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Propeller Dynamics

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The ENYA 29 (and 35!)

Courtesy of Bob Allan , October 2004

Updated 26/11/06, see end of article

IIn the world of model aeroplane engines, the 29 and 35 size has long been a favourite, particularly for flyers of control line models.

The Holy Grail of Enyas

There is no argument about which is the most famous 35 ­ that title, of course, belongs to the venerable FOX 35, which has been manufactured now for something like 5ý decades with little change

The title, however, of most famous 29 is open for debate, and in the following few pages, I would like to present the case for ENYA’s 29 which has also been around (in not that many forms) for half a century or so.

Click to enlarge

The name of ENYA was first associated with model aircraft way back in 1930, when the older ENYA brothers (Ichiro and Jiro) were making rubber powered models, encouraged by their father Hachiro.

Hachiro Enya owned a small machine shop where he produced medical instruments, and it was in this small workshop, just after WW2, that Saburo, Yoshiro and Jiro Enya first experimented with producing a model engine of their own design (Saburo having majored in mechanical engineering at Tokyo University). Ichiro Enya was sadly, not involved at this stage, having been killed in a car accident just prior to the war.

When the first ENYA 29 was released in April 1952 (about 2 years after the 19), it was an instant success, both in Japan and America where modellers found that it possessed both excellent durability and great performance. It must be remembered too, that at that period of time (just after the bitter conflict of WW2) a lot of resentment was still felt towards the Japanese people. To make matters worse, for the Enya brothers, Japanese industry did not enjoy the peerless reputation that it does today, and the words “Made in Japan” were often viewed with scorn and contempt by the average Western consumer.

After the initial success of the sand cast, red head 29, the Enya brothers were sufficiently encouraged to produce a die-cast model ll which appeared around 1953. This new 29 was called a Model 5002 and sported a very attractive exhaust stack, which was shaped just like the section of a C/L stunter’s wing ­ a marketing ploy perhaps, for the huge popularity of control line flying at that time, especially in the United States.

If the ENYA 29 was a success in the U.S., where it had to compete with the likes of Fox, K & B, etc., it must have been an absolute revelation in England where modellers were forced to accept wheezing diesels of indifferent quality (I still fondly remember the story told by a famous Australian aeromodeller who was working in a well known hobby shop back in the 1950’s ­ seems his main job was sorting through each shipment of British made diesels to determine which ones would actually run!).

High import tariffs however, ensured the ENYA and others like it, were only sold in small numbers in England, while modellers in Australia and the U.S. grabbed them with both hands, eager to embrace these powerful new arrivals.

The real turning point for ENYA though, especially in acceptance by the modelling public, came with the release in 1956 of the fabulous ENYA 29 ­ lll, an all new design called the Model 5103. This was a small, lightweight, high power and speed 29 aimed specifically at the ‘B’ class team racing market, which probably explained the prominent transfer passage bulge (in Peter Chinns words “of truly massive proportions”). The well made 29 ­ lll, earned great praise from all engine testers of the day, with glowing statements like “one of the most impressive 29’s we have tested” and “The peak output realised as a consequence of this high torque ­ 0.69 bhp at close to 16,000 rpm ­ is, needless to say, phenomenally good.” In his Oct. 1959 AM engine test, Ron Warring stated simply, “ The new ENYA 5cc glow motor is a superb power plant in all respects “.

Here was an engine weighing only about 6.8oz, putting out the kind of torque (for size) only matched by the likes of McCoy 60’s and Fox 29R racing engines and unlike the latter (which was a real bear) the ENYA remained a pleasant, easy handling engine, which even a novice could operate with confidence. One of the features which contributed to the 29 ­ III’s very high performance was it’s intake system, or to be more specific, the shape thereof.

Previously, most engines of that era featured an oval or round intake hole in the crankshaft, but the 29 ­ III had a large rectangular port matched to a similarly shaped venturi aperture. This had the same effect as a quick lift or“ lumpy “ camshaft in a hot rod engine, in that the intake remains open for alonger effective period of time, allowing more fuel mixture to be admitted. Bycontrast, the corresponding stunt orientated 35 had a similar rectangular portin the crankshaft, but coupled with a circular hole through the bronze bearingthis set up gave a less abrupt opening and closing of the shaft valve.

This new ENYA also established the qualities that, even today, are synonymous with the brand ­ that of build quality (especially the piston/cylinder fit) and sheer longevity. The stories of ENYA’s just refusing to wear out are legendary, with some flyers complaining about the length of time required to run one in.

The Company in the U.S. that used to market ENYA’s (MRC) called them “The Hand Lapped Engine” and used this as a slogan on their clear plastic engine boxes. Whilst it is true that ENYA did indeed, hand lap all their iron piston motors, a first hand witness report and consideration of the millions produced over the years, suggest that this process was more of a cursory one, and less of the time consuming, laborious one so frequently imagined. I suspect that care and attention to fine tolerances in the initial machining of the metal parts had more to do with it, than the (necessarily brief) lapping procedure, but regardless of whether it took 5 seconds or 5 minutes, the fact remains that no other mass produced engine in history can better ENYA’s consistently good piston fit (and this last bit is for the Cox enthusiast) over such a wide range of sizes from 09 to 60. I exclude the V series 29’s & 35’s from this claim, because as mentioned elsewhere, they were much looser.

How ever you look at it, the ENYA 29 ­ lll established new standards for a quantity produced engine with performance akin to a hand built “Special”, and in 1959 ENYA released the almost identical 29 ­ lll B. This motor still came with the popular and convenient option of 3 different size venturi inserts, but also included for the first time, a spare higher compression cylinder head enabling the owner to give his nice new ENYA an easy couple of hours running to bed things in before fitting the H/C head and going racing. Price in Australia in 1960 was 137 shillings, and fierce rivalry developed between the ENYA and its nemesis, the OS Max lll 29. Indicative of just how good both these engines were, is the fact that even now (45 years later) they are still highly prized and sought by T/R enthusiasts. If any stunt fliers still remain un-convinced that the ENYA 29 wasn’t intended for them, just read Peter Chinns July 1964 MAN test report of the 29 - IV where one of the headings reads ­ “ Big First in Racing Engines “, referring to the large number of combinations possible with 2 cylinder heads, 3 venturi inserts and pressure or suction feed. If my mathematics are correct , a theoretical maximum of 16 different set upswould be available for use on the later 29, but some of those would be entirely impractical eg. no venturi insert with no pressure ( incidentally, with the ENYA pressure tap being underneath the shaft housing, the available pressure is  much higher than that derived from a backplate tap ).

The company always intended the 29 to be the racer, whilst the 35 was aimed at the stunt flyer, and for the next 30 years, the 29 was rated at the same power as the 35, indicating a higher state of tune in the smaller engine. This however, didn’t stop modellers from fitting the 29 into their new Nobler, and the result was that ENYA got a bad reputation as a stunt engine, probably even to this day (give a dog a bad name….). One credible report I’ve heard even had one hopeful trying to stunt with the ball race 29 Racing Special ! As an aside, probably the best ENYA 35 for stunt flying was the Model 6001 of 1961, which is hardly surprising as it was produced concurrently with the great ENYA 45 6001 plain bearing, one of the best stunt motors ever. These two engines represent the zenith of ENYA stunt technology, conceived as they were in a time when model engines were primarily designed for the C/L flyer, and the R/C throttle was added later as an afterthought. That process would be reversed in years to come, but back then the ENYA 35 was pure stunt.

Designated the 35 ­ ll, it replaced the earlier 5001, but suffered from a very short production run of only some 3 years (making it one of the hardest to find of all ENYA’s) before the company embarked on a marathon 2 decades or so of producing the familiar 5224 series. Those wishing to confirm the 35 ­ II’s cred as a dedicated C/L stunt engine should contact a certain West Australian propeller maker. The ENYA 35 ­ ll had very steady and torquey running characteristics and was both heavier (only by about 0.75 oz. though) and physically bulkier than the 35 ­ lll which replaced it in 1964. Some idea of the grunt that the 35 ­ II was capable of, is apparent when it is compared with a FOX 35 Stunt from the same era. The FOX produced 0.45 bhp and 46 oz. in. of torque at 7,000 rpm, as opposed to the ENYA’s 0.52 bhp and 54 oz. in. oftorque at 7,000 rpm ­ nothing remarkable until you consider that the ENYA ‘s
 figures were obtained (both Peter Chinn) from the choked down R/C model.

The racing Special mentioned above appeared in 1960, and was based on the standard 29 ­ IIIB but modifications were minimal and the engine was nota great success. Employing a new and heavier front housing for the single rear 11.5 x 24 mm chrome moly ball race, the main visual cue was the FOX 29R style “ashtray” intake designed of course, for pressure feed although the engine did come with 2 venturi inserts. Timing remained the same as the standard 29 but the shaft had both a larger gas passage and intake opening than normal. Like the 15D ­ II, this 29 Special had a hard chromed bore, but the speed flyers for which it was designed had trouble with the piston, which ( like Topsy ) just kept growing, requiring constant lapping.

By this point in time (at the end of 1963), some staff changes had occurred at the ENYA factory. President of the company, Hachiro Enya passed away and was succeeded by the eldest son Jiro (then 46 years of age). A younger brother Goro Enya, had joined the firm in 1956 (after graduating from St Paul University in Tokyo) and by 1968, he was in charge of final inspection and sales. Of the two other brothers (who all apparently enjoyed tinkering with BMW and Moto Guzzi motorcycles in their spare time) Saburo was managing director in charge of engine design, whilst Yoshiro handled flight testing and the design of the smaller ENYA engines, eg. 049 & 06.

Mention of the 5224 series leads me into the next chapter of this ENYA fanatics ramblings, the ENYA 29 ­ lV which appeared in early 1964, and for me at least, the lV is the definitive ENYA 29 and a real classic. Yes, weight had crept up to around 7.7oz due to all new and heavier castings, also a bigger shaft, but the factory claimed an increase in power to 0.80hp. Now sporting a 6 bolt head and provision under the front housing for a pressure tap, the 29 had also lost its distinctive appearance from the 35, both 5224’s being visually identical apart from the 29 or 35 cast into the bypass bulge. On the plus side, these twins had an advantage over the previous, far from shoddily built models with superior fits and finishes, and this beautiful standard of workmanship would continue right through the 60’s and 70’s until a slight drop in quality (mostly in the piston / cyl. fit although some would claim this resulted from the manufacturers desire to reduce running-in time) became evident in the ‘V’ 5225 series, indicating the age of the basic design, compounded by the declining interest in C/L flying. Radio control flyers were now calling the shots and archaic, loop scavenged, iron piston technology was outdated and redundant, Schnuerle porting being all the rage.

To ENYA’s eternal credit though, the factory continued to produce standard venturi engines for the C/L flyer ( by that time an endangered species ) long after their accountants probably told them to, and the 5224 series of 29 and 35 size engines must rate as one of the best ever made on a quality / reliability / performance / price basis. The modelling equivalent of a stone axe.

About 10 years after production of the square venturi Model 5224 commenced, both the 29 & 35 engines morphed into the 29 ­ lV B & 35 ­ lll B Models, now with a round, turned alloy venturi insert in place of the previous square, black plastic inserts. This made it easier for stunt flyers in particular, to tailor make a venturi size to their own requirements (square lathes not having been invented at that stage) and by adding a head shim to lower the compression, and resisting the temptation to use the largest available insert, a decent stunt run could be obtained. While an ENYA ( particularly the 29 ) could never hope to match a Fox for the perfect aerobatic characteristics, the 35 however did a better job at stunt than the Fox 35 did as a team race motor.

Horses for courses, and anyway Duke Fox himself would probably admit that the 35 was just an engineering fluke ­ how else do you explain a piece of machinery which was basically perfect for its intended use, right from the start. That’s akin to the Wright brothers building a 747 to fly at Kitty Hawk.

Along the way, both ENYA’s were available (from the early 70’s) with a twin ball race crankshaft and although a lovely engine in its own right, most modellers stayed away because of the extra cost (most being notorious pennypinchers!) and added weight. These BB models incidentally, had smaller threaded portions on the shaft than did the plain bearing models, so prop nuts are not interchangeable. The early BB’s had a radiused front on the prop driver; later ones were stepped, and while they were rated at 0.05 more hp than their bronze bushed brethren, they also weighed an ounce heavier and had around 6mm more overhang. Still supplied with dual heads, the spare one in the BB box gave half a point extra compression over the plain bearings 9:1 ratio.

In the 1980’s the last of the line appeared and this was the 29 ­ V Model 5225 (35 same designation) which looked very similar to the earlier 5224, apart from bumps at the rear of the crankcase, deeper head fins and one less cyl. fin (6 instead of 7). The 5225 BB had a noticeably smaller front race than the previous model, but weighed the same, due to extra metal mentioned above plus an exhaust bridge.

Other distinguishing features of the last ball race 29 & 35 were the round venturi and the parallel sided prop driver; less visible was the fact that these final models were not supplied with a spare H/C head, but instead used a (cheaper) metal head gasket for the first time, removal of which provided the higher compression. Factory specs for the 5224 and 5225 29’s and 35’s are identical, apart from higher peak revs in the earlier models, both plain and ball raced.

So in the final analysis, the ENYA 29 distinguished itself by its record breaking production run for a 5cc motor, and the fact that it was never emasculated like, for example, the OS Max which (like the ENYA) started off in a builders labourers T-Shirt, but ended up in a lilac coloured suit, with a limp wristpin.

Sadly, these fine engines are all now out of production, but as vast numbers were produced over a long period of time, new in box examples are still fairly easy to obtain at reasonable prices. My advice? Buy one, and enjoy a genuine classic while you and they are both still around.

Post Script

To demonstrate to yourself how good an ENYA’s lapped piston/cyl. fit can be, try this experiment ­

1 Select a new unrun ENYA (09-35 size) which is free turning & well oiled ­ remove glow plug and prop.

2 Turn engine slowly and gently by gripping the shaft threads.

3 On the downstroke, take particular note of how close the piston top is to the exhaust port before the seal is broken ( this actually is the release of pressure as the piston uncovers the transfer port on the opposite side of the cylinder, but out of view ), also how the piston will pop back up again when released.

4 Now install a glow plug, and on the upstroke, the compression should not leak away, even when the turning force is continuous.

This is known as the “ Excellent , Not Your Average “ compression test or E.N.Y.A. for short.


Some Important Updates !!

1) Further to the "first hand witness report " mentioned above, I recently came into possession of an MRC-ENYA catalogue dated 1965, in which it states that - " The machinists in the ENYA factory turn out more than 50,000 engines a month to satisfy a world wide demand." Now, in the 1968 Model Airplane News article done on ENYA, it showed just one person doing the Hand Lapping, and I decided to dig out my calculator to try and figure how many piston & liner sets that one poor overworked machinist would need to produce to supply 50,000 engines a month. I don' t know the Industrial Rules & Conditions ( if any ) which applied in Japan at that point in time, but I worked on a benchmark set at 9 hours a day, a 6 day week, over a 30 day month period. This would mean that, if only one person was involved in the Hand Lapping process, he would need to turn out around 3 sets a minute or about 1 lapped piston & cylinder every 20 seconds ( and that's not including meal breaks or smoko's ! ). I figured there HAD to be more than one person doing the lapping, so I contacted the "first hand witness" and here is his reply ( with non relevant parts edited ) - "I probably visited the factory in 1961, I know I went to see one of the Enya Brothers in their office in Tokyo. There were four Enya Brothers and I met three of them, Saburo was the eldest and did the designing and worked in the factory. The second Brother spoke very good English and ran the office in Tokyo. The third Brother worked in the factory, and it was this one who was doing the Hand Lapping. I remember watching him do this - he rubbed on some lapping paste and sent it up and down the cylinder about TWICE ! I did make a comment at the time about how little lapping was actually done, and they just laughed and said it covered their advertising ! Sorry I cannot give you any more specific information, but you are correct when you suggest that they were lapping about 3 cylinders a minute. " ( end of quote )

2) The 29 & 35 size BB Specials first became available in 1965.



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