Powerup 4.0 - Hammerhead Tetra v1

Take an empty Tetra Pack - e.g., an empty milk box.

Cut away 1 side.

Separate sides and cut away bottom.

Cut small slots at the rear and front.

Draw front and main wings. I also leave a 2cm wide "bridge" between the wings. Then, I also draw winglets for front (0.5cm) and main wings (1cm).

Draw cut-away window for main wings. Draw flaps (front and main wings).

Cut away window, fold flaps.

Unfortunately, I decided to use the other side. For optical reasons. That was a bad decision. Inner side up would be better as it naturally gives you positive dihedral angle. Therefore, I had to use tape to gain stability and avoid wings hanging down.

Put foil underneath and cut. Glue the foil with tape along the sides and on both sides (top and bottom). Again: I think, I should have used the other side. Use tape over the flaps and cut them through again.

Use some paper (transparent paper) for the fin. This is important aerodynamically (keep it fly straight). And, very important, protects the props when crashing.

Nearly ready now. However, I had to put the main wings up and tape them into position to get a positive dihedral.

Now, my second mistake: Due to my bad decision of the wrong side, I remarked that the front "nose" showed downwards instead of upwards. So, I simply cut it away... not taking into account that the front nose is a stable connection holding together the front wings. So, I had to "fix" that - does not look good, but works.
Again: would I have used the right side, the nose would naturally point upwards. Then, maybe, glue the nose to the Powerup module, if necessary. But, don't cut off the nose. At most, cut it smaller.

Ready. To let it fly you have to hold it at the bridge. This is uncomfortable. Another "middle fin" or a longer fin (as long as the main wings) would be a good idea here.
In any case, the thing already flies REALLY nice. The front flaps are the game changer, making Hammer Head my favorite plane.