Prop Manufacture

Ahhh..i knew i'd seen your name somewhere!
cycling being one of my hobbies i can well understand the 150W average though i'm a little above that...but that is to be expected i'm a little shorter in the tooth.
If you haven't gotten anywhere with the CNC guys your talking to now you might want to try http://www.mouldcam.com and http://www.productionparts.com.au/cnc-machining.php
I have had good experiences with both, though awhile ago.

 

I just did the numbers on the 2007 RAAM that finished this week. The overall average for the winner was 14.38mph and the flat stages were around 19 to 20mph. If you do the numbers on the flat stage and assume no wind then the power level is around 160W so very similar to what Greg K can get on a sustained basis. Although there are real issues sustaining that level for days on end.

Thanks for the recommendations on the machine shops I will have a look at them. I am trying to avoid reloading my old version of AutoCad to produce a dxf file. Two firms I have dealt with so far have had some sort of a problem with the the igs and dxf files I exported from Freeship. This is part of the teething process no doubt.

Rick W.

 

Rick, I see now you're going for really long runs. Most of the stuff I've designed for you run out of air in about an hour, so we designed for a 1.2kW sprint and a 600W cruise....But then again there was that cross-channel design on re-breathers...about 8 hours max. Heating the breathing air was the bug-a-boo.

 

Finally

Taken a while but have finally found a shop that can mill high aspect props for me.

I have attached the original drawing and a photo of the product.

Rick W.

 

Rick you may try Henleys in Auckland
http://www.henleyspropellers.com/

 

Nice wheel. I would have made the hub a bit larger but... <shrug>...

I take it you hand polished?

 

John
It is for a world record attempt and was factory polished. I have only seen photos. Will not get to handle it till May when I am back in Canada.

The shaft is only 3/8" so hub does not need to be very big.

Rick W.

 

Should add that the engine is rated at continuous output of 150W so not big torque at 360rpm.

Rick W.

 

Beautiful piece of work.

 

Yes - It is nice to find someone who can do really nice work. It took four props to get the machine set up right. I would have been happy with number 3 but the machine shop owner is a perfectionist.

The blades have an 8% of chord blade thickness in the working part so are quite thin. Hence have to take very fine cuts as the size gets close and the blade needs good support.

Rick W.

 

If looks relate to performance then you look like you've got it... Nice job...

 

Actually it is an efficency issue with the low Vr vs surface drag....Or at least my calculations point that way... .

I should dig out the pictures of our prop sets. And yes the blades are very thin and very sharp...our CR sets picked up the nickname "The Cuisinart".

 

Im itching to say although Im not a specialist with diagrams and computer progarammes but---

Oh here goes,,--- I dont like it!!!

The blades in the middle close to the hub are virtually parallel with the shaft. 90 degrees to rotation. The pitch is enormous.

Every part of that blade needs to be efficient as it can be, it looks like only 50% has any worthwhile effect.

Oh well thats my 2 penneth.

I can say how wonderfull and fantastic it looks too if you want.

 

John
I have attached a JavaProp screen image of the design conditions for the prop. The chord is 37mm. My approach is a little different to JavaProp but result almost identical.

What efficiency do you get for a prop doing 3.33m/s with a total boat drag of 38N?

Rick W.

 

Frosty
Depending on your frame of reference is could be considered an enormous pitch. It is about 23", depending on how it is measured, and diameter is 14" so P/D almost 1.64.

I don't expect or want you to say anything you are not thinking.

I was just delighted to see the job done after trying so many shops without success. The fellow who made it was after a diversion from oil field stuff and actually said it was a pleasure and a challenge. Just nice to work with someone who has an interest in my little projects.

Rick W.