AutoCAD will allow you to insert Images and PDFs which you can scale up to the scale of the model you wish to design. Then it is a matter of tracing. The down sides are the most images not sharp enough after scaling up so some times you trace it at a convenient size and then scale it. The other BIG problem is the most of the images and other documents are not 1:1; vertical and horizontal, so you have to rubber sheet it by making a block out of it and the insert it with the vertical and horizontal scaling number you need to make the span and fuselage lenth correct! I use Bob's Documents and the Smithsonian for sources of better documents!