Put back in the air on June 7 by Hawker Restorations, Hurricane AE977 made its public debut at Duxford's Flying Legends show on July 8-9. Melvin Hiscock looks at the painstaking work that got it there.
The first post-restoration flight of Hawker Hurricane AE977, on June 7, marked not just the debut of the world's eighth airworthy Hurricane and the sixth in the UK, but the culmination of an unprecedented rebuilding programme by Hawker Restorations, based at a small farm in Suffolk. More impressively, AE977 is not the only Hurricane to have been built there. The airframe for Sir Tim Wallis's P3351 recently flown in New Zealand, was rebuilt there, the team is well advanced on BW881/G-KAMM, which should fly later this year, and a couple of projects are waiting in the wings.
The company has also been helping out most of the other Hurricane projects that are under way around the world. It supplied all of the spar materials for Battle of Britain Memorial Flight Hurricane LF363, and is helping the Smithsonian's National Air and Space Museum and the Lone Star Museum.
Hawker Restorations (HR) is a sister company to Tony Ditheridge's AJD Engineering, which is well known for its excellent restorations and replicas of World War One and classic aircraft. Some 18 have been completed in the last 12 years, including several Avro 504's and Percival Mew Gull G-AEXF.
As its name suggests, HR was formed specifically to rebuild Hurricanes, and was created in co-operation with Sir Tim Wallis of the New Zealand-based Alpine Fighter Collection. One of its first acts was to employ Paul Mercer, who was instrumental in rebuilding Stephen Grey's Hurricane XII and Charles Church's Hurricane, which now flies with David Price at the Santa Monica Museum of Flying. HR also started collecting drawings, manuals and anything relating to Hurricanes.
Because of the Hurricane's complexity, Tony initially collated as much i8nformation as possible, and assembled the necessary tools, jigs and materials with a view to rebuilding a maximum of five airframes. This gave the economy of scale that made the project viable. HR was also the first company to obtain A8-20, M5, E4 and E2 engineering approvals essential for this level of rebuild.
The sheer size of the task was brought home to me in March 1994, when I visited Tony to collect my Rearwing Cloudster. As we loaded the fuselage I commented on the pile of rusty tubes and contorted aluminium outside the back door. It was obviously Hurricane, and obviously not too well. Tony told me they would rebuild it to fly, and I have to admit I was amazed. It is a little frustrating that the Cloudster, which only required a new engine, is still on the ground and the Hurricane has flown. Not only that, but P3351 was supplied to New Zealand as a complete airframe with wings, fuselage, engine mounting, tail assembly, woodwork, fuel tanks, cowlings and may other parts in 1995, and the company is now close to completing its third Hurricane.
It has often been said that the Spitfire was far more complicated to build than the Hurricane, and that is why more Hurricanes were available early in the Second World War. The Spitfire had an all-metal monocoque structure, which means that manufacture and assembly were done at the same time in a jig. This was fairly new technology at the time, whereas Hawker Aircraft had spent some years developing the structural techniques employed in the highly successful series of biplanes that began with the Hart. Hawker was simply more used to its process that Supermarine was with the monocoque construction, but the Hurricane is nevertheless a complex machine required the manufacture of thousands of individual parts to close tolerances.
Hawker Restorations is currently completing the restoration of a Supermarine Seafire and has considerable experience with Spitfires, which has give the company an insight into both aircraft. Tony estimates that a Hurricane will require three to four times the amount of labour to restore than a Spitfire. While there are many Hurricane projects, very few have been restored to fly; there are almost ten times as many Spitfires in the air.
Over the past six years I have watched the rebuilding of all three Hurricanes and learned a lot about the techniques involved. The rebuild starts with the basic fuselage structure, centre section and engine mounting. The centre section spars are very difficult to build, as each comprises a nested 12-sided roll formed of spring steel, with one inserted inside the other. This assembly clamps on to an inner tube which itself has another liner tube inserted The tolerances on this assembly are crucial. This is one of the main items that has previously prevented Hurricane rebuilds, and HR teamed up with Aero Vintage, which is building a number of Hawker biplanes.
Guy Black of Aero Vintage discovered that one of the original rolling machines which produced Hurricane spars had survived. New tooling was needed for the various sizes of spar material, both for inner and outer wing spars and for the tailplane, and this entailed a lot of materials science research to determine the original material used. Several tons then had to be manufactured overseas, heat-treated and slit to width. More than 120 18in diameter rollers had to be designed and manufactured for the centre section spars, plus a similar number for the tailplane and fin spars. As can be imagined, this was an expensive exercise.
The steel inner tubes within the spars also caused problems. They has a specific tensile strength that was not readily available. To attain this they needed heat treatment, computer-controlled tube straightening and internal gun boring to high levels of tolerance. The spar web also required specialised materials and heat treatment to match a 1937 specification.
The fuselage and other structures are built up with round, high-spec 50-tonne (T50) tube that is no longer available. Careful selection of batches of high-sepc T45 solved this problem. These tubes are squared off at the ends, and a special tube-squaring machine, similar to that used by Hawker Aircraft, had to be made, along with all the rollers for each size of tube. Within the fuselage and centre section, each joint or cluster of tubes is held together by stainless-steel fishplates, ferrules, spacers, bolts and tubular rivets, as well as a machined component which fits into the end of most of the tubes. Tolerances can be as low at 0.5 thou, and one joint can have as many as 180 components. This level of accuracy is necessary because they are not welded joints, but there must be no movement or play between the parts. Aero Vintage and HR shared this technology, as the same system was used on the Hawker biplanes.
The final fuselage shape is built up in the traditional manner using wooden formers and stringers, and incorporates all manner of subtle curves. The expertise in woodwork that already existed within the company stood it in good stead when manufacturing the complicated wooden structure around the cockpit area ( known as the "dog kennel") and the complicated top, side and bottom formers and stringers which give the Hurricane its distinctive shape. The final covering with Irish Linen was undertaken by Clive Denney of Vintage Fabrics. The outer wing panels of AE977 and P3351 were subcontracted to Airframe Assemblies, as much original materials as possible being retained in both rebuilds. Hawker Restorations can now manufacture its own wings, and these are fitted to G-KAMM.
By late 1998 the main structural members were in place, and attention turned to fitting-out. Originally, AE977 had been fitted with a Packard Merlin, and a rebuilt Packard Merlin 224 was installed along with the newly-manufactured radiator and fuel and oil plumbing. The decision had been made early on to make the internals as authentic as the externals, and the cockpit is fitted out exactly as it would have been in 1942. The instruments and fitting came from a variety of sources, and even the pilot's medical kit will be included. Modern radios will be discreetly fitted so that they do not intrude on the authenticity of the cockpit detail. Guns, ammunition boxes and chutes and even deactivated 0.303in ammunition was ready for fitting after AE977's return from Flying Legends.
Tony estimates that some 50,000hr of work goes into each aeroplane, together with £600,000 worth of parts. What cannot be accounted for in normal terms is the level of skill, dedication and attention to detail that has gone into making this aeroplane so exceptional. Stuart Goldspink, who first flew it, reports that it flies very well, has an exceptional rate of roll and could be trimmed for hands-off flight from the start. Very few adjustments have been needed, other that those that would be expected with components "bedding in". The aeroplane stalls at 69 m.p.h. when "dirty" and climbs at more that 2,500ft/min after take off.
The Hurricane was publicly unveiled at the Flying Legends airshow on July 8 and 9, and will no doubt be seen at other shows during the summer. Meanwhile, Hawker Restorations is continuing with G-KAMM and has several other projects in hand. These, too, will benefit from the incredible investment in time, money and research that has made AE977 such an impressive aeroplane.
