Many instruction manuals have a blank outline of the plane that can be scanned and used in MS Paint as Bill mentioned. Usually, when you do this, you need to spend a little time cleaning up the image so when you fill the outline with color the color doesn't fill the entire screen.

One of my manuals doesn't have the outline so I'm thinking of experimenting by using pictures of the framed up airplane in PhotoShop and creating a second layer over the image to trace the outline.

Hope this helps.

Damon