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Propeller Dynamics

Essential reading for model aircraft contest fliers. This is the only book on the market explaining propeller theory in non-mathematical terms. A rattling good read, I know, I wrote it.



More enya ramblings (or, How I learned to love that little red and yellow box)

Courtesy of Bob Allan , November 2004

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In two previous episodes devoted to this brand of model engine, I mentioned briefly the problems and handicaps that the Enya family would have faced in the 10 or so years following WW 2. Trying to achieve anything worthwhile in the aftermath of a catastrophic defeat would have been difficult enough, let alone choosing to produce an item which most people back then (and more than a few now ! ) would have regarded as a frivolous, unnecessary, luxury toy. As previously mentioned too, the very words 'Made in Japan' were associated with cheap, low quality consumer goods for more then a decade after war's end, so the Enyas' decision to make model engines was a brave one indeed, if not (as they were no doubt told) downright foolhardy.

From these humble beginnings however, the company worked hard and incredibly, by 1969 the Enya Metal Products Ltd. of Tokyo Japan were producing a bigger range of model engines than any other manufacturer in the world « around 50 in fact, including marine and R/C versions, and exporting them to many countries. Japanese industry in general had demonstrated to the world just how to crawl from the ashes of defeat to become a force to be reckoned with. Gone now, were those cheap pressed tin toys that flooded onto Woolworths counters in the early Fifties, created out of desperation.

The Enya 19 holds a special place in the history of the company, because it was a 19 size Enya that first came off the assembly line (table) way back in February 1950 as a production engine. That very first 19 had a red head & prop. drive and with a detachable front bearing housing, it laid the foundation for the millions of other Enya's that were to follow. What makes the 19 Mk. I unique though, is that the housing was held on by only 3 screws « 2 at the top and 1 centrally underneath, and with a quaint looking little flat topped venturi, it had an unusual appearance. Production numbers are unknown, but considering it was their first effort, and the fact that they are so rarely seen now, I would hazard a guess that well under a thousand would have been produced before production began on the Model 4002, with oval exhaust port but 4 bolt front this time, and die instead of sand cast ( like the little 09 this model 19 had an optional factory, cast alloy radial mount with 4 lugs ). Whilst the 3 bolt front 19 is certainly hard to find, there is yet another even rarer ENYA and that is the 1949 ' Type 2' Typhoon 63, which looks unlike any other ENYA engine.

This big twin ball race motor had rear rotary disc induction, and both front and back housings were detachable but production numbers were very low due to almost non-existent sales ( 20 or 30 per month ), and it really doesn't qualify as a production engine. The influence of the American McCoy 60 can clearly be seen in this ENYA, however this ambitious design was soon abandoned in favour of the simpler and cheaper to produce FRV plain bearing ' Type 1' 63 which went on for another 15 years as the familiar 6 bolt front Typhoon 60. The only example of a ' Type 2 ' 63 that I have ever seen bore the Serial # V2 191, so assuming that V2 denotes the 2nd Model 63, that means that at least 191 were produced if they started at zero.

Once designer Saburo Enya had settled on his basic engine design formula, it wasn't long before new sizes began to appear, and about 12 months after the 09 was released in early 1954, the first 2.5 cc Enya engine made it's debut. The new Enya 15 glow was an extremely well made and good looking die « cast unit, and during 1956 it received some improvements to further enhance its performance. These included an increase in compression ratio, reduction of bearing length by 2mm and other minor changes, all aimed at increasing the power output to improve its chances in the then very competitive 2.5cc ' International' class. On test, the power output of the 15-IB was found to be comparable with the best in its category, and pricewise it undercut its OS rival (It must have irked the whole Enya staff at this time to see the opposition's admittedly excellent OS Max I 15 win the 1956 F/F World Power Championship thanks to Ron Draper, but OS had a 15 year start on Enya). This revised model was designated initially as the 15 « IS but later the 15 « IB, and it entered production in January 1957 with nickel plated Phillips screws used throughout, in place of the previous slotted or 'cheese head' screws. A major distinguishing feature of these two early 15 glows was the bypass bulge on the side of the crankcase, to cater for the initial transfer of fuel/air mix outside the liner, then entering via the usual cyl. slot.

All future 15 glows ( from the II onwards ) would adopt the same method as the later O9's ie. machined flutes within the actual liner itself, a successful way that Saburo Enya found to not only lower the production costs, but maintain quality without sacrificing performance, the resulting very thick cyl. liner also enhancing reliability. With the introduction of their 15 size engine, the Enya company at that point in time could offer modellers a choice of 6 different capacity size engines, which were the 09, 15, 19, 29, 36 and 63 « the latter being the only one now with castings which were still produced from sand moulds, and the largest Enya remained that way for another decade, until 1965 in fact. These big 60's were all serial numbered on the RH lug (except maybe for the very last ones), the numbers seeming to peter out before 12,000 so I will let you, Dear Reader, draw your own conclusions on that and the only real difference between a 63 and a 60 is the half millimetre difference in the bore size. Enya offered a full 12 month guarantee with that early 60 which was unusually generous, but it was so ruggedly built that a good sized sledgehammer and cold chisel would be needed to damage it. If intending to use one of these big Enya's, it's a good idea to check the underside alignment of the 2 mounting lugs ( sand castings not being particularly accurate ) and try to keep the revs down with a big coarse pitched prop. 'Typhoon' seemed to be a name favoured by the Enya brothers for their earlier model sand cast engines, including the 10cc and 5cc sizes, the latter going on to become the Enya 29-IIIB ' Super Typhoon ' in the late Fifties, a B class T/R all time classic.

All the Enya's from this period shared a common styling feature, which was a rather long venturi, set at a low angle « sort of stone age ' Ram Air ', and it was about this time also that the company changed the oddball size 36 ( OS also produced a 36 for the US market ) to a 35 and the 63 to a 60, to conform with the capacity sizes we are still familiar with today. Another small design quirk that involved the 09 was the side on which the exhaust was situated, starting off with the R.H. side on the first 09, switching to the L.H. side for about 15 years through the II & III Models, before reverting back to the R.H. side for the final series IV ! Why ? Who knows .Up until 1961, all models in the ENYA range ( except the 60 ) had 4 bolt heads.

A brief word about Enya's sometimes inconsistent ( some would say downright confusing ) model numbering system might not go astray at this point. Actually, the only engine in the Enya range which comes close to following a logical sequence is the 19, starting off at 4002 and continuing through to 4006, increasing by one final digit at a time, every model change. Now it gets confusing « the first 09 was called a 3001, but then the 15 size took over the 3 - - - designation, becoming a 3101 in the 15- 1B, then a 3303 in the 15- III and 3304 in the IV. Likewise, the 35 started off as a 5001, became a 6001 in 1961, a 5224 in 1964 and a 5225 in the last V series. The 29 was even worse, starting as a 5002 with the airfoil exhaust, going to a 5103 in the III series, became a 5224 in 1964 with the 35, ending up too a 5225 ! The 40 size was only ever a 6002 but the 45 started as a 6001, then got promoted to 6002 in the II series. The 60 II was dubbed a 7032 in 1965, ending up a 7033 in the III & III B. Now, is that clear to everyone ?

Peter Chinn and Ron Warring were starting to sound repetitive now in their almost totally unreserved praise for these ever increasing numbers of high quality engines which were emanating from Japan, and to be fair, not just from the Enya factory either ! New standards were being set with almost every new model and it was plain to see that Japanese engines were, even then, equal to the world's best. The designers from Nippon were now ' on a roll ', not content merely to copy or adapt other peoples ideas, but experiment with those of their own, and in 1956 ( along with 3 other new models in the range ) Saburo Enya introduced his first ever diesel « the 15D Mk. I , distinguished by its vertical venturi joined to the front of the cylinder.

The 15D was a very ambitious project, being the first Enya to employ ( single rear ) ball races and, refusing to follow nearly all the other diesel designs of the day, the designer had opted for the unusual choice of loop scavenging, which meant opposed transfer and exhaust ports coupled with fore and aft transfer passages ( actually, it was a single passage in the casting but divided in 2 by the contact of liner against casting ). Although some people thought erroneously this was Schnuerle porting, it was even so, quite innovative for the time, and endowed the 15D with a performance which was second only to the Oliver Tiger Mk. III. Not bad for a first attempt ! Indicative of just how different this diesel was to its glow stablemate, was the fact that the only common part shared was the needle valve assembly, and in the 15D provision was made to fit 2 NVA's ( one high / one low speed ) for use with those early steam powered radio control systems. There were actually about 3 variants of the Mk. I and therein lies a tale « Peter Chinn confessed at a later date that when he was testing the 15D for an American model publication, he had struggled to find something to complain about, on the theory that no engine is so good that it is beyond criticism. In Peter's words « 'eventually, but without much conviction, we decided that the 5mm. threaded shaft end was a possible weak point on an otherwise robust engine─..When the Enya company heard about this, they took it seriously─..Within a few weeks a new type of shaft, in 85 ton chromium molybdenum steel and with a 6mm. end had been put into production. This shaft has been fitted to all production models since the end of last year ( 1957 ) and the current model now incorporates one or two other minor changes.These include a superior type of ball bearing, a con-rod bronze bushed at both ends ( instead of the big-end only ) and slightly enlarged gudgeon-pin bosses in the piston.' How ironic then, that the 15D is remembered today mainly for breaking crankshafts ! Taking the above information into consideration, we can now only assume that these shaft failures were the result of either competition modellers simply trying to extract too much extra power and / or ( as a noted US speed flyer commented to me when discussing similar shaft failures on his Enya 29 racing Special ) ' too many square corners ', meaning the shaft was lacking fillets in high stress areas. Whatever the problem was, Duke Fox faced exactly the same thing a few years later when combat flyers started complaining about breakages in his otherwise excellent 35 X engine. Peter Chinn stated frankly that despite a couple of material changes, the Mk. I 15D was never entirely free of shaft fracture through the main journal, and proffered the opinion that the fault ( conversely to what one might think ) may have been due to the very rigidity of the piston & rod assembly, transmitting too much stress to the journal.

Aware of this problem, Saburo Enya was determined to eliminate it in the 15D Mk. II and it appeared in about 1960 sporting an enormous 11.5 mm. diam. crankshaft and a chrome plated bore which was another bold innovation for that period of time. Power was increased to around 0.332 bhp @ 15,500 rpm which really gave the Oliver Tigers a fright, but unfortunately the overkill solution to the shaft problems meant the weight had now ballooned to over 6 oz. ( remember, the very powerful 29-III weighed only something like half an oz. heavier ! ) so despite the fact that the Enya was very easy to handle for a world class racing diesel, the Tiger III continued to reign supreme. The fact that the Enya used more fuel ( and needed an exhaust prime to re « start ) was the final nail in the coffin of Saburo's attempts to beat the Oliver's at their own game, the ultimate irony being of course, that the very advanced type of porting which gave the Enya parity with the Oliver in 'A' T/R became, in the finish, its Archilles heel. Keep in mind though, that the Enya was very much a mass produced engine trying to compete with a meticulously hand made ( and tuned ) one of unsurpassed quality. The Enya 15D Mk. II was, nonetheless, a great sport engine being also available with a simple R/C throttle and it remained the last diesel produced by the company for 40 years ( excluding of course, the little 06 ) until in 2004, Enya released a new 15 diesel based on the Schnuerle ported SS and featuring modern ABC technology with alloy piston. ENYA now also list a 25 size diesel, presumably also based on the glow SS. Returning to the 15 glow now, and in 1960 the company introduced the lovely little 15-II which as usual was an entirely fresh design, incorporating the internal transfer flutes mentioned earlier, and made in either the usual Enya matt finish or, for the first time, shiny polished alloy die castings. It was in this latter guise that your humble scribe purchased one from the local newsagency ( American translation « bookstore ) as back in those days, in small town rural Australia, very few model or hobby shops existed and the outlet for model engines varied from town to town, depending which business had been convinced by the travelling salesman to stock extra income items. I hold very fond memories of that 15-II ; OK, it wasn't quite as powerful as some other engines from that period, but like all Enya's it was beautifully made ( have I mentioned yet that I like Enya's ? ), very user friendly and reliable as the day is long. Only recently, I was lucky enough to pick up a new, un-run 15-II with the shiny case from Germany ( Thanks Rudolf ! ) and it is one of my most treasured Enya's. It is, in my opinion at least, the definitive Enya 15, and a just plain NICER little engine never existed. Interesting to note that the 2 best countries outside Australia to look for old Enya's is the USA and Germany, thanks to M.R.C. and Robbe, and to a lesser extent Ripmax in the UK. The very dynamic and ' hands on ' approach by the then OS agent in Australia, Tony Farnan, ensured that the OS brand stole a march on Enya back in the late 1950's and they took a while to catch up, helped (hindered?) by some indifferent marketing & spares back-up by the equivalent Aussie Enya distributors.

In September 1966, Enya released ( yet again ) a similar, but basically all new 2.5cc glow designated as the 15-III Model 3303, the most visual change being, instead of the previous cast, bell mouth venturi with metal insert, we now had provision for 2 different size turned alloy inserts, but by this point in time a couple of major changes had occurred. Enya had given up trying to compete with other manufacturers who were producing specialised 15's with a very high performance for expert modellers, contenting themselves instead with providing a reliable, long lasting and versatile engine to the average modeller on a budget. The reason for this of course, was the great upsurge in popularity of R/C flying due to ever increasing reliability, coupled with ever decreasing cost of radio gear, and control line flying was in severe decline.

The new 15-III (in typical Enya fashion) shared no major parts whatsoever with the previous model « the crankshaft had increased in diam. by 0.5 mm. over the II (also with a larger gas passage), and although the stroke remained the same, a new con-rod with a smaller big end O.D. was fitted, as the crankcase was now of a smaller diam. to improve induction and charge transfer through the very thick ( 2.75mm.) cyl. liner. This reduction in case diam. gave a smaller volume primary compression chamber and allowed the 15-III to fit between narrower bearer spacing than the 15-II. Cylinder port timing was quite conservative (due to reasons mentioned above) « the exhaust opening at 63 deg. before B.D.C. & remaining open for 126 deg. of crank angle, while the bypass port opens 8 deg. later for a bypass period of 110 deg.  What really impressed Peter Chinn though in his test on the R/C version was the very low, steady & reliable idle « 2,000 rpm on a 10 x 4 prop. which earned the 15-III the distinction of having 'one of the best throttles ever encountered on an engine of this size.' This new Enya must have impressed other people too, because in the 1970's an almost exact copy of the 15-III appeared, named Thunder Tiger 15 which was made on the island of Taiwan. This Nationalist Chinese clone was (naturally!) not quite as well made as the Japanese original, employing as it did ferrous bushes in the main bearing and con-rod big end, but the internal fits were quite good, even if the exterior didn't quite match Enya's high standard. This replica went on to become the SLH 15-A and, along with some other copies of OS engines, was produced by the Star Light Hou Industry Co. Ltd. of Taiwan.

While all this was happening to the 15 size engine, Saburo Enya had also been busy with development of it's bigger brother, the Enya 19. By the late 1960's the then current model 19 was the 4004, characterised by the cast lug under the front shaft housing, and something new was needed to replace it. This arrived about 1969 in the shape of the all new Enya 19-V, and marked the change from the old 'square' bore & stroke to the more modern 'oversquare' dimensions of 16.6mm. for the bore and 15mm. for the stroke. This change allowed improvements in both higher power levels and ability to rev out a bit more. The really big news though, with the 19-V was that it was also available, for the first time, with a twin ballrace supported crankshaft, and what an exquisite little motor it was, either in C/L or R/C guise.  I recommend that anyone interested in model engines should have at least one of these, either in the V series or later VI (that's the one with the little rectangular bump on the top of the bypass, just beneath the fins) although the 4005 BB's are now getting quite scarce. Most other engines that have their plain bearing exchanged for a pukka ball race job have to make do with a smaller diam. crankshaft « not so with the 19 BB as it actually has a bigger shaft, by 1mm, than it's bronze bushed brother, made possible by using a special type of 12 ball rear race having an O.D. of only 21mm. Not only that, but that bigger shaft was put to good use by employing a larger gas passage (by 0.5mm.) than the ordinary 19-V. As with the larger 29 & 35 ball race models, weight had crept up by ( less than ) half an oz., and overhang was also increased, but only by about 3mm. so that is a very small price indeed to pay for such a lovely little engine. No great increases in power were claimed ( factory quoted 10 per cent ) over the lower priced model, so once again for the sake of a few dollars, a lot of modellers never got to experience the silky,quality feel of a miniature engineering masterpiece at what was, really, a bargain basement price. Saburo had also performed the same surgery on the 19-V crankcase (helped by the 1mm. reduction in stroke) as he did on the 15-III ie. a smaller diameter which meant the 19 would now fit between narrower bearer spacing than the rather broad 19- IV. P.G.F.C. summed the 19-V up thus « 'more powerful, more compact and fractionally lighter than its predecessor,' and in my opinion at least, it is the definitive Enya 19.

By about the early to mid 1970's the Enya 40 and the 45-II both designated as Model 6002 had appeared, both sharing the same shaft ( which at 15mm. was as big as most 60's ), front housing and con-rod. The 40 actually preceded the 45-II and was notable for being the first Enya ever to employ a Dykes ring, also for the fact that it could be regarded as Enya's final and ultimate development of the crossflow scavenging era. Schnuerle porting was by now, almost compulsory if an engine manufacturer wanted to sell his wares to a market saturated with R/C buyers all clamouring for ever more revs and horsepower « the old engines pumping out low down 'grunt' at moderate revs were exactly that « OLD, and not very fashionable anymore. These bigger size Enya's ( 40,45 BB, 45-II & 60 Models 7032 and 7033 ) all had ringed, alloy pistons whilst the only 'big uns' to have lapped iron pistons were the early 45 Model 6001 plain bearing job ( the C/L stunt flyers favourite ) and the sand cast, 6 bolt front 60. By circa 1980 ( that's 25 years ago ! ), the final 5225 series of 29's & 35's were available, and now in 2004 the more expensive & upmarket Enya's are only to be found in very selected outlets, whilst the simple, basic beginner's models have to suffer the indignity of being frequently seen, unwanted and unsold in sports store glass display counters, these last 'toy shop specials' being the 09-IV and the 15-V. Because Enya's were produced in large numbers over a long period of time, a lot of modellers simply don't realise just how long ago some of the familiar models were made, eg. the 5224 series of 29's and 35's started off 40 years ago, the last one leaving the factory a quarter of a century ago ! My, how time flies. Incidentally, the plain bearing 45 Model 6001 mentioned above as being favoured by the stunt fraternity had, as you would expect, great credentials for that specific task which were a factory quoted output of 0.90 max. H.P. for a weight of 8.5 oz. and a compression ratio of 7 : 1. When the R/C version was tested in March 1965, Peter Chinn remarked on it's excellent power-to-weight ratio, the extremely flat power curve and the 'stunt perfect' torque of 75 oz. at between six and seven thousand rpm.
If you can find one, this 45 has the cast, pressure tap lug under the front bearing housing, the same as the equivalent 35-II and 19 Model 4004. Sadly, the following Enya 45 Model 6001 with twin ball race shaft, was aimed squarely at the R/C flyer, being more of a scaled down 60 than a development of the plain bearing 45, with which it shared no parts whatsoever, apart from the ( differently machined ) main crankcase casting. Timing had been substantially modified and weight, of course, increased, for no real gains (maybe 10 per cent) in horsepower over the P.B. model. The Enya 45 Model 6001 plain bearing remains the ultimate Enya C/L stunt engine.

As this is the final episode I intend writing on Enya's , I would like to finish up with a true story « just recently, my wife and I travelled to the National Gallery of Vic. in Melbourne to view ( with about a quarter of a million others ) an exhibition of paintings entitled ' The Impressionists ' containing artworks by Van Gogh, Renoir and Monet to name just a few. The collective worth of these paintings ( if they were for sale that is ! ) would have run into many hundreds of millions of Australian dollars some single paintings alone worth up to 30 or 40 million each. The interesting thing though, was that when they were actually painted back in the late 19th Century, the local art lovers of the time thought they were trash. The only thing that kept a few of the artists from starving to death was a foresighted and generous art dealer, who purchased most of their paintings and held an exhibition to display them in Paris. Even though all the paintings were for sale at very modest prices, not one was sold of the 70 odd on display « worse, the dealer and artists themselves were subjected to all manner of abuse for showing such rubbishy paintings. Some buyers were only interested in purchasing a painting, just so they could get the frame that it came in ! What has all this got to do with Enya's you ask ? Well, I see myself as a bit like that art dealer « I am in the fortunate position to acquire, at absolutely rediculous prices, all these fine, little works of art that others turn their noses up at.


Just as a completely irrelevant footnote, I would like to recommend to any persons interested, the best screwdriver that I have ever found for working on model engines, and Enya's in particular. It's amazing the difference the proper tools make for the job in hand, and in this case it's the ' 6 WAY ' screwdriver by FULLER ( CANADA) This is a large ( over 4 inches long ) handled, reversible type driver with 2 double end bits, giving 2 Phillips head ( larger one perfect for Enya screws ) and 2 slotted head. The handle is red plastic, but be warned « because this driver is so big and heavy, you can really exert a LOT of torque, so care is required when tightening up screws. One modification needed though ( to avoid fouling & bending head fins on Enya's ) is to grind off the 'ears' on the Phillips bit, starting about 2 mm. back from the tip.

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