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Danske Model Motoren – Classic Danish Model Engines By Adrian Duncan and Luis Petersen
It was my personal interest in the Viking engines from Denmark that got this project started way back in 2016. My original intent had been to confine myself to setting out the history of the Viking range. However, to do that I realized that I would need help from some knowledgeable individual(s) in Denmark. Immediately I thought of Danish team-race expert and multi World Championship engine builder/tuner Luis Petersen, who has become a valued friend and colleague over the years. I have published Luis’s work before in the form of his most interesting 1977 comparative test of a number of then-current (and now classic) team race diesels of the mid 1970’s. Recalling this article, I had little doubt that Luis would be the right guy to help out with the Viking project. When I first contacted Luis in early 2016 to see if he could assist me in the preparation of an article for this web-site covering the Viking engines, his initial response was to send me a copy of his own earlier Viking article which had originally appeared all of 26 years previously in a 1990 issue of the Danish modelling magazine “Modelflyvenyt” (issue 1990-1). Naturally, the original article was in Danish, a language with which I have no familiarity. However, Luis very kindly agreed to assist by providing a translation of the earlier article for my reference and editing. It’s hard for me to find the words to express my gratitude.
My good friend Lars Gustafsson from Sweden also got in on the act by providing scans of a number of Swedish advertisements for Danish engines, complete with English translations. This did much to inform my research into the penetration of Danish model engine ranges to other Scandinavian markets. Thanks, Lars!! All of this information was far too interesting to go unused, since it added a great deal of historical context to the Viking story. Consequently, I have elected to create a completely new article which combines Luis’s original 1990 Viking material with the additional information that he, Jens and Lars subsequently provided on other Danish model engine ranges from the pioneering era. The resulting article is an overview of the early years of model engine manufacturing in Denmark. We'll be examining the early origins of the model diesel as well as the history of model engine manufacture in Denmark up to the point in 1950 at which the Viking range first appeared. I've presented our in-depth coverage of the Viking range in a separate article to be found elsewhere on this website. Readers whose interest is confined to the Viking range are directed to that linked companion article. Background
Some ten years later, Thalheim went into production with a series of model engines which were marketed from 1938 onwards under the ETHA label, derived of course from Thalheim’s name rather than from an English rendition of a primary ingredient of the engine’s fuel! These appear to have been the world’s first commercially-produced model diesel engines. It’s a bit of a mystery why it took Thalheim ten years to actually begin to capitalize upon his patent …..... most likely the Great Depression which began in 1929 had something to do with delaying his market entry until 1938. Maris Dislers' review and test of the replica ETHA 1 diesel by Richard Gron may be found elsewhere on this website. During the interim, the idea of utilizing compression ignition specifically for model engines had surfaced independently in Germany. In 1937 the talented model engineer Be that as it may, by the end of 1937 Eisfeld had built a successful prototype having a displacement of 15 cc (0.915 cuin.). This engine ran on a fixed 22:1 compression ratio and was equipped with a high-pressure injection pump and a needle injector. When properly adjusted, it apparently ran very well on regular full-sized diesel fuel. A promising start, but further development of this remarkable engine was halted in view of the far greater ease of manufacture and superior dependability of the conventional spark ignition engines of that time. Even so, following the onset of war in 1939 and working in collaboration with A. Thusius (who went on to produce model diesels under his own name), Eisfeld did resume his model diesel experiments, citing his reasons for doing so as the unreliability of the miniature accumulators then available as well as the problematic availability of dry batteries under wartime conditions. Eventually in 1942 he produced an amazing and successful 3.7 cc (0.225 cuin.) injector-equipped true diesel prototype suitable for model aircraft. Reportedly this unit weighed no more than a comparable spark ignition model with its ignition support equipment. Its compression ratio was a daunting 23:1 - starting must have been fun!
The Eisfeld model diesels were produced in a range of displacements from 0.5 cc all the way up to 10 cc. All of these models were made to a common basic design. A considerable number were manufactured for use by the Hitler Youth organization in promoting air-mindedness among its members. Production of these well-designed and finely-made engines continued for some time after the war. Several examples found their way to Britain, where they were highly regarded by Col. C. E. Bowden and others. In passing, it seems worth commenting upon the surprising degree to which model diesel experimentation and manuacture continued in Germany well into the wartime period. Names like Eisfeld, Kratmo, Kemmerling, Thusius and Mack-Madie come immediately to mind, and there may have been others. According to Col. Bowden, even the famed Mercedes automobile company got into the act by making a high-quality one-off model diesel engine for none other than former WW1 aviator Hermann Goering! Quite a contrast to the situation in wartime Britain, where model diesel experimentation had to await the conclusion of the conflict before really getting off the ground. Despite its later prominence in the field of model diesel design and production, Britain was very much a Johnny-come-lately in this field.
The technological success of the ETHA engines naturally inspired others to have a go for themselves. The Dyno 2 cc model manufactured in Switzerland by Klemenz-Schenk (whose main business was the manufacture of bicycle lighting dynamos, hence the engine's name) was one of the earliest spin-off products, being developed between 1938 and 1940 and making its market debut in 1941. It was a considerable step forward from the ETHA designs, being both smaller and lighter as well as having a higher specific power output. As time went on, the Dyno became one of the most widely-imitated early model diesel designs of them all, as we shall see. Peter Scott has quite credibly noted that the number of surviving Dyno copies and clones doubtless exceeds the number of originals by a considerable margin!
News of the new technology also reached neutral Sweden in 1942, along with an actual example of the Dyno 2 cc engine which somehow crossed war-torn Europe to come into the possession of Gunnar Fahlnäs, then the editor of the popular Swedish technical magazine “Teknik för Alla”, which was widely circulated in all of the Scandinavian countries. Impressed with the performance of his Dyno, Fahlnäs Ivan Rogstadius was soon followed by other Swedish model diesel experimenters. I’ve recounted the story of one of my personal favourites, the improbably-named Swedish Jack-of-all-trades Giancarlo Pinotti, in yet another article to be found on this website. There was also the 1944 Västeråsdieseln 2 cc model produced by the Västerås-based Johansson brothers, which was the precursor of the Komet range which will be the subject of another detailed article to appear on this site in due course. In addition, the prominent Swedish model dealer Hobbycirklarna of Finally, in 1944 the Stockholm model supply house of Svedfeld & Co. began advertising a model diesel which bore a striking resemblance to the published Rogstadius design. Although this was apparently referred to by Svedfeld as the “Typhoon” model, the illustration which accompanied the advertisement bears the unmistakable Rogstadius stamp, also bearing an uncanny resemblance to the early Danish Mikro diesel, of which more in the following section. Despite the fact that both Norway and Denmark were under German occupation at this time, some information regarding model engine developments in other countries was sporadically available to enthusiasts in those countries from German, Swedish and Swiss sources. In Norway, Jan David-Andersen first became aware of the application of compression ignition to model engines in 1943, most probably from his reading of Ivan Rogstadius’s 1943 articles in “Teknik för Alla”, which remained in publication throughout the war and was read throughout Scandinavia. I’ve documented the David-Andersen story in yet another separate article to be found on this website. Another pioneering Norwegian model engine maker was Øivind Andersen (no relation), who was actually the first series producer of model engines in Norway, albeit on a very small scale. His story is included in the above-referenced article about Jan David-Andersen. Pioneering Developments in Denmark
Contrary to the situation in many other countries under German occupation, Denmark was initially viewed by the Germans as a neutral protectorate rather than as a conquered hostile nation. Consequently, most Danish institutions continued to function relatively normally until the summer of 1943. Unlike the situation in Norway, both the Danish Government and the King remained in the country in an attempt to protect the Danish people by somehow maintaining an uneasy working relationship between democratic and totalitarian systems. However, this proved to be impossible in the longer term, since the Danish population became increasingly hostile to the occupying power, particularly after the tide of the war began to turn against Germany in 1942. The final straw was an August 1943 demand by the Germans that (among other things) the death penalty be instituted for Danish actions judged by the Germans to constitute sabotage. Understandably, the Danish government refused to co-operate with this and other hard-line demands. Consequently, on August 29th 1943 the Germans officially dissolved the Danish government and instituted martial law. Thenceforth Denmark was treated by the Germans as a hostile occupied country. An early consequence was the German attempt to round up Danish Jews beginning in October 1943. Thankfully, most of the Danish Jewish population (around 7,000 in all) eluded this round-up and were secretly relocated to Sweden by sea during the following months.
An example of one of these units is pictured at the left. This very well-made example is one of a few such engines which were constructed by employees at the Danish Marine Workshop on the basis of Ivan Rogstadius's plans. When the subject of commercially-produced Danish model engines comes up nowadays, most people from outside Denmark immediately think of the Viking range and stop there. However, the Viking engines were actually relative late-comers. The fact is that Denmark was as well supplied as any other country with a Although a few model engines may have been individually constructed in Denmark during the early to mid 1930’s, the country’s first documented commercial-scale model engine manufacturer appears to have been Carl Rose, who had a pre-war hobby supply business called Modelmateriale located in Tarm on Denmark’s west coast. Rose entered the model engine field prior to the outbreak of war with a series of spark ignition models which first appeared in 1938. He went on to By the outbreak of war, Rose had reportedly sold some 200 CEROS model spark ignition engines having displacements ranging from 4 cc to 10 cc. When the supply of miniature spark plugs dried up following the outbreak of WW2 and the subsequent German occupation of Denmark, Rose began experimenting with model diesels, reportedly making his first such engine in 1940. However, he does not appear to have followed up on this concept until some time after the war, leaving the field open for others in the interim. It seems worth mentioning that an example of Rose's very first model diesel from 1940 was still retained at the CEROS factory when it was visited in the winter of 1950/51 by staff of the Danish modelling magazine "Teknik for Alle". The engine had clearly seen a lot of use, because it had reportedly accumulated over 100 running hours by that time. According to the writer of the report on this visit, which appeared in the February 1951 issue of the magazine, this engine remained in perfect condition despite all this running. In 1946, following the conclusion of WW2, Rose established a small precision engineering business in premises located at Håbets Allé 10 in Brønshøj, a suburb of Copenhagen. The primary business of his new operation was apparently the manufacture of precision mechanical components for the radio industry. However, model engines were in Rose's blood, and a proportion of the company's equipment and human resources continued to be applied to the small-scale production of model engines on the side.
Soon after the 4.9 cc glow-plug model appeared, Rose returned to the diesel fold. He did so by developing a neat and compact 3.5 cc crankshaft front rotary valve (FRV) diesel model, which turned out to be the final CEROS product, at least by that name. This engine appeared in the winter of 1950/51 but did not remain long in production, surviving for only a year or two at most. It bore a striking resemblance both in design and appearance to the contemporary AMCO 3.5 PB model from England. A full review and test of both the CEROS 4.9 cc glow-plug model and the CEROS 3.5 cc diesel will appear on this website in due course. Although they were manufactured in relatively small quantities, the CEROS engines acquired a good reputation among Danish modellers - note the CEROS advertisement in the previously-reproduced photo of the Kastrup tether car track. At the present time, I am unable to state with any authority exactly when CEROS model engine production ended, but they seem to have disappeared from the marketplace by the mid 1950's. A separate article covering the CEROS engines in greater detail will appear in due course on this web-site.
Although the actual manufacturer of the Jaguar 2.5 BB was not named in Truedsson’s catalogue entry, there is some evidence that Carl Rose may have been responsible for this engine. The CEROS 3.5 cc diesel model mentioned above had a very similar cylinder porting arrangement. Moreover, Luis Petersen has found a reference to Rose having made a limited number of smaller units (i.e., less than 3.5 cc) specifically for team racing. It seems not unlikely that the Jaguar 2.5 BB was that very engine. If any reader can confirm this possibility, please get in touch!
At that point in time, Eli Andersen (then aged 28 years) established a small workshop in the town of Kolding, applying the Diesella trade-name to the engines which were manufactured there by himself and Jeppesen. The fledgling Diesella company was located in a tiny workshop on Sydbanegade which According to the previously-noted January 1944 “Flyv” article, the Diesella 2.5 cc model entered production in November 1943. This almost certainly made it the first model diesel to enter commercial production not only in Denmark but in any Scandinavian country, since Sweden’s first commercially manufactured diesel, the Pinotti GP 1.5 cc model, did not enter series production until early 1944, while Norway’s first series manufacturer Øivind Andersen (no relation) did not enter the market until a little later in 1944. The fact that Eli Andersen saw commercial potential in the introduction of a model diesel at this time (after the German crack-down of late August 1943, remember) is significant in that it clearly indicates the existence in Denmark of a market for such products even under increasingly harsh wartime conditions. This in turn implies that aeromodelling remained alive and well despite the progressively more difficult conditions of the occupation. Perhaps some members of the German occupation forces were themselves potential customers. It would be interesting to learn the extent (if any) to which genuinely interested members of the German occupation forces (of whom there were doubtless many) were accepted as fellow model enthusiasts rather than as mere armed interlopers in occupied countries such as Denmark and France, to name but two. The perceived strength of the market which existed at this time is underscored by the fact that Eli Andersen felt able to set the price of the Diesella at no less than 115 Danish krone (kr., or DDK). To put this in perspective, Luis Petersen tells us that in 1940 one could rent a 3 room flat in Denmark for 85 kr./month!!
While retaining a certain degree of Dyno influence, the Diesella embodied a number of original design features and was considerably “prettied up”. A notable feature was its massive streamlined main bearing housing which featured a recessed prop driver along with a ball race crankshaft. The engine's styling was complemented by a nicely streamlined metal fuel tank at the rear. The visual effect which this streamlining created was quite pleasing. The engine was also distinguished by having a single exhaust port discharging through a tubular stack on the right hand side of the upper crankcase. That said, some Reported bore and stroke measurements of this engine were 13 mm and 18 mm respectively for a nominal displacement of 2.39 cc. Although it is generally (and correctly) referred to as a 2.4 cc unit, the manufacturer’s identification plate claimed that this model had a displacement of a full 2.5 cc. No need to split hairs, one supposes! The engine reportedly weighed in at a fairly healthy 200 gm (7.06 ounces) ready to fly. Cited output was 1/6 BHP @ 4,500 rpm. If accurate, this figure implied a pretty serious level of low-end torque development! Personally, I suspect a little exaggeration here ............... The Diesella engines were reputedly very well made. However, their further development stagnated after the war as Eli Andersen became interested in expanding the scope of the business during the early post-war period. Consequently, it appears that only some 200 examples of the Diesella 2.4 cc model diesel ended up being manufactured, making it an extremely rare engine today. As with most other Danish model engines at this time, many of these units were equipped with flywheels for car or boat use. A few examples seem to have been converted to glow-plug operation at a later date.
The Andersens had long had an interest in autocycles, going back in Eli’s case to 1927 when he constructed his first such vehicle at the tender age of 12 years using an old motorcycle engine, a used pram wheel and a drive belt “borrowed” from the coffee grinding mill in his father’s grocery store in Lunderskov! Once established in their enlarged premises, the Andersen brothers’ attention soon switched to this line of business, which appeared commercially promising due to the fact that one needed a permit to buy a car in post-war Denmark. Such permits were difficult to get, making the autocycle (knallert) or moped an attractive and affordable transportation alternative in a country with relatively few serious hills. The Diesella company was in fact destined to become best known for its involvement in the autocycle and moped business. One of its first products in that line was a 50 cc two-stroke engine which could be mounted on a standard bicycle to drive the rear wheel through a roller applied directly to the tyre. The company also made small outrigger motors for canoes using their autocycle engines as the power source. The Diesella company grew fast in the early post-war period, mainly on the strength of their very successful Diesella eventually became Denmark’s largest manufacturer of mopeds and autocycles, peaking in the mid 1960’s with annual sales of some 40,000 units. However, ever-increasing competition from other countries eroded the company’s position in this market, forcing them to seek other avenues for the further expansion of their business. They produced their last autocycle in 1967, after which they moved into the manufacture of parts for tractors and other agricultural machinery, later expanding into the general industrial supply business. They remained in business as of my original time of writing (2016), focusing on the marketing of machine tooling accessories and precision measuring tools as well as a range of testing equipment. Sadly, many of their products were made in China by that time! The company was still owned and managed by the Andersen family. Luis Petersen tells me that Diesella never lost sight of its model engine manufacturing origins. Apart from its retention of the original 1943 name, the company also maintained a display of Diesella model engines and drawings in the reception area. This included an example of the Diesella 2.4 cc model which had been converted to glow-plug operation. It’s nice to see a successful present-day company which doesn’t forget its roots!
The idea of Neilsen producing a model diesel apparently stemmed from one of his employees, who showed up at work one day in 1944 with a Swiss Dyno diesel which he had somehow obtained. Like most of the model diesels which appeared at this time, the original Mikro model was basically another Dyno clone which appeared to owe much to Ivan Rogstadius’s published plans. It weighed in at 220 gm (7.76 ounces) and developed a claimed 1/10 BHP @ 7,500 RPM - a somewhat more credible claim than that made for the Diesella! Most of these engines were apparently used in the 2 cc tether car racing class. A very neat feature of this engine was the wire clip which circled the top of the cylinder head and had a vertical extension which engaged with the compression screw lever. This was a very simple and effective means of discouraging the comp screw from running back during operation. Later versions of the Mikro showed a few detail changes. Perhaps the most unusual of these changes was the addition of a pair of lubrication cups to the main bearing – seemingly the designer was not convinced This model attracted some sales attention from beyond the borders of Denmark. In Sweden, the Mikro engines were being marketed as of 1945 by the noted Swedish model flier, designer and manufacturer Sven E. Truedsson of Malmö. At that time the engine sold in Sweden for a price of 135 SEK. We encountered Truedsson in connection with the Pinotti story which has been related elsewhere on this website. It appears that Kaj Neilsen did not pursue the manufacture of the Mikro diesel with any great vigour. Only around 250 examples of the original sideport Mikro-I model seemingly ended up being produced.
Design revisions were soon put in hand to address these issues, but the damage had been done. A planned production series of 1,000 units was apparently started, but only about 300 examples ended up being completed. A full review and test of the Mikro-II diesel appears elsewhere on this website. In the following year of 1950, Neilsen introduced a potent-looking Mikro 5 cc racing glow-plug unit. Additional details regarding the Mikro range in general may be found in the linked article on this model.
Another pioneering Danish model engine from the early post-war period was the Deofok 45 design, which was introduced in 1945 by the brothers Carl & Leif Kofoed of Copenhagen. The name Deofok was of course their family name spelled backwards, while the engine’s numerical designation seems to record the year of its introduction rather than its displacement, which was 1.8 cc. The Deofok 45 was a sideport diesel of more or less The brothers later produced very small numbers of a Deofok III model of only 0.25 cc displacement. They also made a single example of a 5 cylinder four-stroke glow-plug radial model. This engine was subsequently stolen from the home of the widow of one of the Kofoed brothers, along with the machinery used to make the engines. We would love to learn where it is now ………….. someone knows! An individual whose activities were to play a not unimportant role in the story of Danish modelling in general and the Viking model engine range in particular was Svend Herborg Greig. Prior to 1937, Greig had worked with the previously-mentioned Carl Rose of CEROS fame in his prewar Modelmateriale hobby supply business in Tarm on Denmark’s west coast. According to Greig’s own published account, a 1937 falling-out between Rose and Greig over Rose’s supposedly unattributed use of a Greig model design for his own promotional purposes led to Greig deciding to start his own business. He began by buying Rose’s existing business to clear accounts between them, but Rose promptly started another business in competition with Greig. That business too was purchased by Greig, who thus claimed to have ended up buying Rose out twice! Again, this is Greig’s version of the story – the Rose family might have seen things differently.............
DMI was primarily a kit producer, but the company supplied a wide range of modelling goods both from Danish sources and elsewhere. Supplies of certain products such as power rubber for free flight models (which had come from England) were disrupted by the war, but the company managed to remain active throughout the war years and well into the post-war era.
The presence of balsa wood in Hamburg was due primarily to the fact that it was used as insulation in U-boat hulls. A U-Boat facility was also established in Denmark during the war, and Luis Petersen recalls that when this operation closed down Danish modellers benefitted from the sudden availability of a full pallet of balsa wood! During the early post-war period, Greig elected to go into competition once again with his old rival Carl Rose of CEROS by entering the model engine business himself. He did so with a range of model diesel engines which were sold in kit form as sets of castings and drawings for home construction. Models available in this form included the Greig G1 of 2.5 cc DMI was to go on to become Denmark’s largest distributor of modelling goods, including engines. The business was taken over by Svend Schou in around 1948 but continued much as it had before. Greig went on to operate a new hobby supply business in Odense called Greig Hobby. Svend Schou kept a scrapbook of DMI's activities from this point onwards, and this was an invaluable source of information during the preparation of this article. One of Denmark’s most prominent model engine ranges from the early post-war period was the series of engines which were manufactured under various names by Thorning Bensen, a former employee of the major shipyard at Helsingør (generally referred to in English as Elsinore), a city in eastern Denmark lying on the coast some distance to the north of Copenhagen. Before entering the model engine manufacturing field on a full time basis in the latter part of 1945, Bensen worked as a machinist at the shipyard alongside another individual named Leo Jeppesen, an engineer employed on full-sized marine diesel design. Jeppesen’s design colleague was fellow engineer Bent Haugård. Incidentally, Leo Jeppesen appears to have been unrelated to Eli Andersen's Diesella colleague A. Jeppesen. Thorning Bensen was not himself a modeller - he was primarily interested in machining challenges. However, Jeppesen and Haugård were close acquaintances of two of Denmark’s leading power modellers, Jørgen Dommergaard and Peter Christiansen. These two individuals were both early proponents of model diesels - indeed, Christiansen had written the previously-cited article about the Diesella which appeared as early as January 1944.
However, internally it was a very different story! Luis Petersen tells us that the engine’s rather unique scavenging and timing arrangements were not influenced by any previous model engine but rather were derived from those of a DKW two-stroke car engine which had been designed by a Danish engineer, Jørgen Skafte Rasmussen. DKW was later to evolve into the Audi car line. For those interested, a discussion of the Monsun's highly original porting arrangements (in a model engine context) may be found here on the late Ron Chernich's frozen but still-accessible "Model Engine News" (MEN) web-site. Externally, the Monsun Standard shared the Diesella’s streamlined back tank and massive main bearing housing with recessed prop driver, although some of the construction details differed, such as the omission of the ball races which had been a feature of the Diesella. Dommergaard did not consider ball races to be worthwhile, contending that a well-fitted bronze bushing worked just as well. Dommergaard was also convinced that cooling fins were unnecessary on a diesel – he actually claimed that he only went along with their inclusion on the Monsun Standard because the paying customers expected to see them! A quite revealing article (in Danish) by Dommergaard comparing the design of the Monsun Standard with that of other commercial model diesels then available in Denmark appeared in the April 1946 issue of the magazine “Luftsport”. A preliminary prototype was completed in early 1945, but this proved far from satisfactory. However, changes were soon made, resulting in the evolution of an improved design by mid 1945. Leo Jeppesen and Bent Haugård then supervised the construction of a few more prototypes, with the machining being carried out by Thorning Bensen at the shipyard. These prototypes were extremely well made. One of them was subjected to a bench running test totalling over 100 hours in duration. Luis Petersen confirms that this particular prototype still exists at the Technical Museum in Helsingør. Despite the running time which it has accumulated, it remains in perfect condition. Other prototypes were thoroughly flight-tested by Dommergaard and Peter Christiansen, who reportedly accumulated over 20 trouble-free running hours on one of the engines in the air. In the latter half of 1945, once this testing was completed, Jeppesen drew up the engineering plans upon which the production models would be based. Since the use of the shipyard facilities would clearly be inappropriate for the series production of the engine, alternative arrangements were soon made. Although as stated earlier he was a machinist rather than a modeller, Thorning Bensen was greatly attracted to the technical challenge of producing model diesel engines to the required standard of precision. He was also very keen to start out in business on his own account. This led him to take on the task of manufacturing the engines at his own workshop which he established in the latter part of 1945 in a basement on Mads Holms vej in Helsingør. Leo Jeppesen assumed responsibility for the marketing of the The promotional material for the Monsun reflected this division of responsibilities, specifically citing the engine as a Thorning Bensen product while giving the business address of the venture as that of Leo Jeppesen at Gratiavej 8 in Snekkersten, effectively a suburb of Helsingør lying a little to the south of the main city. However, the quality of the engines suffered greatly through this change of manufacturing venue, possibly as a result of the accelerated production schedule required to meet demand coupled with the fact that Bensen was working alone at this time and possibly using rather basic and perhaps well-worn equipment during this start-up phase. The use of inferior materials may also have contributed to this deterioration. The original prototype materials came from the shipyard, but those available to Bensen from other sources may well have been sub-standard. Whatever the reason, this deterioration in quality led Leo Jeppesen to withdraw from the project quite early on, although he retained his original drawings, which still exist today in the keeping of Luis Petersen. Thereafter, Thorning Bensen continued on his own. Around 100 examples of the Monsun Standard ended up being manufactured by Bensen, although most of them were of far lesser quality than the original prototypes. According to Jens Geschwendtner, who interviewed Thorning Bensen in late 1977, there are no known survivors of this series today. As far as the issue of cooling fins was concerned, the second design to emerge from Thorning Bensen's workshop set the record straight with a vengeance! This was the Thorning Bensen 1A model of mid 1946, which had no cooling fins at all! The name change of course reflects the fact that Thorning Bensen was now solely responsible for the manufacture and marketing of the engines following the withdrawal of Leo Jeppesen. The Thorning Bensen 1A was in essence a Monsun Standard without the cooling fins and with a slightly modified cylinder assembly using a “dog collar" for attachment. It also used the moving jacket system for compression adjustment, whereby the contra piston was moved by the rotation of the jacket upon its installation thread rather than by a centrally-located comp screw. It appears that very few examples of this model were made, although it did achieve enough prominence to receive a specific mention by D.J. Laidlaw-Dickson in his late 1946 book "Model Diesels".
The Thorning III is undoubtedly the best known member of this series since it was made in relatively large numbers – about 1200 examples in all, some of which found their way beyond the borders of their native Denmark. Despite their admittedly unconventional appearance, these engines ran (and still run!) very well. They were also quite well made - seemingly, Bensen had got on top of his earlier quality problems to a large extent, perhaps thanks to his new equipment. The engine was a steady seller right from the start, becoming the most widely-used model engine in Denmark for some years. In a 1977 interview with Jens Geschwendtner, Thorning Bensen recalled that the engine won several Danish championships, also establishing a few Danish records along the way. Its high point was apparently a 3rd place finish in an unspecified International control-line competition. It was marketed by the aforementioned DMI company. The Thorning III was the subject of a published test in the August 1950 issue of "Teknik for Alle", a publication to which we have referred earlier. This magazine was in effect a short-lived (1948-1951) Danish equivalent of the previously-cited Swedish publication "Teknik för Alla" (1940-2001). It was published in Copenhagen. It's all too easy to become confused between the two magazines - I certainly did for a while! You really have to pay attention to the spelling........... The writer of this report found the engine easy to start on all props tested. A peak output of 0.112 BHP was measured between 6,000 and 7,000 RPM. The recommended fuel was apparently 60% ether, 20% kerosene and 20% motor oil. The engine's excellent starting and running qualities as well as its durability assured it of a ready market throughout the balance of the 1940's and into 1950. My own tests have amply confirmed these very positive characteristics.
This original FRV prototype retained the "dog collar" cylinder attachment system of its predecessor. Leo Jeppesen’s original drawings from 1944 had included just such a variant, and now Thorning Bensen began experimenting with his own rendition of this design. Bensen doesn't appear to have followed up on this prototype with any great rapidity. In large part, this appears to have been due to his realization that the competing Danish manufacturer Carl Rose of CEROS fame was embarking upon the development of a 3.5 cc diesel. Bensen appears to have set the 2.5 cc project aside and turned his attention to the creation of his own Thorning 3.5 cc FRV model, maintaining production of the Thorning III in the interim.
The sucess of the Viking 2.5 cc sideport diesel (see below) beginning in early 1950 did not allow Bensen to forget that a response to that model still had to be developed. After getting the 3.5 cc model into production, he resumed work on the 2.5 cc FRV design, making a number of changes along the way. These changes included the elimination of the "dog collar" in favour of a more conventional drop-in cylinder which was retained by a screw-on cooling jacket. In addition a conventional compression screw was now used instead of the former moving jacket arrangement. The engine now featured twin exhaust ports, one on each side, in place of the Thorning III's single forward-facing exhaust port.
The Thorning 2.5 FRV design was the subject of another published test which appeared in the October 1951 issue of the Danish "Teknik for Alle" magazine. The writer of that report measured a peak output of 0.142 BHP @ 8,000 RPM - clearly, Bensen was still pursuing high torque at low RPM, apparently with a certain degree of success! However, the engine came in for a considerable level of criticism from the test reporter, most notably on account of the very rapid wear which developed in the unbushed main bearing. The writer also expressed disappointment at the relatively modest power output, going so far as to state that the new model did not represent any real advance over the trusty Thorning III.
However, the damage had been done. Both engines were advertised as potential gifts for Christmas 1951 by the Hobby Shop at Vesterbrogade 175 in Frederiksberg, near Copenhagen, but the modelling public evidently didn't want to know. The engines could not compete with the lighter and more powerful designs now available from the likes of Viking and various foreign manufacturers. Only about 500 examples of the FRV models were produced prior to the end of 1951, when Thorning Bensen ended all model engine manufacture. He went instead into the business of making printing equipment for newspapers and magazines. He later took up painting and sculpture, becoming one of Denmark's more highly regarded artists. It should be noted here that this FRV model has previously been referred to quite frequently as the Thorning V. Speaking strictly from my own personal viewpoint, I believe this to be an error arising from the fact that the Roman numeral V appeared prominently at the top of the two previously-mentioned tests in "Teknik for Alle". In reality, that numeral referred to the fact that this was the fifth engine to be tested by the magazine. Both reports consistently referred to the engine itself as the Thorning 2.5, as did the advertising, which was quite independent. Although I realize that not everyone agrees with me, I personally believe that to be the correct name. You decide .............or present some compelling evidence to the contrary! A separate detailed article covering the Thorning engines in general and the Thorning III in particular (including a full test) appears elsewhere on this website. In-depth reviews and tests of both the Thorning 3.5 and Thorning 2.5 models are also available here. However, the above summary should suffice for many readers. At long last this brings us up to the point at which the Viking range entered the picture, an event which took place in early 1950. By that time the Diesella, Deofok and Mikro diesels were history, but the Thorning and CEROS models as well as the Greig engine kits were still in circulation. This was the domestic competition that the Viking range had to face. The manner in which they did so is recorded in the separate article on the Viking range to be found elsewhere on this website. ______________________________ Article © Adrian C. Duncan & Luis Petersen First published May 2016 Updated October 2018 |
This was the third article to appear on this web-site on the subject of Scandinavian model engines. Earlier articles had covered the 
My initial intention was merely to edit Luis’s article into colloquial English and present it verbatim with his permission. However, Luis himself comprehensively derailed this plan by succumbing to a fit of enthusiasm which led him to send me a significant amount of additional information on early Danish engines other than the Viking models! He also provided a great deal of photographic and documentary material which had not appeared with his original 1990 effort.
The concept of the model compression ignition engine goes back way further than many of today’s model engine enthusiasts may realize. In the past it has often been stated that the Swiss Dyno 2 cc model of 1941 was the “first” model diesel. While that view may have some validity in terms of widespread acceptance and design influence, the concept actually dates back to December 17
Gustav Eisfeld of Gera, Germany began his own experiments with model compression ignition engines. However, Eisfeld chose a different and far more challenging development path by working on “true” diesels equipped with fixed compression, miniature injectors and high-pressure fuel pumps. This approach may have been directed at getting around Thalheim's patent, which specified the use of conventional carburetion along with variable compression, as the accompanying drawing from the original patent specification should make clear. 
However, the manufacture of the tiny fuel pump and injector required a level of precision which could only be achieved on a series production basis through the application of the most exacting industrial methods and equipment. Such facilities were not available to Eisfeld due to the ongoing war. Since Ernst Thalheim's 1928 patent was set to expire in December 1942 in any case, Eisfeld concentrated thereafter on the development and production of his excellent conventional “diesel” models which were designed in collaboration with A. Thusius. He did however take the trouble to record his earlier experiments in an article which appeared in November 1943 in the wartime German publication “Luftwacht-Modellflug” (pp. 107-109).
Returning now to the pre-war period, Gustav Eisfeld’s abandonment of his original 1937 diesel project left the way open for Ernst Thalheim to introduce the first commercial model diesels, which he did in 1938, ten years after the granting of his original patent. His 
Despite the fact that by the early 1940’s most of Europe was heavily embroiled in WW2, word about this then-innovative type of model engine somehow trickled out of neutral Switzerland to reach a number of other European countries, both neutral and occupied. In a separate article to be found elsewhere on this website, I've recorded the amazing history of wartime efforts in German-occupied Czechoslovakia (now the Czech Republic) to develop model diesel engines under very difficult circumstances. The inspiring story of the 1941-42 
Stockholm somehow managed to arrange for the importation of a number of Dyno diesels to Sweden in 1944, as an advertisement from the September 1944 issue of “Teknik för Alla” proves beyond doubt.
Along with neighbouring Norway, Denmark was occupied by the Germans on April 9
diverse choice of domestic model engines during the wartime and early post-war periods, long before Viking arrived on the scene. Until 1947, when control-line flying reached Denmark, most of these early engines were used in tether cars, boats and free flight model aircraft. The illustrated tether car track at Kastrup, near Copenhagen, was a popular facility which remained in use into the late 1950’s. The young Luis Petersen spent a lot of time there, since it was only 1 km from his home!
produce a number of very well-made model engines under the CEROS brand name (an anagram for his own family name and initial). 
During the early post-war period, Rose returned to the manufacture of spark ignition engines, then still in widespread use in the mid and larger displacement categories. There were 3.5 cc and 4.7 cc models of this type. However, Rose was quick to recognize the sweeping impact of Ray Arden's late 1947 introduction of the commercial miniature glow-plug, and a CEROS 4.9 cc glow-plug unit duly appeared in 1949. This was heavily influenced by the design of the far smaller K&B Infant .020 cuin. model which had appeared in the USA in late 1948. 
Having followed the CEROS story through to its conclusion, we return now to the wartime period. The first commercially-produced model diesel in Denmark seems to have been the Diesella 2.4 cc model. According to a Danish-language article by the then well-known Danish model flier Peter Christiansen which appeared in the January 1944 issue of the magazine “Flyv”, this pioneering model diesel was the product of a collaboration between Eli Andersen and one A. Jeppesen, two mechanically-gifted individuals who had reportedly been building their own model spark ignition engines of varying displacements since 1938. In early 1943, the impossibility of obtaining miniature spark plugs under wartime conditions led the two men to commence their experiments with model compression ignition engines. By the latter part of 1943 they had a design which they felt merited series production.
seemed barely large enough to accommodate the two men and their equipment! The primary business at this point was clearly the manufacture of model engines, since the sign on the storefront proudly proclaimed that the premises were occupied by a “Fabrik for Modelflyvermotorer” (Model Airplane Engine Factory). The chosen company name clearly reflected this business focus.
Despite its high selling price, the Diesella attracted quite a few buyers because it had no domestic competition at the outset. Luis was kind enough to share what has become my favorite story in relation to the Diesella. Apparently one of Eli Andersen’s first customers in late 1943 was an individual who was active in the growing Danish resistance movement. However, immediately after placing his order this customer was caught by the Germans during their late 1943 crackdown and was sent to a concentration camp before he could take delivery of his purchase. Happily he survived the war and returned home to Denmark .............. to find his carefully-stored Diesella model engine awaiting him as a coming-home present! A nice happy-ending story which reflects well upon all concerned!
A competing Danish engine which appeared in 1944 was the 2 cc Mikro-diesel. This engine was manufactured by Kaj Neilsen of Kronprinsensgade 8, Copenhagen who had established his own business in 1938 primarily as a repair workshop for photographic equipment. His original equipment consisted of a single turret lathe! 
Greig’s new business was known as Dansk Modellflyve Industri (DMI - Danish Model Aero Industries). The venture began as a part-time business conducted out of Greig’s father’s attic, but soon expanded to the point where it became a full-time activity. In 1938, new premises were secured in Skern, with a further move being made in 1942 to the company’s final location in Odense, a city located in south-central Denmark on the island of Fyn. An interesting illustrated 1943 article (in Danish, but with an effective translation option) about the early years of DMI may be found 
Interestingly enough, in that 1943 article Greig recalled that long after the war began he was still able to obtain supplies of balsa wood from Hamburg, Germany. He also obtained a variety of modelling materials through Sven Wentzel in Stockholm, Sweden.
displacement, the 4.0 cc Greig G2 and the daunting 10 cc Greig G3. Later there was also a pioneering turbojet design which was not successful. The illustrated replica of the Greig G2 was made by my late and much-missed Swedish friend and colleague Kjell Lindqvist to his usual superb standard.
As one of Denmark's pioneering diesel users, Dommergaard soon developed some very definite ideas of his own regarding model diesel design. Beginning in early 1944 he began to collaborate with Jeppesen and Haugård on the design of a 2.4 cc sideport diesel which they called the Monsun (Monsoon) Standard. While still seemingly paying homage to the Dyno in basic design terms, the Monsun Standard was apparently just as strongly influenced by the Diesella, at least in terms of its external styling. 
finished products. 
Thorning Bensen made some changes to this design in order to simplify its manufacture somewhat. He then made preparations to go into larger-scale production, acquiring some new equipment and taking on two additional workers besides himself. In late 1946 he began production of the engine with which his name is most widely associated today - the 2.41 cc Thorning III sideport diesel. For reasons which are now obscure, the Bensen portion of the name was dropped at this time, never to reappear. 
In late 1949 Bensen produced a prototype of a planned 2.5 cc crankshaft front rotary valve (FRV) replacement for the increasingly out-dated Thorning III sideport model. This appears to have been a response to the news of the incipient release of the competing 
The resulting 3.5 cc model was closely modelled upon the design of the very successful 
There were apparently some problems with the production of the required permanent molds, but by early 1951 the new 2.5 cc FRV design was finally judged to be ready for release to the public. Production of the venerable Thorning III ended at that point, or possibly a little earlier. Like its 3.5 cc companion, the new 2.5 cc model was identified simply by its displacement - the two designs were called the Thorning 2.5 and 3.5 respectively. 
Thorning Bensen moved rapidly to address some of the concerns highlighted in this test, including the incorporation of a bushing in the main bearing. Although it was on the verge of ceasing publication, the Danish "Teknik for Alle" magazine nontheless hastened to get a condensed but still informative addendum report on this revised variant into its December 1951 issue (its last issue, as far as I'm aware). A slightly improved output of 0.152 BHP @ 8,500 RPM was cited in this test report, together with the observation that the main bearing wear issue had been satisfactorily addressed.| |