I've never had one of these things, but it seems surprising that it would not be fit for looping. Just for grins I did a search and found the assembly manual. Good thing it's not a Lanier, I would not have paid to look at it.

http://www.acehobby.com/manuals/plane/markii.pdf

A quick look through the book shows that there is indeed a plywood wing joiner. Wonder what kind of abuse the planes had been put through before they failed?