The Wisdom of the Wrong Way: Lessons in Shaping the Britannia's Engine Nacelles
The engine nacelles for the model Britannia are of hybrid construction. Given the constraints of my 3D design abilities and the necessity of maintaining control over consecutive construction steps, I opted for a combination of techniques and materials. I began by consulting historical and contemporary photographs and sketching the components to visualize the intended structure more clearly.
For the engine cowls, I chose 3D-printed ABS plastic primarily for the symmetrical precision that the process would provide. I then designed the mid-section of the nacelles using the 2D software, Affinity Designer, and began experimenting with the physical setup.
Prototype 1: Flexibility Issues
The first prototype involved cutting the profiles and selected frames by hand to form the basic framework. Once I began to fill the gaps with Polyurethane (PU) model board, it quickly became clear that this framework was too flexible. The resulting distortion compromised the intended shape when the model board was installed.
The profile section I used for this prototype was too thin causing distortions after the installation of PU model board.
Prototype 2: The Alignment Snag
The second version was more meticulously designed, with the components cut by my reliable Cricut Maker. This time, I opted for 0.75mm styrene plastic, which the machine was set to scribe rather than cut. I doubled up on the 0.75mm plastic for critical sections like the main profile and decided to embed a metal bar along the side to reduce the plastic's tendency to warp after the model board was installed.
Despite this careful planning, the problem arose in a different area: the wing contour. This resulted in a slight misalignment, causing the inboard nacelles to have a two-millimeter difference between the firewall and the wing's leading edge. In this case, my overconfidence and hastiness were to blame, as I had assumed the careful preparation of the parts was sufficient.
The Final Version: Structure and Material
Yet again, I chose to start over, this time with a strengthened assembly and an entirely different approach. I decided to permanently attach the power plant to the mid-section framework first, ensuring the entire unit was perfectly perpendicular to the aircraft's lateral axis before installing the model board pieces.
As my supply of medium-density model board was running low, I ordered a high-density model board instead. While this new material proved more difficult to cut with a saw, it was significantly superior when sanding it to the desired shape. Crucially, I made sure to take my time, verifying that the shape of each nacelle remained straight after every consecutive step of the model board installation. The high-density board had the added benefit of requiring very little, if any, body filler to achieve the final contour, allowing me to move straight to Milliput Superfine for the first coat of surface filler.
