Hawker Restoration (
www.hawkerrestorations.co.uk) and its sister company Hawker Racing are passionate about what they do. Indeed, the former is the world’s foremost restorer of the Hawker Hurricane aircraft, having restored or worked on 13 of the 15 remaining airworthy planes. Meanwhile, the latter has established a high level of success restoring and replicating pre-1966 grand prix cars and sports cars, gaining honours in many races for its customers.
This type of work requires many parts to be manufactured from either original blueprints or ‘fresh’ designs. Company owner Tony Ditheridge says: “There are literally thousands of parts that we have to manufacture — from suspension, gearbox and steering components on the cars to undercarriage, wing fittings and hydraulic components for the aircraft.”
As well as working on the ‘relatively modern’ Hurricanes, Hawker Restorations also works on older aircraft. Mr Ditheridge currently has a nine-cylinder rotary engine that is waiting to be restored and fitted to a replica 1916 Sopwith Camel (being built for an overseas customer).
Often overshadowed by the Spitfire, the Hurricane was in fact far more successful, shooting down 656 enemy aircraft compared to 529 by the Spitfire. The Hurricane was also a more complex aircraft than the Spitfire, which had a monocoque frame; this complexity probably accounts for the fact that only 14,583 Hurricanes were built, compared to 22,000 Spitfires; and only 15 remain airworthy, compared to 45 Spitfires.
The intricate construction of the Hurricane meant that Hawker Restorations almost didn’t ‘get off the ground’, as it could not justify the cost of tooling and materials required to restore these aircraft. It was in 1993 that Mr Ditheridge was approached by the New Zealand-based businessman and aviation enthusiast Sir Tim Wallis, who funded the materials to restore the first three Hurricanes. One of these was shipped to Sir Tim in New Zealand, the second went to Microsoft co-founder Paul Allen, and the third went to Steven Grey for The Fighter Collection at Duxford.
Machining capability
Restoring such aircraft requires a machining capability; and while many of Hawker Restoration’s 15 employees are highly skilled tool makers who could make use of the factory’s manual machines, the company sub-contracted most of its machining to fellow aircraft enthusiast and Rolls-Royce Merlin engine specialist Maurice Hammond at Eye Tech Engineering. However, with the level of business increasing, Mr Ditheridge decided to complement the service provided by Eye Tech and its XYZ machine tools (
www.xyzmachinetools.com) with a new in-house machining facility.
“We have more than enough work to keep Eye Tech busy, but we recognised that we also needed our own CNC machining capability, particularly for our historic racing-car business, so we decided to invest in some XYZ machines of our own. This means that every machined part we use on our aircraft has been on an XYZ machine at some point — whether ours or Eye Tech’s.”
The XYZ machines bought by Hawker Restorations are an SMX 3500 bed mill and a ProTurn SLX 355 lathe. Both feature the ProtoTrak CNC/manual control system, which was a logical first step for the team, who had no experience on CNC prior to the machines being delivered.
Mr Ditheridge says there was initially some resistance to change, as the norm had been to get on a manual machine and ‘handball’ every job, but the simplicity of the ProtoTrak control soon won over the doubters and it quickly proved its worth. “An example of the difference was when we had to cut a large-diameter hole in an aluminium plate. Previously, this would have been chain-drilled on our manual machine; with ProtoTrak it was a simple job of programming the machine to interpolate the hole. In fact every job is so much easier with the ProtoTrak control.”
Machine detail
The XYZ SMX 3500 bed mill, which sits in the middle of the XYZ bed mill range, features a 3.75kW 5,000rev/min ISO 40 spindle with two speed ranges. A wide variety of components can be accommodated by the 787 x 508 x 500mm work envelope (in addition, there is a quill travel of 128 mm), and the machine’s 1,372 x 356mm table has a maximum load capacity of 600kg. Further versatility is provided by the fact that the head can be tilted 45deg either side of the vertical.
Meanwhile, the XYZ ProTurn SLX 355 has a 360mm swing over the bed (225 mm over the cross-slide) and a between-centres distance of 1,000mm. Also featured are a 5.75kW 4,000rev/ min spindle and a substantial cast bed that provides a highly stable machining platform. As with the SMX mills, the SLX lathes can be operated under full control of ProtoTrak, in full manual operation or in the Traking mode.
The latter allows the operator to wind the handwheel to move the machine through a program and is ideal for those who want to check a program before committing to full CNC mode, giving the operator greater confidence; once happy with a program, the operator simply presses the cycle start button and the program runs automatically.
To ensure that the potential of the ProtoTrak control is maximised, three tool makers from Hawker Restorations underwent training. They initially spent one day at XYZ’s Waltham Abbey showroom to learn the basics; once they had
familiarised themselves with the system, they had a day of more-advanced training. For on-going support — and as they start to look at more-complex components — the operators will have full and free access to XYZ’s programming hotline, which provides support to all customers who feel they need any extra advice on either the ProtoTrak or Siemens controls fitted to XYZ machine tools.
This extended support may well come into play with one project that is currently in the planning stages. Sitting in the workshop of Hawker Racing is a 1934/36 Parnell Supercharged MG K3 racing car; it has the original twin-cam engine fitted — the only engine of its kind in the world. Hawker Racing now has the patterns and drawings, and the plan is to manufacture brand-new engines of this type, with all of the machining being undertaken on the XYZ machines.
Restoring a Hurricane
Mr Ditheridge says that restoring a Hurricane is not like restoring an old car. “For cars, you can use your own judgment whether to repair, replace or ignore corroded parts. In aviation, if there is any corrosion to speak of, you have to replace. You can’t just cut a bit out and weld a new piece in.
If a Hurricane has been left outside for the last 50 years, all the wood and all the steel tubes and spars will need replacing. Some of the heavier forgings may be re-usable, but once you remove the corrosion, you have to have them stress-analysed and approved before re-use. The saving grace is that all of the joint plates and complex brackets that hold it together are made from stainless steel, and once cleaned up, they are usually perfect.
There are thousands of small parts that are reclaimable; most importantly, we always try to preserve the seat, the controls and the rudder pedals because they are the parts that the pilot touched when he flew the plane. The best percentage we have re-used was about 65% on a Hurricane retrieved from India. It was uncrated and re-assembled in 1951 and then parked at the back of a college, presumably as an instructional airframe, where it remained until 1994.
“There are still plenty of Hurricanes left, but they are often in desolate inaccessible places. About 3,000 were sent to Russia during WWII, and most are still there. There are huge lakes in Siberia which froze in the winter. Pilots in difficulty would land on them, but in the spring when the lakes thawed, the aeroplanes sank. The freezing-cold fresh water and silt can preserve them very well.
“We pulled out a Messerschmitt ME110 that was still covered with paint; moreover, its guns were armed, its air bottles were still full, and the undercarriage still worked. However, getting them out of these places is fraught with problems; and then when you do retrieve them, the rebuilding cost is enormous.”
Although the Hurricane featured a doped-linen covering, a bolted-together tubular steel frame and a plywood cockpit and appeared to be more an evolution of WWI bi-plane technology than its contemporaries, it was made up of thousands of machined components, bolted, riveted and glued together with incredible accuracy. “The Hurricane was designed to be assembled fairly quickly by relatively low-skilled people, but the manufacture of the parts was very time-consuming.
The components for the Spitfire were easier to make but it was a far more difficult aircraft to assemble. The Hurricane was also far more tolerant to damage than the Spitfire, because enemy fire would often pass straight through the fabric and tubes without exploding and any such damage could be more easily repaired in the field.