aero and automotive engines and engineers
The Armstrong Siddeley Sapphire
The Sapphire Car
The Sapphire car engine was almost certainly the first car piston engine in the world to be designed, in part, as a result of considering the use of a gas-turbine as an automobile power unit!The company first considered the use of gas-turbines in cars in 1946, when it was suggested that an old Heppner scheme be adapted for automotive use. F. A. M. Heppner was a German refugee retained by Armstrong Siddeley during the war to work on highly complex gas-turbine schemes [6 turbo-fans with contra-rotating combined compressor/turbine wheels, suggested thrust - a mere 11,500lbs - and all that in 1943!] that would have been exceedingly profitable had they worked. Heppner had the unshakeable backing of both Sopwith and Spriggs (the senior directors of Armstrong Siddeley and its parent, Hawker Siddeley). Senior engineers, including the chief engineer [Stewart Tresilian], who openly questioned the viability of Heppners schemes, were quite simply required to leave in early 1942. Heppner was formally declared insane in 1945. Shortly afterwards, Bill Saxton, by 1945 the Chief Engineer, told Spriggs that he considered that none of Heppners many patents were of any value. Spriggs asked, or rather required, him to reconsider his position. The result seems to have been a patent describing the use of a Heppner gas-turbine in a car. The advantage of the described pneumatic coupling within the gas-turbine [an illustration will eventually be put here] is that a gear box would not have been required, save for the steepest hills. Had it worked, it would also have been smoother than any piston engine.
However, I must stress that the unit was never made, and that it was not the late W. H. "Pat" Lindseys [the patentee, later Armstrong Siddeleys last technical director] idea. Someones name had to appear on the patent.
In the meantime, the car divisions engineers (especially [the late] John Densham) and sales staff - and Chapman, the companys overall day to day manager and later managing director - considered the new and otherwise generally splendid 16hp cars (Lancaster and Hurricane introduced in 1945) to be somewhat underpowered for the brave new post-war world, and especially one with the dohc Jaguar engine whose existence was known. This view was generally shared within the car division. Sid Allen, on the aero-side, and of rocket and vaporising combustion chamber fame, was asked to prepare an urgent report considering how the 16hp's output could be improved.
Paraphrased, Allen's January 1946 report was that the engine should be redesigned. For reasons that remain unclear, Sid Thornett was more in favour with senior management than the more able Fred Allard, who left in a bit of a huff and joined Singer. Thornett, who started car work in 1912 and was not an engine man, set about designing a nearly square (80 x 86 mm 23.8 hp RAC - high tax for 1946) 6 cylinder 7 main bearing aluminium engine of 2.6 litres (but referred to as the 2.5), which was very far from being a successful production job, despite the heroic efforts of John Densham, the car divisions talented experimental engineer. [Many of the experimental papers were found at the end of 1993]. A detailed account of the trials and tribulations of the ASM "2.5" were given in the last edition of "The Sphinx" [The Heritage Trust's, Coventry Branch, magazine]. All that needs be said is that had there been any way of making a go of the inherently flawed design, John Densham would have found it. It leaked both oil and water, overheated, suffered from chronic cylinder wear, bad consumption, bad fuel distribution between the important 1250 to 2500 rpm running range, and had valve timing and clearance problems. The position of the main bearings within the crankcase could be clearly felt by hand at most running speeds. John Densham had at a very early stage pointed out to Thornett that there should only be four main bearings [as in the Lagonda V12 on which the young Densham had been a draughtsman during 36-38], but Thornett was quite unable to understand why.
In some ways, almost a re-run of Colonel Fells Mk. 11 Deerhound. [The disastrous 7 x 3 21 cylinder 1500hp air-cooled radial of about 1938 with, as Dr. Harold Martyn painfully recalls, a deliberately flexible crankshaft ....]. You may be interested to know that before the war, that furthest outpost of the Hawker Siddeley empire, Templewood Engineering of Slough, designed a light alloy car. Overall design was by Stewart Tresilian, later ASM chief engineer (1939-1942). That project was almost certainly financed or part financed privately by Roy Fedden. The car was to have all independent rubber suspension [sic] and a 4 cylinder 4 main bearing massively oversquare 75 x 100mm 2.35 litre "aluminium" engine rated at 90bhp - this was the grandfather design of the 2.5 litre BRM 4 cylinder ohc engine. The designer in charge of the gear box was, and still is, Norman Barcham [later a well known aero-gear designer at Armstrong Siddeley, Bristol Siddeley and Rolls-Royce]. The project was unfortunately never completed.
On 15th March 1948, John Densham, on behalf of the car division,tested the new Lagonda 2.6 litre engine that had been designed by Donald Bastow, W. O. Bentley and others before the Lagonda company was sold to the David Brown Organisation. It generally compared very favourably with the ASM "2.5" aluminium unit. Whilst outwardly Armstrong Siddeley appeared to be interested in licensing the design, the actual motive seems to have been whether it was now worth pursuing a suggestion first made by Tresilian in mid-1939 when he became the ASM chief engineer that W. O. Bentley act as a consultant.
Bastow and Bentley had already been contacted by either Sopwith or Chapman and had completed various sketches before the Lagonda unit was tested. As W. H. Lindsey and others then at ASM [Mervyn Cutler, Dr. Harold Martyn, then head of the aero-engine Stress Office which also did some work for the car side, and John Densham] have recalled [in the early 1990's], the company wanted to be able to use Bentleys name as prominently as was legally possible and have the benefit of Bastows widely self-proclaimed experience. Lagonda had come seriously unstuck using Bentleys name in an advertisement towards the end of the war and were successfully sued by the Rolls-Royce subsidiary, Bentley Motors (1931) Ltd, which owned the Bentley name trade mark. I have a few copies of the case available for inspection tonight. It is interesting to note that the High Court Judge found as a fact after many days of evidence that there were very few people who were aware that W.O. Bentley was involved with the design of cars that had carried his name. It surprised me to be told be several W.O. Bentley devotees that Rolls-Royce had either paid the judge or the witnesses .... Some of these statements were, maybe unwisely, reduced to writing! The case report is called Bentley Motors (1931) Ltd v Lagonda Ltd and Walker Owen Bentley 64 (RPC) 33, especially page 39, line 48 to page 49, line 30. [RPC = Reports of Patent Cases, the case was reported in the 1947 volume and is available in its entirety on this link.]
As is generally well-known, Bastow and Bentley were then retained to design not only a 6 cylinder 3 litre car engine but also a completely new chassis and body. There is no time tonight to go into any detail of that project, save to add that whilst the engine very nearly produced its design output on its first test run, a feat almost unheard of, the power curve was unusual - this was later discovered to be due to an incorrect exhaust arrangement. However, there were serious heating problems in the head (though Bastow was much later to deny this or at the very least say that he did not recall any such problems). There was also a general lack of attention to detail, such as drives to the oil pump that sheared in cold weather. Further, there were little - but apparently annoying - points that did not conform to Armstrong Siddeley (or general motoring) practice, such as the wide use of B.A. thread screws in non-electrical areas instead of 3/16" and 1/4" BSF screws.
Whilst the Bastow/Bentley team were busy designing the exciting new engine and chassis, the car division [John Densham] continued work on increasing the output of the existing cars until the all-new model was ready. As has been set out in the Sphinx, these included trials with various forms of petrol injection whose results were disappointing, and the 18hp stop-gap variant (the 16hp bored out). As a matter of record, a decidedly sporty camshaft for the 18hp was designed by John Densham, but was never made available.
At the same time, the office of H. S. Rainbow, which looked at ASM future projects (mostly on the aero-engine side), was investigating the use of practical gas-turbines in the existing Armstrong Siddeley chassis. Their design was for a very neat two stage 30,000rpm centrifugal unit of 5:1 PR, 130bhp, and a practical (for car use) turbine inlet temperature of 1050K. Its weight was only 250lbs, very much less than an equivalent modern piston engine. The unit which would have taken the existing car to at least 96mph. However, its best projected fuel consumption was 6mpg. At 90mph consumption would have been 4 mpg! There was also the small problem that the design involved miniaturising a gas-turbine, which in turn means miniaturising already minimal clearances in the interests of efficiency. That was one of the designs four fundamental weaknesses, the others being consumption (obviously related to clearances), initial cost and then maintenance costs.
But in the same report, dated mid-1949, Rainbow compared his 130hp unit with the latest 1949 season Cadillac V8 5.4 litre 133 bhp unit. The installed weight of the V8 was more than three times the estimated gas-turbines weight, but their external dimensions were very similar. However, the Cadillac used at least three times less fuel and would have been very much cheaper to manufacture and maintain.
The company already had a V8 Buick convertible for use by senior staff, and there was a gradual, if hesitant at times, acceptance that increased power could be obtained by following more traditional and above all cheaper routes than that selected by Bastow and Bentley with their 3 litre DOHC engine.
It can not be overemphasised how important reducing the cost of the new car were to the company. This fact was constantly impressed on both the Bastow/Bentley outfit, and on Armstrong Siddeleys own car engineers, until the end of car production. It was a message that some of car engineers did not want to hear (or did not believe).
After a while, towards the end of 1949, the Bastow/Bentley project was finally halted, due to the estimated cost of both the Bastow/Bentley team and of the final car as a production job. This was almost certainly after a cheap-to-produce Chevrolet V8 engine was fitted by John Densham to an existing chassis as an experiment, with very acceptable results. Fred Allard was then tempted back to ASM to work on a new "in-house" car. Chapman, Sopwith and Spriggs decreed that the new all-Siddeley model had to be launched at the October 1951 motor show. Colonel Siddeley, who in effect had responsibility for the car division said that that date would be met. The all-Siddeley Armstrong Siddeley was proposed in internal a brochure of 4th November 1949.
Allard set about designing an engine that would produce at least 125bhp, and which was more economical to build but just as refined as it was hoped the AS Bentley unit would eventually have turned out to be. Both John Densham, by now the car divisions chief experimental engineer, and [the late] Mervyn Cutler, who a little while later was to return to Armstrong Siddeley to oversee the Sapphire car project as the car divisions Technical Manager reporting directly to Chapman, have confirmed that the machine tools then available for car production at Siddeleys were undoubtedly more suitable for the large scale production of an overhead valve unit than an overhead camshaft one. This and cost were the main reasons for choosing the OHV arrangement, albeit the relatively unusual one featuring a high camshaft with angled but usefully short and thus light pushrods. The other reasons that are usually stated, namely less timing chain noise and greater ease of servicing, were secondary at that time, but later eagerly adopted by the marketing people as the main reasons ....
Cylinder dimensions were square, to reduce engine size and thus weight, to enable a high engine speed at reasonable mean cylinder velocities, to allow suitably wide bearings and the use of large valves.
However, the first units did not feature hemispherical heads, but the Ricardo type squish head. Thornett was particularly keen on this feature after it was found to benefit his troubled ASM aluminium "2.5" design. However, Allard and Densham wanted to employ a hemispherical heads. The late Wilf Johnson used to recall how, when later challenged by Thornett, Allard would pray in aid learned thoughts on the subject of hemi-heads of a former Siddeley chief engineer [Stewart Tresilian] at the beginning of the war. A compromise was reached whereby both would be tried. As an aside, during 39/40, an all new car was being considered and at least one very advanced and luxurious prototype ["EYO 9"] made behind sheets in the tinsmiths shop. Dr. Rowell, general manager 1941-44, who was actually a car man, and C.S. Oliver the general manager until 1941, also seem to have been involved in that project, but no other details have survived save, probably, for two photographs. This slide is probably of that car. Later, Thornett, Allard and Holister, the then gear box man, kept a small design office going at Crackley Hall during the war. The first prototypes of their work appeared in about early 1943. John Densham found the distinctive recessed head lights of the 39/40 car just after it had been very discretely broken up in an aero-shop at Parkside and used them in one of his John Densham Riley Specials. [There has recently - 2000 - been some suggestion that EYO 9 was kept at a facility near Leicester for much of the war]
Returning to the Sapphire project, what may not be known is that two [sic] sizes of the 6 cylinder engine were designed: The 3.4 litre for use in the all-new car, and a version scaled down to 2.4 litres for use in the existing 18hp, though the 18hp was to have major changes to the body, especially at the front and on the front suspension. Much more work was done on the 3.4 than the 2.4, mostly for lack of money. It was realised from the outset that the 3.4 was the far more important project to the company. (For the avoidance of any doubt, this 6 cylinder 2.4 engine was not the protoype of the 4 cylinder 2.3 engine used in the later ASM 234 nor was it in any way related to the 2.3 engine used in the later ASM 236).
On the engine side, parts of the Bastow/Bentley design were utilised to save money. There is some suggestion that the Sapphire crank was inspired by the Bastow/Bentley design. Interestingly, a then outside consultant who had successfully re-stressed the Rolls-Royce PV12s, later Merlin, crank and who has been described by [the late] Walter Hassan as having a legendary reputation for having done so, had given advice to Bentley on the design of Bastow/Bentley crank. The design brief to Bastow/Bentley called for a crank that did not require a torsional damper - the lack of which was not then common on straight 6 cylinder engines.
On the chassis side, it was decided to use as much of the Bastow/Bentley design as possible, save that Allard (not Thornett) was not impressed with the great relianceplaced by Bastow on the central X section for torsional stiffness in that design. Bastow was then known as the High Priest of the X or cruciform chassis - and not only at Armstrong Siddeley. Several engineers have said that Bastow didnt always get it right! Allard placed so-called old fashioned transverse members in what he considered to be the correct positions and immediately improved torsional stiffness by a substantial amount. John Densham is still impressed  by the improvement. Allard also changed several of the steering and front suspension angles by varying but small amounts - all to good effect. The then expensive (for a big car) rack and pinion steering was changed to the less expensive Burman recirculating ball box. Cheaper brakes were [unfortunately and against John Densham's advice] substituted. The optimal position of the rear axle in relation to the leaf springs was found so as to give the desired amount of understeer. Bastow and Bentley originally wanted to use independent rear suspension on the AS Bentley design whilst Bentley had also suggested the de Dion set-up as a better alternative to the traditional so-called live rear axle set-up with leaf springs. The de Dion set-up was also briefly considered for the Sapphire, but was again rejected on cost grounds - as was Allard's wish at least to experiment with the sliding tube de Dion [yet further manufacturing costs as well as patent royalties]. The sliding tube version did not appear on any mass produced car until much later when Rover adopted the idea [virtually claiming it as their own idea].
However, whilst all this excellent work was being done, the day when the completed design would be ready for display was slipping seriously. The first engine only went on test on 7th September 1950. By about March 1951, it was decided not to proceed with the Squish head. By then 41,704 miles had been completed in test cars with 3.4 litre hemispherical heads, namely the "Grey Whitley, the Green Whitley and the Graber drophead coupe". The coupe had been specially commissioned after the war for use as a very special 2 litre demonstrator for favoured clients, overseas agents, and distributors. As an aside, Mervyn Cutler said that the Grabers silvery grey body was really very pleasant to look at and he greatly enjoyed driving it, once as far as Switzerland in about 1947/8. Returning to the engines teething problems with the hemispherical head, these included noisy valve gear, poor distribution at low speeds, and loss of power in the then newly redesigned hemispherical unit.
By October 1950, Chapman and the other directors realised that there were going to be problems in exhibiting at the October 1951 Motor Show, due to a delay in deciding the final design. This was mainly down to a long running squabble between Allard and Thornett that I will refer to in a little while. This delay in turn would lead to a delay in the issuing of production drawings and thus to a delay in ordering materials - then a complex process due to the continuing post-war government material restrictions. To make matters worse, Sopwith and others was making adverse comments about the Whitleys suspension! By the end of the year, Chapman was emphasising the need for still greater mileage testing.
By May 1951, 67,112 miles had been completed in the test cars with the 3.4 litre hemi, and this had increased to 69,543 by July 1951. It was still hoped to put the car into production by February 1952, despite Chapman complaining about the serious delays in 1950 and the continuing delays in issuing production drawings. A final specification had still not be chosen. It was noted that the slow running characteristics of the engine were unacceptable. In the meantime (7th June 1951), two of the old AS Bentley chassis with 18hp engines and special Mulliner bodies were transferred to the service department, Experimental retained one 3 litre engine and one chassis with the 3.5 litre Chevrolet engine. All other parts are recorded as being disposed of.
In mid-1951, John Denshams suggestion of a name for the car - The Sapphire - to give the impression of a precious stone and a link with the successful turbojet of the same name made by the company was rapidly accepted, especially by various departments involved in financial considerations on both sides of the business ....
By September 1951, total tested mileage was just over 73,000. It was now clear that there was a weight problem and great efforts were made to bring about a reduction. In the end, at least 268lbs were lopped off without ill effect.
Chapman and the other directors were becoming increasingly worried about time slippage. This of course also affected the material supply position, materials still being not freely available. When it became clear that the new car would not be ready for the October 1951 show, the directors decided that Col. Siddeley, an ill man, was to take a major part of the blame and it is sad but fair to say that he was eased out of the picture - he also did not see eye-to-eye with the then slightly brash John Densham. By October 1951, car operations were running at an overall loss. Chapman, with the approval of Sopwith, had already asked Mervyn Cutler, who left the company for a second time by mid-1949 and become deputy chief engineer of engines at Morris, to return and head up the project on the technical front. Mervyn Cutler and John Densham have recently recalled that Allard and Thornett often used to try and score points off each other and thus did not keep their eye on the ball - a settled specification was required in the very near future if the car were to be displayed at the 1952 Motor Show. Allard was required to submit to each Car Meeting a summarised version of John Denshams all important daily reports (which were of the greatest use). Later, Chapman was to request the same be delivered directly to his desk each morning.
By January 1952, three new cars were allocated to the experimental department, and John Densham was finally able to carry out extensive testing and modifications. He had been pressing for permission to carry out these seemingly obvious stages, but had been told that there was no money and in case it was not necessary!! The figures speak for themselves. Total test mileage very quickly increased to 111,115. It was hoped to have 25 sets of new cars by the end of March, and then further supplies at the rate of 42 per week, but this inevitably slipped back. Tooling costs were estimated at very nearly £250,000. Chapman noted, no doubt with concern given the anticipated October launch, that the actual expenditure on tooling was still low, very low.
By early April 1952, the 2.4 was finally shelved as a production job, but 3.4 test mileage had increased to 143,668. It was during this time that the Church played a small but important role in the development of the engine. The distributor was originally mounted much lower on the engine. Every weekend, John Densham, whose vital role in the successful development of the car as produced cannot be over-emphasised, would take a car for endurance runs. One Sunday, a little while before lunch, he was driving the car across a narrow ford. The distributor was flooded and the car came to a halt in the middle of the ford. Whilst he set about drying it, the local vicar arrived in his car. By the less than godly language used by the good vicar, John Densham was left in no doubt whatsoever that the vicar was going to be late for his lunch. The distributor assumed its high up production position within a matter of days after that.
At about the same time, Chapman asked Cutler to consider a 4.5 litre V8 engine design [nothing to do with the November 1959 all-aluminium V8 ohc design]. Whilst a report was prepared on 17th April 1952, there was no great enthusiasm given the slow development until just a few months before. An updated version of the current 18hp car with the same chassis and engine, but with a modern body and coil IFS, was also considered at this time. The company was keen to dispense with torsion bars due to the difficulty and expense in machining and matching bars, the production complications of building a torsion bar i.f.s and a need to reset after some hundreds of miles. As another aside, Lagonda had had enormous difficulties in 1937 finding anyone at all in the UK willing to make the 5 bars for their V12, and initially had to reject over 66% of the bars. At about the same time a three valve head for the Sapphire had, at Fred Allard's request, been designed by Stewart Tresilian, whilst the latter was still a consultant at BRM though soon to become assistant chief engineer at Bristol (aero) Engines. [Fred Allard was one of only a very few ASM employees or ex-employees to attend Tresilian's funeral in 1962]
By 27th May 1952, Sopwith was doing much testing in his car as well. An in-house three speed synchronised box had been on the books, but was then replaced by a four speed in-house unit, that itself was replaced by the eventual Rootes/Humber Box. A steering problem that no-one (including Allard and Densham) could solve (or even find the exact cause of) was successfully resolved by the late W. H. ("Pat") Lindsey, the brilliant ASM chief aero-engineer, later to become the overall company technical director [and who was brought in at the last moment over the Star Sapphire engine].
Whilst on the subject of boxes, an enormous amount of work went into developing the electro-mechanical mechanism for the finger-tip preselector box. This was done as many who saw the Bastow/Bentley car chassis were impressed with the Cotal box that featured such gear change. Later, this preselector box did not prove to be that easy to manufacture as a production job.
The entire time, everyone, but above all Chapman and John Densham, was keeping a close eye on competitors' cars, and inevitably the Jaguar Mk. VII - which was acknowledged as a fine piece of engineering and able to be produced at a highly competitive price. However, not all were too worried that the Sapphire would be severely disadvantaged, as by now the Jaguar had the reputation of being a certain sort of Bentley ("The Wardour Street Bentley", etc), and a "real" English man would not want to be see dead in one - all very politically incorrect in the 1990s [and beyond].
It now looked certain that the car would be ready for the October 1952 show - but questions remained about production. May 1952 car complaints were the highest ever on record. The only remaining serious known problem was preselector gear box noise in neutral and judder in take up. Chapman said that the box was unacceptable, and he wanted an aero-engine outlook to the problem - which happened.
By late September 1952, the test cars had completed 215,217 miles and 1602 engine hours on the test bed. The Hobbs automatic box was being investigated, and a licence was eventually taken - but that is another story. Mervyn Cutler was not happy with the braking performance, but there was presently no further money available to rectify the situation. He also wanted to consider disc brakes [sic]. These were considered in 53 and 54, both on paper and on actual Sapphires. Interestingly, the [mainly aero-engine] Labs under [the late] Doug Manndid sophisticated tests for BRM on their discs (whose disc layout, including the rear "bacon-slicer", had been suggested in 1938).
The Car was very well received at the Motor Show, though, perhaps not so surprisingly given the financial constraints, the twin carburettor model on which much work had already been done was not announced. Really rather fine wines were served in liberal quantities at the press launch. Surprisingly, the Gentlemen of the Press severely damaged only one of the demonstrators laid on after (!) lunch. The car was driven at speed straight at one of the old style large roundabouts. It took off and landedin the middle on its side. Motoring Press ethics being what they were, no-one ever reported the incident. On the darker side, Chapman had to reveal that a loss on the combined sanctions of the first 2000 cars was going to be in the order of £107,000.
But not only was the car well received, the faults in early production were all of a minor nature save for changing the crank and its case slightly (due to following too closely the design concept Bastow/Bentley crank but with a quite different crank case??? - suggestion that the same crank consultant was retained for the rework design), and the paintwork. The latter was due to the paint. The paint manufacturers in the end had to pay compensation to the company. The only early problem to be marked "URGENT" were very stiff switches!
Given the financial and time constraints imposed on the project, I do hope that you will agree that the Sapphire that did eventually appear was a magnificent piece of work.
© Richard Hodgson 1994, 2000 - may not be reproduced in whole or in part without permission