Custom 4 bladed cleaver - New design experiment.

[Christian Holmstedt]

Tinkering is fun....

Just took delivery of a custom 4 blade cleaver. I still need to tweak the hub/axle interface a bit more to make it fit a 3/16" axle. This one needed a fair amount of manual fitting, phew.

I've designed it for P-Spec/P-Ltd FE Tunnels but it will take until the PX300 is ready to find out if it actually works.

Design specs are as follows:

Diameter: 42 mm

Base pitch: 55 mm

LE pitch: -5 mm

TE Cupp: +23mm

Rake: 20 deg

Weight: ~8 grams

The material is 90/10 Bronze.

The delivered cast seems to be just about 0.5 mm smaller than designed in diameter but otherwise it looks good. The blades are very consistent. It still needs to be sharpened and balanced.

 

[John Beardslee]

Hi Christian

I did a number of custom 4 bladed Octura X series props in the larger sizes. The most difficult thing was having room to remove material from the back side of the blades to balance and sharpen them. Tidewater (ABC) did a few S series in 4 blades and the same there, the larger sizes were bad enough I didn't want to even think about trying to work on the small ones, glad there were none around in those days.

Thanks John

 

[shoboat]

Christian,

I just worked a really nice Octura P-741/4 for an electric boater.

It had too much transom lift when it was tested. It looks like a

nice propeller, but I think that motor is going to struggle to pull

it with good RPM. You may want to reduce the blade area and

round the tips of the blades for a little less diameter. Remember

the more blades you have the less blade area you will need. I

learned about that up in Fond de Lac, Wisconsin at Mercury Racing.

Let Us Know How It Works?

Mark Sholund

 

[Christian Holmstedt]

Mark & John,

Thx for the comments!

I'd like to test this prop yesterday but it was more fun working on this than the boat so, well...

There are tons of work left to finish it.

The prop looks more like an Octura V-series but with much less Pitch/Dia factor (~1.3 @ center of blade compared to 1.8-1.9 for the V series) and the blades are quite narrow (looking at it from the hub). 4 blades are used on the big F1 tunnels and that was the initial inspiration but since the blades are narrow it 'looks' right with four. The blades do not overlap.

The dimensions as of now are basically a stab in the dark with a starting point taken from props that seems to be popular / good for a P-Spec/P-Ltd FE Tunnel. It might be way off and it will likely take several more iterations to get it right.

The prop doesn't have a big tongue on the LE as most other available props have so it might be sluggish on take-off because of it.... but that's just unsupported speculation.

There will definitely be a test 'report' here at some point. Ideally I'd like to have a built and ready-to-go competitive tunnel as a testbed and the kit here just doesn't build itself

.

Christian