In flight, aeroplanes can rotate about three different axis. Pitch, the axis across the aeroplane through the wings. Changing pitch causes the nose to move up and down. Roll, the axis through the length of the plane, front to back. Roll and one wing goes up and the other goes down. And finally yaw, the vertical axis running up and down through the centre of the plane. Changing the yaw moves the nose left or right pointing the plane to a different heading. 

I'm experimenting with poseable character design; this is where the aeroplane information comes in, I'm working on a head/neck joint that lets a head pitch (nod) and yaw (shake).

My first draft.

Starting with a roll of paper for the neck I added a sleeve which is free to rotate near the top of the shaft. I held the sleeve in place with a couple of fixed rings of card. This takes care of the yaw. 

To add pitch I made a tube with a couple of sets of tabs at the top. 

I joined the base of the tube to the rotating sleeve on the neck.

I then added an oval piece with a couple of holes matched to the tabs and fixed the tabs down with a disk of card whilst still allowing the oval piece to rock back and forth.

To complete the joint I fitted the head over the top of the oval piece. The completed prototype worked well.

Not bad for a first draft. But I reckon it could be a lot more compact. Here's the second version. I've made the rotating sleeve a lot less tall. It is only 7mm high with the end stops being 5mm each.

Instead of the whole, complicated tube with different types of tabs at each end, I've made a simple piece that will fit directly to the rotating sleeve. 

Like this.

I then fitted the same oval piece to the tabs and fixed them into place with card circles.

The head fixes to the oval piece. Simple pitch and yaw from a paper toy.