Alnico Cylindrical Bar Magnet
Ideal for a range of switching and security applications
Company Name: Royal Air Force, Battle of Britain Memorial Flight (BBMF)
Location: RAF Coningsby, Lincolnshire
Eclipse Service: Re-magnetisation
The Royal Air Force Battle of Britain Memorial Flight (BBMF) operates from RAF Coningsby, a Typhoon and fighter base, located in Lincolnshire. Their mission is to maintain the priceless artefacts of Britain’s national heritage in airworthy condition in order to commemorate those who have fallen in the service of this country, and to promote the modern day Air Force to inspire the future generations.
The flight operates six Spitfires, two Hurricane Mk IICs, a Lancaster, and a C47 Dakota as well as two Chipmunk aircraft which are primarily used for training. Flown by regular serving RAF Aircrew from May to September each year, these aircraft can be regularly seen in the skies over the UK celebrating and commemorating public and military events; from State occasions such as Trooping the Colour, to major air displays and simple flypasts for public events.
The Mk XIX was the last photographic reconnaissance variant of the Spitfire, combining features of the Mk XI, with the Griffon engine of the Mk XIV. The first Mk XIXs entered service in May 1944, and by the end of the war the type had virtually replaced the earlier Mk XI. A total of 225 were built with production ceasing in early 1946, but they were used in front line RAF service until April 1954.
The Rolls-Royce Griffon engine was designed to meet Royal Naval specifications for an engine capable of generating good power at low altitudes. Named after a bird of prey, in this case the Griffon Vulture, the Rolls-Royce Griffon is a British 37-litre (2,240 cu in) capacity, 60-degree V-12, liquid-cooled aero engine designed and built by Rolls-Royce Limited, capable of producing approximately 2000 B.H.P..
Design work on the Griffon started in 1938, and in 1939 the engine was adapted for use in the Spitfire. The engine finally went into production in the early 1940s, where it was the last in the line of V-12 aero engines to be produced by Rolls-Royce. Production stopped in 1955, but Griffon engines remain in Royal Air Force service today, including in the Battle of Britain Memorial Flight.
Retro Track & Air (UK) Ltd, based in Dursley, Gloucestershire, is contracted to carry out the repair and overhaul of the Rolls Royce engines for the Battle of Britain Memorial Flight. As part of the overhaul process, the company was asked to assist in the overhaul of the magneto.
Stuart Watts at Retro Track & Air (UK) Ltd asked Eclipse Magnetics to re-magnetise the ignition magneto for the Mk XIX Spitfire. Over the life of the magneto the magnetism was suspected to have been depleted, and therefore needed to be re-magnetised at overhaul.
An ignition magneto, sometimes referred to as a high tension magneto, provides the current for the ignition system of a spark-ignition engine. The magneto produces pulses of high voltage for the spark plugs to the engine when required, during all aspects of flight.
This type of magneto contains an alnico permanent magnet to produce the magnetic field which, combined with the motion of the armature, produces the electricity for the sparks. When the magneto was originally manufactured in the 1940’s, the magnet would have been fully charged. Despite being called 'permanent', permanent magnets can lose their strength for a variety of reasons including; use, age, temperature, and possibly vibration.
Eclipse Magnetics was able to re-magnetise the alnico magnet within the ignition magneto by exposing it to a very strong magnetic field, therefore restoring as much of its strength as possible.
Eclipse Magnetics typically magnetise alnico motors/generators with the rotor in place, as it gives a better magnetic circuit by which to magnetise the alnico. Taking the rotor out can result in the magnet’s demagnetisation, therefore decreasing the electromotive force (back emf) when re-assembled. For example, if the rotor had been removed for cleaning or maintenance purposes in the past, it is possible that this could be the reason why the back emf measurement was low.
To re-magnetise the alnico magnet, Dr Ewan Goodier at Eclipse Magnetics removed the case in order to carry out the measurements, due to the need to verify which end was north, and to check if the magnetising was improved successfully.
Eclipse Magnetics used its own specially developed re-magnetising and measuring equipment to measure the initial strength of the magneto's magnet and its polarity. The alnico magnet was then re-magnetised with the same polarity, and the resultant magnet strength was measured. Retro Track & Air (UK) Ltd were then provided with a detailed performance report showing all measurements and figures from before and after the process. The process was successful, and Eclipse Magnetics was able to increase the magnetic output in both units to very similar levels.
Dr Ewan Goodier CEng BEng Hons MIEEE MIET, Technical Sales Manager at Eclipse Magnetics Limited said: “We were very pleased to be a part of the overhaul on the Griffon engine magneto. Although we cannot guarantee that the magnet will be back to its brand new 100% value, we do know that it is significantly better than it was and will certainly generate a higher electromotive force.”
Wg Cdr Andy March MSc BSc(Hons) CEng FRAeS Finst LM RAF, the Assistant Type Airworthiness Authority for the BBMF aircraft, said: “The Ignition Magneto is classed as a Critical Engine Component and as such it is vitally important that it performs reliably and as it was originally designed to do. The work carried out by Eclipse and the evidence provided of the magnet’s performance helps to underpin the aircraft’s Safety Case and is part of the evidence set we use to demonstrate the aircraft is safe to operate at airshows and flypasts throughout the UK. Without specialist companies such as Eclipse who are experts in their field, it would be impossible to continue to fly the BBMF’s historic aircraft.”