I heard that Matt Kania designed the Ringmaster, Junior and Baby. I don't know who designed the others. Sterling had a habit of not putting the designer's names on plans, like Goldberg did. Regardless, I've been having a blast flying my Ringmaster Junior with OS .15FP-S and 8x4 prop. Flies 4 second laps on 50' lines, 5 second on 58's.
The kit was one of the last before the Sterling Corp. became Estes property. They did things to it like too light a gage of landing gear wire easy to prang, luan plywood cheek sides, standard die crunched wing ribs, etc. But I've replaced over half the wing ribs due to hangar rash, shipping, toddler handling and crash damage.
One of these days I'll build me one of the Ringmasters or larger variants.
