I understand the SPA has a list of approved planes a competitor can choose from to compete and they also have an engine size restriction. My question is this, are you allowed to alter or mod say the wings or tail feathers of say a Dirty Birdie? By “mod” I mean make the wings slightly longer or alter the wing airfoil or make the fuse slightly longer?

Nevermind I just found my answer lol.

"Don't ask, don't tell"...lol. I was amazed at the number of mods I have seen at the SPA contests. Now how of those mods actually help?...that's another discussion altogether.

can you elaborate a bit more as to what “mods” you’ve seen? Knowing that mods are not allowed I’ll follow said rules, but I’m curious now as to what folks are modding.

Minor rudder shaping, wingspan length, landing gear location, adding flaps, etc. We all must realize that when these planes were new, competitors modded them on a regular basis. There were no rules that said no mods were allowed.

I agree. I can’t recall ever hearing anyone in the 80’s not modding a Tipo or a Dirty Birdie to make them a bit more competitive.