I have owned two MDS 40 engines. (Don’t mock, there must be thousands of us closet MDS owners around the country !) The first was in a Ripmax trainer several years ago, it performed well for a few flights, and was briefly a credit to its species. Then it decided it had had enough of life. I would start the engine; let it warm up, check that it continued running when the model was held vertical for ages. The model would take off, reach 50 feet, and then the engine would die. I became expert at “deadstick” landings, but not normal ones with a real approach, these were sudden wheel bending affairs. I tried careful carburettor adjustment, all might be well for a flight, and then the engine would die again. When the press heralded the new MDS engines, fitted with the “new improved super wizzo” carburettor, I rather pluckily decided to try again. For a few flights I had a very well behaved engine, then the rot set in, and it followed the lemming like tendencies of its predecessor. In both of these cases I changed the engines for Irvine 40’s, and the problems were resolved, no more suddenly quiet engines. I assume this rules out the possibility of a fuel tank, or fuel delivery problem. I had also tried several different glow-plugs, from the merely warm to the thermonuclear hot types, in case this was the problem, but it wasn’t. For months these engines have just skulked about in a drawer, not even called into service as paperweights or objet d'art. Whenever I opened the drawer, there they were skulking in the corner, blinking in the light. I am an electronics engineer, so the finer points of the bodily functions of engines are probably far beyond my simple grasp. However, what I do understand is that the carb sort of squirts fuel and air in, the piston goes up and down, the con-rod sort of follows suit, and eventually the prop goes round, all aided by a glow plug with a platinum coated wire. As far as I can tell, a well behaved OS engine (for example) and an MDS may be of very different quality and design, but essentially they both rely on the same principles for their operation. I have therefore decided to attempt the miracle of bringing one of these engines back from the dead with a carburettor transplant. All the problems appear to my simple brain to be carburettor related …. well maybe ! I spoke to the very helpful people at Just Engines, and we decided that their T2 carburettor would be a good choice. MDS 40 with the new Carburettor fitted, old carb seen alongside.

The next problem was what to put this new “Lazarus” engine in ? We have umpteen models, ( to the consternation of “her indoors”, who considers one should be more than enough for anyone). But they are all happily fitted with good reliable engines. They are also in one piece (yes I know the wings detach, you know what I mean !) and since I would like them to stay that way, I decided a new model was called for, as a test bed. What was needed was a tough model, preferably one made from whatever they make aircraft “Black Boxes” out of. If they can survive plummeting seven miles vertically out of the sky at full speed into an explosives factory and emerge unscathed, perhaps it could even survive the shortcomings of an MDS motor! However, models made of this material appear to be somewhat elusive. So the next best alternative is something cheap’ish, a model with strong nerves and little regard for its personal safety. I did consider a Mitsubishi Zero, as they are a very appropriate subject for plummeting out of the sky, but I couldn’t find a cheap one. However, after scouring the Internet for something appropriate, I decided on something totally inappropriate, but it did look like fun! The Fun Star ARTF is reasonably cheap, at £70 quid. So Dear Reader, the thrilling prospect of the review of a model, and an attempt to breathe new life into an MDS motor in one go. There is little that is unconventional about the Fun Star, and building it is fairly straightforward. The instructions are in glorious Technicolor, and are very comprehensive. After checking that all the (carefully wrapped) bits are present in the impressively sized box, let construction commence. Nice big box, all parts in protective wrapping too!

The wing is already in one piece, and furthermore the ailerons are fitted, and pinned. So nothing much to do there, apart from fit the two servos. An exit hole needs to be cut in the centre of the top of the wing, for the servo leads. I carefully drilled an 8mm circular hole. The servos leads, with short extensions, are threaded through the wing, to the hole that you have made. Since the wing covering is transparent, this is easily done. I grabbed the servo leads with the short end of an Allen key, to get them out. Then to tidy things up, I made and screwed a clamp to secure the leads. The aileron servos and push rods are then fitted. The push rods are simply bent to length, and one end is secured with a swing keeper. The supplied clevises are plastic, and I usually change them for metal ones, however I threw caution to the wind, and used them. Naturally I used the supplied, short pieces of tube to ensure they didn’t come undone. The control horns and plates are secured to the wing, then the whole lot is connected. That’s about it for the wing. Aileron Servo and push rod detail. Constructing the fuselage is again fairly conventional. Firstly the film must be carefully removed from the slots for the tail and the elevator. Then the parts are slid into position and a pencil line marked to show where the film needs to be removed from the tail and elevator. This should be done with extreme care, only cut through the film. Do not cut into the balsa or it will weaken the structure, now epoxy and fit those surfaces, elevator first, a hinge on the bottom of the rudder fits into the fuselage as the rudder is attached. I used a tiny amount of epoxy on this hinge, then drilled and pinned it with a length of cocktail stick to really secure it. The steerable tail wheel is fixed to the rear of the fuselage, then a hinged bar is secured to the rudder by two nylon clamps, and by two screws that are slightly too short for the job ! Next I fitted the elevator and rudder servos. Simply cut away the film add an extension lead to each servo, hold the fuselage vertical and drop the lead down through the middle of the fuselage, then attach the servo by its four screws to the fuselage. The elevator and rudder servos, use push rods, control horns, and plastic clevises to connect to their respective control surfaces. Again don’t forget to use the short lengths of tube to ensure the clevises don’t come undone. Elevator and rudder servo connection detail. Next I assembled the fuel tank, and pushed it into place. I used a small piece of plywood epoxied the width of the fuselage to secure the tank in place. The engine mounts are already in place, and are metal. I was a little unfamiliar with this, and even more so when I discovered that the engine is clamped in place with two metal plates, and four bolts. I used thread-locking solution on the bolts to ensure that they didn’t vibrate undone. I used some spare snakes, rather than the supplied wire link from servo to carb, I just prefer snakes. Engine mounted on metal clamps. The radio and battery installation is fairly easy, and there is adequate space to accommodate these. I made a sort of clamp to hold the Receiver down. The battery is tie-wrapped to a piece of plywood. You may also notice that I have added 5mm square doublers to the fuselage under the cockpit. I did this because it looks worryingly delicate at this point, and because I have seen an Irving Wild card ARTF, (which looks like the same plane to me) crack at this location. I kept the aerial as far from servo leads as possible, I drilled a small hole just behind the cockpit, threaded the aerial through a bit of snake inner to keep it clear of the fuselage, then onto the tail. The extra lead in the photo goes to a battery monitor. Battery and radio installation.

Now to the best bit, flying the thing: The only propeller I had to hand was a bit huge for a 40 size motor. Also the wheels supplied with the model were a bit small. The MDS engine with the new carburettor started amazingly easily. For an MDS the fact that it started and just kept going was fairly astounding. In fact it was a problem to stop the engine, it appeared to be able to tick over so slowly you could almost count the revs. The engine was warmed up, the model was held vertical, the engine still ran, without missing a beat. It had been raining overnight, and the grass runway was very soggy, and definitely in need of a trim. With an encouraging push, the model was off, but not airborne. In spite of umpteen attempts, a combination of damp grass, tiny wheels, and huge prop ensured the model couldn’t reach the speed necessary for take off. So I gave up, and took a trip to the local model shop, for a sensible size prop, and some 3 inch wheels. When these were added, it was back to the strip for another attempt. This time it flew, and the engine kept running. The model was a little tail heavy, and twitchy when the centre of gravity was at 120mm from the leading edge. Moved to the foremost recommended 110mm it was certainly a lot better. So this time it flew, for 60 seconds, then the engine died. The carburettor was tweaked, and the same thing happened again, and again, and again. The new carb had apparently had no effect on the recalcitrant MDS’s bad habits. I remembered an SC52 engine that we had “knocking around”, so we swapped that for the MDS. The tank and plumbing were unchanged. This time the model leapt off of the runway in 20 feet, and flew as it should, and kept flying until the fuel ran out. A couple of clicks of trim to elevator and ailerons and we had a model that was very well behaved. This was done with the recommended throws, -50 percent exponential, and even with those settings, loops are very tight, and the roll rate is impressive, and it is very happy to prop hang. A relative “pussy cat” on low throttle, and even fairly “floaty” when we forgot to land it, and ran out of fuel! In short, a real fun fly model, that I would recommend to anyone. In fact with the throws greatly reduced, even to a relative beginner. Unlike a trainer it doesn’t wallow about, just goes where you point it. I realise this is a radical suggestion, but I could never get on with a trainer (too wallowey), and learned to fly with a Ripmax Xtreme Lite 3D, with the throws turned down. The finished article. As to the MDS engine: In spite of every effort and tweak, it just wouldn’t run reliably. I bought it a nice shiny new carb, sealed this carefully in place, ran a tank-full of fuel through it. But it just wouldn’t keep running when in the air, don’t know why, it just wouldn’t. Somewhere I am sure are owners of good reliable MDS engines, but I haven’t personally met one. I have however met plenty of disgruntled ex-owners, and I am now reinforced as one of those.

Article by Peter McKechnie for Bumpy Green Model Aerodrome
October 2004