Creative Commons License  This work is licensed under a Creative Commons
 Attribution-Noncommercial-Share Alike 3.0 License

The ED Story —
Radio Control Units,
Kits, and Accessories

While mainly remembered for their engines, Electronic Developments Ltd (ED) initially set out to provide for virtually everything a modeller could want with kits, Radio Control units, accessories, fuel, even the first engine powered, plastic ready-to-fly (RTF) control-line model! Success varied and none came close to the acclaim that their diesel engines achieved. This page looks at these other offerings.


By the start of the 1950's, ED was offering quite a broad range of accessories to the land, sea, and air modeller. Some items, such as the ED Clockwork timer seen here, were simple "badge engineering" jobs, while others must have consumed valuable resources in terms of machinery investment, production scheduling, and most important, the budget for advertising and promotion.

The range also included airscrews (propellers) in "plastic" and "Hydulignum". The latter is a "densified" wood laminate, still commercially available today. When carved into a prop blade section, the thin laminations make for a quite attractive appearance. Naturally, like any wood prop, they were easy to break, but then so were ED's "unbreakable" plastic props!

Other offerings included rubber tires for the race car craze, brass boat props, and bits and pieces from their radio control units that would be of use to people building their own radio units from scratch—which is how most did it in the late 1940's and early 1950's. Add clutch units for cars and the odd magneto or two and you have an inventory and spares nightmare that would make a modern MBA run screaming from the room. Probably just as well that they hadn't been invented yet.


The initial kit offerings were a hydroplane called the Challenger (try not to get too confused yb the later RTF model of the same name), and an airscrew-driven car appropriately named the Aerocar. Following ED's historic first English Channel crossing by a radio controlled model boat named Miss Ee Dee in September, 1951, a kit of the model in reduced scale was added to the range. This was named Miss E.D. 2, having a length of 36" and a beam of 10". By this time, both the Challenger hydroplane and Aerocar had been dropped. The other nautical offering was a 30" cabin cruiser named the ED Junior Cruiser, 30" LOA, with a 9" beam.

The most ambitious model kit was an aircraft named the Radio Queen that appeared in 1950. This was designed by Lt Col HJ Taplin, a noted English authority on models and designer of the Taplin Twin. The Radio Queen was a high-wing cabin model with a seven foot wingspan. Designed for rudder only control, or free-flight, the Radio Queen was very typical for radio models of the late 1940's and 1950's. It was intended for the 3.46 ED Hunter diesel and as recounted in the ED Story, was used by ED in their record-setting Channel by air in 1954. This flight was made using a wing borrowed from Taplin, the ED team having broken their own the day before in testing.

All the kit offerings were relatively short lived. By 1956, mention of them in ED advertising had disappeared, although stocks probably lasted longer on dealers' shelves. Most likely, management was discovering that the cost of production and promotion of such a broad product range comprising engines, fuel, accessories, and kits was a drain on the budgets for R&D and advertising. With kit sales in the hundreds (possibly) and engine sales in the tens of thousands, the answer should have been obvious to Blind Freddy and his dog; concentrate where the return was and drop the rest.

Radio Control Units

Although the volume sales of ED R/C units would not have matched that achieved by the engines, this was a market niche with relatively little initial competition and probably a decent profit margin, so ED persisted with this venture longer than they did with kits and accessories. We are lucky today that the "other" English aeromodelling magazine, Model Aircraft, ran a feature on the domestic commercial R/C offerings, including circuits, which allows us to see in detail just how crude these early sets were. ED were not alone in this, the others were no better! But with very few proponents indulging in what then was a very expensive and difficult aspect of the hobby, the sets did not have to be any more sophisticated. Operating two sets in range of each other at the same time was impossible, but as flights were few and each one considered a genuine achievement, this did not matter greatly.

Right from the start, ED had offered R/C units designed by George Honnest-Radlich who they termed their chief back room boy[1]. One of the ED founders, Honnest-Radlich was an established author on the subject of radio-control for models. His ED Mk I single channel unit first appeared in early 1949. This is way before the advent of the transistor, so all receivers were of the single valve, super-regenerative type, carrier wave operated (I've carefully not said vacuum tube as many early receivers used the gas-filled, or "soft" type valve, sometimes called a "thyratron"). The transmitter used two vacuum tubes wired as a multi-vibrator with a tank circuit to constrain emissions to somewhere near the 27 M/cs band (same as MHz, but that name came later). With not a crystal in sight, transmitter frequency drift and battery voltage drain was a problem, so careful tuning just prior to short flights was the order of the day.

The Mk I receiver was followed by the "crashproof" receiver—essentially the same design wired on a paxolin board using gas-filled triode, but housed in a paxolin tube. This tube was actually a former normally used to wind large HF radio coils on! The solder tags on the ends of the coil former provided convenient lugs for the battery and relay connections, and bent back, served as hooks for rubber bands that allowed the receiver to be suspended in the cavernous cabin. The intent was to provide some vibration isolation of the sensitive relay, and perhaps, some degree of crash protection.

In contrast to R/C development in the USA, ED's circuit designs for single channel did not progress significantly during the 1950's. However they did progress in packaging the airborne components in a way as to lower the effort and knowledge required to enter this side of the hobby. The ED Boomerang single channel unit, marketed from 1953 to 1958 is a good example. The transmitter was still a multi-vibrator, carrier only, ground-based type, housed in a black crinkle paint finished hat-box with a plug-in fly-lead to the microswitch "key"—a term borrowed from Morse code. The super-regen receiver now used a subminiature type valve, either hard or soft (meaning evacuated, or gas filled—while the term "vacuum filled" is sometimes used, it's a bit of an oxymoron).

Most significantly, the receiver came completely wired to the switch, battery box, escapement, metering socket, and potentiometer (don't ask), greatly simplifying installation for the non-technical modeller. The escapement was of a "current saving" design that used a tapped coil and wiper switch to reduce the current after the armature had "pulled-in", battery drain being a problem in the days of "dry", non-rechargable batteries. Crude as it seems today, the Boomerang was the proverbial bees-knees and worked, mostly, exactly as advertised. But then expectations were much lower back then when a free-flight with occasional radio interference that did not terminate in a spiral death-dive was considered a success. Landing in the same paddock that you took off from was considered a roaring success.

While ED enjoyed success with their single-channel equipment, even exporting to the USA via Polk's Hobbies, New York, and Australia through the Model Dockyard, Melbourne, their efforts to develop equal reliability in multi-channel, reed-based systems were more protracted. There is no doubt that success could be achieved. Honnest-Radlich had been developing reed banks right from the beginning and had demonstrated that they could be made to operate reliably for extended periods in the '51 and '54 Channel crossings. But mass producing reliability proved far more difficult. The early three and six channel units used a ground based, tone modulated transmitter with a fly-lead connected "beep-box". This key-switch unit included the potentiometers used to tune the separate channel tones to the resonant frequency of the individual reeds. This was meant to be a operation performed on the ground, listening for loudest "singing" of the reed, indicating the correct tone had been found. Again, un-stabilized circuits and drift were the enemy and if the model stopped responding to a particular signal, well, the pots were right in front of you and what more did you have to lose?

ED finally went hand-held and "hybrid" towards the end of the '50's. The Black Arrow four and six channel reed receivers used a soft-tube type super-regen receiver, with a transformer coupled transistor audio amplifier for the reed bank. The matching Black Prince hand held multi-channel transmitter could be supplied with up to eight channels and ED still thought front panel mounting of the channel tone pots was a good idea. The transmitter was also available as a single channel, tone version called the Black Knight for use with ED's new Transitrol hybrid receiver.

The last radio set developed by ED was released in 1962. By this time, reliability had improved as had the number of modellers knowledgeable and experienced in what had been an arcane art. For the beginner, this meant that finding help and guidance in the average model club was no longer impossible with the result that increasing number became willing to give R/C a go. ED may have sensed this because as the advertising says, the ED Autopilot single channel set was intended to bring radio control within the reach of all. The set was about as successful as the new "ED" engine featured in the May 1962 Model Aircraft ad; which is to say, not very.

ED never developed a multi-channel "servo" as such, although they did have a wide range of offerings for rubber, clockwork and electric motor driven escapements. All the rubber escapements were of the type termed "bang-bang sequential"—ie, they did not employ any type of speed governor to reduce the sensitivity while the rubber torque was high. And being "sequential", ie, neutral-left-neutral-right, it was easy to miss a position and end up with left rudder when what you really, really needed was right! But provided the model did not crash, the pilot could always claim that the flight went exactly the way he'd planned it. Comparison with developments in the USA over the same time period show how far behind ED was falling. They were saved initially by import tariffs on US equipment, but as the market in the US bloomed, bringing down unit prices, imports became more attractive, and ED, hamstrung by lack of R&D could not compete.

The Challenger RTF

One thing that ED can't be faulted for in their early days was vision; this they appear to have had in spades. While we can, with hindsight, question the viability of the the broad scope that their product range attempted to encompass, they sure picked what should have been the leading edge in emerging hobby trends. The fully wired and ready to go Boomerang R/C unit of 1953 was one example. The idea of a ready-to-fly control-line model was another. It's hard to say from literature search just how involved ED was with this venture. The first advertisements for the model appeared in October of 1951 under the manufacturer's imprint: Cascelloid Ltd, of Leicester. The model had a span of just 13-1/2" and fitted with an ED Bee, must have had the same glide ratio as an anvil thrown off a roof! But then, the later plastic RTF offerings in the USA from Comet, Aurora, Cox and others were no better.

The first October 1951 advertisement and Trade Notes photograph below show the model fitted with a wire undercarriage. This was presumably a prototype rushed into print to generate demand for Christmas as the December '51 ad shows the final dural legs, secured under the engine mounting lugs. The Challenger was offered complete with engine, handle and lines, or as an airframe alone. Although never featured as an illustration in ED advertising, it does quietly appear as a line item[2]. Whether this indicates a financial association between ED and the maker is not known. Whatever, the concept, later to prove such a winner in the USA, did not catch on in Britain and the model swiftly faded from view. We can conjecture what may have happened if the model, or a manufacturing franchise could have been exported to the USA. The diesel would not have been popular there, but the idea may have stood a better chance of an early take-off in a market with a greater population base having more disposable income. Sad, really.

Excerpt from "Trade Notes", Aeromodeller, October 1950


[1] ED advertisement text in the Model Engineer issue number 2639, December, 1951.
[2] ED advertisement in Model Aircraft, September 1951 (see top of this page).


Creative Commons License  This work is licensed under a Creative Commons
 Attribution-Noncommercial-Share Alike 3.0 License


Back to the ED Story page


This page designed to look best when using anything but IE!
Please submit all questions and comments to