Alright, so I figured I would post a link to the following just so people can look at the general shape. I have been working to get a good solid model of a kort-esk prop built as well as finding a reasonable way to produce it. Shapeways may actually work out rather well. Pair of rough kort props by archer183 on Shapeways Basically, what is linked is a 1.5" pitch 1.5" diameter prop., I've got the model set so that changing pitch is easy (so easy I just type in one value and the whole blade shape changes). changing airfoil is a bit harder but relatively straightforward. I'd like thoughts (from visual inspection) on that current shape and if there is interest, what sizes and pitches. if shapeways works out it would be easy enough to have a huge variety in pitch and size. Cost is higher than what I would like but there is always the option of further material removal to cut down costs / stacking more together. Due to tolerances in the process, tapped holes would have to be tapped by end users.
right now the most cost effective seems to be the stainless steel-bronze that is at the link. Can you tell me the diameter, pitch, and shaft size you are interested in and I can get it modeled and see what it would cost.
is that tip pitch? Pitch on these is progressive, so it changes root to tip. hence the inches designation.
What is the cost of these going to be compared to Prop Shop How are you going to solder on stainless props
II'm confused... there is no soldering. these are rapid prototyped from a stainless powder then infused with bronze
Checking the shapeways drawing I think the airfoil is a bit too pronounced and the directionality of the airfoil is unnecessary, based on looking at prop shop props and milling one for snipehunter to test two years ago. I played games with lowering the pitch near the hub and couldn't do the undercut to make the blades overlap near the hub like with 3 axis milling, and it underperformed maybe 15-20%? I don't recall exactly. Boat prop design is a lot more complicated than you would think, the blade edge profile and the overlap near the hub has some considerable influence on the thrust generated. I think more testing is needed. Some Light Cruiser props: Bob based on the material I would imagine you could braze the shapeways ones to a shaft if you want.
The ones in the pictures are milled from 6061 aluminum, but could be made from something else. At this point I'm not offering anything for sale. The shapeways model Greg made is not sintered, but manufactured this way according to shapeways: How it's 3D printed To build steel models, special 3D printers deposit small drops of glue onto layers of stainless steel powder, one layer at a time, until the print is complete. We carefully remove these models from the printer. At this stage of the process, the objects are very fragile, similar to wet sand. The models then go through an infusion process that replaces the glue with bronze, creating a full metal product. Models are then processed to achieve your desired finish, sprayed with a sealant, and shipped to you. Stainless Steel Specifications Alloy Family: 420 SS+ Bronze (40% bronze) UTS: 99 KSI (682 MPa) Yield: 66 KSI (455 MPa) Modulus: 21.4 MPSI (147 GPa) Elongation: 2.30% Hardness: 20-25 HRc You can machine it, drill and tap it, weld it, and even RAM or wire EDM it. A machinist evaluated the material as tough enough to need a carbide bits to mill or drill it. There are customers who printed turbine impellers and run them at 3500 rpms for testing purposes. Plain old 420 Stainless Steel has up to 1620MPa UTS, 1420MPa Yield and 10% elongation, a lot tougher than this "alloy". So the bronze is what gives it strength, the stainless is more or less a filler material but is important for providing a lattice to infuse with bronze when the glue melts out. I don't know how well this will hold up as a combat prop material until somebody tests it by running over some rocks with a brushless drivetrain. Interestingly Shapeways uses lost wax casting for plain Brass or Bronze parts.
yep. I am just playing with them right now since I don't have analysis capability right now (hope to have it back in next 3 months or so) but then the bigger question becomes... what is the figure of merit to use to test with.... -Greg
I made the large prop specifically to test in Snipehunter's drivetrain since he has a datalogger set up in his ship. Makes comparing things simpler. Similar or better performance than propshop kort props has to be the target, otherwise there is no point making them. I'm set up with a decent 4th Axis on my mill now so I may play with it again sometime.
I'm talking about soldering them on to the drive shafts. You addressed that later. 3D printers, print a better pump.
I use mechanical attachment (drive dog and shaft screw) like the gas boats use. I can take it apart and yes it can take itself apart too.
The problem with pumps is that our pump specific speed is so far from (very low) what is typically done in centrifugal pumps that the fancy vane shapes enabled by 3d printing really won't do us a whole lot of good. I did come across a paper a while back that had a pump impeller design with pump curve (centrifugal) that looked like it would get half unit orifices to ~1.3-1.5+gpm without a C-D nozzle on the exit, and with reasonable power consumption.... however it had one major downside ... nearly a 5" diameter impeller.
What did you come up with for a specific speed for a regular pump? I have been using Ns = 800 for a long time.
I assume you were using english specific speed (metric is different than english) Even 800 is fairly low, particularly at our flowrates. I have gotten them in the 800-1400 but generally that required either running the motor faster than I want to or a very large diameter impeller. I'd have to go get my design spreadsheet out and check a few... the fancier vane shaped ones I ran fast to get the speed up in the 1000+ range. The biggest problem with low Ns pumps is exceptionally poor efficiency (when they even work remotely well). We are in this very bad pump region of wanting high heads with relatively low flow rates. The paper I have at home had some info on high efficiency (>15%+ shaft efficiency at 30m head 4-10L/min) low specific speed (<400) pumps that is very interesting....
Yes I use English units for this application. Any literature for centrifugal pumps in this range is pretty rare to be sure. The best book I was able to find back when I had access to a decent library in the early 90s had a couple of chapters on Barske impellers, concentric bowl forced vortex high head/low flow pumps, but the information on several types was intermixed and presented so poorly it took me years to figure out what it actually said. Basic parameters for best efficiency with the formulas in that book at Ns = 800 worked out to an open faced 4 bladed impeller around 1.05 inch in diameter and blades 0.15 inches tall, blade sweep and angle not terribly important. Needs 15k rpm or more for decent output volume. Best guess for the actual shaft efficiency is around 30-40% but it is difficult to separate the pump body and motor efficiency in practice. I couldn't even do a halfway decent guess at the pump body efficiency until I went to brushless motors. Can you point me at any papers suggesting a different design? Seems like the petroleum industry would have some decent pump designs for our use but I haven't ever found any good design descriptions.
