Supports are optional, depending on your printer and settings, for printing "Chassis.stl", "Nose.stl", "Fuselage.stl" and "Tail.stl". My prototypes printed to my satisfaction (with minor filing and sanding) without supports.

Study "Assembly.skp" or "Assembly.stl".

Print all pieces as shown in "Assembly.skp" or "Assembly.stl". Supports are optional, depending on your printer and settings, for printing "Chassis.stl", "Nose.stl", "Fuselage.stl" and "Tail.stl". My prototypes printed fine without supports.

Test fit and trim, file, sand, etc. all parts as necessary for smooth movement of moving surfaces, and tight fit for non moving surfaces. Depending on the colors you chose and your printer settings, more or less trimming, filing and/or sanding will be required.

Place wide rubber bands around the circumference of all wheels for traction.

Assemble as shown in "Assembly.skp" or "Assembly.stl". Start by assembling all axles and gears into "Chassis.stl" except for the rotors and their gears. Next, attach "Fuselage.stl" onto "Chassis.stl", then add the rotors and their gears, and finally, attach "Nose.stl" and "Tail.stl" onto "Chassis.stl".

Apply light machine oil on the moving parts.

To make a pull toy, slip a length of yarn into the lower front hole in "Nose.stl", tie a large knot, secure it with glue, then pull the yarn back so that the knot rests against the inside of the hole.

Once fully assembled, tested and aligned, a small dot of thick cyanoacrylate glue between the gears and axles will aid in holding the gears in position.

If you desire a more "grandkid / youngster" proof toy, I recommend printing the rotors and axles at 100% infill.

Feel free to comment if you have questions.

Hope you like it!