For those who may be unfamiliar with the term, a fall front is an alternative to a fly closure for trousers or breeches.
The front of the trousers can open close to or right along both of the side seams in which case they would be "broad falls"or "whole falls" or you can make a narrower front panel that would be called split falls. There is an under lap which includes the waistband, and then the trouser front is closed by lifting up the fall and buttoning it onto the waistband.
We most often make split falls as they were very common from the mid 18th century through to the Victorian age. They were certainly still used for "court" dress into the 20th century, and used for sailor trousers into the 1970's if I recall correctly, and still used on Lederhosen for instance.
Anyway, there are many ways of cutting and making split falls, the most commonly used technique has a visible placket and the placket is quite often plain and straight.
For one pair of our 19th century breeches I cut a split fall with a variation of the usual placket shape.
These have a curved placket that is cut on the bias.I like to inset the seam for the under lap so when the fall flap is closed it is hidden, but these also would have worked if I had cut them so the end of the placket was more like the end of a welt pocket.
Here you can see what it looks like underneath the fall front. The waistband and under lap still need buttonholes and buttons. You would close them first, then the flap will have buttonholes and it will button up and close as in the first photo.
The placket itself was a plain bias piece which was fused with bias fusible, then shaped into a curve at the iron. Once that was done, the pattern piece drawn out on it, then sewn to the fronts. I cut a separate flap facing which was then used to finish the top and the edge of the curved placket.
The under lap is composed of the fabric layer and finished on the inside/lined with silesia.
I didn't take a photo of that, sorry! The under lap piece is deep enough that the placket is secured from the top through all the layers and the silesia extends right across to the side seam giving support for long term wear and tear.
Variations on the theme make work interesting!