Dr.1 Kit, Early Progress

I am designing this Dr.1 kit on a solid modeling CAD system, Autodesk Inventor as seen on in the figure. The reasons for using this system are many. First, a full set of accurate drawings are produced from the virtual model. These will be used for specifying the lazar cut and photo-etched parts and also fully define the 3-D parts. Second, solid images like the one below are possible. These will be used along with photographs in the builder manual. During design they help me see if things are looking “right” from any angle.

The image shown is of the entire plane, as far as I have gotten to date. The lower wing is complete and it is simply copied in the right locations for the mid and upper wing. Since the mid wing is virtually identical to the bottom one except in span, this is close to correct. The top wing is longer than the mid-wing and has ailerons, so the model looks a little funny.

The engine in this figure is in place and nearly complete. The fuselage is only roughed in and the tail feathers are correct but not detailed. I am still working on how to make the fuselage for the kit and these drawings are helping a lot. All-in-all this virtual model is about 50% complete.

Because I want to stop drawing and get my hands dirty, I have started building early versions of the lower wing. The rest of this blog will introduce this structure and subsequent blogs will detail it.

The bottom wing on the original Dr.1 had a span of 5.725 meters (12ft 9 in) and so the model wing span is 358 mm (14in). The chord is 1m in full scale, so it is only 62.5mm (2 ½ inches) on the model. All three wings have the same construction, a major box beam with capped wooden ribs. Each rib has seven lightening holes so they only give shape and transfer the aerodynamic force to the very strong spar. The Dr.1 is the only major bi-plane or tri-plane of WWI with no external wire bracing on the wings. This means that the spar carries all the lifting load and also provides torsional stiffness, two roles commonly provided with external wire bracing, Structurally, this was very radical for the time. Also, the plywood cap on the leading edge provides even more torsional stiffness to the wing. It is curious that nether the Hasagawa kit nor Fine Art Models pre-built planes (http://fineartmodels.com/fineartmodels.com/Fokker.html on eBay at $8,000) have the leading edge with this plywood cap. I am not sure why.

The image shown for the lower wing is not complete but close to it. I will begin building a rough version of this and then get Model Airways to lazar cut parts for the assembly of a better one. If all works with that one, then attention will move to the other wings. In parallel to this I am refining the engine and fuselage, which I will describe in later blogs.