The MIT Lincoln Laboratory is developing near-silent toroidal propellers!

[Christophe]

I printed the toroidal in 250 mm...it's a bit dirty (probably because I crushed it in Z at 10 mm) but for a test of a few minutes it will be enough!

[Christophe]

Well I passed the three-bladed toroidal on my home test bench!

bench d'essais toroidale.jpg (183.63 KiB) Viewed 314 times

This bench is an original homemade design since it is based on a tilting arm on a landing and calculation of the moments on a simple scale (kitchen scale for the small model)... It is much simpler to do than a direct axial measurement and probably more secure, even more reliable (security coefficient > 20)...

This one I had built and used in 2019 to test on coaxial contra-rotating propellers for the project that you know, finally those who know me!

I have a "real size" scale 1 for the same project, on this one I have to use professional scales at 100 or 200 kg !

Well, the toroidals, I suspected a little that it was not terrible well it's worse than expected!! I can't believe how crap it is!! Absolutely all the measurements are in the red and well in the red!

Table of comparative measurements:

toroidal test bench 250mm.png (21.46 KiB) Viewed 314 times

I did not exceed 100 grams on the scale for the painting because anyway it was extra crap!

But I pushed it a bit and I got struggling to exceed 150 g on the scale (I was then around the 1450 ppm set point, i.e. 45% of the max!) where the equivalent 250mm propeller exceeded 400 g !

On the dB, where it was supposed to be a hit, no better: I have +6dB for the 100 gr measurement!! Almost silent my c... !!

Is this toroid story a bad joke or what?

I didn't go any further, safety first! I don't want the propeller to explode 1m from my face!

Good at toroidal discharge:

a) The impression of the toroidal was not terrible at all and it vibrated a lot...
b) I also changed the pitch of the toroid to match the 10mm pitch thickness of the classic...maybe that was a mistake?

So the next, two-bladed toroid, I'm going to print it in its original proportions and I hope the print will be better (less cantilever angle = better print)...but hey frankly, I have little hope of a great improvement given these very insufficient initial figures! (unfavorable factor of almost 10!)!

The classic propeller tested:

Given what I have just measured, this whole business of toroidal propellers seems to me a nice scam but in hydraulics it can behave very differently from in aero! In any case for the aero part... I don't really believe in it anymore...

To be continued...with a two-blade printed in better quality! Might as well enjoy the bench since I put it back on the road!

ps: the measurements of Watts at low power and 12V (< 100W) are not very reliable because they are greatly reduced due to the sensitivity of the shunt (but comparatively they are). This wattmeter is made for higher amperage (up to 100A) and higher voltage...So don't take into account absolute values ​​<100W but for comparative measurements like here, it's acceptable...

reps: ps: how many % of RNA vaccines are there at MIT?

[Remundo]

at a glance, you feel the finesse of the blade on a classic propeller.

The toroidal, blade junctions I've seen are rough and definitely generate drag.

[Christophe]

Yes it is certain that the quality of the print influences and we will see with the next one…I will pay more attention to the quality of the print!

But frankly, I don't believe in miracles in physics!

We are not in the 30% to catch up but in the 1000%… so there is something other than the state of the surface, especially since the measurement carried out was at relatively low RPM!

ps: another hypothesis I got the direction of rotation wrong?? Meaning trigo seen from the front for these tests…

[Christophe]

I printed 2 two-bladed toroidals without changing the Z scale and in better finish :

a) One 145 mm in diameter (baby propeller )
b) One 250 mm in diameter

I have already passed the 145 mm on the bench: it's better but not so much better than the three-bladed, it is less good than a classic propeller in all cases and on all criteria! As it is better printed and therefore balanced, I was able to go all the way without risk.

toroidale_145.jpg (200.56 KiB) Viewed 170 times

toroidale_145_2.jpg (223.62 KiB) Viewed 170 times

I will pass the 250 mm and will give you the readings of the two-blades and my conclusions.

This will not be famous for the toroidals!!

So my tentative conclusion is:

a) Either this whole affair is a scam (surprising all the same because MIT is behind it...)

b) Either the models on the Internet (at least the ones I found and tested) do not have the right profile ... and that they are not toroidal propellers but mediocre ersatz ...

Those in the MIT report are different at the pen level: https://www.ll.mit.edu/sites/default/fi ... peller.pdf



c) Either it doesn't work in aero (which would surprise me since the MIT report mounts it on drones)!

d) Either I am wrong in the direction of rotation (which would also surprise me because it is very symmetrical, unlike conventional propellers), I rotate like this:

toroidale_145_2_rotation.jpg (230.27 KiB) Viewed 156 times

To be continued !

[Christophe]

Here are the raw results on the 145 and 250 mm and some analyses.

According to my tests, there is nothing good in aeronautical toroidals: the performance is always less good and they are always noisier for the same thrust!

The two-bladed toroidals are nevertheless less crap than the three-bladed!

The delta dB is relative to the background noise (between 52 and 56 dB depending on the tests)...

Trials of toroidal helices.png (43.08 KiB) Viewed 146 times

Toroidal helix tests Analyses.png (26.3 KiB) Viewed 146 times

I couldn't do the test the other way around: the motor (or ECS) didn't like the 190W peak with the 250mm at full throttle (probably too much torque)...it doesn't works better (loud noise when empty) and I don't have a spare on hand! In any event, this would most likely not have changed much given the symmetry of the toroids!

I will send an email to the MIT lab to ask them for a "correct" model because there, I see that as an explanation!

[Christophe]

I hadn't seen, there is the patent link in the .pdf: https://patents.google.com/patent/US10836466B2/en?q=(Toroidal+Propeller)&oq=Toroidal+Propeller

For those interested:

US10836466.pdf

(635 KB) Downloaded times 7

ps: their axial test bench is crap!

[Christophe]

I will send an email to the MIT lab to ask them for a "correct" model because there, I see that as an explanation!

Do :

Mail_MIT.png (38.53 KiB) Viewed 134 times

I don't expect an answer but who knows? On a misunderstanding?

[Christophe]

Waaaaw, I had an answer in a few hours!

I think it's a semi-automated answer but there was still a human behind!

Mail_MIT_réponse1.png (60.52 KiB) Consulted 100 times