Back in the late 90's, ex LDMCC Chairman, Malcolm Meinertzhagen came across a slightly odd 2¾ frame (well, actually the front half!). It eventually turned out to be from one of the early spring frame machines. I was then contacted to see if I was up for the challenge of trying to reproduce the missing parts. On researching the early spring frames, we found that Douglas came up with at least 4 different designs. The first was a true swinging arm type that was controlled by leaf springs. Later designs had a pivoted rear triangle with coil springs in compression - then springs in telescopic spring boxes - and finally with a system of links and springs. These later versions were more complicated, and presumably more expensive to manufacture. We came to the conclusion that the earlier versions probably suffered from inferior handling. We eventually decided that as Malcolm's frame was numbered in the 1918 range, we would rebuild it as an early version with the leaf springs. Scanning the patent documents relating to the spring frames revealed a fair amount of detail, but we still had to use a bit of 'poetic licence' to come up with a working system that looked the part. Attached is a photo of the re-created rear suspension prior to painting.
From the photo of Zurcher and his machine, it looks as if it may have the third version of the spring frame, as it has a full rear triangle with the springs mounted horizontally in boxes.
In our searches for details of the spring frames, we didn't find anything dated later than 1922, so Douglas probably decided it wasn't viable to carry on with the development at that time.