I have another question. The photos above show a stringer that runs along the top and bottom of the fuselage. How would you create the stringer move it into place? I was thinking I could use a side view of the plane, draw and pad the part and then move it into place and do a cut. Will that work?
Can you select a part move it with your mouse or do have to move by changing the data in the data tab?
You can move parts with the mouse using the Draft > Move tool. There are a few things to note when doing so. First is, if you use a Sketch and Pad, moving that part can only be done by selecting the Sketch and moving it to place the part, so doing a mouse move snapping a center line to another center line takes thought when making your Pad as you will be snapping the Sketch, not the part. in this case you would use the Symmetric to plane opting in the Pad dialog. I personally think that using either a simple copy or Draft > Clone for parts made from Sketches that I will be moving is a good option. Make your Sketch and Pad it to create the stringer then make a Draft > Clone or Simple copy of that part and then use the Draft > Move tool with ONLY
the desired snapping action turned on. only have 1 or 3 snap options turned on at most or you will start to run into problems. The Passive snap will really give you fits so don't use it until you have a good grasp on FreeCAD's Draft > Snap workings.
Another option would be to use a Sketch or Draft object to define the spline profile and lay out a path for it and do a Part > Sweep. This is a good option if you have a lot of bends and curves involved with your stringer or any such feature of your assembly.
Edit - if you haven't seen it yet, here is a video on Placing Parts in FreeCAD