[hpv-boats] Carbon Fibre Blades for Folding Propeller

[Rick Willoughby]

I now have a mould for making CF folding blades:
http://www.rickwill.bigpondhosting.com/CF_Prop_Blades.jpg

The resulting propeller has a diameter of 330mm and weighs 160g.  I  
have tested the blades to 16kph, which corresponds to 65N thrust.   
This is more than twice the thrust needed to achieve 12kph, which is  
the sustainable speed for a pilot in good shape.
http://www.youtube.com/watch?v=ONk3fUnHamI

The pitch was close to what I calculated below 12kph but it is  
possible there is some blade flexing due to loading because the pitch  
was apparently reducing as I increased speed.  Usually the speed to  
cadence increases as speed increases due to reduced slip.

The prop is suited to a gear ratio of between 6 to 8 depending on the  
boat and pilot although the boat needs to be easily driven.  I was  
running at 7X.

I could get 5kph in reverse spinning flat out.

The blades do not deploy as quickly as heavier blades.  I plan to use  
a stainless steel core to add some more weight and possibly reduce  
blade flexing.

Overall I am pleased at how the blades worked out.  It only takes a  
few minutes to lay up the blades but overnight to cure.  Hub is the  
same nylon rod I have used for stainless folding props for the last  
couple of years.

I plan to do durability testing over the next few months.

Rick Willoughby
rickwill at bigpond.net.au