This is a difficult print. Your bed must be clean and level. The settings are critical to success. The layer thickness is mandatory. Also, the direction of the layers is critical. The 50% infill must be along the axis of the fuselage. The layers for the wings must be along the wings. Here are the Cura settings I changed. They are for PETG. I have also included some screenshots showing the layout on the print bed and the layer angles.

name = Airplane PETG definition = creality_base

type = quality_changes quality_type = super setting_version = 20

adhesion_type = none layer_height = 0.2 layer_height_0 = 0.2 material_bed_temperature = 85 support_enable = False

intent_category = default position = 0 setting_version = 20

infill_angles = [ 0] infill_pattern = lines infill_sparse_density = 50 material_initial_print_temperature = 240 material_print_temperature = 240 material_print_temperature_layer_0 = 240 retract_at_layer_change = True roofing_layer_count = 2 skin_angles = [90, 90 ] skin_material_flow_layer_0 = 110 wall_line_count = 1 z_seam_type = sharpest_corner

The print and bed must be cool before you remove it from the bed. If you try too soon you will curl the wings or tail. The wings need folded up to 10 degrees of dihedral and the tail needs to be folded up about 45 degrees. There is a crease printed in to allow the bends. To trim the glider, curl the stabilizer pieces slightly concave when looking from the top. If the glider flies in a wavy pattern then you have curved them too much. This is a fun toy but it really takes practice to print and fly.