I can’t be sure since i haven’t so good understanding yet.
My basic question comes from this:
I haven’t seen a single person here doing a theoretic sizing attempt of propeller vs load, i have just seen trial and error method. For me this means that there might be large gains not found yet in motor/propeller combination.
When someone then finds 5-10% gain with a novel design swirl end cap then i wonder how this is verified. Is the propeller optimal before adding end cap swirls? Is the result real?
The poular Metr.at logs won’t be able to prove such a small difference as variation in riding/wing angle/throttle/environment alone could give this. Even motor heating in different runs could cause 5% lower efficiency…
I don’t want to write any academic papers here, nor can I. A camera test in a pool has already proven that the wake vortices can be largely eliminated with this technology. Such a vortex always causes increased energy consumption. A normal spinner should bring about 100 watt savings, a spinner with blades correspondingly more.
Still, 120 simulation runs gained 1% in total efficiency.
The guys in the paper could very well be poor achademics (they’re out there too) but a guesstimate design is not so likely to be better than six scholars focused work.
It’s still interesting, where can i find this video?
Lars, theory is quite simple, but I agree that the fins might only be 1% gain, the rest come from cone.
Industrial shaft propellers normally have very small hubs to reduce drag. In our application it’s about 1/3. Which is substantial. In pleassurecraft this does not matter so much because the drag is minimized through having the exhaust gasses pass though hub and create vortex and pressure equalitation instead.
If you do not have exhaust through hub then you use cone to minimize drag.
Best everyday example is normal stern drives. Volvo penta duoprop vs for instance mercury bravo that use diff ways of expelling exhaust gas.
I have wondered why the commercial props end with a funnel, if it’s for the exhaust gases then i get it. otherwise it seemed like a poor design for drag.
I guess when printing a cone you might as well have the swirls, at least they look nice
Will post the results here about 17:00.
Will probably have to use the Xmatic app instead of Metr as the latter is still very glitchy.
Thanks @nice2cu Robert for making a nice design, lets hope it’s balanced
Its really nice to ride in the swedish autumn, when launching from dock and not getting wet at all.
@nice2cu cone adds +10% energy use. It was also abit more nervous to ride with. Some drops of water also entered the cavity not helping witg balance. Anyways the vanes have to high pitch and are not shaped according prop design. This is the most likely cause. Correct it robert and I will ride it again😉
I could only ride my cone for a short session and with low batt and also lower avg speed. Even if it shows some advantage avg speed is 4kmh lower then ref, so result can not be trusted. Also 1 vane broke when removing it, so 1mm vanes in ABS is on the weaker side, but it has same pitch as FR.
Since the resistance in water and air increases exponentially with speed the ”no cone” is the clear winner with the modest consumption at the highest speed.
It would be interesting to have a spinner cone without blades compared.
Do you think you keep the angle of attack and turning curvature and speed constant for three 7km runs? I must say it seems impossible. When you have ten repeated runs all showing lower consumption for a design then it is interesting to compare results.
Overall great effort, it’s better to test than to write on internet forums😀
You should get out and ride more than doing literature studies😉
I’m quite confident that i can keep close to identical runs.
I normally only differ 2w/km on the test track. I’ve done about 100runs there, altering props, wings etc.
However the most important factor is how high you ride and to keep that constant as well.
During the wait for David to start making magic for the DIY scene i present another learning.
The frankenprop! I made some of these before joining the forum and getting my first FR prop.
So this is a solas amita, a quite good prop actially for outboards in 8-10hp range. Originally 7,8x7” But cut down to 6” diam and sharpened on the leading edges.
It’s been lying around a year now untested, so today I thought why not. Its more fun riding when testing something new or old. And since we’ve been exploring cones lately why not test something made for expelling exhaust gasses
I study in the last days some videos and documents about that cone with the small blades.
On your picture I see that the position from the small blades to the propeller blades are wrong!
