Bulldog, Flying

A new Fatigue Meter for the Bulldog aircraft (Part 5)


This is a direct continuation of PART FOUR, picking up where I left off, with the design and fabrication of a suitable enclosure for the flight unit.

Enclosure design


Using the Sketchup web package (free online here) I designed the enclosure to house the SSL, see Figure 1.

Figure 1. View of the SSL enclosure design using Sketchup


3D Printer

I procured a Flashforge Creator 3 Pro 3D printer to fabricate the enclosure. This choice was driven by the desire to print in polycarbonate (filament type “PC”) — for strength — as well as polylactic acid (filament type “PLA”) — for prototyping. The printer is shown in Figure 2.

Figure 2. Flashforge Creator 3 Pro 3D printer for fabricating the SSL enclosure.

Printing the enclosure components

Given the complexity of the structure — with its various cutaways, internal shelves, etc — it turned out to be difficult to print the enclosure as a single monolithic structure. After a few failed attempts, I opted instead to split the job into multiple components which could then be assembled together later. Figure 3 shows the collection of individually printed components, pre-assembly.

Figure 3. 3D printed components for the SSL enclosure. For this prototype, I’ve selected PLA filament (a final production version will be printed in polycarbonate for added strength). The design incorporates hexagonal inserts with steel nuts glued-in for final assembly.


Figure 4 shows the enclosure partially assembled with the internal SSL components visible.

Figure 4. SSL enclosure partially assembled, showing the internal mounting of the SSL components.

Figure 5 shows the fully-assembled SSL with the enclosure components bonded together using epoxy resin. For comparison, the legacy fatigue meter is displayed on the right..

Figure 5. Fully-assembled SSL enclosure (with the internal SSL components installed), alongside the legacy fatigue meter.


Figure 6 shows the SSL installed in the Bulldog aircraft in the location where the legacy fatigue meter is ordinarily installed. The new instrument is a plug-and-play replacement of the legacy instrument. No changes whatsoever are required on the aircraft.

Figure 6. Fully-assembled SSL installed in the Bulldog cockpit. The installation is plug-and-play, utilising the same shelf and mounting bolt-holes and electrical connectors as the legacy instrument.

Next steps

In summary, the following steps remain from the original list in PART ONE:

  • Make any final adjustments to the software based on further flight tests — ideally across the full dynamic envelope of the fatigue meter (+6g, -1.5g) and against different legacy instruments (i.e., rather than just the single instrument used in all tests so far).
  • Submit for mod approval via the LAA for installation on my Permit-to-fly Bulldog.
  • Calibrate the SSL via the ground-test company (if required for the mod approval process). This may be required to reach the extreme ranges (+6g, -1.5g) if unable to achieve those in flight.

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