Kestrel – A 50 Years Old Flight of Fancy??


Happy birthday to the world’s most powerful single engine diesel locomotive – the HS4000 – “Kestrel”. Well it was the most powerful when it began its short working life in 1968. The design also served to pioneer later used in the immensely successful HST power cars, and which still provide the Brush Traction legacy to this day.

50 years ago, in January 1968, Brush Electrical Machines handed over the 4,000hp Co-Co diesel locomotive to British Railways. It has been described in some quarters as a “technology demonstrator”, powered by a Sulzer 16LVA24 diesel engine, and fitted with an alternator instead of the usual generator. The traction motors were still DC, but supplied through an advanced design of silicon rectifiers, which helped increase the power output and overall performance of the power train.

British Rail’s requirement was for a high-powered locomotive suitable for heavy freight and express passenger services. The Sulzer power unit, which had also been deployed in the Class 47, and which was also built at Vickers’ works in Barrow-in-Furness, drove the dc traction motors through an alternator, and not a generator. The control systems made extensive use was made of modular electronic units for power control, wheelslip detection, dynamic brake control and other functions.

Kestrel diagram from Railpower Jan 1968

Cutaway view from ‘Railpower’ January 1968 (Courtesy of the Railway Industry Association)

Whilst the design was begun in 1966, and built in 1967, completed at the company’s Loughborough factory in November/December 1967, where extensive technical tests were undertaken, before being handed over to British Railways at Marylebone Station on 29th January 1968.

Service trials proved the value of 
the ac/dc transmission adopted 
for the High Speed Train prototype 
in 1970 and for the class 56 freight 
locomotive in 1974. Further orders for Brush for this same power equipment came from British Rail for the production High Speed Trains and the remainder of the Class 56
 locomotive fleet,

The running gear, with six axle hung traction motors shared a common design practice with the Brush Type 4 (Class 47), however, with the body as a stressed skin (Warren Truss) construction – common in the aerospace industry – no underframe/chassis was used. All of which provided an impressive power to weight ratio – 4,000hp in an all up weight of 133 tons.

Principal Dimensions

Overall Length 66ft 6ins
Overall height 12ft 9 3/4 ins
Overall width 8ft 9 3/4ins
Bogie Wheelbase 51ft 8ins
Weight in w.o. 133 tons
Axle loading 22.5 tons
Engine Sulzer 16LVA24
Max. Output 4,000hp (2,985kW) @ 1,000 rpm
Main alternator Brush (flange mounted to engine)
Continuous output 2,510kW / 2,520kW @ 1,100 rpm according to loading
Traction motors 6 x Brush 515hp, 4-pole, series wound, force ventilated
Braking systems Vacuum, straight air, automatic air and dynamic, with hydraulically operated parking brake
Brakes Mechanical clasp brakes
Max speed 110 m.p.h.

However, this came with an axle load of 22.2 tons – more than 3 tons greater than the amount specified by Britsh Railways. The bogie side frames were of one piece cast construction with coil spring suspension, connected by 4 transverse members; two internal and two at either end.

After the Hither Green rail crash, British Rail issued a directive that all locomotives should have an axle weight of no-more than 21 tons. In an attempt to comply with this, Brush fitted the locomotive with modified British Rail Class 47 bogies.

So, we have a reputable manufacturer who delivered a prototype / technology demonstrator that did not meet the buyer’s specification. A design fault or too much technology??

In this prototype, extensive use was made of the then state of the art electronics, controlling much of the locomotive’s operations, including traction motor field settings, electrical load management, control of wheel slip, automatic voltage regulation. The braking system too included automated load and proportionate load regulation, determined by the loco’s speed.

Operationally Kestrel spent a great deal of its time on freightliner services between Hull and Stratford, along with coal trains betyween Shirebrook and Whitemoor. The modified bogies to meet the BR axle load requirements rode well, and for a six week period, Kestrel was rostered for the 08:00 Kings Cross – Newcastle service & 16.45 return – normally a ‘Deltic’ duty. HS4000 on the ECML was comfortably able to maintain the Deltic diagram timings.

HS4000_Derby Sulzers

HS4000 after bogie modifications at Cricklewood Open Day, 12th July 1969

Despite this success in main line service after its modifications, BR did not place any further orders, and in 1970, the loco was sent to Vickers in Barrow-in-Furness, where the company refurbished the Sulzer diesel engine. On its return to Brush, the loco was sold to the USSR for £127,000, and in July 1971 left the UK from Cardiff docks on board the MV Krasnokansk.

Kestrel at Barrow 1971 - Jordan Aspin Facebook

This view taken in 1971 shows Kestrel being shunted by a class 25 approaching Devonshire bridge at the western end of the Barrow Dock system.

derby Sulzers at Barrow hs400016lva24

The 16 cylinder engine seen outside the Barrow Engineering Works of Vickers Ltd in 1971 where it had been removed for overhaul, before being refitted into the locomotive. Photo. Courtesy of Geoff McEwen

Of this hugely powerful design, only 5 engines were built, one was used as the type test O.R.E. engine, but was later scrapped by Sulzer at their Oberwinterthur site, the other three were used as standby generators for power stations at Schaffhausen, Switzerland, and Dunkirk, France.

In Russia, the locomotive came to something of an ignominious end.

Kestrel in Russia 1980s - Facebook Stephen Powley

British Rail had a wealth of experience with Sulzer power in its diesel fleet – most obviously for main line passenger duty, the Brush-Sulzer Type 4 (Class 47) – and with Vickers construction and maintenance experience, it is a mystery why BR chose the complexity of the “Deltic” over “Kestrel”. But, of course, BR were also developing fixed formation train sets, such as the HST (InterCity 125), which arrived a couple of years after “Kestrel” was sold, and the ill-fated APT. So maybe the locomotive hauled services, with Mark II, then Mark III were not in the future plans, and it was only a flight of fancy to see what could be possible.


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