Y-Wing

Start with bird base. On the image it is hard to see, but the slotted part is the lower half.

Valley-fold the upper tip and unfold again.

Slip the folded tip inside.

Flip.

Fold the top to the right such that the fold aligns with the diagonal edge underneath. Then unfold again.

Likewise to the left.

Now flip the top down at the tip of the triangle that sits underneath and unfold again. You actually want this fold to be a mountain fold so the picture is a bit misleading.

Now squeeze the outer edges together.

Squash-fold.

Mountain fold the tip such that the resulting edge aligns with the models horizontal center-line.

Valley fold the top left and right edges of the top layer towards the center line.

Again valley fold both halfs of the top layer towards the center line.

Fold the top part of the lower layer to the right along a diagonal line that is parallel to triangle's edge of center layer at a distance of 6-8mm. Then unfold again.

Likewise to the left.

Then valley-fold it down at the location where the two previous folds cross.

Flip the model and squeeze together the top edges of the layer that now came to the top.

Squash-fold.

Valley fold upwards at the widest point.

Flip again.

Valley-fold both edges of the lower layer to the center.

See the previous fold from the side above, with the top layer slightly bent up. Note how the fold is aligned with the models center line.

Again valley-fold both edges to the center.

Also for this step check that the fold's edge is aligned with the center line as shown above.

Inside reverse fold both legs outwards and slightly upwards.

Again inside-reverse-fold to back downwards. The engines are almost complete now.

Inside reverse fold the engine tips.

Flip.

Mountain fold the cockpit along its longitudinal center line to give it a three-dimensional shape.