The ED "Bee"
Series I and II

Created: July 2004
Last update: July: 2007

Name ED Mark I ("Bee") Designer Basil Miles
Bore 0.437" Stroke 0.400"
Type Compression Ignition Capacity 1cc (nominal)
Production run 300,000 + Country of Origin England
Photos by Ron C Year of manufacture 1948-1963


ED Background

Electronic Developments (Surrey) Ltd burst onto the aeromodelling scene in England very shortly after the end of World War II. A detailed history of the company's rise and decline can be read on the ED Story page. ED produced some of the first commercial compression ignition engines, and the first commercial radio control outfits to go on sale in quantity in the UK. For a considerable time, their product offerings were prolific and well respected, both domestically and throughout the British Commonwealth—especially in the engine department—almost dominating the bouyant industry catering to the "air-minded" youth of the 50's. Wiser and more knowledgeable heads than mine now seem to agree that their decline was occasioned by a lack of sustained R&D, poor quality control, and a huge tax burden occasioned by their bet that a challenge to the application of Purchase Tax to model supplies would be successful. It was not, and ED, like others, were hit with a back tax bill for which they had unwisely made no contingent provision. In 1963, a fire destroyed their premises and most of their engine dies. Although ED rebuilt at a new site, they could not regain their market position and eventually faded from the scene. Their last engine, the 1.5cc 'Hawk', was manufactured off-shore by Webra.

The ED "Bee" series

The Bee (aka "B"), was officially designated as The E.D. Mk.I. One c.c (Bee) Diesel. It was introduced in late 1948. As an almost-square rear rotary valve induction design (ie, bore and stroke are close to equal), it was quite an advanced diesel engine for its time in a local market dominated by long-stroke, side-port models. The very first engines produced featured a two-bolt head and a 4BA left-hand thread crankshaft. An ED advertising picture appearing in Aeromodeller of February 1949 shows a conical, hexagonal spinner nut and the two bolt head. It is believed that very few of this style were produced[1] and for a fact, they are rarer than the proverbial rocking-horse droppings today, commanding astronomical prices to serious collectors. By 1949, when quantity production started, the head was being secured by three bolts. The delicate 4BA left-hand thread on the shaft was also changed, possibly in response the number of shafts being broken by over-tightening while the owner was trying to loosen the nut! The shaft diameter was increased at the same time.

Mk I Series I

It's probably worth noting that the "Mark One" applies to the Bee as an engine in ED's line (The 2cc "Penny Slot" side-port was the Mk II; the Mk III was a 2.49cc FRV, and the 3.46cc RRV "Hunter" the Mk IV). Major variations in the design were designated by the "series" number, so the first model is the "Series I". This model remained in production with minor variations from 1948 through 1955 when the "Series II" was introduced. The Series I Bee is readily identified by having the cooling fins turned integral with the crankcase, a plain, turned head, and an "L" shaped compression screw (although some late models may have had a "tommy-Bar" style screw factory fitted).

Internally, the design is quite conventional, having a hardened and ground, unbalanced shaft (ie, a circular crank web) running unbushed in the cast aluminium crankcase. The conrod was case hardened steel. Piston and contra-piston were flat-topped and turned from cast iron. They ran in a case-hardened steel liner. The gravity die-cast crankcase incorporated the cooling fins, the latter being turned during manufacture. The rotor disk appears stamped from aluminium and is permanently rivited to the turned backplate. With a bore of 0.400" and stroke of 0.438" (7/16"), the actual capacity was 0.060 cuin, or 0.98cc. Reference [1] notes that the very first model (the two bolt head) had no external adornment whatsoever. Early three-bolt engines had "ED" stamped in the front of the bypass. This was soon changed to cast-in, vertically aligned, raised lettering on the front of the bypass as seen in the photo at the head of this page. The standard fuel tank was an aluminium stamping, but transparent plastic tanks were available (in clear, green and yellow) as an option. The tank was suitable only for upright mounting use.

The "B" was the subject of Lawerence Sparey's 18th engine review for Aeromodeller in the October 1949 issue[2]. Sparey liked the engine, commenting on it's small size and easy starting nature. He also goes to some length on the near-square short-stroke design, being mildly surprised that this feature had not imposed any obvious detrimental effect, then explaining in some detail why common wisdom of the time leaned towards long-stroke designs. It is worth noting that the engine depicted in the three-view drawing appears to carry the cast-in "ED" lettering, allowing us to say that engines with a stamped "ED" will be from the first months of production. Serial numbers were generally stamped on the lower front of the crankcase face. Reference [1] goes into detail on the numbers and letters used, observing that it's generally possible to determine the year of manufacture, and perhaps even the month from the number.

Another review of the Series I Bee appeared in the Model Aviation Planbook for 1949[3]. This annual publication, co-edited by Ron Warring and Bill Dean, carried a review of the engine written by noted competitor and model shop proprietor, Henry J Nicholls. The attractive air-brush rendering of the engine shows what appears to be mirrored counter-balance holes in the crank web, although their position as drawn would have little beneficial effect. In any case, these were absent in actual production engines. The reported performance curve indicates a maximum BHP of 0.064 at 9,000 rpm.

A much more recent Engine Test review of the Series I Bee appeared in Model Engine World of March 1995[4]. The results of the BHP and torque curves in the MEW are a little surprising showing 0.075 BHP at 9,500 rpm, compared to Sparey's Aeromodeller test figures—later condemed by Aeromodeller itself as overly optimistic—of 0.061 BHP at 10,500 rpm. All of which illustrates, methinks, the difficulty of obtaining meaningful, repeatable figures for small engines. Better to compare the numbers from a single tester using a consistent method as relative data only. Reference [4] questions how it was possible to position the induction hole correctly on a screw-in backplate. The answer is simple: drill each individually, on assembly! Very time consuming and non-interchangeable, but a sign of the times when labour was cheap.

Mk I Series II

With sales for the Series I estimated at over 300,000[5], a major refinement of the "B" appeared in 1955. The crankcase, head, and backplate were pressure diecast, allowing thinner sections and very fine detail. The steel cylinder liner carried integral fins and the porting was totally revised. About the only parts recognizable from the Series I are the spinner nut and prop drive washer. In fact, apart from the general RRV design, bore, stroke, and name, it could be considered a completely different engine!

Ignoring the obvious external differences, general construction remained the similar. The hardened and ground shaft remained unbalanced and unbushed. The rotor disk was aluminium, and the pistons, turned from cast iron, were still flat-topped. The conrod however was changed to an aluminium forging (forging can add up to 50% strength increase to aluminium). ED must have decided by this time that individually fitted and drilled RRV backplates were for the birds, as the Series II uses a rear cover retained by four 6BA cheese head screws. Serial numbers were now stamped on the end of the left side mounting lug. References [5] and [7] note that the Series II underwent changes about eighteen months after initial release. First models may be identified by having six cooling fins on the steel liner and a step-up at the cront of the crankcase journal. Later models with revised transfer porting had five fin cylinders and a straight journal. No change in designation accompanied this revision.

Aeromodeller tested the early Series II "B" in the September 1955 issue[6] (Aeromodeller engine tests now being conducted by Ron Warring, using the eddy current dynamometer developed for the purpose). Performance is quoted as 0.068 BHP at 10,900 rpm (taken with the usual pinch of sodium chloride). The text notes that "...the bore and stroke remain the same...", though my HP calculator disagrees with their slide rule over the capacity: 0.0605 cuin stated compared to 0.0603 calculated—big deal. Warring does note that at 3-1/4 ounces bare, the Series II is heavier than the Series I by 1/2 an ounce. This is surprising for a pressure die cast design. Presumably the change to the fined steel liner is mostly responsible. The review noted the unbalanced crank and quaintly advised "This is undoubedtly one of those engines which will give its smoothest performance with a slightly unbalanced propeller, the heaviest blade being set opposite the piston at top dead centre." (!) and goes on to note that vibration caused problems with both eddy-current dynamometer and torque-reaction testing rigs. Warring suggested that the integral tank design requiring long, unsupported engine bearers probably exacerbated the vibration problem. The text also observed that the four-bolt backplate made it impossible to alter engine timing by rotating the backplate—not something I'd have thought to try!

Rival publication, Model Aviation published their test report over a year later in the December 1966 issue[7]. So they were able to contrast the revised Series II Bee with that reviewed in the Aeromodeller. The test report is uncredited, but gives an excellent description of the changes and observes that of the two models tried, the later model was the more pleasant to handle being less critical of adjustments. Note in the photo opposite that the heading picture shows the earlier Series II model, while the side view and exploded picture are of the revised engine. Apart from the external differences noted earlier, the most significant change was to add an extra transfer port (making three in total) and mill these on the outside of the cylinder. The article also comments on the change to the case casting in the area of the nose, resulting in a "..stiffer main bearing housing, the bearing itself now being bushed with a special alloy developed for this particular purpose." Strangely, my own example of this engine, with the five fins and "stiffer bearing" has no signs of any such bushing, unless it is the alloy itself. The performance curves indicated maximum BHP of 0.062 occurring at 10,700 rpm. The weight quoted is 3.2 oz. with tank, slightly lighter than the Aeromodeller figure, but still heavier than the Series I.

The 150,000th "Bee"

As noted by Ron Moulton in his brief history of ED Ltd[8], Aeromodeller for April 1954 announced that the 150,000th Bee would soon be sold. The lucky owner was to receive the princely sum of ten pounds (not so shabby when you realize that this was nearly four time the price for a single engine). As seen in the announcement from the inner back cover of the issue, the winner was to be matched against the engine serial number. This number was known only to the ED Managing Director, Jim Donald, and would appear in the June issue.

Well June arrived with a rather obscure entry in the Trade Notes column delaying the announcement to the July issue. We can speculate that serial number returns were slower than anticipated, or even that the awaited number just never showed up. When the announcement did appear in the July issue (again in Trade Notes), it announced the name of the winner, but disappointingly, not the serial number of the 150,000th engine. Had the number actually been published, that engine's value today would have skyrocketed—if it still exists.

Now, we know that the Series II Bee appeared in mid-1955. So perhaps the most significant part of this episode is that ED has officially documented the fact that some 150,000 Series I engines sold in the period up to mid-1954. The Model Engine World article by Kevin Richards[5] states: 1955 ED's had sold over 300,000 Bees...

If this is true, they must have manufactured and sold as many engines in the next year as they had in the previous seven! Hmmmm. I don't think so. Ron Moulton states that the 300,000 figure was achieved, but not until 1962, and included both series of the engine[8].

The OS "Bee"

Now for a surprise ending. The engine pictured here at first appears to be a Series I Bee which has been sexed up by a spot of anodizing. The lack of an embossed and boxed "ED" on the front of the bypass would indicate that is was an early model. I had prematurely id'd it as such to a reader, but was quickly corrected by ECJ Editor-in-chief and head bottle washer, Tim Dannels. Tim pointed out that OS (yes, THAT OS) had made a copy of the Bee circa 1949/1950. These copies bore no designations or serial numbers, but could be identified by the "V" type tommy-bar compression screw, a flare on the brass venturi tube, and red anodized spinner nut and cylinder head. This was confirmed by David Owen who observed that no OS "B" had ever been seen with a tank fitted, probably because the flare on the end of the brass venturi would prevent fitting one that did not immediately leak away over half the contents. He was also able to supply a photo of the original box clearly bearing the OS logo. In other words, the "watzit" engine, down to a "T" (or possibly, a "V" ).


[1] Richards, Kevin: The ED Story Part 1: A swarm of bees, Model Engine World, Volume 1, Number 1, May 1994, p12.
[2] Sparey, LH: Engine Analysis No. Eighteen: The E.D. MK. I "BEE", Aeromodeller, Volume XIV, Number 165, October 1949, p 46.
[3] Nicholls, Henry J: E.D. Bee Test Report, Model Aviation Planbook, 1949, p42. [Date derived by deduction; this Planbook being undated, unlike the 1948 and 1950 issues.]
[4] Roberts, Dick: Engine Review ~ Mark 1 ED Bee, Model Engine World, Volume 1, Number 11, March 1995, p8.
[5] Richards, Kevin: The ED Story Part II: A String in the Tail!, Model Engine World, Volume 1, Number 2, June 1994, p1 2 (sic).
[6] Warring, RH: Engine Analysis No. 13 [new series]: The 1 c.c. E.D. Bee series 2, Aeromodeller, Volume XX, Number 236, September 1955, p690.
[7] anon: Engine Tests: The E.D. Bee Series II 1 c.c. diesel, Model Aviation, Volume 15, Number 186, December 1956, p430.
[8] Moulton, Ron: E.D. On The Inside, SAM35 Year Book #8, Dorking Litho Printers, Surrey, England, 1994, p24.




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