Diamonds are a Man's Best Friend. Returning to Soaring after 30 years

By Mike O'Neill

Way back in the early 1980’s, and for a brief time only, I rubbed shoulders with some of the (then) notable names in r/c gliding: Sean Bannister, Chris Foss, George Stringwell, Chas Gardiner, Alan Head, Nick Wright, Colin Paddon, Bill Dulson, John Goldsmith, Steve Mettam, John Shaw, Dick Edmunds, Graham James(?) etc. etc. etc.

I designed a big V-Tail open class model based on the E193 airfoil, with aileron control and half span, quarter chord flaps to assist rapid (and safe) launching, improved thermalling and offering phenomenal landing performance when the flaps were lowered to 90 degrees.  With virtually no experience of competition flying, I took this glider up to Radioglide 84 in Scotland and, by a combination of radical/original design and incredible good fortune, scored three perfect scores in the rounds over the unsuspecting competitors, and a perfect score in the first fly-off. Nobody expected what this plane could do: in particular (as George Stringwell wrote at the time) “...the approach and landing was a joy to behold, since the plane appeared capable of maintaining a 70 degree dive with no increase in airspeed”. I was unlucky in the second fly-off in that an aggressive and well known pilot flew into me as I approached the landing circle, taking the tail off  his plane and depriving mine of the energy to make the landing circle. I placed 9th instead of somewhat higher, but I did win a special design award that I cherish to this day. And me and Colin Sparrow came 3rd in the team trophy.

Fast forward 30 years, one marriage and three grown up kids later (jeebers, where does the time fly) and I still liked to think I had  r/c planes to fly even though I’d not had time to do it.  But as I reached for my r/c stuff to do a bit of flying in my rediscovered leisure time, I realised just how much time had ravaged my ambition. My old Futaba Gold and Sanwa Black Custom sets were – apart from having duff batteries – severely short on functionality compared with the now prevalent 2.4Gz radio control equipment. And my planes hadn’t fared much better. The veneer had started to de-bond from the cores of the foam winged models, the dope and spray paint was cracked and crazed from wooden fuselages carved originally to look like sleek fibreglass moulded efforts, and the solarfilm coverings were looking decidedly dog-eared.  What is more, I’m still working and I have a house to run on my own and many other commitments and I don’t have the kind of time needed to restore my old stuff right now. But I do have enough time to nip out and fly briefly and, as if to taunt me, my new house is one minutes drive from the lovely and peaceful field where the Timperley Model Club do their flying. Something had to be done.

Happily, oh so happily, we now live in the age of the internet, so that I could start researching and reading up on what the modern model flyer was getting up to.  Much as I drooled over the state of the art hand built Czech competition models and what they might do in the air, I didn’t want to spend that kind of money (I’d been fullsize gliding in the intervening years and a ¼ share in a fullsize K6 cost me less than one of these things would have!). But I did want if possible to find something that would fully engage my interest in soaring in the way that fullsize gliding had done.

From my researches, I became aware that lithium polymer batteries were now becoming safe enough for ‘normal’ use by modellers. This opened up the possibility of an electric glider whose soaring ability would not be unduly compromised by battery weight. The idea was attractive as it would dispense with time wasting bungee deployment and allow me to set up and pack up much more quickly. And for any after work flying sessions, the sooner I could get airborne the greater my chances of catching the last of the day’s thermals before they disappeared. I really didn’t want one of the foam moulded toys (as I saw them) but began to change my view when I visited the Timperley MFC field and saw the Parkzone Radian in action. Several people had one and they all recommended it as the best option for me.  I had to concede it was a pleasant, impressive and forgiving thermalling machine for light wind conditions: the electric motor simply substituted for the bungee that a pure glider would have needed. But I just fancied something a bit more challenging and potent, more able to handle windier days, and preferably larger so I could fly higher and further and still see it.

And so I started searching to find out what ready to fly electric gliders people had been opting for, and what they thought of them.  Nothing apart from the Radian really jumped off the pages of the various internet blogs and forums, until I came across the Art-Tech Diamond 2500.  This was one of only two suitably featured RTF electric gliders I came across with a span as big as 2.5m (the other being the same design, but branded and marketed by Multiplex). And it was offered absolutely ready to go including 2.4Gz transmitter, motor, speed controller, 6 servos (2 aileron / 2 flap / 1 elevator / 1 rudder)  and 4 cell LiPo battery pack, all for a little over £200: an incredible deal.  It got good flight reviews and it looked great, with a cavernous fuselage (should I want to install telemetry gear, FPV , whatever) and landing wheel. There was some suggestion that the component quality was not all it could be, but it seemed to me – reading between the lines – that none of this was a deal breaker.  And so I bought one, in the summer of 2014. It took a little doing, as everyone was out of stock. But my local model shop – Steve Webb Models in Frodsham – reckoned they could order one in within a week, and their price was the best I’d found also.

One week later and the Diamond was in my hands. I opted to buy a decent new transmitter and receiver (Spektrum DX9) as I wanted to do some fancy mixing of flaps and aileron surfaces to replicate the equivalent functions in a fullsize flapped glider. This was not possible with the cheap Tx and Rx that came with the plane, but they could be reassigned for use with my old simple gliders (Graupner Amigo, wooden Chris Foss Centiphase, 1948 Thermalist, Algebra Open Class etc.), so they wouldn’t be wasted.  It took no time to fettle the Diamond ready for flying. I put a strip of fibreglass adhesive tape along the underside of the fuselage and wing tips to protect them against abrasion, and I worked all the control surfaces to remove stiffness before putting the servos to work, in order to avoid undue strain on them. I also replaced some of the cheap tape covering the wing servo wire channels. I mastered the mixing (on the DX9) of flaps and ailerons, how to mix in elevator trim compensation, plus switchable coupled aileron and rudder, aileron differential, switchable motor disabling, and how to start timers from key controls (e.g. throttle up).  And the DX9 had voice options too, which I made good use of. I set the wing surfaces up for launch, speed, cruise, thermal and landing configurations. In the last case, the flaps move down to their 45 degree limit and the ailerons move about half that in order to ensure good control response etc. though I’ll experiment with the settings in time.  I removed the supplied metal weights embedded in the wingtips in order to lighten the plane. These weights are interesting. Some owners think they are there to dampen roll sensitivity and make the plane easier to fly. This may be true, but I wondered if they might also be there to reduce overloading that part of the wing where the long aluminium tube wing joiner ends and the wing becomes pure unreinforced foam. By fitting weights out near the tips, the outer panels are forced down by centripetal force when the plane is pulled out of a dive. This reduces the strain on the vulnerable section where the joiner ends.  Anyway, I removed them, and I’ve flown a few loops since with no ill effect, though I have a mental note that I should be careful with all this.

The plane flew really well from the word go, and all the various flying settings worked a treat.  A few things though were still left to address.  First, I’d read that the plastic folding prop was prone to shedding a blade due to the power being put through it. A consequence of this could be to rip the motor out of its mount. Second, there was a very audible whistling sound as the plane flew overhead and close. Lastly, the aluminium spar/joiner was very long and weighed a bit, and might also be prone to bending.  I had read that a carbon fibre spar could be got that would fit perfectly and that it would save yet more weight.

So I bought a decent prop and fitted it. And because I suspected the extremely blunt trailing edges to the control surfaces was the cause of the whistling, I decided to address this and to increase the wing area and control response of the plane in one move by glassfibre taping balsa trailing edge stock to wings, elevator and rudder. By doing this I added about 10% to the wing chord and aimed to reduce the drag caused by poor airflow separation at the trailing edges. The next flight proved the worth of all of this. The new prop gave a much crisper climb to height (near vertical climb out to 500 feet in just a few seconds).  The whistling noise vanished, and the plane was altogether more capable when it came to slow circling flight. It seemed to fly quicker too when flaps were set at a negative (speed configuration) angle. And obviously the braking effect of flaps improved, and the elevator and rudder controls became more efficient as smaller deflections were needed to achieve the required degree of control.  This was now a really capable sports glider. It was easy to thermal and was very stable in the turn (I have a set up for coupled aileron / rudder if I’m feeling especially lazy, though it barely needs it and will almost turn rudder only due to the curved up outer wing panels ).  It moved across the sky very respectably and handled loops and rolls, the latter despite me opting for a 2:1 differential on the ailerons (this is primarily a soaring machine after all). It managed about a dozen bungee height climbs on a battery pack. And it could be landed at very slow speed, with a steep approach, into a confined space, and under good control.  It wouldn’t compete with serious competition machines obviously, but then it was probably much easier to fly than they are (and a lot cheaper too). And it looked great, resembling a fullsize design with its generously proportioned fuselage and pleasant lines. All in all, the Diamond 2.5m gave  me a plane that I could just go out and fly if I wanted, but that I could fiddle around with and fettle, should I choose too. Looking ahead, I might for example decide to make it some fancy sectioned, properly sparred longer wings for extended thermalling and distance flying.  And as soon as I can source that carbon fibre tube for use as a wing joiner, I’ll definitely try out that mod.

It’s good to be back flying. And it’s amazing (but not surprising) that the (flapped) features I had no option but to spend a lot of time designing and building for myself all those years ago have now become a readily available feature on an RTF plane costing so little to buy, and taking no time to make.

Mike O’Neill