title_body: "Rogallo wing" balsa rubber-band model plan - do you have one?
upvoted_answer: I found this plan online, which might be similar to what you want. The wingspan is about right, it uses a Rogallo wing and the text in the bottom-right suggests it was in a magazine called the "American Aircraft Modeler", if that rings any bells? (Your profile indicates America, so it sounded promising.)