Z coord at a given x & y on a surface?

[leighs]

Hi,

Caveat: My knowledge of CAD of any kind is very sparse ....

I have the geometry of a (symmetrical section) wing in an IGS file, made up of various edges for the root, tip, leading and trailing edges and two faces for the upper and lower faces of the wing. The co-ord system origin is where the trailing edge meets the root.

I need to find the z coordinate of a point at 80% span (length from root to tip) and 1/4 of the way from the leading to the trailing edge

I can open the file in FreeCAD and move the cursor around and from the co-ord info on the status bar get an estimate of the x & y co-ords of the leading and trailing edges at 80% wingspan, calculate the x & y co-ords of the 1/4 chord point at 80% wingspan and then move my cursor to that point to get an estimate of the z value from the status bar.

However, that is all a bit hit and miss, and there must be a hopefully simple way of getting that info accurately from FreeCAD?

Can anyone help me out in this please?

Love the ethos of FreeCAD, I am now fully Linux at home (although currently Windows for work), and so applause to all responsible

Thanks

Leigh

[freedman]

Don't know what your using in FreeCAD but you need to measure full lengths (by selecting edges) and then draw lines with respect (your pecentage) to those lengths. This should give you a point to draw a Z line.

[Bance]

Maybe this can help?

https://forum.freecadweb.org/viewtopic.php?f=3&t=44568

Steve.

[chrisb]

If you just want to measure there are some tools in Part workbench, see Std Measure Menu. The addon "Manipulator workbench" has a caliper tool for measuring.

[leighs]

Thanks!

I managed to work it out with your help

I am currently booted up into Xubuntu and hence am using:

OS: Ubuntu 18.04.4 LTS
Word size of OS: 64-bit
Word size of FreeCAD: 64-bit
Version: 0.18.4.
Build type: Release
Python version: 3.6.8
Qt version: 5.9.5
Coin version: 4.0.0a
OCC version: 7.3.0
Locale: English/UnitedKingdom (en_GB)

This is what I did:

1. I first had to search what WB meant - Work Bench
2. Measured the total span length of the wing (y-dirn.) with Part WB > Measure Linear
3. Created a cross-section of the wing surface in the plane perpendicular to the wing span (x-z) at a y value of 80% of the total span with Part WB > Cross-Sections
4. Created a ruled surface after selecting the two edges of the cross-section of 3. with Part WB > Create a ruled surface from ....
5. Measured the chord length at 80% span from the positions of the LE & TE vertices of the section in 3.
6. Calculated the x position of the 1/4 chord at 80% span
7. Created a second cross-section in the plane perpendicular to the cross-section of 3. (y-z) with the cross-section of 3. at the x position of the 1/4 chord with Part WB > Cross-Sections
8. Moved the cursor over the upper vertices of the second cross-section ('line') of 7. to find the z coordinates of the two points (upper and lower wing face) at 80% wingspan and 1/4 chord length.

Probably not the best solution but I got the values I wanted, I hope.

I did notice that the first cross section surfaces I made splined the surface of the wing to give a smoother foil section than in the original surface which actually 'looked' better but probably gave me very small 'errors' in my final z-values, I think.

Is there any way to export or copy the co-ords of the two vertices (not points) of the section ('line') in 8. above, to avoid having to read them off of the status bar? Or a 'properties' of the selected vertices to read off of?

Thanks again, that was fun to learn something new again

Leigh