Thank you
@Hai-Lee.
Why do you think the spar is particularly weak in this plane where others aren't?
The wing on the Explorer is effectively a scaled up Tiny Trainer wing in its basic design and the spar whilst a double thickness has the paper running front to back. The only resistance to folding forces is the foam itself albeit 4 layers of it and effectively 2 spars.
There is no dihedral brace included and there are no external wing struts to augment wing strength.
As people increase the planes all up weight by adding extra payloads the real weaknesses of the design become obvious.
It is an old design and has never been updated.
I built mine without dihedral and a straight through spar of a different design with a length of CF and after almost 3 years it has been gifted on a few times and is still flying!
Build the wing without dihedral, (Aileron wing only), and using a CF spar reinforcement your bird will be around for many years, (subject to crashes.
It worked for me!
Have fun!