How to fit gear leg fairings so they don't crack
Let's discuss this a bit. Think about how the legs on the Wittman gear bend in service: They mostly bend aft and outboard - except in a ground loop, where they bend inboard and aft...bad things happen almost immediately in this situation...
So, if the legs bend outboard, and aft, they will need room to do so inside the fairing - else the fairing will deform, and crack. Thus, the leg needs room to do it's dance without touching the leg fairing.
In flight, the leg is straight, so it can touch the fairings along its inside/lower surface. It should have about 1/2" clearance between the upper/outer surface of the leg and the upper/outer surface of the fairing. This 1/2" of 'wiggle room' keeps the leg from trying to bend the fairings, and the fairings can then live long and prosper (Thank you Mr. Spock).
Builders can shoot about 3-4" of expanding foam inside the fairing to make this space happen, using a small block of wood as a spacer while shooting the foam in place. The spacer can stay in place after the foam hardens.
if you are building an F1 with the supplied upper and lower fairings, the instructions will tell you to have those fairings in place quickly after shooting the foam in so the shape stays correct.
If you are using those same fairings on a different type of plane, it would be a good idea to follow these same directions.
Questions?
Carry on!
Mark