Turret Window Scan & Modeling Project for Halifax 57 Rescue

You never know what you might find in someone's garden.

Halifax 57 Rescue (Canada) is restoring and building a Halifax bomber for the Bomber Command Museum of Canada (BCMC) in Nanton, Alberta. The Organization is dedicated to preserving the Handley Page Halifax bomber aircraft, used during air combat operations in WWII. Rapid3D was contacted by Karl Kjaarsgard, the Curator of the Bomber Command Museum of Canada, to help with a scan and modeling project to help recreate some broken bubble windows on a rare Boulton Paul rear turret.

Figure 1: "Imperial War Museum Photo: CH 11320 (Part of the Air Ministry Second World War Official Collection). Boulton Paul Type ‘E’ tail gun-turret, mounting four .303 machine guns, on a Handley Page Halifax Mark II of No. 78 Squadron RAF at Breighton, Yorkshire. Photo taken by Flight Lieutenant G Woodbine." Source: https://archives.wartimeni.com/wwiini-halifax-bomber-gun-turret/

The turret was found in the garden of a family in London, England. After being sent photos of the cupola, Karl immediately made the decision to purchase the rare, nearly "impossible to find" turret, even with the damaged bubble windows.

Figure 2: Image of the Boulton Paul turret found in London, England.

The turret had three windows that needed to be remanufactured due to broken sections. The aircraft being rebuilt with this turret is for display purposes only, but we wanted to get the newly manufactured windows in an acrylic-polycarbonate plastic to be as close to the original shape as possible.

Rapid3D scanned three of the windows on the existing turret for this project.

Figure 3: Locations of the windows scanned for this project. The left and right bubble windows were not expected to be perfectly symmetrical, since manufacturing facilities in WW2 did not have the capabilities to make mirrored copies.

We received the broken, disassembled windows at Rapid3D to prepare for scanning. Since laser scanner technology requires the surface to be scanned opaque, we needed to coat the window in special scanning spray called AESUB. AESUB is a scanning spray which coats any surface temporarily white, and then disappears with no residue after a certain amount of time.

Figure 4: The broken bubble window.

Figure 5: The window coated in AESUB spray and targeted with adhesive targets, ready to be 3D scanned.

For scanning, we used Creaform's HandySCAN Black+ Elite to capture the unique geometry of the bubble window. The Black+ Elite has amazing data quality and is traceable with the ISO standard 10360, so we know we can trust the scan data results.

Figure 6: Scan data from the HandySCAN Black+ Elite.

The scan data was then trimmed and aligned to a coordinate system using Geomagic Design X. Design X is an extremely powerful reverse engineering tool, capable of working with large scan datasets to convert into CAD models. Using Design X, an Applications Specialist or Engineer at Rapid3D is able to create hybrid CAD models, applying CAD-correction or design intent to areas that need fixing (like the cracked window surface), while also maintaining original dimensions and positions of things that must stay as-built (like the positions of the bolt holes to reattach the windows).

Figure 7: Final CAD model deliverable of the bubble window. This CAD model will be used to remanufacture a new bubble window for the turret.

Once the model is complete, we always compare the original scan data to what we have modeled. By doing this, we can see if there are any areas that are significantly out of tolerance and adjust our model accordingly. For this colourmap below, we can see the majority of the surface is in the "green" zone, and the model is more than acceptable in comparison to the original broken surface. The grey area shows where there is no data to compare.

Figure 8: The final comparison of the original scan data to the newly modeled CAD. Everything in the green zone is within +/- 1mm.

Once the bubble windows are remanufactured, we will provide an update with new images of the parts installed in the rear turret. To learn more about the Bomber Command Museum of Canada, please see the information below.

Contact Information:

Bomber Command Museum of Canada: www.bombercommandmuseum.ca

Halifax 57 on Facebook - REBUILDSHOP showing the Halifax Bomber shop

Rapid3D: www.rapid3d.ca or email 3dinfo@rapid3d.ca

To Donate:

The Halifax 57 organization runs on donations to sponsor these historic projects. To keep these Halifax restoration projects active, you can support the team here:

On Fundrazr - Fundrazr 417498 - Support the Recovery of a RCAF Halifax Bomber