In the late 1950s the management of F.Perkins Limited, although already a successful manufacturer of diesel engines, was concerned about the future and started looking at the potential of other forms of power. This resulted initially in agreements with the Oliver Corporation to manufacture two-stroke petrol outboard motors, and with the Solar Corporation to manufacture small gas turbines: both of these ventures reached production and are covered in earlier articles. Other areas investigated included the possible commercialisation of a novel rotary engine invented by Felix Wankel. So what happened to this idea?

In February 1959, Mr Douglas McNair, the director of F.Perkins Ltd with responsibility for New Products, was approached by Steer-Webster Consulting Engineers regarding a potential venture with one of their clients, NSU (Great Britain) Limited, to manufacture the NSU 50cc engine for use in ‘Quickly’ mopeds in the UK. By December 8^th, 1959, the discussions had reached a point where a number of possible collaborations were being considered:

1. Manufacture of the 50cc engine for the Quickly.

2. A licensing arrangement with NSU for production of other engine designs for industrial or agricultural purposes.

3. NSU distributing Perkins outboard motors under the NSU name.

4. Perkins interest in the recently-publicised rotary Wankel engine for diesel and outboard motors.

It would appear that little follow-through occurred on items 1 to 3, but the Wankel engine did remain on the agenda. Meanwhile press reports on visits to NSU by British manufacturers together with a lengthy report by Harry Munday in ‘The Autocar’ of February 1960 on the engine and its problems, and another report in ‘The Engineer’ of Feb 26^th, document growing industry interest The later report mentioned the potential for a diesel version ‘provided that the ratio of the two main axes of the trochoid is laid out so that a sufficiently high compression ratio can be realised’.

By May 1960 NSU (Great Britain) Ltd had identified main policy points for any Licence agreement, and in June it was noted that Perkins could be granted a diesel development and manufacturing licence even though similar arrangements were in hand with German manufacturers. It also appeared that NSU were continually modifying their approach to licensing, after being ‘caught out’ by the agreement with Curtiss-Wright in the USA, for which it appears that C-W paid £2 million and then ‘jumped the gun’ in announcing substantial progress.

There is no further documentary evidence regarding the licence finally negotiated between Perkins and NSU, but it would appear that the agreement concerned just the Wankel for diesel and outboard applications, all the other proposals outlined being dropped eventually due to NSU’s lack of interest. A listing of licensees from the early 1970s confirms the Perkins signing as August 8^th, 1961 making them the fifth company to sign an agreement, ahead of most major companies: another example of the forward thinking of the Perkins board in those days!

Perkins started work on the spark ignition petrol engine with first development running using NSU-supplied engines. From this work concerns over rotor sealing and oil consumption were quickly identified. Engineering analysis resulted in some new ideas which were passed on to NSU as part of the agreed two-way exchange of data.

Details of the work on the engine are scanty, but one (undated and incomplete!) résumé report records that engine running started at Perkins in December 1961 using the NSU KKM.400 engine. By May 1962 the unit was moved to a fully operational test bed where better instrumentation allowed proper investigation to start, with initial concern with regard to apex seal materials and spark plug development.

The first Perkins-designed PRW.500 engine was assembled on 12/13^th September 1963 with start-up on the second day. In the following months considerable running experience was gained on both the NSU and Perkins units, the later series of engines comprising vertical and horizontal petrol engines and a vertical diesel engine. Over 600 hours in total were run, on various test beds.

The report goes into considerable detail regarding the problems encountered during testing, in particular with the material and mechanical aspects. Briefly, the areas requiring work were the trochoid housing (to develop wear-resistant surfaces), the rotor apex seals (wear and chatter), side seals and housings (wear) eccentric bearings (wear and debris clearance), oil distribution, water cooling and spark plugs.

As a consequence of this considerable range of problems, little performance development was achieved on the gasoline engine. The limited work done suggested that considerable attention was required to air utilisation and scavenging to ensure that specific output could be enhanced. The Perkins outboard design included a change to use water-cooling rather than the oil cooling used on the original NSU design.

The small amount of field-testing achieved with the spark-ignition Perkins-designed outboard motor prototype showed that increased seal wear occurred, due to corrosive air conditions (salt spray exposure) and the lower running temperatures encountered under part-load conditions. Lubrication was suspected of further contribution to the problem. However the performance of the engine as an outboard motor was said to be encouraging compared to the conventional two-stroke engine – the unit was smooth and quiet, clear of blue smoke under low power conditions, gave good response and had favourable torque characteristics. It was however a long way from achieving the standards of reliability and endurance needed. The Wankel power head was fitted to a lower unit taken from a Johnson ‘50’ motor, and the engine was fitted on to a small military assault craft, selected to allow easy access to the engine and to give working space afloat. With a crew of three the lightly laden craft ran up to 28-30 knots at 4850 RPM, using an 11 inch diameter x 11.5 inch pitch propeller.

The ‘horizontal’ engine version was a derivation of the original outboard configuration, with the intention of developing an engine suitable for use as an inboard or ‘Z-drive’ application. Minimal design changes were made, these mainly affecting the oil lubrication circuit and water cooling drainage. Unfortunately water flooded into the eccentric bearing area, causing severe damage. Although improvements had been designed, no further work was undertaken.

The final testing on the spark ignition versions was on a high compression ratio unit with premium petrol. Considerable problems were experienced, including seal sticking and high wear of the apex slots in the hypereutectic aluminium rotor, which caused loss of sealing. The rotor chosen had been designed originally for the diesel version, with a ‘pimple’ combustion chamber and an effective compression ratio of 12.35:1. Exactly why this combination was chosen remains a mystery. The data obtained appears to have been of little practical use, showing retarded ignition characteristics, poor spark plug positioning and susceptibility to detonation. Due to the poor sealing performance the compression pressures were reduced and pumping losses increased.

A small amount of rig test work was undertaken, using a motored engine with a Pyrex window in place of the lower side housing, originally to study combustion in the diesel cycle. Flame travel phenomena were assessed for the petrol version.

Design evaluation was undertaken to determine the best way to convert a PRW.500 petrol engine to diesel form for initial experimental work. Unfortunately no notes have been located to understand this 1963 work. The main outcome has been recorded however as favouring the use of a low K-factor pressure-charged engine.

Thus one engine was converted to run at about 13.5:1 compression ratio with pressure-charging to study the diesel cycle. It was accepted there would be major mechanical limitations encountered, but it was judged that even limited information would be valuable. The engine ran first on 1^st January 1965.

One interim report dated 24^th August 1965 entitled ‘Evaluation of the ‘Diesel’ Wankel Engine –Part 1. A Study of Combustion’ has survived. The introduction states that ‘this is the first of a series to be issued on the evaluation of the Wankel engine operating on the compression ignition cycle’. It was to be introductory to the whole programme of future study, highlighting the areas in which further investigation is required and outlining the more important experimental techniques to be employed. However no further reports appear to have been issued.

From the limited testing done however, conclusions were drawn suggesting that there was very much work needed on the design of a more suitable engine before more meaningful results could be expected. In particular the design of the combustion chamber, positioning of the injector and better thermal insulation needed to be addressed. Not surprisingly, the specific fuel consumption attained was disappointing, although the engine ran up to 3000 RPM with up to 12 PSI boost.

The intended new engine design would have taken the work further, with improved mechanical reliability from lessons learnt and greater inherent flexibility to explore combustion characteristics, etc. However this never took place as the whole project was terminated, due mainly (as far as one can judge) to pressure from Massey-Ferguson to drop this engineering side-track to concentrate on development of the conventional engines. With the project cancelled the prototype engines were donated to interested parties during early 1966. These included Kings College, London and the Royal Military College at Shrivenham. It appears that two units were retained for the ‘Perkins Museum’ – unfortunately exactly what became of these units is now a mystery, certainly no trace can be found!

Interest in the Wankel engine within Perkins engineering circles, especially the research area responsible for forward and future projects, did not disappear completely however. A number of later articles, cuttings and comments were retained in the files, including the work at Rolls-Royce on their two stage engine. Most of these records are from the 1970s, although even in the 1980s there was some contact between Perkins senior engineers and the Norton Motorcycle Company during the time when the latter’s interest in racing and production motorcycles had extended to the possibilities of fitting Wankel engines to unmanned drone aircraft – the Perkins involvement being with respect to using diesel rather than gasoline to enhance aircraft flying range. (No record of this involvement has come to light beyond the personal recollections of one of the engineers involved however!)

With the benefit of hindsight, it is possible to conjecture that dropping the diesel side of the project was sensible. With the limitations of combustion chamber shape, surface area to volume limitations, etc., it seems unlikely that a successful compression ignition engine would have been possible. With the very limited success of the Wankel spark ignition engine in other applications, one wonders too about the outboard engine, although some success could have been achieved. With today’s emphasis on emissions and economy it seems unlikely that better results would be achieved, even with the availability of modern computer techniques.

It is fascinating to be able to record a little of this unusual product story, although few facts remain beyond isolated memos and reports and some photographic evidence! If any of our readers can shed more light, we would be pleased to add fresh information to the historical records.

David Boulton November 2010.

Wankel Engine parts Wankel Engine testbed