Modelling a propeller

Are you trying to make a solid hub propeller for a high HP application? Reinforcement for structural purposes can be made without cutting the hub. Tabs may be welded between the exhaust and the inner hubs.

 

No it is staying rubber hub. I'm not reinforcing anything, I'm trying to modify the blade geometry from the original so it looks more like the photo I posted - the blades continue through the exhaust hub.

 

I'm curious, what do the sections of the blade inside the exhaust do?

 

Attach the blades to the hub, but the exhaust gas also flows over them, so I figure if they are angled then the exhaust will be propelled out and exit more efficiently.

 

The flow of gas will be faster if there is no turbulence.

 

I'm looking to get a 3D model printed once I've finished my design, anyone have any knowledge on different forms of plastic? Generally available ones are ABS, PLA and Nylon. Looking at ProPulse props it seems they chose Nylon, although it is fibreglass reinforced.

 

Do you plane to use the 3D printed propeller as a propeller mounted on an outboard? If so you should do some basic estimates of bending moments and the corresponding stresses, and then compare the results to the properties of the available plastics. I would expect such an analysis in a fourth year project on propellers by a Naval Architecture student.

Another approach to making the propeller would be to 3D print a pattern, and then have the propeller cast.

 

You can get 3D printing in metal too. For casting, you would need to decide what kind of pattern you are going to make. For example, there is the type you press into the sand and then remove. A popular type is made of styrofoam and uses the same method as lost wax casting.

 

The main purpose of having one 3D printed, at this stage at least, is just for display - we have to do a presentation once the project is complete. I am just considering whether it is possible to create a propeller cheaply that I can at least try it out.

Creating a metal model of the propeller is not my primary objective at the moment. If I have time after I have finished my new design then I plan on looking into various materials and methods of producing a model.

 

The "metal" material for low cost 3D printing is metal powder in a plastic matrix. I'd expect the mechanical properties to be close the those of the plastic matrix, not the metal.

 

They can make it in solid metal with Direct metal laser sintering:
https://www.stratasysdirect.com/solutions/direct-metal-laser-sintering/
http://www.eos.info/systems_solutions/metal

 

If you want to actually use the propellor, Nylon would be the best choice of the polymers and will take a reasonable load, the downside is that printing leaves a rough finish and it's hard to smooth out properly. The epoxies are easy to smooth but brittle and relatively easily damaged in my experience, great for visual mockups and maybe some simple mechanisms. ABS is a bit in between.
I've used nylon for working prototypes taking in excess of 80psi load. Some clean up and fettling was required for a perfect mate and seal as the system was for use with domestic water supply, but it worked well. Note how small outboards use glass filled nylon for props, so you could even run the prototype at low speed. I'd be a bit careful of bits disintegrating if you really put some power through. Melt point should be in excess of 110 deg C so, make sure your exhaust is cool enough...

I've had stuff done in aluminium through lost wax printing and that was not bad at all, especially as it was good alloy and heat treated. I've seen some stuff done with printed metal sintering and it is pretty good, not actually done one myself, at least not yet...

 

Nylon won't be able to take the stress of stainless steel unless you dimension it so thick the propeller will be useless. Propellers need a material that has little volume for its strength.

 

I was only suggesting nylon as suitable for idle speed and just off....

but it might be enough to prove the principle before going to a more suitable material. Prototypes come in all types of purpose...

 

Project is coming along quite nicely, I've just about finished modelling the modified propeller.
Having some problems just now naked edges on my Rhino model, mostly due to tolerances in trimming... If anyone has any advice on how to repair these that would be very much appreciated. I've managed to track down and correct the majority of them but there are still some difficult ones remaining.

Cheers