Lee's idea is probably as good as any. Making another Gyroc clone I might use Tyvek for the hinges and attach them with CA then store with the flaps deflected. Or use a material that I have used very successfully for control surface hinges on small RC models - Scotch clear Mulit-Task tape - installed after painting.

As I vaguely recall having my first couple of Gyrocs back in the day (yes I had one when it was "Free with a $5 order"), I ran into exactly what you're describing and for the BMS clone I have now I think I've had the same issue (though that model has had other issues, too.....)

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Bernard Cawley
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