This will be the last contribution about the construction of the Kolibrie model; The model is now ready and is proudly displayed (for the time being) in our living room. Before I present some pictures of the model as it stands now, first something about one of the last major components: the windshield.
In the past months I had to conclude that the solution for the frame I chose initially, although reasonably similar to the large example, was still too fragile and offered too little support for applying the transparent parts. The thin frame, combined with the use of the wrong glue, see below, eventually led to having to make a second frame, significantly more robust than the first model.
Figure 1 below clearly shows the difference between the two frames, with the first and now demolished prototype on the left and the final used frame on the right. Again I used different semi-finished products and joining methods. It has remained a brass frame, where I have used both tube and rod. Where possible, pin and eye connections have been used, which are either soldered or connected with superglue
Another big issue was the attachment method of the transparent parts on the frame: the adhesives I experimented with do not adhere (wood glue) or leave stains too easily on the acrylic, superglue. A friend of mine looked at whether chloroform offered a way out, but that didn't yield the desired result either. Figure 2 shows two tests, in which I used different methods to confirm the "transparencies" on the framework. These options were loosely based on
@Dean62's idea of two backing frames and
@RussF's proposal to use bolts or pins. I did start on implementing Russell's idea, but having pins in certain areas blocked this option: drilling the holes became near to impossible.
In the end, double-sided adhesive tape offered the solution; The first layer of adhesive is used to attach the tape to the frame and the second layer of adhesive then bonds the acrylic to the frame.
This solution did mean that a cover strip was needed to hide the tape from view. Also, I could only use superglue between the cover profile and the frame of the windshield, to prevent glue from getting on the acrylic.
I used brass for the frame, acrylic for the transparent parts and extruded polystyrene for the cover profiles.
See Figure 3 for the construction details
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Figure 1 Figure 2
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Figure 3
The acrylic for the transparent parts turned out to be relatively easy to apply, it turned out that it was not necessary to shape the parts in advance by heating them; a test showed that it was not really necessary. During this test, it also turned out that heating parts, covered with masking tape, which I had used to prevent scratches, with a hair dryer led to irregular deformations. It also became clear that free, i.e. unsupported, heating also resulted in uneven deformations. During a conversation with
@Peter Voogt it turned out that this is also his experience with polystyrene profiles; he eventually proceeded to manually heat and form the parts in question.
Figure 4 shows the (temporary) installation of the windscreen frame, with part of the paper templates for the transparent parts.
I used tape on the acryl sheet and traced the shapes of the templates with a soft pencil on the acryl/tape.
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Figure 4
The windshield took an undue amount of time: a) at a bad moment I was no longer motivated to finish the model, in fact, the project was in danger of ending up in the trascan and it was at the insistence of my wife that the model was spared this fate and b) it took a lot of effort to think out and try the right construction methods. All in all, a large number of parts have been made two or three times...
The model is now ready, after more than a year and a half, from the visits to the archives of the Aviodrome and the NLR to the finalization of the model.
I cannot and will not pretend to have made an exact or correct copy in scale 1:24 of the Hummingbird; the available information is not sufficient to accomplish that feat.
Also, in my humble opinion, making an exact copy is virtually impossible, regardless of whether or not one has a complete specification of the full-scale example.
For example, if you look at the cross-section of the rotor head, it is clear that this cannot be replicated in scale 1:24, with all the bearings, sealing rings, slip rings, bolts, nuts, et cetera in this assembly. Or take a bolt in the large example with for instance a diameter of 8mm. This will be 0.34mm in this scale, which is way beyond my capabilities, I'm not a watchmaker, not to mention the availability of these small nuts and bolts. By the way, bolts with a diameter of 0.8mm and 0.6mm have been used, but this has really reached my limits; in particular, installing nuts is very time-consuming and often not possible due to the limited space. In those cases I cut of small bits of tube of the appropriate diameter and used those as nuts. Not as it should be, but a feasible solution.
Summarizing, my model is a bit cartoonesk at best; it resembles a Hummingbird, but differs from the great example in many ways.
By the way, don't think I'm dissatisfied with the end result; the contrary is true, I am pleasantly surprised and consider the model as a fitting tribute to my father and his colleagues, who together designed, manufactured and certified this helicopter in the fifties of the last century.
At the moment I don't have any definite plans for the next model. I do plan to complete the digitization of the Hummingbird model and have a somewhat disturbing idea to make a second Hummingbird model, but at the same time I also find the Fokker “Zilvermeeuw” (Herring Gull) and the Boeing Clipper, model 314, interesting candidates...
Below a couple of pictures of the finished model:
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