New Mini Big Bertha Fins

After losing my mini engine Big Bertha at a previous schoolyard launch, I printed and made another one.
I wanted to make a post about the carded, 3 ply fins.

The fins are printed on 110 lb. card stock.
When printed they are like a butterfly wing, one side is a "reflection" of the other, joined at the leading edge.
The leading edge is creased and folded over cereal box cardboard.
The leading edge is round, but after trimming the outside and trailing edges remain square.

You can round the edges (to a small degree) with a bead of white glue. This glue bead also seals the exposed edges.
To the upper right is the glue bead applied right out of the bottle.

Run your finger over the side edges and take off the excess.
Leave a bead of glue on the edge. Look close, there is white glue on the edge.
Let dry and lightly sand round with 400 grit.
Be careful not to sand off the printed color! Sand just the edge.

Apply another bead of glue and smooth again. Let dry and sand.
You'll end up with a rounder trailing and outside edge.
These three-ply carded fins are about 1/32" thick and much stronger than balsa would be at this thickness.



Here's the new Mini Big Bertha on the pad from last Thursday's launch.
It flew beautifully with a 1/2A3-5m engine.

I almost lost another!

Patreon members: If you'd like to make a carded Mini Big Bertha, email me at oddlrockets@bellsouth.net and ask for the Mini Bertha PDF.
Print, glue and fly!