Digital Edition – December 2019 (#225)

Operation Improbable

The Rebuild Of 75 Squadron Mosquito YC-Z



by David Child-Dennis


There are very few of the older generation who have not heard of a de Havilland Mosquito. But few have had the good fortune to see one in the air, although many enthusiasts have seen them as static displays, essentially museum models. No matter when or how you see the Mosquito, you cannot help but be impressed by the beauty and grace of the aircraft.

Geoffrey de Havilland and his chief designer C C Walker revealed their true genius in designing this aircraft, against a wall of official denial and obstruction. It was only after the first privately funded machine flew at Hatfield on 25 November 1940, before a doubting Air Ministry, that things changed. According to Walker, “when they saw it fly, even the RAF understood what the Mosquito was all about.” The fact that it was nearly 100 mph faster than the Hurricane and about 60 mph faster than the best German fighter of that period, the Me109E3, might have changed their opinion!

It also explains why the first production aircraft were all photo-reconnaissance machines. In September 1941 a Mosquito PR-1 photographed the French Atlantic coast while being pursued by Luftwaffe Me109s, and simply out distanced them. So successful was the design concept, that in 1944, when it had become obvious jets were to be the next advance in military aviation, de Havilland was asked to design a jet bomber based on the revolutionary Mosquito. The first Canberra entered squadron service 1951, and they remained in RAF service until at least 2006, a PR-9 or T-7 being one of the last aircraft in regular squadron service.

YC-Z started life as an FB VI, a paddleblade, cannon and rocket armed ground attack machine built at Bankstown, Sydney, Australia, in 1946, by the Commonwealth Aircraft Corporation. It was transferred to the RNZAF soon after the end of the war against Japan in August 1945, as part of the ground attack force preparing to meet communist guerilla attacks in Asia, following the surrender of Japanese forces.

Like all Mosquitoes, she was primarily made of wood, the most abundant material throughout the Commonwealth at the beginning of the war. An additional advantage was the vast number of woodworking tradesmen available to the aircraft industry in Australia, Canada and Britain, which produced 7,781 Mosquitoes, between November 1940 until some time in 1946. The problem for reconstructors is the laminated plywood pine construction. Exposed to weather and the rigours of combat flight, the airframe and skin life was only a few years, which for an aircraft expected to survive about 500 hours in combat was more than adequate. Unfortunately, this ‘limited service life’ has proven to be a nightmare for those attempting to restore them.

It’s important to appreciate YC-Z is a rebuild, not a replica, only one of three airworthy Mosquitoes.

This makes it much more valuable as a historical aviation aircraft, but complicates the project exponentially. It raises the question whether Glyn and Mike are ‘on a mission from God’ or suffering a bout of collective insanity? I suspect it’s a bit of both!

YC-Z was recovered from Riwaka, Northland, in a pitiful state, after having been declared surplus to airforce requirements and ‘flogged off with indecent haste’. The farmers were in the main only interested in the balloon tyres for trailers, and at 50 pounds an aircraft, were a very cheap purchase. All the airframes had their wings chainsawed off just outboard of the engine nacelles, making it easier to tow them, tail first.

Once the wings and tail planes were removed – usually to be burnt as rubbish – the problem of building replacements became even more difficult. To add to their already growing list of problems has been a British Aerospace (successor to de Havilland) refusal to release plans and drawings for the Mosquito. BA claim they would be exposed to damages should there be an accident with the aircraft. I can’t see how liability would attach to BA, given the aircraft must meet Civil Aviation certification criteria prior to being issued an air-worthiness certificate. With over 7,000 being manufactured, it’s hardly a ‘proof of concept’ risk!

Not to be deterred, Glyn set about travelling the globe, searching for the vital information and components needed to rebuild ‘Z’. “It’s the bits hidden away inside the aircraft that present the greatest problems,” he wryly remarked, as we watched Mike fabricate a radiator vent cover that fits under the inboard section of the wing, between the fuselage and the engine nacelle. Mike was using an original, which had corroded and was damaged beyond use, as a pattern. This involved carefully measuring each piece, hand cutting it from aluminum sheet, and then, after bending and drilling, riveting them together. The original manufacturing plants had jigs and dies to ensure everything was in the right place before riveting. None of these jigs and dies were retained as aircraft manufacturers stampeded into the jet age. A few voices in the restoration wilderness cautioned against dumping such treasures. If only they’d been heeded!

By far the greatest challenge has been constructing the fuselage. Being moulded ply, in two halves, it required Glyn and Mike to become cabinet maker-boat builders. The original production lines had used concrete moulds to form the steamed ply into the required sections. Glyn decided that hard wood boat building moulds would be more successful and offer a greater flexibility of type. The two moulds allow for the production of either the fighter-bomber or bomber fuselage, the positioning of hatches and attachment points being different. Like a boat hull, the fuselage halves had to be extremely accurate in section and profile, otherwise the aircraft could become unpredictable during ground handling or flight.

Mosquitoes require a fair degree of pilot skill when taking off, due to the enormous amount of torque produced by the Merlins under full power, which tends to make the aircraft swing left. Everyone told Glyn that making such moulds without the original plans was impossible. With the third aircraft at around 60% complete and the second – a bomber version – flying on 29 September at Ardmore, the doubters might have to concede the point!

The completion of ‘Z’ is still three years, and another million dollars, away. But, with the able assistance of Mike (who an aviation friend of mine tells me is an unrecognised genius – another Richard Pearce) the aircraft moves steadily towards completion. Glyn and Mike still have many problems to overcome, but at least with this being the number three aircraft, they have learned much that will speed the process. Strangely enough, it can be the simplest of things that cause the greatest delays. A major problem is the small components like ‘L’ brackets and linkages. Each has to be cleaned and carefully inspected. New components must be individually stamped with a unique part number, then laboriously recorded in the build logs.

But it’s getting all the interconnecting parts to assemble in sequence. The original builders had sub-assemblies feed the final assembly lines. Glynn and Mike have no such system. Everything has to be assembled from scratch, without any instructions as to the most efficient order of assembly. Often, they find it requires an assembly to be stripped and then reassembled just to fit a minor component. During the war, Britain relied on thousands of pensioners being organised into assembly units. Up to five people would sit around a kitchen table building fuel pumps, hydraulic valves and all manner of things for aircraft. In my opinion, their contribution has never been fully appreciated, but alas, Glen and Mike have no such support.

I suppose the real question is; are such huge, time consuming and unbelievably expensive projects worth it? Emphatically yes! There has been a major industry formed around restored and replica aircraft, even to the extent an engine rebuild facility has been created for the Packard-Merlin engines common to many World War two aircraft. Without this, none of these projects would have been possible.

Similarly, a wide variety of skills have had to be relearned as a new generation of aircraft engineers entered the restoration business. I just wish I had the space to relate some of the amazing stories about the sharing of construction techniques between strangers who have the same passion for old aircraft.

But what about the indirect economic benefits? The annual airshows at Wanaka, Hamilton and Ardmore are testimony to the huge public interest in anything that flies. They generate millions of tourist dollars with little support from government, which, from the GST taxes alone, does very well out of the industry. Historical aviation tourism has been growing since the 1970s, despite resistance from the airforce.

There are spares for many aircraft the RNZAF has operated, at Weedons and Woodbourne, including spares for the Mosquito, Harvard, Vampire and Canberra. The refusal to allow the release of these vitally important spares to restorers is incomprehensible. The RNZAF stock of aircraft manuals is a treasure-trove in its own right and should be the core facility of a restoration library. A national database of people who have worked on these aircraft should be included, so that restorers have access to first hand experience, before it’s too late.

With a little effort, and a small investment, New Zealand could become a restoration mecca for the Pacific region, if not the world.


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elocal Digital Edition – December 2019 (#225)

elocal Digital Edition
December 2019 (#225)