Propellers and Ducts


#187

In low speeds the thrust and efficiency is pretty good. I can foil at 1600w in apx 18kmh with 90kg rider, and a huge foil wing. In higher speeds it’s not very efficient, but it’s capable of about 35kmh. We lowered aoa from 5Degrees to 3 degrees and made the sections slightly thinner, which helped in higher speeds seemingly without decreasing low speed thrust/efficiency. Prop diameter=142mm

Prop distance to walls is important, we use 1mm (max2mm as our 3d printed is a bit off).


#188


#189

Wow, great info. I’m shooting for foiling at 1000-1200W(or less) but giving up top speed.
Going with a direct drive outrunner but otherwise its similar to your set up.
thanks for the info! much appreciated


#190

Do you know the pitch of your prop? Is it the same prop PM used?


#191


The prop is here. We designet it for 3d printing in PLA (thicker sections). Don’t know the exact pitch

Note that the duct profile aoa should be lower. Altho the one on instructables also works well.


#192

I cant remember where I read it, but I read an article about Kort nozzles that said when a prop gets too close to the duct, cavitation increases. Counter intuitive, i know. Im going to give it about 3 mm clearance, still pretty close.


#193

Hi Aaron,
i am very interessted to see your nozzle design.
would it be possible to send me the step-file?
bowi_k@hotmail.com

thank you so much.

Thomas


#194

Despite I never seen it in my life, I’ve been asked for a sample design of a printable prop for 80100 direct drive motor. @DavidC is building one of this pod and could give it a shot, or at least evalutate if it can work and how to improve it. This is the link to the .stl file:
80100-160/132mm

This have been designed in Javaprop and then scaled and made more real in Solidworks, I did it just for fun, so take it as an exercize…pheraps could help me getting better in prop design and revert this back on my Efoil.
Diameter 160mm, Pitch 132mm, I calculated little less than 4KW at 6500rpm, ideal speed of 25kt which is the speed I took as reference even for my geared pod.
In my opinion, the 80+mm hub cause some problem, I rather have liked to add a piece to close the motor tube smoothly reducing diameter, to get close to 50mm at the prop…or less.
For who’s alreadt running on that big motor, which prop size and specs are you using?


#195

I have my motor cone tapered down to 50mm . this picture is of the version 1 but the outside diameters are the same in version 2


#196

Anyone ever looked into using/testing inducer impellers, very interesting stuff and im going to give it a try as it may help boost slow speed thrust without losing top end speed.

We just started working on the inducer impeller to feed and pre-load our main impeller.
A little on the topic here:



How to get a good impeller (for jet propulsion)
#197

Yes this might help get more efficiency. We did kind of stator vanes like in turbofan jet engines. However we were not able to get below 1,8kW power usage during riding.
At that time we were already working with ducted prop as well. As we are able to ride now with only 700Watt we changed to ducted prop. We still see potential now to get below this value… This means currents below 20Amps… No cooling required anymore…regardless which ESC you use…
Remember one of the key factor ist the efficency of your wings… Most on the market are not very good.
Esp. those from china…We soon might deliver a very efficient front wing profile to the crowd here… so you all can benefit from this…
Give us another month to decide;-)
And remember, the need of water cooling like the one one liftfoil will cause serious problems after some hours in salt water…We wanted to avoid this, and why we worked hard on the efficiency of wings and propulsion…
.Always keep some water under your wings.;-)…


#198

Nice article.

https://www.placediverter.com/home/product-category/jet_boat-impellers/ shows the outcome of their research.


#199

This video might help explain the theory.
Duct theory.


#200

Yes, I have read and watched several videos on inducer impellers and some of the big major jet companies and and builders use these and they do dramatically improve low speed thrust, which is when most jet drives are cavitating and very inefficient. Really interesting stuff.


#202

So, as a rough estimate, the best impeller “consumes” 1KW more than the best nozzle.

IMHO, providing a front wing with thickness to chord ration less or equal to 11% will not be enough. Supfoil Front wing profile is 13 to 15%. They provide lift but bring a lot of drag.

My suggestions here in this post. The Hydrofoil “plane” itself can be modified.


#203

Interesting, we at VeFoil have a backer who designs many foils and he has proven these thick foil wings for more lift cause so much more drag than a thin and slightly larger surface area its dramatic. wing foils for air he states are not the same in terms of performance in the water because of the density of water.

The foil fish is super thin and works incredibly well for its size vs a super thick foil I found in terms of drag, less power required to move forward.

We are looking into some of his super simple designs for increased performance.


#204

Well guys it`s not all about thickness and ratio…All correct at certain views…but… The profile must be good for best efficiency… and most foil designers use profile designed for completey different usage…
Mostly designed for Reynalds numbers above 2 000 000…But with e-foils we are in a range of about 1-200000…
Just to give you an example:
We tested the Moses Windfoil Wing 683 which is really a very good one, easy ride and I would say very good for efoils as well… Power needed 1000W at 20km/h -compared to the takuma foil with about 1200W quite good…same setup…
Using our wing profile (where we did long research on) with same size and thickness with our profile we were riding with 800W same setup… total weight about 100kg and in sweet water…

You can see there is a lot possible with the wings design…not only the propulsion :wink:
And we could push that even more, but our main goal was to find an easy to fly wing and second point was the eficiency…


#205

Is it possible to use a brushcutter 52cc outboard to push a hydrofoil board? Thanks.


#206

A Moses Front wing for a windsurf board is not the best profile if I may add something.
The kitefoils have always beaten up the windfoils severely and that is where the innovations are. They have less weight constraints also.
Not that I don’t trust you but I am a bit sceptical. I’ve been witnessing the French guys launching the kitefoil activity since 2008 (10 years now) based on Carafino design. The best guys from Spotz (closed down), Taaroa, Manta, F-one (all French) then Banga bought by Enata and today Chubanga going at 45knots+ with a kite and you’re telling us you have thought about something they didn’t :grin:
Why not ? I would have been convinced straight away if your bench mark front wing had been one from Enata or Chubanga who are leading the Kite Hydrofoil Pro Tour. Then, the stabiliser profile is also important. A mismatch and you loose a race.


#207

Lot of development based on CFD and experiences in race kitefoils since the last few years, I do kitefoil since many years at the same spot where the founder of Moses kite also, and Luca, the guy who launched Banga, Enata in UAE and now is back to Italy producing Chubanga is a friend, we live quite close so I had the chance to see how he work, own one of his foil and broke and have the same modified many times. The exceptional flow and performances of such a race wing can’t be ok for our motorized foils.
We weight to much, never lean against the foil nor have the same variable support that foilers have.
I build 3 foil, full carbon, between my first old style Moses and the Banga, effectively the RE number consideration is real and not all the profile behave as expected, if you go thin you’re half way, then anhedral, span to cord ratio…all play its role. First Banga was straight but feedback during gybe and reach was not perfect even tho a “flat” wing is more efficient on paper (software). I think a mix between racekite and huge surf foil could be where to look…