3D Props

I've been using Alibre to model props. The hope is one off props can be made from these to test different ideas. Other solid modeling programs should be similar but with different quirks to get around. I'm not sure that the current low cost 3D printers are good enough to make props yet. High cost machines can print wax patterns directly, but the cost is still too high for ordinary uses. I think finish machining of castings in high strength materials (NC grinding) will be needed to produce accurate test props with thin blades to absorb that high power electric motors and gas engines can produce. We'll see how accurate 3D printed, investment cast props can get. Wax molds could also be machined from the drawings and would be the way to go for production props.

Surface piercing props have several characteristics that need modeled:

1. Helical pitch - no successful racing propellers have straight helical pitch

2. Pitch progression - many props have a gradual increase in pitch from the leading edge to the trailing edge

3. Cup - most successful props have trailing edge cup, a sharp increase in pitch at the trailing edge

4. Rake - the newer propeller designs have the blades raked to direct the thrust cone more to the rear

5. Edge cup - many racers curl the outside edge of the propeller to help contain the water flow

6. Projected blade shape

I model the prop blade as two helices traveling in different directions from the same cross section. In Alibre you need to create two planes, each with the same cross section, at the same place; one for each helix. The cross section controls blade thickness, cross section shape, rake, and edge cup. Progressive pitch is controlled by the variable ratio of the forward helix. Cup is also controlled the same way on the rearward helix. I start the helix with the same pitch both directions then change the ratio. As an example, if the ratio forward is .5, the pitch at the end of the revolved blade will be 1/2 the start pitch. If the ratio to the rear is 3, the end of the cupped section will be 3 times the start pitch. The projected blade shape is determined with a projected outline using the extrude cut command along the shaft axis. You will have issues with the leading edge thickness toward the forward leading edge, but hand finishing and sharpening will be required in any case.

The propeller examples pictured used a triangular cross section for the helix. I would add thickness to the outside edge as well as some curl or even a tip plate. Testing how these variables affect performance under controlled conditions would be very interesting.

Lohring Miller

Lohring,

I was the lead design engineer for PPI. (Precision Propellers Inc) They are a 100% OEM supplier to yamaha outboards. You will find that there will be a BIG difference between the prop you model and the prop you pour. The tolerance stack between the method of RP you use as a core, to the ceramic or whatever coating you use, combined with the heat of metal, add gravity and you get sag,.. then add variable environment conditions,. temp humidity, etc.. and you will soon be chasing your tail to get the prop you actually want. I would make a prop,.. laser scan it and compare the scan data to the original model, the adjust the original to compensate and do it all over again until the scan data matched the original cad data as best as possible.

Smaller blades of course have lower mass and these problems will be lessened with the smaller size, but will exist. I used ProEngineer as a modeling tool and Faro laser equipment to scan. Unless you really want a lot of props,.. or your doing it all for fun.. your probably better off to CNC the whole props..

Also,.. after looking at you models,. you may have problems getting your cavities to fill completely. You cannot pour a corner less that o,06 thick,.. at least not without special process and lots of issues,. you may want to plant your "raw" part,. with material that makes it easier to pour,.. then some data on your finished. part.

just my thoughts,.. you may be way ahead of me on this .. models definitely look cool though..

Hi Lohring,

and here is your prop cnc steel .

Moore later.

Lohring, my modelling approach is completely different to yours, thanks for explaining it.

For the production of prototypes look into Direct Metal Laser Sintering. Should be able to accurately produce a prop directly from the CAD model. Hand finishing would be required but the accuracy should be much better than going through the plastic printed prop and investment casting process. Materials can be cobalt chrome, stainless steel and titanium.

Hi Lohring,

the prop showen is from a friend . But as written by Ian the best way for a hand full of props is lasersintering.A friend from me worke as a production engineer at EOS , http://www.eos.info/en ,a world leading lasersinter firm.He has sintered the propeller for Jörg in burnable plastic.Since some years the can do also in steel ,cobalt crome and titanium.i have some propellers in steel 3 blade and titanium 2 blade. I used a new design with stronger blade (thicker blade) to stand the electric power.On the suckside of the blade you will see the weege shape at the leading edge,that will force the waterflow to form the cavitation pocket to start early this low resistanc flow.

If you like ,i can aske me friend to sinter some propeller for you .I give you my word that i will never use your design for any other .I gave this word also to Jörg as he designed his propellers for his recordboat ,no other has ever get this propellers including me .I have only one for my samplingbox. By the way Hydro&Marine Germany offers a line of lasersintered steelpropellers you can order.

I prefere the laser sintered burnable plastik propeller as you can cast it in dental steel thats very strong crome mangan alloy .

For your propeller i would designe a conical hub that becomes smaller dia from the leading edge to the trailing edge with the angle of the rake .This helps a lot if you are preforming in burnable plastic out of a conventional cfk mold.

pics of cnc milled propellers and lasersintered in plastic (something like foam that can wax infiltrated) and than cast in steel.

Nice worke with your 3D tool.

Wow! You are all ahead of me. As a dentist, I'm familiar with vacuum assisted lost wax casting of parts in chrome cobalt alloys and have the equipment to do that. I've also been thinking about machining props for a long time. I talked to Joerg when he set his record and understand a little of his design criteria. He was using dental castings with a lot of hand finishing. I was not trying to develop a design method, only to try to model some significant characteristics. I assume laser sintering is quite expensive for model props. Anything over $100 per prop puts it out of the model category. Below is another picture showing edge curl and a more castable leading edge.

I'm very interested in all your efforts.

Lohring Miller

Hello Lohring,

this edge on the blade will help to hold the water .Have never test such edge but i think it's good.The Thai used propellers on there long tail raceboats that have a spoon like design that hold also the water on the blade . http://www.youtube.com/watch?v=kqZ6qIH7dkg .

I have some itressting pictures about this propellers but can't find them and a search in the web gives only one result that fit.

You are a dentist ,thats fun ,my wife is a dentist and we are close to 3M ESPE . They have researched the lava chairside scanner http://www.dentalproductshopper.com/lava-chairside-oral-scanner-cos , and they work together with EOS lasersinterproces to fastprint the model of the tooth from whitch you can make the full ceramic base for many dental products like bridge ,veneers ,crown and so on. Very intresting but also very expensive for all at this time as they bill for each scan extra.If you come to Germany feel free to visite us. I know many dentist joining this hobby.

This is my favorite prop for my 40 mono.

Have run it for 4 years and it is holding up very good.

What if you mold a blank close to the size you want then do the finish on a CNC?

Seams the cycle time are what keep the cost high.

David

I'm getting ready to run for the gas scale two lap record. I may steal some of Brian's best props to measure and model. I also have several Prop Shop props that usually run a little slower. It will be interesting to look carefully at their differences.

Christian, do you know what it would cost to have a prop laser sintered? You can e-mail me at [email protected]

Lohring Miller

Christian,

I would like to see how much it would cost to do also.

I have many profiles that would be great propellers if I

didn't have to do them one at a time. Not enough hours

in a day right now.

Thanks,

Mark Sholund

Hi,

as the company where my friend Albert is working is not producing prts by order ,as they are designing the lasersintermaschines .i can only aske for some free example .With some luck we can get a place at a test run of a new maschine as they have to do some addjustment and pertest befor life starts. So give me some days to get in contact with Albert. In the waiting time i will show what Albert is doing with this maschines for his hobby modelhelicopters.He designed a smalls speedheli for 3S lipos .The whloe chassi and Aerodesign is one part .Albert is a helicopert engineer so he knows how do do and this heli is a masterpice. Have a look at one of the forst flight test , http://helidaily.com/sneak-video-the-small-pulse-450-is-airborne/?ref=nf . I will place some pics first a look of the design chassi with gear and parts. Chassi is powder plastig sintered and the gear is titanium sintered.Gear get no extra finish on the tooth run straight from the sintermaschine.

Hi,

some moore pic to show how lasersintering can be used for modelbuilder and an other video of one of the first fly,

.
I am dreaming doing the same with a boat .But it need a lot of time working with solid works or other 3D construction program .And Albert build up 4 or 5 version destroing 3 or 4 with testfly.

lohring said:

Wow! You are all ahead of me. As a dentist, I'm familiar with vacuum assisted lost wax casting of parts in chrome cobalt alloys and have the equipment to do that. I've also been thinking about machining props for a long time. I talked to Joerg when he set his record and understand a little of his design criteria. He was using dental castings with a lot of hand finishing. I was not trying to develop a design method, only to try to model some significant characteristics. I assume laser sintering is quite expensive for model props. Anything over $100 per prop puts it out of the model category. Below is another picture showing edge curl and a more castable leading edge.

I'm very interested in all your efforts.

Lohring Miller

Click to expand...

Lohring, I have been working at modelling sections of a blade at 5% radial stations. I model the LE and TE pitch and the change in pitch between them, then project the section onto cylindrical planes to create the sections at each station. The final blade surfaces will be created by lofting between the sections. Rake etc is also parametrically controlled.

https://www.intlwaters.com/gallery/displayimage.php?pid=18193&fullsize=1

Greg, that is the step I am stuck at in Inventor too, it worked on a simpler test I did, so then I modelled the whole thing and I cant get it to work. It is a pity as I have full control over practically every aspect of the prop design that I want otherwise.

My first attempts used Multisurf. With it I could take an airfoil section and wrap it around the propeller axis on a helical surface. That concept looked ideal. but the cost was too high and the surfaces the program exported at that time weren't solid enough for the CAM programs I tried. Alibre is much more limited in generating helical forms, as I expect most standard solid modeling programs are, but you can model the main features of our props. I plan to measure the prop we just used for the two lap gas scale record and see if I can match it.

If I get an interesting model, I'll send you an .stl file, Lucas. Then your friend can play with it. Very impressive helicopter parts, by the way.

Lohring Miller

Hi Lohring,

good news,spoke with my friend and he says ok . stainless steel ,you have to finish it ,but thats no problem for a dentist.

I will send you a e-mail . we discused your design and Albert say that the edge on the tipp will rise resistance .Have a look at the lattest design my other friend is doing .We discus to reduse proplift and i show him the drawing ,see pic . offset the propellerblade on the hub will have much effect and i think that this will also will work in the way you want to go.

That's very interesting. The other thing I see is a relatively high aspect ratio on the blades. Some people would disagree on tip curl, at least in conventional propellers. Remember, the propeller drawings I showed have all the features exaggerated so they show up. I'll carefully measure the propeller we used to set the gas scale two lap record with the setup below and try to model it. Since it drives a 20 pound boat to close to 12 second 1/6 mile lap speeds, it's a good strength test prop. It would be interesting to see how a sintered prop would hold up.

Lohring Miller

Hi Lohring,

here is the site ,showing the posible materials, http://www.eos.info/systems_solutions/metal/materials_material_management .

in the propellerdesign i am looking not for a lap record im am moore interested in a straight line .I will show you next the latest motor we test .390 gram weight doing 9800 watt with no problem .For this powerhouse i am looking for strong blades that will not bend.The airplanepropeller has a tippspeed over mach1 incredible sound .

If you guys have wire frame models of the props your working on,.. if you send me the models I can surface them very quickly.. send you .stl file it .stp that can be used for all types of rapid prototyping.