On the left is the fin root edge, looking straight on.
The inset picture shows the fin outside edge looking straight on.
The back corner of the fins are glued on 5/8" up from the back edge of the main air frame tube.
A paper strip was taped around to make sure all four fins were set at the same height.
The fins are glued on a simple 90 degree cruciform.
Tape is set down on the inside of the main tube to keep paint away and off the engine mount tube and engine hook.
TIP: To start, tack on the fins first with very little glue. In the past I've had to remove a fin and re-position it after realizing it was slightly off. If your first glue bond is light it's easier to remove it and re-glue the fin.
Fillet once with wood glue then fillet again with Titebond Molding and Trim Glue.