My first scale project ...
Research 1: What to believe?
Like I said in my introduction, building the F.K.41 is a challenge.
The length of the fuselage has been quite a mystery. The Koolhoven
F.K41 and the licence produced Desoutter Mk.I were supposed to be
identical in construction (apart from some details). Yet, Koolhoven
documents specified span 10,50 m. and length 7,80 m; whereas articles
on Desoutter aircraft (some of them showing the Koolhoven built
G-AAGC) stated span 36 ft and length 27 ft (span 10,97 m. and length
8,23 m.).
When Desoutter received G-AAGC some modifications were made like
a lowered stabilizer. The Desoutter production had some more changes
like the shape of the wing tips which could be the reason for the
difference in span. Did Desoutter also lengthen the tail of Koolhoven's
design? On the other hand specifications in publications are known
to be wrong sometimes and these errors got repeated by other reporters.
What to believe?
According to this copy of a 1:25 drawing of a F.K.41 on floats, the length should be 7,67 m. which makes 7,80 plausible. The drawing is somewhat inaccurate, yet gives the best resemblance to G-AAGC, so I thought it to be the best choice for a base. (I also have a copy of an earlier Koolhoven drawing and a Desoutter drawing.)
Still, this drawing raised some more questions like the position of the wing, because in the side view the chord and profile is drawn far to big and the photograph below of the G-AAGC flying shows the wing a lot more forward.
With only the photographs as truthful reference I became a little obsessed in finding a way to reshape the photograph below into a perfect side view by neutralizing the perspective of the fuselage side. After a lot of experimenting with the tool Transform Perspective in Photoshop I figured it out. It did not entirely do what I was hoping for because the so called perspective was basicly a proportional transformation. Still, it was useful for checking hypotheses and in the end I was able to produce a non-perspective side view when I had the measures to adapt the photograph to. More on this transformation on the next page.
Because the Desoutter Mk.I of the Shuttleworth Collection is said to be 27 ft long (8,23 m.), I was led to believe that the Koolhoven production was not identical to the Desoutter production. This assumption kept me busy for a long time. The curator of the Koolhoven Aeroplanes Foundation however pointed out that a fundamental change in the design would have meant a complete recalculation of the structural forces for which Desoutter at the time lacked the expertise. So I had to investigate this notion as well; most importantly the distances between the formers as specified on a Desoutter construction drawing. The position of the wing I wondered about would follow from the position of the formers.
The heart-to-heart distances between the formers from firewall to
tailpost were: 750/400/650/700/700/700/700/700/700/602 mm.
(Yes, Desoutters were built using the metric system since its design
was Dutch.)
In my first Photoshop experiments on transforming the side view photograph,
the cabin formers already seemed to comply to this sequence. I first
checked whether the formers left and right of the door were indeed
at a 650 mm. distance, by measuring both wheels in the
original photograph and with help of the specified track width, calculate
what their size would be at the fuselage side. (The wheels were also
650 mm. diameter as I could read on the tyre when I enlarged the photograph.)
It turned out to be correct: the formers left and right of the door
were certainly not closer to each other than 650 mm.
Next I transformed the photograph
below, neutralized the perspective of the fuselage, to check whether the aft
cabin formers and the first tail formers were indeed at a same distance.
It all added up. In the same way I transformed a photograph of another
F.K.41 'in the bones' and concluded that all tail formers were at the
same
distance; except for the distance last former to tailpost which
complied to the last figure in the sequence.
So the curator was right: the basic fuselage construction of the Koolhoven F.K.41 and the licence built Desoutter Mk.I was identical. Now I could use the specified distances between the formers as a base.