. It feels like a ‘not too much waste and get the job done’ kind of thing. I am beginning to think he might just get someone to Mars. I wish him the best of luck.
IMG_2752 2.jpeg

RIP Starship. Maybe next time! Lots of issues with the actuators and looked like the booster had an actuator issue even after the initial delay and replace. Maybe time to up security, based on your observation! Very cool.

[KayakDoc]

HOORAY! HOORAY! HOORAY! Some Wind is Good interaction! Hi AJ. I am in Galveston right now and I got up to watch the launch on line. If you were up it must have been an early rise! Lots to celebrate and some to maybe worry a little about. It was good to see the booster get all the way to separation. Sad to see the tumble and the dead telemetry, but way to use up all the fuel first. The Starship stage was interesting. It looked like things were fine through a lot of the fuel burn and then I noticed what looked like a few big gas clouds in the coverage that looked like big ignitions. I have been thinking that maybe the vacuum Raptor engines ignited, failed and exploded. I don’t know if SpaceX planned to use them before orbit, but if they did it looked like the firing sequence, after a lot of fuel use in the sea-level Starship engines, may have been the issue. I think the day was very cool too! It is a really interesting “test-to-failure” attitude they have at Space X. I hope to see a little more of that in the DIY foil assist community taking place within the dark-web-not-many-reveals-wind-is-good project. I hope that the open proximity at the launch site didn’t lead to somebody monkeying with the actuators, but good catch AJ as someone could get close to the boosters. Thanks for the thoughts. Cheers, KDoc.

Re Space X security; In the pics you can see that the fence separating the Starship storage facility is not very secure (there are 3 Starships in the storage shed). The pickup trucks in front of the Starship facility were construction workers vehicles. I parked next to them. The pic of me is proof that I was here and the beginning of my astronaut training.

[AJSpencer]

I see you photoshopped out Leonardo DiCaprio.
I thought I could see a little “puff” right at Max Q, kind of like something gave.
Hopefully next time we’ll get to see that booster return to the cradle!
Ok, I digress — back to downwind foiling.
Personally I prefer winging upwind and doing short downwinders and not requiring a driver/transport, but you guys have at er. lol

[KayakDoc]

Leonardo DiCaprio is my stage name.

[KayakDoc]

So a few questions!?

Anyone building their own batteries? If so, what cell type and why?

Here we go. I have built a number of batteries using 18650 cells for my DIY ebike, Argosy trailer break-away brake system and generally farting around with rechargeable stuff for BLDC motors and super obnoxious, massive lumen, blind-and-piss-the-other-guy-off flashlights (when they wake me up in the middle of the night at Nitinaht with a 4th drunken listen of Free Bird at 1:30!!!!). I recently pulled apart a commercial efoil battery with 196 18650 (25C) high discharge cells (photo). These batteries (not the cells) are way too heavy for foil assist. The 18650 cells are falling out of favour with a lot of efoil builders moving to 26650 high discharge cells (pic) for their battery packs. Great for us salvagers of 18650 cells, but it begs the question “is the larger 26650 cell battery “better” for foil assist?” For those that do not know 18650 describes the dimensions of the battery cell 18mm wide x 65mm long (26mm x 65mm for the 26650 cell). Both of these cell types are li-ion rechargeable cells. Both have been used extensively in ebike, efoil, Tesla vehicles, etc. Are those switching to the larger cells getting higher discharge rates and more power with limited weight penalties? This is the big question. Any responses of an informed or inquisitive nature greatly appreciated and hoping to hear.

Now on to a bit of a deeper exploration. If huge discharge rate is what we are after for short, sharp bursts of big amps to get small, large, larger / young, older, oldest / strong, weaker, weakest foil assist users up FAST should we be considering, OR are people already using, 200 amp (rated) Headway 38120 3.2 volt 8AH cells (pic) for super big discharge bursts (these are lifepo4 chemistry cells vs li-ion cells). I ask because why not jump straight from 18650 past 26650 to 38120 cells? Or is this asking for trouble or has it already been done? (None of the new foil assist systems are using such high discharge cells, as far as I know….yet.) From a Headway cell seller; “These are big cells with a crazy amount of power. Each cell is rated up to 120 A continuous discharge (15 C) or 240 amp pulse (30C) and can be charged at a continuous (10 C). You can start a car with 4 of these in series. Please be careful with these and do your research. This is a massive amount of power!”

Also, any DIY e-foil builders using, or efoil users using, gear reducers with their BLDC motor drives? The low KV (140 to 200) motors coupled to high voltage batteries are spinning the props at super high RPM’s. Seems like a serious engineering flaw or availability flaw such that tiny plastic inefficient props compensate for such huge power output! Kind-of-like running flat tires on a road bike to keep the speed down. Asking because I do not know!

PS If any DIY efoil /assist builders are using gear reducers with their BLDC motors and feel like sharing the details I would be grateful.