Does anyone have a CNC capable of milling Props from an STL or similar?

Power System
1

I’ve spent a few years writing software to create props, based on about 12 years research and over 1 million CPU hours of CFD genetic-optimisation - I’m good with software, but no so good with making things that are bigger than my FFF printer…

Is anyone interested in collaborating on an “ideal prop” ? I’ll supply the design, your task is to make and test it.

Background: two different mates of mine made their own props: one used a chainsaw and a fence post (no joke - he’s a not-so-wealthy farmer) and the other cannibalised an industrial air-conditioner and used the nylon blades out of it. Both of those worked almost exactly as well as my stupidly-expensive “blah blah optimised” helix carbon prop… which lead me to the realisation that even the really expensive prop-sellers who claim to have great designs, are either wrong or lying.

My (free) software is a Fusion360 add-in (foils.pro) - but the released version does not include the optimised sections for air-screws (the new DB is 67 gigs - too big to ship as an update…).

Chris

2 Likes
2

If you’re wondering about possible efficiency improvements - here’s something worth considering: at 2250RPM my boat draws 2750watts while providing 40kg of static thrust (measured pulling a rope through scales tied to a tree)… that’s a whopping 500%+++ more thrust per watt than a typical paramotor. Yes, water is dense and incompressible, which is why my boat prop is smaller than my hand, but it stands to reason that optimising our props for the actual (and narrow!) conditions we actually use them in has possible the largest scope for improvement that can be made to our power and range goals…

3

Chris - I may be interested in collaborating. I’ll PM you. However, your design may be outside the envelope of what I can do in my shop old video of what I have here: Workshop - YouTube. Project I’m working on here: XTM 5500 - YouTube

4

I imagine you’d be able to lay up a pretty decent prop with a 3d printed mold and carbon fiber uni-tapes (and then countless hours of sanding).

5

I’ve just discovered that dipping an FFF printed part into SLA resin then curing that in the sun leaves it with a gorgeous flat mirror finish… but CNC milling wood makes way more sense at the development stage: once the testing on wood is over, moving to carbon fibre might be OK.
One advantage of wood that’s worth keeping in mind - when you have a prop strike, the wood breaks, typically without damaging your motor or drive shaft. Carbon fibre can be too strong, and damage other stuff (both your motor/shaft, and what it hits - e.g. cage/keel/sail/…).