That sounds vicious

Another quick test today to see amps at full throttle on 14s.. peaking around 180a.. guessing 50v under load....so, 9kw... that's 12 horsepower according to Google..through a 7 inch off-the-shelf prop!! It is so insane I can't quite make sense of it.. Some losses along the way, but that prop hub is still probably seeing 7 or 8 kw .. it's just incredible.

Lolol, don't know how I managed to miss this post.

I think it was to do with speed that they wanted out of the heli or maybe it was lift. One thing to note is that commercial aircrafts have to comply with noise regs. Military aircrafts don't :-) So it could be that the tips help speed or lift but create lots of noise. Again civilian aircrafts have fuel consumption specs that they must adhere to, military aren't very bothered. Can't remember much, had a few chats over a coffee with a few of the blokes that used to work on testing the blades. Quite often when testing stuff you were never told why the tests were being carried out as that might bias the results. Some of them also worked on the Concorde engine and intake development and testing way back. Used to be some interesting conversations. There was a Red Dwarf episode where part was filmed in the test cell where Concorde intake ducts were developed!!!
 
I remember doing flight certification test for RR Trent 500  (civilian) and they were trying to get me to 'tweak' the thermodynamic calcs. I thought it was a bit iffy so had a chat to our mathematician to confirm that the 'tweaks' would alter things in their favour!!!! I was in charge of the data and calcs that would be submitted to CAA to gain the engine flight certification. Unfortunately we never did the chicken ingestion tests :-) Lots of water and ice but no chickens.

As for your props, way above me mate. Thermodynamics I had a reasonable understanding of, well calcs anyway not theory.
Always interesting to hear about the lengths you go to to build your crafts.

Very interesting mate! Thanks for the link! It would be interesting to hear the findings of the testing.. rotor blades still look unchanged on commercial heli's, so I guess there must have been trade-offs. The faster the advancing blade, the slower the retreating blade, so there must be a max speed for the advancing blade on a heli. But for our application, it is just the blade rotational speed coupled with the forward speed at 90 degrees to rotation that dictates the actual tip speed, some kind of trigonometry to work it out, above me lol. But making supersonic tips work would mean you could use less pitch, which i turn means some static thrust.. unlike an 11x27 haha!

Interesting that there have been blades designed for supersonic use, but I imaging it was polishing a turd somewhat.

There are a few non secret details of early dev on blade tips here: https://www.bahg.org.uk/puma.htm
I worked for DRA/DERA/QinetiQ testing jet and gas turbines :-) I knew a few who worked on the tips testing.

Thanks for the replies, wondered if it was still worth posting on here.

Yeah prop tips have to stay sub-sonic really or there is huge efficiency losses and potential for blade failure from the pressure waves. I haven't cared in the past, as that was the only way to get the pitch speed up using off the shelf props...but for 500kmh+ I'm going to need every bit of efficiency. Interesting that there have been blades designed for supersonic use, but I imaging it was polishing a turd somewhat.

And yes..that collet lol.. will have a slot milled in it to key the yoke in..the shaft-collet friction will be the issue, but may go up to an 8mm shaft on the motor to add surface area for that transfer of power. 8-10kw will destroy just about anything.

I am also working on another route to 500KMH electric.. using this rewound Scorpion 4535 at 14s/200a with an 11x27 Powercrocco prop on an HJK Monster F3S plane. Serious stuff this time ;-0

Its so tiny I like it, not in two colours, but looks like it could be usefull.

You're going to have to do that collet up mighty tight (}

Looks nice. What sort of speed can prop tips go without causing issues?
I know that a military helicopter had special blade tips developed to enable them to go super sonic, if I remember correctly that is, can't say more than that, you know official secrets etc.... :-)