The Typhoon Legacy Company, based in Comox, British Columbia, is adopting its own singular approach to returning its example of the Hawker fighter-bomber to airworthiness
“If you had a full aircraft to start with, it could be restored. If you had a full set of original drawings, it could be built, but when you have little bits of everything, you need to dig deep to put the pieces together”. While this statement from Ian Slater, project lead for the Typhoon Legacy Company, may read as obvious, it does set the scene for the remarkable work being carried out to rebuild Hawker Typhoon Ib JP843 to airworthy condition.
This was one of the fourth production-batch Typhoons, built as a ‘car-door’ example in 1943. Serving with No 197 Squadron initially in a bomber configuration before modification to a sliding-hood canopy and having its bomb racks replaced with RP-3 rocket rails, JP843 would be assigned to No 609 Squadron in June 1944, where it saw combat over Normandy with both 609 and No 198 Squadron. While with 609, JP843 and its pilot, 20-year-old Kiwi Plt Off Peter Price, RNZAF, were lost while attacking German positions around Tilly-la-Campagne on 27 July 1944, a sortie which also claimed the life of Plt Off John Buchanan, RCAF, in MN494.
Slater set his sights on returning a Typhoon to the skies at an early age and his career path in aviation has been with this goal in mind. Identifying that the bulk of any rebuild’s costs would be in specialised labour costs, he chose a profession that would allow him to gain the experience, skills and licences required to complete as much of the work as possible himself. His time in the Canadian Armed Forces also saw him serve with two former Typhoon units, Nos 438 and No 440 Squadrons. By taking this ‘in-house’ approach, Ian would be able to channel available funds into specific tooling, materials and challenges, like reverse-engineering the highly complex Typhoon cockpit structure.
Working with Canadian engineering firm e3D Technology, scanning available Typhoon parts and surviving sections has allowed for detailed CAD (computer-aided design) models to be created. While original Hawker drawings are important, they do not always provide the details required to re-create the final production parts or assemblies. “There can be many readability issues with the information on the page”, Ian says, “and there are often errors that were corrected by the tool-makers or fitters without ever getting corrected in the drawings. The CAD verification processes used by our design team can sort these out too, but it takes a massive amount of time and patience.”
That “massive amount” of time equates to years of Typhoon Legacy’s hard work developing the meticulous CAD models that allow for each piece of Typhoon to be modelled and assembled virtually before metal is ever cut. “Our digital cockpit assembly contains well over 6,000 parts”, Slater says. “Many of these had to be scanned before we could even consider assembly verification, and many others had to be designed from drawings and manufacturer standards. The time required to fit all of these items together, inspect, correct or pass was phenomenal! It has taken two of our designers years of work and thousands of hours to produce production-ready CAD design information for this key section of Typhoon structure.”
As the design comes together, the materials required for JP843 cause equally head-scratching moments. “We need to be using materials carefully selected to meet the original design intent of the production parts”, Ian explains. “This takes searching for the original specifications and all superseding documents, verifying mechanical properties and chemical composition, and cross-referencing modern available materials for substitution. This process becomes increasingly difficult when you look at the manufacturing process of each part, either machined from wrought, cast, or a forging.”
Much fabrication for JP843 has been accomplished already. The fixture for the monocoque has been completed with most frames produced and fitted. While Ian has made a start on the Typhoon’s radiator fairing and fittings, the focus has been further back from that glorious scoop below the nose.
The Typhoon’s fuselage was conceived with an eye for manufacturing. It was designed in four sections that could be brought together and assembled quickly by multiple fitters working together. For a one-off Typhoon, though, this approach is not going to be followed as it would be time-consuming and not cost-effective. “Our fixture design was made to assemble all frames and skin the assembly in one fixture. It was essential that we had the ability to make adjustments to each frame location and to be able to remove the fixture from within the completed structure. The design was created by Bruce Slater [Ian’s father] and exceeded all expectations.”
Typhoon Legacy’s eye is never on just one area of JP843. Division of labour has meant progress can be made across the aircraft as a whole and, when a wall is hit in one area and more information is needed to progress the design or fabrication, effort applied elsewhere. For example, when Nicolas Walter — who had led the CAD work for the cockpit — moved on, it allowed Bruce Slater to transfer to that area and proceed with verification of the work that was completed. As Bruce settled in on the cockpit, he was also finishing the radiator fairings while providing the information Ian needed to continue with the monocoque. This multi-pronged approach meant, as multiple areas evolved, more troublesome elements, such as the rear monocoque fixture being built up by Martin Oldfield, could be supported.
The rear monocoque is the section to the aft of the famous/infamous transport joint. A lack of information here means work on this section of the airframe is rather stop-start. Built in two separate sections, the rear monocoque and the vertical stabiliser are brought together as one assembly. The approach Ian and his colleagues adopted was to take on the vertical stabiliser first. To understand the construction, Martin referred to the original drawings and a visit to the sole surviving complete Typhoon, the RAF Museum’s MN235, while it was on loan to the Canada Aviation and Space Museum in Ottawa. Measurements of various sections were taken, which Martin then applied to the design. From this, all the tooling and fin ribs were produced in-house and have been heat-treated ready to go into the assembly jig once completed.
One feature of most of Ian’s YouTube progress videos is the forward monocoque visible in the background, the frames on the jig and looking just about complete. Is it? “No, but there is a reason”, Ian laughs. “Work was progressing very nicely for this section but I needed to make a few detours. The first little side project took me nearly six months to complete”. This was a second set of fuselage frames for the static Typhoon rebuild under way at the Jet Age Museum in Gloucester. Using the same tooling produced for JP843, the frames were well-received and will be mated to the very original early Typhoon cockpit the museum is building. The second detour is one that has caused much debate by followers, and detractors, of the project.
The Typhoon’s engine, the 36.7-litre, 24-cylinder, 2,200hp-plus Napier Sabre, was one of the most powerful piston engines ever built. It is now also one of the rarest. Ian, working his contacts, learnt of a late-model Sabre VII in New Zealand and approached the owner. “I was offered a trade opportunity if I could come up with an operational Rolls-Royce Merlin on a trailer. A Typhoon isn’t a Typhoon without a Sabre, so this is something that had to be done”. A Merlin III was sourced and the team, including Typhoon Legacy’s very own ‘R-R’, Rob Roy, set to work to return the unit to running order. This was completed in 2023 with this quiet part of Canada being awoken to the melodious symphony of the Merlin, before being delivered to its new owner. The Sabre VII was duly exchanged, arriving in British Columbia earlier in anticipation of the successful runs. For now, the powerplant and the efforts required to return it to running order will have to wait as the spotlight returns to the fuselage and cockpit, which were temporarily put aside to concentrate on the Merlin.
Ian turned to that most troublesome area of the Typhoon, the transport joint. The type is remembered today as both a ‘tankbuster’ and ‘the aircraft the tail used to come off’. Fact, as usual, is more objective than these legends. But while the tank-busting credentials have been well-debated, including in this magazine, the knowledge of the harmonic resonance issues with the Typhoon that caused 27 examples to be lost when they shed their tails means this is an area for special consideration by Ian. The answer to ensure JP843 is safe comes in the form of the Typhoon’s successor, the Tempest V.
“The transport joint is a big deal”, he explains, “not only because of the history of tail failures at this point, but also because we have decided to go with the extruded frames used on the Tempest V Series II and the Tempest II”. Extrusion is the process of forcing metal through a die rather than it being cut or forged. “The original Typhoon joint had several modifications that eventually resolved the failures, but it was still a very poorly designed way of mating the forward and rear monocoque sections. While all of the other frames in the monocoque section were of formed sheet metal and producible in our own shop, this heavier, extruded frame needed to be stretch-formed to capture the correct geometry required for a proper fit.”
As work went ahead on the Merlin III, Bruce set to designing the frames and tooling required for a Tempest-style transport joint and Ian brought on board Versaform Canada Corp, a metal forming company, to ensure the extruded frames meet the requirement for JP843. Ian visited Versaform as it completed the extrusion, and reports, “they stretched the extrusions to perfection.”
The other great area of concern for the rebuild of a Typhoon is its wing. With little surviving documentation, understanding the form and structure of the thick wing is one necessitating much investigation and ingenuity. Again, MN235’s visit to Canada paid dividends. While in Ottawa, it was possible to conduct a full 3D scan of the wing. This will supplement the engineering data and the recovered Typhoon wing section in the group’s possession. This recovered wing represents most of the closed structure and areas where information was thought to be lost. Stripping of the wing torsion box to confirm these details and those of the front spar has begun.
Returning to the cockpit, Typhoon Legacy is on the verge of assembling the 6,000-piece puzzle that would be recognisable from nearly every Sydney Camm-designed Hawker aircraft until the ‘Tempest Light Fighter’, the Fury/Sea Fury. With the CAD and pre-visualisation completed, all the tubular material has been sourced for the rebuild, as well as the massive steel blocks from which the new wing spar fittings will be machined. With most of the fixtures and fittings in Hawker’s cockpits being constructed and secured with the company’s own design of gusset plates, nuts, bolts and ferrules, it has been a labour-intensive journey to get to the point where assembly is possible. A vital aspect will be the squaring of the tubes that make up the cockpit structure.
Ian set himself the challenge of building the tube-squaring machine in-house and has now turned to its final elements. “I’ve fabricated a base for the machine now and have started to build up and install a reduction gearbox to help reduce effort and control feed rates. Bruce has again been involved with this and has designed the entire set of tube-squaring dies for all Hawker profiles. My next step is to complete the guide system for the tube-squaring base and finish machining the die sets.”
While the goal continues to be to fabricate as much as possible in-house, Ian and Typhoon Legacy are working with industry partners to complete essential tasks. Among them are the eight main spar fittings on the cockpit structure, which form what Ian calls the foundation of the rebuild. “Before anything else can be assembled, we will need these to build up the spar panel sub-assemblies. There are four different fittings here along with four on the opposite side. Each of these are complex in their geometry, and in their metallurgical requirements. All of these items have been designed and verified for production, and we are now working with several specialised organisations to ensure production is spot-on.”
Typhoon JP843’s journey back to the sky is progressing well, despite perceived Merlin-shaped distractions. Typhoon Legacy is in the enviable position of having researched all the main structural elements of the airframe; it is now just a matter of bench time to get them fabricated and out of the backlog. “We have many years ahead before the aircraft begins to look complete”, Ian says, “but we’ve solved all the biggest issues that have prevented Typhoon rebuilds in the past”. With quiet persistence, the next few years look incredibly exciting for JP843 in its new home on the west coast of Canada.