Creating pitch on a propeller

Anonymous · ‎01-21-2016

Hi people, new to Fusion but not completely new to modeling...

I have a need to create a small propellor for a new product. What I started with is AutoCAD geometry, just a center hub and the 3 blades in the shape and size I need. These are solids from extruding a pline. Is this valid geometry to start with in Fusion as a base model, or should I use the base geometry only as a guide and create the actual geometry in Fusion?

It seems it should be fairly easy to grab the end of one blade and put the twist on it while keeping the attachement to the center hub.

Appreciate any ideas or tips. I've tried to convert surfaces and make segmented faces but upon editing the faces I am then left with what looks like extra geometery in the original location.

Thanks!

vex · ‎01-21-2016

I would not recommend using the DWG. It's so simple you would be wasting time bringing it into in Fusion and then adjusting it. I would recommend, however, depending on how efficient you want to make it using javaprop or similar to design the appropriate airfoil and pitch angles along the radius of the blade. It's then a simple matter of going about modeling that information in fusion.

Anonymous · ‎01-21-2016

I'm making it much harder than it should be I am sure. I will look into javaprop.

Thanks vex.

vex · ‎01-22-2016

Be aware that JavaProp does not provide you with modeling data--just the airfoil shapes at specific locations along the radius of the propeller and at a designated pitch. Depending on the particulars (RPM, Altitude, Fluid, etc) it will adjust the airfoil chord length to maximize efficiency. There are of course other variations on prop design depending on what you're after. Everything from constant Reynolds number to shock mitigation on high RPM props. It all depends.

Some rules of thumb for design: The most efficient propellers are going to only have 2 blades. This is due to vortex shedding and other aerodynamic events that interfere with the following blade. You will get more lift/thrust the more blades you have, however doing so will reduce your efficiency (IE the power required to produce a specific thrust). This is in part due to the fluid you plan to operate in and the associated viscosity (in essence it takes more power to produce more thrust as more power is absorbed by moving the fluid out of the way.

As for modeling the propeller I would approach is from a parametric modeling process. Creating airfoil profiles at specific radius from the hub center. Then lofting from the hub to the tip matching the various profiles and their associated pitch.

innovatenate · ‎01-22-2016

Here's a screencast recording with one suggestion about how you might go about "twisting" a blade.

http://autode.sk/1neRVHn

I hope that helps.

Nathan Chandler
Principal Specialist

Anonymous · ‎01-23-2016

That's a great example Nathan, thank you for taking the time to record and post this. I'll work a little more with it and see what I can come up with.

One thought I had was trying to use the projection command to project the flat 2d plan profile on the blade which would give me the outter contour shape.

The pitch and airfoil I can tweak along the path such as your example.

Again I appreciate the use of the software and the examples you have provided.

Dan

MicroFPV

Fusion