The Elfin 50

by Adrian Duncan

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    Production history

Here we examine the 0.54 cc Elfin 50, a very rare little diesel from the 1950's which showed great promise in design terms but failed to make the grade in the marketplace for a variety of reasons. In consequence, it is undoubtedly the most elusive and little-known member of the British 1/2 cc diesel family of its era.

The Elfin 50 was the smallest-ever member of the Elfin family of model diesels produced by Aerol Engineering of Henry Street, Liverpool 13. The history of this company has been recorded in our companion articles covering the later Elfin ball-race models and company founder Frank Ellis. For convenience, we will summarize the main points here, but for more detail about the company's early years, visit the Elfin Ball-Race page.


Aerol Engineering was established in late 1946 by a gentleman named Frank Ellis, with financial backing from Colonel Thomas E. H. Davies of the old-established Liverpool cotton brokerage firm of Davies, Benachi & Co. The Aerol company began life as an adjunct to a scrap metal business which Frank Ellis had previously established with a number of associates. The workshop was equipped with a small inventory of well-used machine tools which had given its best to the war effort before becoming surplus and hence cheaply available following the conclusion of hostilities. This well-worn equipment was originally housed in a metal shed in one corner of the scrapyard! Later an expanded brick-built factory was constructed on the same site.

Using these undeniably basic facilities, production of model engines commenced in mid 1947 with the introduction of the 2 cc Aerol Gremlin diesel. This was soon followed by an updated model called the Aerol Hurricane. The Aerol series was finally supplanted in mid 1948 by the first of the Elfin range, the iconoclastic 1.8 cc model.

Many years later in around 1990, family friend Jim Woodside taped an interview with company founder Frank Ellis in which Frank (then some 85 years old) was very forthcoming about this and many other matters relating to the affairs of Aerol Engineering. We all owe Jim a great debt of gratitude for his care in preserving this material and for his kindness in making it available for study. Our summary of this interview may be found elsewhere on this site in our Frank Ellis tribute pages.

Frank recalled that he was very impressed with the general design of the radially-ported front rotary valve (FRV) engines of Ray Arden, seeing them as pointers towards the future in contrast to the sideport engines which then dominated the British market. The Arden influence is very obvious in the design of the early Aerol engines and their 1948 Elfin successors with their radial mounting, 360 degree porting and updraft FRV induction. All of these early radial-mount units featured very sturdy gravity die-cast cases.

In 1950, designer Ellis abandoned the Arden-influenced radial-mount designs in favor of far more conventional beam-mounted engines having 1.49 cc and 2.49 cc displacements and featuring downdraft FRV induction along with pressure die-cast cases. Since the beam-mount 2.49 cc model did not equal the performance of its radial-mount predecessor, it has often been asked why the company made this change. In his later reminiscences, Frank stated that the sole reason for the switch was that demand was rising and the company was under pressure to make more engines. The revised pressure die-cast engines could be manufactured at a faster rate with the equipment available. However, the die-cast cases were less sturdy and far more prone to distortion than the earlier gravity die-cast components. In hindsight, Frank felt that they should have continued to develop their former designs, even if it meant accepting lower production rates.

The plain bearing beam mount Elfin 1.49 cc diesel was a huge success and was the most popular Elfin model of them all. It remained in production for some 7 years, achieving an enviable record of stellar competition successes along the way. These triumphs included first place in the 1952 World Free Flight Championship as well as a very creditable fourth place in the same event in 1954. The main Achilles Heel of the 1.49 was a decided variability in quality, doubtless arising from the enforced ongoing use of well-worn production equipment. A good one was really good, but not all of them came up to that standard ...

Despite the 1950 switch to the more conventional beam-mount designs, Frank Ellis had lost none of his admiration for the Arden layout. Moreover, circumstances were unfolding which would give him one more opportunity to express himself in that direction. In October 1950 a really significant event occurred in the context of the British model engine manufacturing industry—Alan Allbon introduced his trend-setting 0.55 cc Dart model, thus setting a fashion for half-cc diesels in England. International Model Aircraft soon joined in the fun with their 0.5 cc FROG 50 model, and E.D. too were not far behind with their 0.46 cc Baby.

Frank Ellis took note of the very positive reception of the Dart and decided that if the next British modelling fad was going to be 1/2 cc diesels, he was not going to be left out! He decided to enter this field himself with a new model which would prove to be his most openly Arden-influenced design of them all.


The Elfin 50 was announced shortly after the appearance of the Dart, although its actual entry into the marketplace was delayed until January 1952, likely as a result of production difficulties, of which more anon. When it finally appeared, there could be no denying the fact that to all intents and purposes it was a reduced-scale diesel version of the famous Arden spark-ignition and glow-plug engines! It featured an identical conical radial mount with screw-in backplate, 360-degree porting, updraft FRV induction and an under-slung plastic tank, all derived directly from the Arden layout. The only major departures in fact were the use of compression ignition coupled with a plain bearing instead of the Arden's twin ball races.

Frank Ellis clearly favoured under-square engines, and the new 50 followed that trend. The measured bore and stroke of the illustrated example are 8.36mm x 9.78mm, giving a calculated displacement of 0.54 cc, a little above the nominal displacement, just like the similar-sized 0.55 cc Dart. This displacement was later repeated in Alan Allbon's excellent little A-S 55 of late 1959.

Apart from the Arden-inspired features described above, the Elfin 50 was basically a perfectly conventional radially-ported plain bearing FRV diesel of its day. As such, a detailed description does not appear warranted. Although it was basically a very compact little engine, its bulk was considerably increased by the presence of the under-slung tank and radial backplate mount. Without those features, the engine would have been remarkably compact. Checked weight all complete as illustrated without prop was 1.5 ounces (42 gm).

As supplied, the engine was clearly best adapted to free flight use—the standard tank would have been useless in a control line application. This may in fact have worked against it in terms of its marketplace acceptance. However, other factors appear to have contributed far more to its downfall, as we shall see in the following section.

Production history

The Elfin 50 was initially promoted quite vigorously, with advertisements appearing in Aeromodeller magazine more or less continuously from January 1952 to August 1952, after which it quietly disappeared from the market. It has always been assumed from this that the engine was not a success in the marketplace and was withdrawn for that reason. In fact, the real reason for the engine's disappearance is far more complex and interesting...

In the above-mentioned recorded interview with Jim Woodside, Frank Ellis clarified this very point in some detail. As stated earlier, the machinery used to make the engines was well-used wartime surplus equipment which had given its best to the war effort and had been obtained cheaply when Aerol Engineering started up in 1947. Basically, it was knackered to begin with, and by early 1952 it was well past it, having put in a further 5 years of hard grind making Aerol and Elfin engines. This explains the fact that the Elfin engines were well known to be a bit spotty from a quality standpoint, although if you got a good one, it was really good. The designs were excellent—it was inconsistency of production standards that let them down.

Frank recalled that initial tests on the Elfin 50 prototypes were extremely encouraging, showing that the little beastie could run with the best of them! Present-day experience bears this out completely—the engine is more than a match for any of its 1952 British half-cc competitors, including the Dart. But the problem was that like all small engines, the little 50 required an even higher degree of manufacturing precision than its larger relatives. And therein lay the problem! Despite intensive efforts, it proved impossible to produce this little engine in quantity using the tired equipment which was all that was available. An unacceptably high proportion of the completed engines proved to have manufacturing defects which precluded their being offered for sale. Even some of the ones which were released to the trade by Aerol Engineering were returned as un-saleable.

The company had invested quite heavily in the new model—Frank recalled that each new set of dies (which were produced by the same Blackpool firm which did the castings) cost them 500 (a chunk of change in 1952) before they saw a single casting! On top of this, the fact that they could only sell a proportion of the engines that they did make, coupled with the need to maintain a more-or-less competitive price (3 7s 6d, or 3.37 in modern terms), meant that they were actually losing money making this model. In addition, their reputation was under threat.

It was clear that if the 50 was to remain in production, the company would have to invest in new production equipment. However, they were still in debt for their expanded factory and existing equipment, hence being unable to finance the required new equipment themselves. Accordingly, they approached their original backers Davies-Benachi once again. Colonel Davies remained very well-disposed towards them and agreed to back the financing of new equipment, which was duly ordered. Problem solved, it seemed!

However, in one of those cruel twists of fate by which future events can be so greatly influenced, Colonel Davies unexpectedly died on May 5th, 1952—the very day on which the new machinery arrived at Henry Street! Having lost their financial guarantor, the company had no recourse other than to send it straight back on the same truck. Frank's quote: "If Colonel Davies hadn't died when he did, that business (Aerol Engineering) would still be going today!"

After this set-back, Frank decided that they had no choice other than to stop making the Elfin 50 and cut their losses. This action was taken with extreme reluctance, since Frank sincerely believed in the merits of the design. However, he felt that there was no option, and the consequence was that the engine suffered a premature demise, never coming close to repaying its development costs. We might re-phrase the earlier quote from Frank by saying that if Colonel Davies hadn't died when he did, there would be far more surviving original examples of the Elfin 50 today!

Years later, at the time of his interview with Jim Woodside (c.1990), Frank still held to the sincere belief that the Elfin 50 would have been a great success if they could have kept making it. He stated that the good ones that did get shipped found ready buyers and that market resistance was not a factor in his decision. As far as he could recall, the company only ended up selling a few hundred examples of the Elfin 50, which explains why it's such a highly prized and high-priced item among today's collectors.

Looking at this matter objectively, it actually appears quite probable to me that the engine would eventually have encountered a fair degree of sales resistance, Frank's views notwithstanding. The more or less simultaneous entry of four British manufacturers into the 1/2 cc diesel field quickly resulted in an over-saturated market in which only the best could hope to survive. In performance terms, the Elfin was indeed up there with the best, but this was by no means the only factor affecting the engine's sales potential. For one thing, the British marketplace had by then come down firmly in favor of beam mounting as the preferred installation arrangement. Moreover, the general layout with the under-slung tank forced the engine to be mounted in an upright position if the supplied tank was to be used. This would perhaps be OK for free flight, but the engine's relative bulk by comparison with its direct competitors as well as its radial mounting and inconvenient layout for mounting positions other than upright would likely have resulted in a progressive erosion of its position in the 1/2 cc marketplace unless modifications were made. However, other factors supervened before this could be put to the test.

The Elfin 50's tenure in the marketplace was so short that the engine was never the subject of a published test in the contemporary modelling media. I haven't run my own example for some years now, but my notes record that it was pretty much comparable to the category-leading Allbon Dart in the performance department, with if anything a slight edge in torque production at the lower speeds. I may get around to a re-test at some point, in which case I will append the test results to this article.


Due to the very low production which was actually achieved, the Elfin 50 is extremely rare today, especially in complete and original condition. Finding a good example is pretty much a matter of being in the right place at the right time with the right amount of purchasing power, a position in which I was fortunate enough to find myself in the dim and distant past.

The scarcity of original examples opened up a market niche for a replica production of the engine. The noted Swedish enthusiast Arne Hende took up this challenge, arranging for the manufacture of a series of replicas of the Elfin 50 many years after the withdrawal from production of the original. Arne's engines were made to a very high standard, hence being fine collectibles in their own right. There's actually a better chance of finding one of his Elfin 50's in mint condition than there is of finding a complete and original Aerol example.

The Elfin range continued for a further 5 years, the highlight being the appearance of the twin ball race reed valve models beginning in October 1954. However, the equipment issue continued to plague the company as the already-tired equipment became even more worn, and the resulting quality control issues led to increasing customer dissatisfaction. As of early 1957 the company gave up the struggle, and their last advertisement appeared in the January 1957 issue of Aeromodeller. They were still in debt to their various creditors and had to sell everything to get clear without declaring bankruptcy. The range was picked up briefly by Auto-Vaporisers Ltd. of Lymm, Cheshire, but they too threw in the towel in mid 1958 without ever re-introducing the Elfin 50.

The relatively few surviving complete and original examples of the Elfin 50 stand today as a testament to the enthusiasm of Frank Ellis and his unstinting admiration for the designs of the great Ray Arden. Anyone who is in a position to enjoy owning one of these fascinating and highly individualistic little units may indeed count himself fortunate.