Nice duct !
We have ordered and received two props identical to yours. I thought that we could screw tightly the prop to the shaft, but the prop is not adapted for that. It looks like the prop only holds thanks to the pin breaker or whatever you call it. I am puzzled because breaking the breaker would then allow the propeller to escape.
So Silvio did you find a trick to prevent the prop from escaping if the breaker pin breaks ?
Thank you.
No pin in front ?
You can drill a hole through the propeller , like i did for the solas
You want the holder to break otherwise something else will break ( shaft gear foot…)
Its called a shear pin.
I had a trunk boat in Amazonia with a 40-horse Yamaha engine for a year. I broke at least one shear spin every single day due to UFOs (unknown floating objects). But I have never lost a prop. Sure the pin should break, but I need the prop to then spin freely but not escape…
So make the shaft with a smaller diameter all around the holder , like a groove for a o-ring , it Will spin free
The Shaft Will unscrew before the pin or the holder break i think 
I don’t have think of this problematic yet.
My prop is fixed by a shear pin and a split pin:
Hard to break together, the shaft will certainly rather unscrew from the gearbox and I will lose it with the prop 
More probably my motor’s pinion will unglue and I will lose nothing 
It is maybe better to not weld it, finally. My second gluing with Loctite is yet OK.
I would not just go for any shear pin purchased in any hardware shop, but instead in a marine shop for an appropriate one (light motorboat).
We want a prop fuse which will snap first before anything else, but not too fragile neither…
Extract from a forum talking about it :
When making replacement pins, use the same material. Particularly don’t replace brass with stainless, as the stronger material could result in prop damage. In the same way substituting a stainless pin with a brass one will result in early failure as it will bend under load and be difficult (more likely impossible) to remove even in the workshop. There is also the probability of electrolytic corrosion if the wrong material is used.
Read more at http://www.ybw.com/forums/showthread.php?4118-Making-my-own-shear-pins&s=d3c43ecce0c74767e3d7fe4da800dfd6#lJ6ZCr7PlorIKrs6.99
This is my duct after 13 hours of 3D print:
Not very robust but better than nothing!
I wonder at how many watts I will take-off and cruise now…
I’ve made it with a little diameter reduction (2°)
Why not use a tube with correct diameter or bend some aluminium?
Yes, I thought about that but my 3D print duct has a NACA profile which should produce less drag than a simple tube.
I wonder if it is possible to 3D print a lost mold from soluble material and fill it with fibers and resin. Especially the duct and props would be a good candidate for this, as thick profiles produce lots of drag.
You could 3d print split molds, reusable for more than one part, good for any wet lamination process build, at “room” temperature. Well… if you print ABS, ASA or similar, you could even cure your laminate at 60° C
It’s time consuming, though. Further than this, accuracy wont be as high as a directly 3d printed part.
Alternatively, and it works great, you can print a positive 3d part “flanged”, then use each of the side to build a 2 parts glassfiber mold. It works very well, did kitefoil wings with that tecnique. Again, time consuming, not worth for a single shot, but more reliable if you print carbonfiber.
I think, the precision of a mold could be very good, because you could build very thick walls with a light infill to make it stiff.
In case of props, you would need almost no overhangs, so the precision becomes higher than an ordinary 3d print with support material.
In case of ducts with integrated struts, you could print 3 parts: inner, outer and a top or bottom.
As we are experimenting a lot with the design and details, it would not be a drawback, that its lost.
Anyhow you could build a reusable mold from the perfect part.
Question remains is if there are soluble materials good and stiff enough for the first lost mold?
Precision, in my experience, could be spoiled on the junctions between two halves of the mold, when even a thin glassfiber goes squeezed in between. Molds made of plastic can’t take that much of pressure,but they work. Tried many times.
Hey @Silvio,
You haven’t posted for a long time now. Are you busy flying around ?
Question : do you still recommend your set-up to beginners ?
Cheers.
Hi there. Can you reuplpoad your files?
Hi all,
I didn’t fly for some days because I burnt my ESC and I am on another project for now.
@philgib: I think my setup is not bad for beginners because it is not over-powered (small motor) and it take-off at slow speed (SUP foil). With a propeller protection and a voluminous board, it’s perfect for beginners.
@mark_myronchuk: You can download last version of my files here.
Thank you, Silvio! really like your build
Yes your set-up could be nicknamed the “Easyglider” or “Bixler” (basic, cheap and reliable standard RC glider plane ) of Efoils…
Do you have any idea of what could have caused your ESC to burn ? Where you trying to beat your own speed record ? Plastic bag around the prop ?
