Rick Willoughby,
I am very impressed with your original approach and hard work developing your human powered boats.
I am digesting the material, pictures, links, data that you have given us.  I will digest them before I ask any more dumb questions that you have already answered.  You have a huge body of work that will take me a while to study....and grok.
Thank you.
JIB (John Wright)    

---------- Original Message ----------
From: Rick Willoughby <rickwill@bigpond.net.au>
To: harryproa@yahoogroups.com.au
Subject: Re: [harryproa] Re: Mirrored Foil Sections / human power
Date: Tue, 31 Aug 2010 07:51:33 +1000

 

Colin

Here is the full link:

http://www.rickwill.bigpondhosting.com/Pecadillo_Pedal_Thruster.png

This shows the second configuration of the shaft to overcome the buckling problem.  It has 1.2m of aluminium tube and 1.5m of 11mm spring steel - although you cannot see the spring steel in this photo.   

Up till the last year I have only painted the spring steel to avoid rusting.  It does rust when the paint gets damaged.  The reason I have been trialling fibreglass wrapping and sleeves is to provide corrosion protection as well as increasing the torque rating. The spring steel acts as the former.  I have also tried to find a convenient source of high strength stainless but so far without success.  

Any prop inclined to the flow will have unequal blade loading and this induces vibration.  If the prop is large diameter with high aspect blades the out of balance forces are very high.  It is possible to bend heavy shafts that are rigidly supported at the prop. So it is important to have the shaft aligned to flow.

There are alternatives to the curved shaft such as submerging the gearbox like a typical outboard leg.  I have used universal joints but the diameter gets large for the required torque rating.  The objective is to get the prop aligned with flow.

Rick

On 31/08/2010, at 6:42 AM, Colin wrote:

 

Thanks Rick.

What about rusting in salt water?

Your Pecadillo link didn't link,

Cheers,

Col

--- In harryproa@yahoogroups.com.au, Rick Willoughby <rickwill@...> wrote:
>
> Colin
> I have a couple of Mars electric motors and trialled one for an
> outboard.
>
> The issue is one of gearing. I made a 400mm diameter prop for my set
> up with a 2:1 reduction. I used a submerged right angle drive that
> had the required capacity. You can get over 80% propeller efficiency
> with something like this. The bigger the diameter and the slower
> revving the more efficient but it can just get too big.
>
> The limitations with the high aspect blades is cavitation and bending
> strength. If you are aiming to get above 15kts then cavitation could
> be an issue - unlikely unless you push the motor beyond rating. The
> blade strength will depend on how easily driven the boat is although
> you have to think of powering into a strong head wind as well.
>
> A prop that is aligned to the flow has steady blade force so fatigue
> is not an issue; hence welding is acceptable.. I expect you could
> make a reasonable blade from 60mm wide by 6mm thick stainless
> flatbar. Probably about 8 hours work to cut blades, partially shape,
> weld to hub and final shape. I can do all the calculations if you
> want and give good indication of performance. The NACA07510 mirrored
> section is a beauty because it has almost constant Cp across the
> blade so less inclined to cavitate and it has a lot of meat so good
> bending strength and not a lot of grinding. Some of the early
> thinner sections I used had thickening near the hub to increase
> strength where needed.
>
> I design the curved shafts to work well within their elastic range so
> the hysteresis losses through the cycling loading are very low. I
> know how high I can stress them before I exceed the endurance limit
> of the steel or aluminium. I mostly use high strength spring steel.
> It has yield around 1450MPa, depending on diameter. The thickest in
> this range is 11mm diameter but it will transmit a huge amount of
> power. I use range 2 of this stuff:
> http://www.onesteel.com/products.asp
> action=showProduct&productID=134&categoryName=
>
> I have had a problem with a pedal drive I made for an 8 tonne
> catamaran with an unsupported shaft that would buckle swinging an
> 800mm diameter prop when the blades bit and then release as the
> blades skewed but once the boat got moving over 2kts I could get it
> to run stable:
> http://www.rickwill.bigpondhosting.com/Pecadillo_Pedal_Thruster
> With a proa you could use the curved shaft to enable raising and
> lowering the prop but it would be best to use a strut near the prop
> that can take the thrust so you are not putting the shaft into
> compression. You could easily raise the prop for sailing and lower
> it for powering. The shaft would only be used to transmit the
> torque; not thrust as I do with most of mine. I am currently
> experimenting with fibreglass sheaths and joints to protect the steel
> from corrosion and for connections with low stress raisers. There
> are many ways to connect the spring steel shafts however stainless
> fittings tend not to have sufficient hardness for use with spring
> steel. It cannot be cut with a hacksaw. I cut it with the grinder.
> It cannot be threaded either because it is harder than most thread
> cutters. It can be bent into very tight radius and I have made some
> neat connectors this way.
>
> I would need the hull files and loaded displacement to do the
> performance predictions or a known drag at the required speed.
>
> Rick
> On 30/08/2010, at 11:40 PM, Colin wrote:
>
> >
> >
> > Hi Rick,
> >
> > Your latest propellor setup has spurred me out of my lurking lethargy!
> >
> > I'm in the process of replacing one of the Honda 15 outboards on
> > Rare Bird (15 meter Harryproa) with an electric motor (a
> > Marselectric 48volt 100 amp).
> > I'm curious about how different your propellor is from the usual -
> > can you comment on whether a propellor like yours would be suitable
> > in a higher power application?
> > I'm also wondering if I understand right about your drive shaft
> > bending 15 degrees. What is it made of, and doesn't the constant
> > bending absorb more energy than than its drag?
> >
> > Cheers,
> >
> > Col Campey

Rick Willoughby

rickwill@bigpond.net.au

03 9796 2415

0419 104 821