ED Baby 0.46cc Diesel

Name ED .46cc Baby Designer Basil Miles
Bore 0.3125" (7.93mm) Stroke 0.375 (9.52mm)
Type Compression Ignition Capacity 0.46cc (nom)
Production run Unknown Country of Origin UK
Photo by Bert Streigler, Tim Dannels, Adrian Duncan, Ron C Year of manufacture 1953-62

 

Background

In the early years of the 1950's, British engine manufacturers turned their attention to the small diesels market, most likely in response to interest sparked by the eruption of "1/2 A" glow engines in the USA. The choice of compression ignition over glow was logical, given that this was the predominant type of motor being used by modellers in England and Her colonies at the time. Consequently, it was the type with which both they and their customers were most familiar, and even though their small diesels were more expensive than their larger counterparts, and required more experience with regards to handling, all manufacturers' products were market successes.

With a broad range of choices available, individual aeromodellers could support their favoured maker: Allbon with their 0.5cc Dart, Frog with the Frog 50, Elfin with their now rare and highly prized bulkhead mount Elfin 50, and Electronic Developments (ED) with a slightly smaller 0.46cc diesel. In this review, we'll look at ED's product, announced first in Aeromodeller of April, 1952, and appropriately dubbed the "Baby".

Models and Variants

In the next paragraphs, mention will be made of the two versions which for clarity, will be referred to as the Mk I and Mk II. ED themselves never drew this distinction. Neither, on careful inspection, was the label applied by the Aeromodeller in their mini review of the later version that appeared as an appendix to the Allbon Bambi review in the August 1954 issue; the first version of the Baby, pictured here, having been reviewed in the June 1952 edition. Production of the "Mk I" appears to have lasted only for the first year of the engine's ten year production life, and even though no official distinction exists and the changes are subtle, they are sufficiently significant that we'll continue with the designation for the purposes of this article.

The engine was announced first in March 1952 issue of the Aeromodeller. It featured front rotary shaft induction with the needle valve swept distinctly upwards and rearwards; a nice feature given the nearness of the needle to the prop of such a small engine—although this effectively prevents the needle and spraybar from being swapped side for side. Another notable feature of the engine is the ocean-liner like "port-hole" exhausts, eight in number. Note also that the photo depicts a conventional "Tommy-bar" style compression screw and the engine lacks a venturi insert.

Although later advertising retained the Tommy-bar comp screw, close inspection of this photo from the October 1953 issue shows some evidence that this may have been drawn in. The more conventional, common and cheaper to make comp screw was a bent "L" shaped affair, similar to that seen on the ED Bee and Miles Special of the same page. The timing of this photo is odd too, because as we shall see, the Mk I port-hole head model it shows was a thing of the past by this time!

The design was quietly revised in 1953 with the new model featuring for the first time in the February issue of Aeromodeller that year—less than twelve months after introduction. Outwardly, the port-hole exhausts had been replaced with a more practical arrangement of three radial slits and the comp screw reflecting that actually fitted to production engines. The photo also clearly shows the addition of a venturi insert that extends the inlet and permits a conical opening.

Apart from reducing the number of operations required to produce the cylinder head, the change in the exhaust arrangement made port priming easer as it reduced the ease with which the Mk I could be flooded by a vigorous squirt. To explain: the small size of the openings (3/32" in diameter) made it hard to dribble a little fuel through to the liner; it required a serious blast. But once through the holes, surface tension on the meniscus formed in the ports tended to hold the fuel in the annular cavity between the inside of the head and the actual cylinder ports. To avoid a major flood, the most practical technique was bring the prop up to close the exhaust, give a hearty squirt, then bend down and blow away most of the fuel. The new head with slit exhausts cured this problem and normal port priming became possible.

Inwardly, the conical top on the piston and corresponding concavity in the contra-piston were replaced by simpler to manufacture flat-topped items. Even though the conical design should improve scavenging, it was found that in practice, there was no measurable difference. The steel "dog-bone" conrod was retained, as were all other features of the earlier model, including the neat little soldered in elbow on the spray bar which enabled the fuel line to assume a quite compact path to the tank. The tiny, narrow-necked spray bar had no "seat", so metering was less than perfect. Fortunately, on small sport engines, once set to a running position, precise fuel regulation is not critical—a fact noted by reviews of the engine.

Between these two models, a twilight variant appeared where the lands between pairs of port-holes was milled away to produce four rounded end slits (the left-hand motor in this picture). This arrangement produced the best compromise between opening size and strength, but I shudder to think about the cost of manufacture. So apparently, did ED with the final slit port arrangement. As to strength, I had the opportunity to witness first-hand what happens when all three posts separating the exhaust ports of a Mk II head let go at the same time. This happened during the ROG of a small free-flight model from a taxiway at RAAF Amberley air base in the late 1960's. The cylinder head and liner must have shot 50 feet into the air to the great amusement of all present. Took us ages to find it in the grass, and worse yet, it was my engine!

The venturi insert mentioned earlier is worth comment as not all engines had one. To complicate matters, the presence or absence is not related to the "mark" number, insertless ones having been reported of all types, including the twilight model. The only theory I can offer is the difficulty of screw-cutting the thread on the top of the crankcase where the tool is likely to clobber the venturi top before the required thread reach has been achieved. This forces the venturi to be very short and even though it works, raw fuel drops can be seen leaping from the venturi while the engine is running. Extending the casting would make it way too difficult to screw-cut, hence the need to permanently insert an extension. This needs to be done after the threading operation, but before the spray-bar drilling and ideally, before shaft bush drilling and reaming operations. Altogether, it complicates manufacture and adds significant cost for a small gain in fuel economy. This may account for why ED occasionally made a batch without the insert.

The first mark of the Baby was reviewed by Ron Warring in Aeromodeller, June 1952. A month later, rival magazine Model Aircraft carried another review. Although this piece was un-credited, it was most likely written by Peter Chinn.

Production of the Baby continued until the Great ED Fire of 1962 as described in the ED Story, the Baby being one of the designs that did not manage to rise, Phoenix-like, etc. Perhaps it could have, but the market had moved away from small diesels and ED had a golden excuse to drop it from the range, eventually replacing it with the slightly larger although generally uninspired ED "Pep".

Design and Construction

The Baby is a plain bearing, front rotary induction compression ignition engine designed by Basil Miles, designer of the related 1.46cc Hornet with which it shares its transfer design. As detailed in the analysis of the Hornet, the cylinder liner has three exhaust slits made in a seating flange. Immediately below this flange are three more transfer slits. The lower extension of the liner is somewhat smaller than the opening for it in the crankcase, being centered and pressed down to the case by the cooling jacket which screws onto a male thread on the upper crankcase. The space between crankcase bore and lower cylinder liner forms a 360° transfer passage and while the whole arrangement is gasket-less, experience shows it works quite well at Baby and Hornet sizes. As with the Hornet, the design restricts the transfer period significantly while forcing a rather early opening of the exhaust. Strangely, this does not seem to matter and once the starting technique and settings are understood, a Baby will start quickly, run well, and provide a flexable range of running adjustment.

The crankshaft runs unbushed in the die-cast aluminium crankcase and is tapered at its forward end for the prop drive washer. This carries a boss in its center, presumable because ED knew that most suitable props would have a larger hole in their center than the major diameter of the small 4BA protrusion of the crankshaft. While the crankweb is unbalanced, this is no bother at all at this size. It should be mentioned that the shaft was a one piece unit, just like larger engines of the time. In contrast, the MBI General Arrangement drawing at the head of this page shows a more practical screw-in stud arrangement, better suited to amateur construction where hardening of the shaft without inducing distortion would be extremely problematical. The steel conrod, gudgeon pin and piston were quite conventional, though tiny.

Completing the engine is a screw-in backplate with a threaded central boss for the 8BA screw which holds a plastic tank in place. This was moulded from a translucent plastic material—some were green, others yellow. The fuel tube fitted to early engines was not transparent. The backplate was tightened by the usual arrangement of a saw slit across the diameter, requiring the tank to seal on its front face rather than the locating lip on the backplate. This pretty much amounted to a leak waiting to happen when the tank plastic distorted. The filler hole and fuel line exit were good leaks too, but in practice, fuel did not leak away faster than the wee beastie could be started and a quick squirt before release could provide a minute of running—more than enough to loose a small free flight!

It was ED's practice in the early 50's to stamp all engines with a meaningful if not always accurate serial number. This was generally applied to the edge of a mounting lug, but being rather on the small side, the Baby received its number in an arc on the front face of the crankcase. The designator for the Baby was the letter "B" and the numbering scheme follows that detailed in Part II of the ED Story.

A last note on the subject of lugs. Unlike the .5cc offerings from Allbon and FROG which had the conventional four bolt mounting pattern, the Baby lugs had only two elongated holes. This permitted a degree of side-thrust adjustment if the case was not too tight between the engine bearers—sometimes intentionally, sometimes not!

Operation and Conclusions

The Baby can be a delight to operate, or a right pig of a thing. The difference is in the fuel, technique, and how run-in, or run-out the example happens to be. Like all small diesels, it is happiest with a higher ether content fuel, say 40%, although good performance and easy starting is possible with straight 1:1:1 mix and experience. The normal prop would be in the 6x3 range to 7x4 range [1]. The photo shows a replica turning a 6x4 Master paint-stirrer at 7,700 rpm which is typical for the original. Starting is best accomplished from a rather wet-ish port prime and a backed-off compression setting. So prime, wind back the compression almost a turn and holding the comp screw, give the prop a hearty belt. Advance the comp as it fires and starts to run out the flood, then you're away. As noted by Warring in the Aeromodeller review, the needle, once set, can mostly be forgotten.

A number of kits were produced for the British 0.5cc engines, several specifically for the Baby. Keil Kraft had a delightful little symmetrical wing "stunter" called the Joker which I'm sure could have performed well in hands other than mine. Many plans for small free flight models specifically showing the Baby appeared, including a number of quite intricate scale free-flight biplanes and innumerable sport free-flight cabin designs, not to mention flying wings, deltas, and even the odd flying saucer!

The Mk II Baby was the second engine I bought new as a very young lad and I recall the long cycle ride to collect it from the Nundah Sports Store in about 1956. Being a bit lacking in experience, I had some initial trouble with starting as noted in the Model Aircraft review [2]. But it was finally mastered to the extent that all my young flying friends were envious of how easily it could be started. It was with this engine, in a Veron Percival Provost profile trainer that I learnt to fly control line, running around in circles with one arm hooked about the Hill's Hoist in my aunt's back-yard. Years later, it powered my first free flight models including cabin, low-wing, and delta types. Ahh... Fine nostalgic memories all, and ample reason to declare the ED Baby as a wonderful little engine for young and old.

Footnote and Confession

None of the Babies at the head of this page, nor in this photo, are completely kosher. Of them, the one at the right, the Mk II variant, is closest. It has a genuine ED comp screw, die cast crankcase, crankshaft, backplate, and spraybar. All the rest were made from scratch to restore the "bones" to running order. Spurred by this resounding success, the plans were polished, a pattern made, and replicas of the original and twilight versions made from castings poured by Mystro Roger Schroeder. You can read more about this on the ED Baby Reproduction page and follow through how to make your very own in the ED Baby Construction Project pages. See Roger's web page for details on how to obtain a sand cast crankcase from my original pattern and Roger's rather cunning application of old Dymo labeller technology to mimic the ED logo.

References:

[1] Warring, R: Engine Analysis: ED Baby, Aeromodeller, Volume XVII, Number 197, Model Aeronautical Press Ltd, GB, June 1952, p346.
[2] anon: Engine Tests: No 37, The E.D. .46 "Baby", Model Aircraft, Volume 11, Number 7, July 1952, p310.

 

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