Compute normal vectors for this airfoil

Question

Given a data-set of X-Y coordinates in a matrix of 61x2 for points of an airfoil. How would I go about creating normal vectors along each point along the airfoil. I've plotted the airfoil so far:

Answer 1

Let us assume that your airfoil is closed.

To calculate the normals at each points you can average the normals to each segment.

This should take care of the trailing edge issue…

I suppose your data is x, y

xtmp1 = [x, x(1)]
ytmp1 = [y, y(1)]
xtmp2 = [x(end), x]
ytmp2 = [y(end), y]
nx =   (diff(ytmp1)+diff(ytmp2))/2.0
ny =  -(diff(xtmp1)+diff(xtmp2))/2.0

nx will contain x-component of your normal and ny will contain y-component of your normal

of course you can normalize the result if you want normals of equal length

ntmp = 1.0 ./ sqrt(nx.*nx+ny.*ny)
nx = nx .* tmp
ny = ny .* tmp

As suggested you can also normalize each segment's normal and then average as such

xtmp1 = [x, x(1)]
ytmp1 = [y, y(1)]
xtmp2 = [x(end), x]
ytmp2 = [y(end), y]
nxF =   diff(ytmp1)    
nyF =  -diff(xtmp1)
nxB =   diff(ytmp2)
nyB =  -diff(xtmp2)
ntmp = 1.0 ./ sqrt(nxF.*nxF+nyF.*nyF)
nxF = nxF .* tmp
nyF = nyF .* tmp
ntmp = 1.0 ./ sqrt(nxB.*nxB+nyB.*nyB)
nxB = nxB .* tmp
nyB = nyB .* tmp
nx = (nxF+nxB)/2.0
ny = (nyF+nxB)/2.0

And then normalize nx and ny