Simplex Pleasures

If you're old enough to have been browsing the shelves of WH Smith back in May 1964, you might remember seeing RCM&E. The cover was an acid-yellow that month (how could you forget?) with a grainy black-and-white shot of Vic Smeed's Ohm 8 biplane trainer, a coverline inviting readers to build a relay-less servo from a kit, and a price of just six shillings (30p).

I say 'just', but back then, of course, the average wage was £1000, and the £3360 that those average wage-earners were paying for their houses makes you realise what an expensive hobby R/C modelling was: a single-channel radio set-up, for example, would have cost the princely sum of £16 10s 0d. Yes, for the equivalent of about £1500 in today's money, Radio Control Specialists of Hounslow would have been happy to supply you with a Tx – a box with only one button but featuring something called 'a silicon planar epitaxial output transistor'! – and an Rx that looked like a tobacco tin. You'd also have received RCS's accessory kit consisting of an escapement (essentially a rubber-powered servo), a battery box, wiring harness and switch. You'd have needed a licence before you could actually press your Tx's one button, of course, and for this you would have had to write to the GPO's Radio & Accommodation Department in London enclosing a £1.0.0 postal order to pay for five years' cover.

So, however quaint things like rudder-only models, superregenerative receivers, and 3.6V deac batteries may seem now, their simplicity didn't mean that R/C was cheap. Even the DIY servo kit that I mentioned – the Ergomite from CS Developments – cost a whopping £6 5s 0d.

Mind you, what the '60s hobbyists may have lacked in terms of ARTF accessibility and affordable technology, they more than made up for in terms of practical skills and innovation. People were relentlessly designing, developing, flying, crashing, repairing and publishing plans of super little models that other balsa-bashers would go home, build and fly for themselves.

Now, if instead of buying the May 1964 edition of RCM&E you'd picked Aero Modeller as I did, you'd have found the plans for Simplex inside. Designed by the US modeller, Dick Stouffer, it's a 36 span rudder-only model that could be made from just four sheets of balsa – three of 36 x 4 x 1/8", one of 36 x 4 x 1/4" – and a few off-cuts. However, such was the elegance and integrity of the design, the simple sheet wing was more than able to offer the gentle climb and excellent glide that was essential when you had no throttle control. Moreover, the model was so stable that, with neither aileron or elevator to manage roll or pitch, it could be ruddered through a full turn and still remain in balance.

Indulging in this sort of nostalgia is all very well, but I couldn't help wondering what it would be like to build and fly the Simplex again after all these years. As luck would have it, a flying pal of mine, Peter Cook, had kept the Simplex that he built all those years ago, complete with its rubber-powered escapement. What's more, he'd also kept a set of the original plans. Well, that did it – I had to build another one! So while Peter's wife Beryl kindly photocopied the plans for me, I rushed out and bought four sheets of balsa…

As you can see from the drawings that we've reproduced on this month's free plan, the fuselage is a simple box made from 1/8" soft balsa sheet – "soft," Aero Modeller specified back in 1964, "because it has been found to be the most suitable shock-absorbing stock size." The sides are joined using two identical formers, one at the leading edge, the other at the trailing edge. The sides are then drawn together at the nose around a 1/4" ply firewall (F1), and at the tail using a piece of 1/4 square balsa. "The fuselage," Aero Modeller continued, "now adopts its own plan shape and all one needs to add are the 1/8 x 1/4" spacers at the positions shown."

The wing, meanwhile, is simplicity itself. Made from the sheet of 1/4" balsa, it has a flat underside and a topside that is sanded to a sort of thin Clark Y-section airfoil. Actually, this shaping is probably the most time-consuming part of the build, though I'm not convinced that it's crucial: it would probably still fly if you left the thing square.

"[The wing is] then cut at the centre to give a 21/4" dihedral under each wingtip, and reinforced with a bandage or glass fibre covering for at least 4" of the centre area. It is advisable," AM cautioned, "to also add reinforcing strips at the leading and trailing edge." The wing is held in place using the timeless technology of rubber bands.

Working from the 40-year old plans and construction notes, it's interesting to see how much more initiative was expected of the average modeller back then. For example, no mention is made of fitting the dowels for those wing-retaining elastic bands, or making the hardwood dihedral braces – it was simply understood that you would read the plan, interpret what was required, and get on with it.

In the same way, responsibility for positioning the radio gear was passed to the modeller with the wonderful phrase: "Now plan the installation of your particular choice of equipment." In the case of the original Simplex, this involved the Elmic Conquest escapement, whose rubber band stored and provided the motive force for controlling the rudder. What you also have to remember is that the control the escapement gave was very coarse: pressing the button on the Tx (once for left, twice for right) released the escapement and gave you either full rudder deflection or none at all. No wonder the rudder throw was limited to just 1/8" either way: any more and the model would probably have been on its back before you could say "swinging sixties," or words to that effect.

For this 21st-century version youll be pleased to hear that my installation of choice was a contemporary set-up, using a Futaba three-channel micro receiver, 250mAh NiCad battery, and a pair of micro servos to give me fully proportional control of not only the rudder but of the elevator too. I know this isn't wholly in keeping with the vintage experiment, but having an elevator gives your flying much more scope.

Although the Simplex will take any glow engine of between .020 and .049cu. in. capacity, I decided to stick to period power, and dusted off my .049cu. in DC Merlin diesel, which is attached to the beam-mount engine bearer; a 71/2cc commercial metal fuel tank sits in the compartment behind the ply bulkhead. As the original plan points out, when mounting the engine you'll need to give some thought to side- and down-thrust if you're to maintain the model's straight-and-level characteristics. This is particularly true if you're using a large engine, as the original reviewers found that a .049 Cox Babe Bee turned the Simplex into something of a 'hot' ship; when fitted with a .020 Cox Pee Wee, however, the model's flight characteristics were far gentler, and the glide much improved.

Talking of engines, you'll have noticed that I've made no mention of a throttle servo, and that's because I decided to stick with the original design in this regard, which also intended the engine to be a non R/C version. The idea is that you let the model climb to a good height before the motor cuts so that you then have plenty of gliding time to set yourself up for the landing. If this 'all and then nothing' approach doesn't appeal to you, you could always do a little designing yourself and add a throttle servo to the radio bay. Theres plenty of room!

Once the radio and engine fit are complete, the top and bottom of the fuselage are planked-in, again using 1/8" soft balsa sheet, and remembering to include the access hatch if necessary. It's worth noting that if you're using an engine at the lower end of the Simplex's power range, you can save some weight by covering the top and bottom of the fuselage with tissue.

In keeping with the techniques of the time, I finished the model with dope and yellow tissue, with black tissue detailing, and some Humbrol black enamel on the front end to provide a little extra fuel-proofing. This brought the model's all-up weight to 12oz, which is three to four ounces lighter than my original – in line with modern dietary thinking, I suppose!

All in all, it took me about a fortnight to build the Simplex, though really it could be done in a weekend – I see no reason, however, to rush things just to test AM's claim that the model, "can be made and flying within seven hours!"

Now, my recollection of the first Simplex that I built is that it was an absolute delight to fly, though I admit that there may be a touch of rose-tinted retrospection here as she once took me to second place in one of the then popular South Eastern R/C meetings at Golden Cross.

Mind you, if the object of this exercise was to keep those sort of happy memories intact, then I couldn't have picked a better day for the test flight: a light wind was blowing, a flick of the 7 x 4" prop' had the engine running on song, and after a quick range check and topping-off of the tank, the Simplex was ready to go. It felt just like old times.

I press-ganged my number one launch ace Eric Pearce for the bung, and after the customary nod the Simplex was flying – for all of 25' before the engine cut. "Ah yes," I can hear the cynics saying, "just like old times." This performance was repeated for the next three or four launches, by which time Eric was getting fed up with throwing the thing. Could it be fuel surge? No, the same thing happened after even the gentlest of launches. In the end we gave it best for the day, though we did at least take the model home along with the knowledge that, if the glides she'd produced were anything to go by, when she did eventually fly, she'd fly very well.

Back home, I checked that the two holes in the spraybar were facing fore and aft in the venturi – all okay – and then inspected the needle and jet. There didn't appear to be any problems there either. The needle did look a bit on the blunt side, though, so I swapped it for a spare that was quite a bit sharper.

A few days later I was back at the field for another go. Once again, the engine ran up a treat but this time she flew from Eric's launch without a hitch, which leaves me wondering if a sharper needle can really make that much difference?

Anyway, once the Simplex was in the air my initial impression was one of speed: surely my original model wasn't this quick? And if it was, how on earth did I manage to fly it with just one button to press on the tranny?

My next thought was that 71/2cc of fuel gives more than enough flying time when you have no throttle control! After what seemed like an age, however, the motor cut and the Simplex settled into an excellent glide that brought her back to the field where the modern luxury of elevator control produced a flair that turned what would once have been an arrival into a landing.

Since that first outing, I've had about five flights with the Simplex, during which the model has learned to fly loops – something it couldn't do 40 years ago, of course – while I've been learning to make power-off spot landings all over again. All in all, then, she's proved a super little model: it's been well worth the long wait to build her again and rediscover the pleasure of going flying with just a can of fuel and a transmitter.