That equals my tests…
2 Blade for the win
10" at 50kV vs my 6" 80kV Motor (should be 6.25 to equal the 10" 50kV)
But all over all, i tried many props, 2, 3, 4 Blade, Diameter 120-160mm, Low, medium and high Pitch, all over all, If parameters are in a certain range, it doesnt matter that much.
I have a good working smaller 4blade, a good 2Blade. A medium 3 Blade, that performs Well as Allrounder. All work accepable, the diffences are not huge. Some are better at low speed, some better at higher speed.
That’s pretty much the crux of it.
Do you want slow speed efficiency. Then select a prop for it…
Do you want high speed, then you need something different.
Also a massive consideration is how much of the mast do you want to sacrifice to prop size.
Numbers will be up one day ( my metr at works now ) just missing time right now to do everything … but I have a 3 blade apc airplane prop lying around for 1 year now , will try it for sure and probably a 2 blades as well …
Ran an 11x10 apc prop cut down to 8 inch diameter on my 80100 80kv with my naish thrust wing. Prop was more efficient once on foil but took a lot more amperage to get up on foil.
As much as 120amps to get on foil and as little 25 amps foiling. Speed felt the same as my other 3 blade prop but I did not have a way to measure speed. My 3 blade prop takes 60 amps to get on foil and around 38 amps foiling.
I feel the 3 blade prop I was using was a better pick overall.
I know the mounting of the apc prop is not very hydrodynamic. Just needed something quick.
If you check all the outboards and powerboats propellers, except for the surface piercing type, they all look the same. They are way thinner and extremely “cambered” than airplane ones.
There should be a reason for that.
But, as marine engineers already realized lately, electric propulsion is all a different beast, boat hull (planning hulls) should be tuned for flat curve torque of such motors which makes legit to think about a similar new approach in prop design. Still…air is not water, efoil ain’t a tug boat, etc. etc.
Plus…if nobody from time to time ever tests anything weird and unlikely, humanity would stand still century after century till the end of time. So welcome thin cord blades test
Like what jezza said regarding reynolds #, my tri was spinning around 13-14 k rpm. Around 800kv if i recall well onn 3/4s. Also, very fragile build for water
I totally agree. All the human powered stuff is designed for minimum power and maximum efficiency which is what we also need when using batteires which compared to gasoline have a fraction of the run time.
Great point thank you!!!
That’s a Wow ! Thanks @s9tim and your data logging system !
How many seconds does it take to be on plane ?
We could program a gradual ramp up on the remote to reduce the current demand and use weaker ESCs, motors and batteries. Then the limit would be human: could an experienced rider bear a 6-8 second rise time before reaching the plane ?
With a 240mm diam prop, you can be 3-5 cm lower than a FR nozle, if you lower the fuselage aft part in case of a pusher (lower the fuselage front part in case of a puller). We need to separate the fuselage into 2 pieces with a flush piece of plastic looking like a piece of mast and that can be 3D printed.
And it is a "quick and dirty test " without a profile that is really suited for water like a H105. We can probably do lower than that. What is nice with the thin chord blade props is that we can hand make them 100% carbon more easily than a FR style one… (except @virus of course) with 10-15 strips of carbon plus epoxy into a 250mm long 3D printed mold. Not any 3D printer can print such a mold though
What do you think about to try those and cut it to 20-25cm
US $18.01 10%OFF | JMT 4Pairs 12x5.5 3K Carbon Fiber Propeller CW CCW 1255 CF Prop Con For Multicopter Quadcopter Hexacopter Drone F06791-4 https://s.click.aliexpress.com/e/CNG24WNi
These are really thin, superb and really cheap (2.25USD per prop) . 30cm reduced to 25cm why not.
This kit is for a quadricopter (4 arms), 2 motors per arm = 8 propellers = 2.25 USD per propeller
Possible issues:
1 - They look like rotating knife blades:
2 - Stiff for sure but how much for our use : I am not sure they will not bend under load. We are 100kg /2kg = 50 times more heavy. We have to try.
3 - The extremity of the motor axes could be adapted with a kind of T-nut where you can lay those props flat, maybe maintained with an invisible pressing screw hidden behind a nose like @Gobbla pod one…
I think you missing the point. With a 240mm prop you need 240mm of water to ride in. That’s 10cm more than a 140mm prop. There’s less margin for error, and less margin if you happen to run through shallower water. If you were foiling you’d understand what I’m saying.
I agree with you on that Jezza, you want as much height as possible before the prop starts lifting out of the water and losing thrust. 10cm is a lot too, especially if using a shorter mast.
No sensible foiler rides in 240mm of water even with a 140mm prop. If I don’t have chest deep, I don’t kitefoil, I do something else.
I think you are missing that we are trying to write a new page of the sport. To cut amps drawn by a factor of 2 to 3, we have to think differently… :
1 - either adapting the existing gear without reducing the mast length
2 - or introducing new concepts to reduce drag and wet surface. For this, IMHO, the canard is the best platfom for extended flight times since you can use 550cm2 at the mast that will add up in terms of lift to the 250cm2 of the front wing. That’s way better than a 900cm2 front wing in a conventional setup where the 350cm2 stab with negative lift (mounted upside down) will introduce a lot of drag. Yes, a canard might be difficult to ride above 30knots but it is not the target since the setup is OK at 20 and even 25.
A canard is nearly drag-free since both front and rear wing are operating at their optimum lift/drag ratio angle. That’s why Zeeko has met an enormous success since the initial launch and introduced the XLW and XXLW front wings afterwards.
I have had good success using cut-down model aircraft propellers on my efoil, and have qualitatively compared them to traditional wide-blade marine style props. With the same pitch and diameter, I can foil significantly longer using the model airplane props.
The reason traditional boat propellers look different from aircraft propellers is two-fold: structural strength (required for 800x higher density fluid), and control of cavitation. The very wide (low aspect ratio) blades of traditional marine propellers create a lot of unnecessary drag (due to excess surface area), especially at the high speeds and low loads of foiling, which can be greatly reduced with a higher aspect ratio blade, while still maintaining adequate strength and rigidity for our application, and still without cavitation issues. 14 - 18" diameter model propellers (glass reinforced thermoplastic) cut down to 6 - 7.5" diameter are plenty stiff & strong. Pitches ranging from 7 to 12", and 2 & 3 blades have been tested successfully. I am just now hooking up my new e-logger to get quantitative efficiency & speed data.
Theoretically, the narrowest blade (highest aspect ratio) prop of the correct pitch & diameter for the motor, that does not deform or cavitate under maximum lift conditions, will be the most efficient. Two blades should be more efficient than three, however, my experience has been that two blade props have not been quite as smooth, maybe because they are running in the wake of the mast (so the mast wake interference is synchronized to both blades).
Also - I agree, a canard should be the most efficient wing & stabilizer set-up if properly executed!
You might think you are always in chest deep water, but there’s no guarantee when you can’t see whats under the water. You might be riding much shallower once up on the foil.
I get that you are trying to create something more efficient, but it will come at a price somewhere else.
No matter how you structure the fuselage, the larger the prop, the less height you have, as it will always require the prop to be submerged properly.
As for the canard concept, that brought other complexities in airplane design and as a result was not widely adopted. You might very well find it to be the same hydrofoils…
What is interesting is what the designer of the spitfire foil thinks: For glide and speed a standard foil will win. For carving or free-ride, a canard would be better.
With more and more people enjoying the efficiency of their FR 2 blade folding prop (no duct), I was wondering if sbdy had done some further tests with a high AR APC air style prop ?
Hey @visor360, this is another field where applying your process: 8" diameter blade prop with high AR (8-10" pitch). Airfoil section ? Very thin Eppler 817 + twist ?
! Thanks 
