Incorrect direction for normal using surfnorm(x,y,z)

Im currently working on a vortex lattice code for my thesis and am having issues with the way the MATLAB function [] = surfnorm(x,y,z) produces normal vectors. I have since chosen to use the plane equation for this purpose but was interested in knowing if anyone has had a similar issue or if there is something stupid i've done.

Essentially, I want to produce the normal vector to the surface of a wing with an airfoil camber line describing the z-plane. When entering the x,y,z grid coordinates, surfnorm produces the vectors in the opposite direction (pointing inwards, rather than pointing outwards).

Here are the x,y,z coordinates for an example of a simple, unswept wing with no taper, twist or dihedral.

x =

         0         0         0         0         0         0
    0.3333    0.3333    0.3333    0.3333    0.3333    0.3333
    0.6667    0.6667    0.6667    0.6667    0.6667    0.6667
    1.0000    1.0000    1.0000    1.0000    1.0000    1.0000
  y =

         0    0.6000    1.2000    1.8000    2.4000    3.0000
         0    0.6000    1.2000    1.8000    2.4000    3.0000
         0    0.6000    1.2000    1.8000    2.4000    3.0000
         0    0.6000    1.2000    1.8000    2.4000    3.0000
  z =

         0         0         0         0         0         0
    0.0194    0.0194    0.0194    0.0194    0.0194    0.0194
    0.0160    0.0160    0.0160    0.0160    0.0160    0.0160
         0         0         0         0         0         0

Attached is an image of what happens when surfnorm is used.

Thanks for your help!

Answer 1

[Björn]

Try surfnorm(x',y',z').

[Jack]

Thanks very much!