Pedal Powered Boats

Vic
I have never bothered calculating the buckling stress. I do a push test at the design thrust to see how the shaft distorts under compression.

What I have observed is that a small OD shaft set up in a nice even curve will fail in the middle if the cyclic stress is too great for infinite life. It means the buckling stress is significant in the failure.

Both shafts I have broken on V14 were at the strut because the gearbox output shaft angle was too shallow. It was not an even curve.

Rick

 

I need propping up

Oh, so this is where the art and science of gam powered boats is occurring in earnest.

I was looking for pictures of the folding prob and not finding any on your personal website. Thought it might be the subject of more discussion and that there would be links to videos and the like.

Where is this puppy hiding?

Bruce

 

Bruce
Hard to find unless you have some vague idea of when the post was made. See p26 post #367.

The testing on the day was not conclusive because it was very windy. You can see this by the variation in speed despite working at steady input power.

More exhaustive testing since indicates a slight improvement in efficiency over my last fixed bladed prop as I determined given the blade profile.

Overall it is a tremendous improvement as it will shed fouling in a fraction of a second by momentarily coasting.

Rick

 

Looks to be water resistance powered, unless there's some springs that can't be seen in there. The incomplete tuck of the blades would seem to be an advantage, as it is less likely to pinch strands of weed and jam up hinges. Coasting should be safer if you're getting much of a flywheel effect- don't want to get feet tangled in pedals at full power. Maybe Geo's wave bike could benefit from a flex shaft and folding prop. http://www.roanoke.com/outdoors/biking/wb/xp-4890 Gliding over rocks in shallow water should be much easier than with a fixed prop of the same size. You have a winner!

Vic

 

dear sir
I'm a naval architect working in western marine shipyard.I need badly NAPA and
GHX.Would u plz tell me where can i find these softs.

sincerely
shehab

 

You are in the wrong place.
Try the Software Forum.

 

Vic
The blades stop against each other before stopping against the hub. If a single blade hits something it will go to almost in-line with the shaft before it stops in the hub.

Everything is too light to have much flywheel effect. It requires very little retarding force to come to a complete stop for a brief period.

Rick

 

Folding Prop.
Hi Rick
Help wanted on the design and manufacturing method for the hub as I am at last starting to make a folding prop.
Is the slot open ended through to the spinner point of just a simple closed slot.
How did you cut this slot, I have both a lathe and verticle mill and can not see what type of cutter to use if the slot is not open ended.

Dennis

 

Dennis
The prop I made has a large pitch up around 700mm on a diameter of 380mm. The slot I cut for the blades is in line with the shaft. I profiled the blades so they have the required AoA near the hub.

If you have a lower pitch to diameter then you will need to angle the slot. And the two slots will form an acute cross.

My hub started as 40mm diameter aluminium bar. I machined tapers on either end. Then I drilled a hole through the middle and slotted it out with a 6mm end mill. The slots need to run to the back of the hub to enable the blades to fold back. I left about 6mm thick at the aft end of the slot so the slot cannot spread.

Of course my blades fold back in line with the shaft but if the slots are angled the blades will fold back at that angle.

I used 3mm thick stainless bar for the blades and strengthened the root with another 3mm thick piece. I shaped this to get the required profile.

I designed the prop to suit the method of manufacture. You need to do the same. I can help if you need it.

Post #387 has some renderings of a 4-bladed prop I designed for Mike Lampi. It was not built. It does not show the slots cut out behind the blades to allow folding but the blades are angled. This prop would have an efficiency around 80% in his application.

Rick

 

Folding prop.

Rick ,thanks, I had not considered thickening up the root of the blade to make the slot and the end mill cutter wider.
I am using 3 x 35 MS strip for the blade with a slightly modified VERANO type outer profile and a Clark Y airfoil. This profile is very similar to the 16" APC prop. and easy to make as the nearly straight trailing edge simplifies the fettling of the airfoil .

Dennis

 

Have you thought about how you will twist the blades to get the required pitch?

Also I believe the Clark foil is 12% thick. The 3 x35 will be about 9%. That is quite different. It is not particularly critical but it may not work as you expect.

Rick W

 

Folding Prop Blades

Rick
I make a series of templates using the angles from Java Prop. The unshaped blade blank is then twisted in a vice with a large adjustable spanner to suit , after which I shape the outer profile. The airfoil is then shaped last. Re the thickness being not correct, this is the third prop I have built to this method taking around 6 hours to make a rigid prop,the others have perform well, but I have nothing to compare them with.
There will be some compromise on angles at the hub but looking at different aircraft props, I have concluded that the root of the blade is not to critical.

Dennis

 

Dennis
Sounds similar to what I do. I simplify the twisting by approximating an optimised pitch curve to two straight lines. So blade is twisted from a central point with it clamped alternately at the root and tip.

The portion of the blade at the root of a small hub does not do much so not very critical. Helps if it is thrusting rather than braking but a Clark-Y section provides lift at quite high negative angle of attack.

Will be interested in a photo when you have the prop made.

Rick

 

CF folding RC props

Rick and Ian, Ran across this while surfing

http://www.icare-rc.com/propellers_folding.htm

Do you think something could be cobbled up from the CF Graupner blades listed at the bottom and either an existing machined spinner, or perhaps by adapting something else? I know it wouldn't be as efficient, but maybe an easy way to get a folding prop of some kind for us machine shop challenged folk? I'm thinking it might work for low power electric, though maybe not for the huge torque demands of HP.

Rick, if you don't plan to keep the folder proprietary, will there be a set of machine shop plans for sale in the future?

Thanks,

Vic/Porta

 

Vic
The Graupner blades have quite low pitch. You might get something suitable for electric drive but would need tall gearing for a pedal boat.

With the folding prop they are best designed for each application. Each application varies and the best prop will be made to suit. If someone is going to the effort of making one then it should be the best design for the job.

The hub was not very complicated.

Rick