Dunkirk Spirit Pt.1

  • This article was first published in 2006.

When it comes to doing something out of the ordinary, people are inspired by many things. For some it only takes a glance at an interesting or unusual feat and they want to either have a go or do even better, whilst others admire the efforts of famous people and strive to follow in their footsteps. The only inspiration I need is when somebody tells me I can’t do something; that’s like a red rag to a bull, as I like nothing more than a good challenge! When I first pondered flying an electric model across the English Channel it was, at the time, a little beyond the realms of possibility due to the available hardware not being up to the job. However, the recent advent of highly efficient brushless motors and Li-Po batteries has moved the goalposts a country mile and, as such, the project became practical.

When discussing my proposals I was met with more than a little negativity, but there was one person who thought it was a fantastic idea, was totally committed to joining the project and was even prepared to use his contacts to obtain the gear needed to bring the project to fruition. I’m talking, of course, about Brian Collins of BRC Hobbies. So it was to be a team effort, combining Brian’s expertise in selecting the optimum motor / battery / prop combination and my dubious ability to design a model capable of using this set-up in the best way possible.

All well and good but how does one follow the model across the channel? With only a low budget at our disposal the use of an aircraft or helicopter was out of the question, so it would have to be a fast boat. My point of contact was the Dover Sea School at Ramsgate, Kent, where I spoke to Mike Oram. Mike’s a very experienced Instructor / Examiner with the Royal Yachting Association and has an extensive CV covering all things nautical, including a role as Escort pilot for ‘Channel swimming and other forms of accepted Channel crossings’... handy, that! He told me that they had a 6.5m ‘RIB’ (Rigid Inflatable Boat) powered by a 200HP outboard motor that was capable of cruising at up to 35 knots in ideal sea conditions.

I duly set off to Ramsgate to see the boat for myself and get an idea of what we’d have to do to follow the model from its launching point on Dover beach to landing on the beach at Sangatte in Northern France. On arrival I was greeted by Mike and his son Lance, two fine fellows who couldn’t have been more helpful or informative. I held them back a whole morning discussing every aspect of the proposed trip, from how and where we could launch the model to how we would recover it from its landing point in France. They showed me the boat, which appeared to be rugged and capable, and as I set off for home I felt the project starting to knit together, Mike and Lance agreeing to join forces with Brian and myself to get the job done.

I decided that the airframe to make the trip should be a Tucano (as presented in pro-plan form in RCM&E a while back). I didn’t think Brian would consider this the ideal aircraft for the job (most people would probably opt for a high aspect ratio, electric-powered sailplane), but as it turned out he was all for it, particularly as the model satisfied our requirement to not only cross the channel but do so with a simple balsa aircraft using commercially available, off-the-shelf powertrain components. No high-tech, high-budget organisation here, we’re talking a one-model, one-shot attempt on a shoestring!

Brian is one of the most determined people you'll meet.

As you’d expect, there’s a certain amount of bureaucracy involved with such a project. We established that our BMFA insurance was valid for the trip, and one excellent advantage of adopting the Dover Sea School’s pilot boat services was that given their involvement with so many cross-channel swimming attempts etc., they have special dispensation with the French authorities to spend a short time on French soil without the need for Police or Customs involvement. This allows swimmers to get wrapped up in towels and recover body temperature for the return journey in the pilot boat following their arduous swim.
One unforeseen problem was that we’d have to transmit on 41MHz (the French R/C aircraft frequency) as 35MHz is used for other purposes in France. This involved having to ask permission for, and have a special license granted, to use a 41MHz R/C system both in the North of England where the testing would take place, and from the Dover coast outwards. This involved contact with the MOD (who own that frequency in the UK) and OFCOM, the Telecommunications body. Negotiations here were made easier by the involvement of the BMFA, which gave us total support throughout the project. Truth is, I involved the BMFA from the outset and received invaluable guidance from Chief Executive David Phipps and Records Officer John French. Without the efforts of these true gents we would have tripped over many-a hurdle on the way!

Dave contacted the French modelling and military authorities and made sure we had permission to make the flight, and their reaction was one of complete support and encouragement. He also put me in touch with Robin Donoghue of OFCOM, who liased with the MOD and various ‘spectrum managers’ across the UK to establish that we’d be able to transmit on 41MHz without any frequency conflicts. With the application form complete a license was duly administered... we were cleared for action. Except, of course, we didn’t yet have a set of 41MHz radio gear! Another ‘phone call, this time to those fine chaps at J. Perkins, soon had a GWS 6-channel Tx and Rx heading in our direction.

A 4th Li-Po pack dictated some internal modification.

From the BMFA perspective, an absolute UK record for ‘Distance in a Straight Line’ was also possible, and to this end the model would have to be designed within a strict specification of weight, wing loading etc. Accordingly, there were many protocols that would have to be adhered to in order to make the attempt eligible for claiming that record. For a BMFA record, the prop must be turning for 98% of the timed flight, and in order to ensure this, a small 4mm square spruce block was glued to the transmitter body to prevent the throttle stick from being fully closed. With the stick against the block and the trim full up, a fast idle could be maintained, and for landing the prop could be stopped using the trim... simple but effective!
I set my sights on a 54” (1372mm) span Tucano, not dissimilar to the 45” (1143mm) RCM&E version but built specifically to accommodate the required battery payload. If I could get the completed model (without batteries) down to 2.2 lb, I figured it would carry its own weight (i.e. another kg) of the highest capacity Li-Po flight batteries and still be well within the required specification. My only concerns were whether 1kg of Li-Pos would provide the necessary duration and cruising speed, and what the model would fly like at that weight!
Using a 3-view of the full-size Tucano I set about designing this potentially record-breaking airframe. It had to be wide enough to take as many Li-Pos as possible, stable enough to fly ‘hands off’ in a constant cruise and (of greatest importance) it had to be stall-resistant, even at the reasonably high wing loading it would suffer due to all those Li-Po packs! To that end a flat sheet wing was in order, as it’s basically impossible to stall (as proven with my 45” Tucano design).

So, I cracked on with the build, and thanks to careful wood selection the prototype airframe weighed just over 15oz. Covered and with servos fitted it tipped the scales at less than 20oz; my 1kg target weight was looking more and more achievable.

Whilst all this preparation was going on it turned out that a local TV production company was researching material for use in a series of documentaries, and that our project fell nicely into their criterion. I met with producer Gary Johnson of the ‘Proper Television and Wireless Company Ltd.’ and we discussed the attempt and how it would fit into the documentary. Gary thought it was a great story and would make powerful television, especially given the fact that Brian is disabled and wheelchair-bound.
As well as the obvious technical achievement we wanted to use this cross-channel attempt to promote the hobby in the best way possible, and especially to the disabled community who may not have considered aeromodelling as being within their reach; something Brian has taken to the highest level! The prospect of the whole story being documented from start to finish seemed an excellent way of demonstrating that this hobby is supposed to be fun, and that anyone can do something special by being determined enough.
Throughout the building, covering, testing and planning stages we were joined by Gary and cameraman Rik Caulder. The two 30-minute episodes have been screened locally already and may go global on satellite TV at some point in the future, but if not you’ll be able to purchase a DVD of the project, aptly named On a Wing and a Chair, soon. Through this project Brian and I aim to raise funds for the Spinal Injuries Association.

Mike Merrick at M.troniks made this bespoke ESC after cooling issues with off-the-shelf examples.

Whilst I was doing my PR bit with the TV guys, Brian was eagerly evaluating the various options we had regarding the set-up of the model. The problem is, new brushless outrunner motors and high-capacity Li-Pos are appearing on the market by the day, and Brian ended up changing his mind on several occasions before presenting me with a pair of Hyperion 3025 motors, a 10-wind and a 12-wind. The motor would be powered by Hyperion Lite-Storm 3700mAh 3s Li-Po packs, and we initially hoped that three of these in parallel (i.e. 3s2p) giving 11,100mAh of capacity would suffice. Although said to be capable of well over a 100A, the pack would actually only need to provide 1 to 1.5C and therefore wasn’t even likely to get warm, let alone hot!
The combined weight of these packs was about 32oz, and the estimated 12 - 15A current requirement indicated a theoretical duration of around 50 minutes. If the model flew at an average speed of 30mph, that would give a range of 25 miles; Dover to Sangatte is 21 nautical miles so it would be pretty tight and with very little in hand, but hopefully just enough! It was time to start some practical testing to see where we were with the theory, and whether or not the theory would be borne out in practice.

To start with we tested the potential duration of the package on a workbench, taking a constant 12 - 15A setting (130-160W) that I calculated the model would require. As the current was so low we decided to use a Tornado 40A ESC that would theoretically be working well within its limits; this proved not to be the case as after about 22 minutes it began to smoke and then completely failed. In fact it had got so hot that the output plugs on the ESC had completely de-soldered themselves from the printed circuit board and shorted out!
We were a little baffled but decided to go up to a more substantial Castle Creations 60A ESC, programmed for the optimum outrunner setting. Things went fine for just over 30 minutes but then the power began to fade and the ESC smelled hot. We allowed it to cool down and tried again, but within minutes the same thing happened. Clearly the thermal cut-out was being triggered and the speed controller was cutting the power to the motor.
We were now faced with an unexpected problem. Why wouldn’t a 40 or 60A ESC stand up to a relatively low 12 - 15A constant current? The answer came from electronics genius Mike Merrick at M.troniks. He’d explained to me last year that ESCs had become ‘fashion accessories’ in that everyone wants them to be smaller and smaller, to the extent that they’re simply not able to dissipate the heat they can potentially produce. A 40A ESC will indeed handle 40A of constant current, as the FETs (Field Effect Transistors) aren’t doing a great deal of switching; at the varied throttle settings used during everyday sports flying the FETs do build up heat, but it’s generally manageable. However, at a constant cruise setting the FETs do most of the switching and as a result produce the most heat, which has to be dissipated by a size-compromised heat-sink that allows the ESC to be small enough to be commercially accepted. It all boils down to basic laws of physics: if you have a specific amount of heat energy to dissipate, you need the corresponding mass and surface area to dissipate that heat for it to work within acceptable temperatures.

Always up for a challenge, Mike and his team very quickly designed, developed and produced a bespoke controller for the Tucano. Ironically it only weighed a couple of ounces more than the Castle Creations 60 but in operation at a constant 12 - 15A the lower heat-sink didn’t even get warm. This is a valuable lesson, especially for anyone planning on electrifying a fairly large model where a little extra weight is neither here nor there. Use an ESC that’s designed within the parameters required and not the smallest, most fashionable unit you can find!

While the Tucano might seem an unlikely model for the attempt, it would prove itself more than adequate for the task.

Following a test flight with the 3s3p pack and the 10-wind motor, I achieved a disappointing duration of just 40 minutes. That said, the 4 lb 10oz model had unlimited vertical performance, suggesting that the set-up was probably more suited to performance than duration! The model’s behaviour, though, was faultless. It was easy to launch, easy to fly, easy to land and would fly extremely slowly without the slightest hint of a stall... just what the doctor ordered. In fact, despite feeling like a wing-equipped breeze-block on the ground it actually flew very ‘light’, giving the impression that it would take another pack of the Hyperion 3700s, giving 14,800mAh of capacity for a pack weight of 42oz (1200g).

Brian also suggested that with the glut of power the model had available it would be more efficient to use the softer 12-wind motor on the same 12 x 8” APC ‘E’ prop, as long as we had sufficient power to launch such a ‘fat’ model in calm weather. The motor was changed, and the battery area re-arranged in order to take the extra pack. Unfortunately, to balance the model as before, the canopy floor had to be cut away and this fourth pack sat in the cockpit area! This was a shame as I’d intended to have a clear canopy and scale cockpit area on the model, but in the end it was sprayed silver with just the framework detail in place.
With just two days remaining before setting off for Dover, we had everything crossed as the Tucano headed skywards to test this latest set-up. An 86-minute flight drew a collective sigh of relief, and there was an added bonus in that the model was even more solid in the air. This would pay dividends in turbulent conditions, and further tests showed that a good underarm ‘lob’ (far safer than an overhead launch) would get the Tuc’ away every time. Another unexpected advantage was that the silver canopy really stood out in the sky and made the Tucano much easier to orientate, something that would be essential if we were to keep it aloft from a moving boat.

With the model ready a phone call to Brian confirmed that he was up for it, and another to Mike Oram confirmed that the forecast conditions looked suitable. Time, then, to pack toothbrush and Tucano and head south...

Part.2 will appear towards the end of July.

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