Many thanks, Jeff. I purchased a Billings 'slip' and did my best to get square fitting on the ribs (my last effort was not fully symmetrical), and this appears better. I used balsa for the filling, and though it is coming along nicely, it is a beast to work with - albeit that I altered technique to substantially shape the blocks before installation (I tried to cut/sand the first few after they were glued in situ - typical army pioneer approach!). But I am happier this time. I envy your 'aviation' interest - I had thoughts on building a 'chopper' but never got round to it.