Helix Sweep

[gsandy]

I am trying to model a shaped blade, as shown in screenshot attached, which is on a helix sweep. Any suggestions would be appreciated.


OS: Windows 10 (10.0)
Word size of FreeCAD: 64-bit
Version: 0.20.25429 (Git)
Build type: Release
Branch: master
Hash: acce57a25d82b0408fa07b9452ed31c8a06c7a1b
Python version: 3.8.10
Qt version: 5.12.9
Coin version: 4.0.0
OCC version: 7.5.2
Locale: English/New Zealand (en_NZ)

[chrisb]

I guess that it is only caused by the perspective distortion of the photo that the helix looks thicker in the middle.

For such a helic you need only one of the helices, e.g. the outer.
- create a sketch in XY plane with a section of the helix
- attach it to the helix with mode Frenet NB
- create a sweep with the section and the helix
- mirror the sweep
- make a union of the sweeps and the center.

[gsandy]

Its not a distortion, the blade is thicker in the middle.
The only reason the inside helix is there is because I was trying solve the problem by creating an inside and outside "airfoil" shape and make an extrude on two rails (from outside to inside airfoil).

[chrisb]

A two rail sweep exists in addon Curves workbench.

[gsandy]

That's the one I tried but could not get to work. I could create the two rails but could not create the right inner and outer profile sketches.

[chrisb]

You may have to create two sweeps, both based on slightly different 3D parametric curves (addon macro).

[papyblaise]

you research the dimensions of the heliptical parts, you place them on planes tangent to the hub, in the middle and tangent to the outside diameter
you make a loft, then a common with a cylinder with the outside diameter
it is a rustic propeller for river transport boat or canal with a low efficiency due to strong cavitation because of this little tapered shape

[gsandy]

Thanks papyblaise you have given me a clue on how to proceed. I will work on it today. Cheers Sandy

Thanks Chrisb I will investigate 3D parametric curves (addon macro).

[hammax]

... based on helix helper (and a lot of placement) a 2-blade prop by eye and "flexible" profiles

Profil_gen_2.PNG (37.14 KiB) Viewed 1919 times

[gsandy]

Thanks Hammax but a question - Under your "Loft" is "Mixed_Curve_1" and under that "Sketch001" and "Master_Prof_001". How did you create "Mixed_Curve_1" with "Sketch001" and "Master_Prof_001"?
When I downloaded your file there was nothing under "Mixed_Curve_1" as shown in screenshot!