RE: WW1 Maltese Cross proportions
I couldn't find a formula either - So I scanned a photo of a Pfalz DIIIa into a graphics program (Xara), drew over it, make a jpeg file and Gary at Getstencils.com make a great set of stencils. The photo I used was from a lower wing of a plane standing on it's nose! Obviously there were variations between planes, especially considering the field painting that took place. Here's the jpeg I used. Incidentally a program like Xara can be very useful for electronically reproducing all kinds of images; lettering, instrument gauges, etc.