Curve fitting/approximation is not a really straight-forward topic. A good fitting algorithm also contains a smoothing algorithm to counter the oscillation @davidcockey was explaining.
In practice, manually modelling it is just the faster and more rewarding method. Even in other CAD with better fitting tools, the results are often mediocre.
I often start with an order 3 Bézier at low curved parts, and then increase the degree to better fit, and finally blend the strong curved areas.
Sometimes, e.g. for circles, it is very difficult to fit a non-rational Bézier, simply because of the shape’s nature. To sufficiently match a circle with n.-r. Béziers you would need 4 of them with an order of 7!
This particular examples show that a rational composite spline (e.g. Nurbs) can be superior.
If you still want to automate it, fitting algorithms usually make use of regression methods (Non-Linear Least Squares) or of more abstracted recursive-annealing. For smoothing, I have seen soap-film-dynamics. But in general, this is quite advanced maths. Maybe as someone working with airplane foils you have that knowledge, but my tries in creating own interpolation and approximation algorithms was rather disappointing. In the end, the question remains, does it give you any value for automating it?
Note this topic is 5 years old: