There have been a variety of cheaper and more accessible combat classes to F2D at local level. Half-A combat with 1.5cc engines has been very popular in SA and Victoria, as well as the UK and New Zealand over the years. Just as in the USA where newer, more powerful engines have eclipsed the Cox TD 049, a new breed of high performance 1.5cc diesels from specialist manufacturers in the former USSR are set to revolutionise our half-A combat class. When matched with modern models of F2D type, they promise much better performance than before, while retaining the crash resistance that is so desirable. Earlier engines of modern type, like the CTAH and CS, have been joined by 1.5cc diesels from Fora and BGS. The latest offering from Cyclon Engines of Novosibirsk, Russia, headed by Alexander Kalmykov is the JAK 09, a number of which have been imported into this country. We set out to find out just how good it is.

As we’ve come to expect from this company, the JAK 09 is a first class piece of work. In particular, the satin finish on the superbly cast crankcase gives it a look of quality more akin to a digital camera than a combat engine. Perhaps with crash-resistance in mind, the lower crankcase profile is smoothly contoured. The engine has generous cooling fins and the rearward facing exhaust discharges via an outlet tube with 8mm I.D.

This is angled in the usual manner to make side-winder mounting in a combat model more practical. The engine has no machine screws in its construction, which helps to keep weight down to 94g, or 99g with muffler.

The general design is more conventional than some of the Cyclon F2D engines. In usual F2C manner, the threaded aluminium cylinder head has a 7mm dia. push-pull contra piston, adjustable with a 5mm Allen key. A pin-spanner with 2.5mm diameter pins spaced 20mm apart is required for its removal. The aluminium cylinder is of the drop-in sleeve type with a wall thickness of 1.25mm.

The finish on the hard chromium plated bore is excellent. Examination after one hour’s running showed no sign of distortion or out of roundness. The conventional three-port Schnuerle porting is somewhat mildly timed – exhaust 138 degrees, transfers 116 degrees and boost 111 degrees.

The piston is machined internally to prevent unwanted rearward movement of the conrod when running. This presents a problem for disassembly, as there is insufficient rearward movement with the cylinder removed to disengage the conrod from the crankpin.

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Alexander recommends the use of an L-shaped lever applied at the big end of the conrod to do the job. Never the less, it is not something to be done without a genuine reason.

The hardened steel crankshaft has a 4mm dia. crankpin. Owing to the conrod removal problem, it was not possible to see whether or how the crankweb is profiled to counter-balance the reciprocating parts. The gas passage is a very generous 7mm diameter, which by necessity is angled at the back away from the crankshaft axis, to clear the conrod and retain adequate strength for the 10mm dia. main journal at the intake port. The intake opens 24 degrees after BDC and closes 50 degrees after TDC, giving intake duration of 206 degrees. The front of the crankshaft is reduced to fit the 5mm ID of the front ball bearing and is threaded M5 for the aluminium prop nut. A regular glowplug spanner fits both prop nut and backplate spigot. The prop driver seats on a tapered collet and its rear edge is recessed slightly into the crankcase to minimise the ingress of grit.

The venturi insert is of the peripheral jet type, but quite unusual, as the two jet holes (facing fore-aft) are located around 5.5mm away from the spraybar location. An annular fuel chamber of significant volume, formed by a deep and long groove in the insert’s outer wall, connects the spraybar and jets. The air intake is a long hole of 2.7mm diameter, with a shallow flare at the top and slight chamfer at the bottom.

On the bench

Alexander recommends a fuel with 10% oil content. We opted for a more conservative brew consisting of 15% castor oil, 30% ether, 55% kero and 1.5% added DII. This suited the engine well enough and as the JAK showed only gentle tendencies towards overheating, the fuel with lower oil may well be perfectly safe and add a few more RPM.

As is normal now with top-shelf equipment, there was no particular need for running in the engine, although we took it a little easy for the first 15 minutes. The first series of tests were made without the muffler. This made exhaust priming simple enough, but it was not found necessary. Choking or a carburettor prime worked well. While it would not be a problem in the typical side-winder position in a model, filling the carburettor’s fuel chamber in the upright position during tests was a bit of a pain. This of course made starting less reliable. Aside from this, the JAK was not particularly fussy for starting, either hot or cold, but can not be regarded as foolproof in this respect. There was no need to adjust compression, but opening the needle a bit from the very leanest running setting was necessary for reliable restarts.

I found the response to mixture setting too coarse. Perhaps the NVA was originally designed for the Cyclon F1C or F2A engines, which use a lot more fuel than the JAK?

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A Nelson NVA was later substituted and worked very well, as would any regular NVA with a 4mm spraybar diameter. By contrast, compression adjustment is very fine compared to engines with “full-bore” contra pistons. As mentioned earlier, the engine does not suffer from overheating, but over-compressed settings do drop power output. Adjustment for peak revs was not easily discerned by ear and it was therefore best to set the needle just short of a lean misfire and wind up the compression, while monitoring revs with a tachometer. Final tweaking of the needle would optimise the tune.

The range of compression adjustment available in the head made it possible to load the engine down with large propellers without needing to add head shims. It would pull an APC 9x4 prop well enough, despite this being some way below its truly useful running range. The main observation was a tendency for the engine to surge owing to fluctuations in mixture supply. This got progressively worse as speeds went up. No amount of adjustment of mixture or compression would eliminate this and the problem, while tolerable with a 7x4 prop on board, was quite acute at the top end of the speed range.

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A significant improvement

We’ve experienced problems in the past with some venturi designs with single or multiple surface jets. Such arrangements must overcome the Coanda effect, where fluids can stick to a surface despite the forces of pressure and gravity. Take as an example, the annoying dribble of wine down the outside of the wine bottle that forms as the bottle is raised closer to vertical. In model engines, this effect (perhaps in conjunction with pressure pulses governed by the valve port opening/closing) can lead to large drops of fuel periodically entering the engine, rather than the desired fine mist.

This effect is typically minimised by providing the venturi throat with a divergent taper or step downstream of the jets. It then remains to provide an appropriate shape upstream to provide orderly flow past the jets. The JAK’s venturi looked decidedly suspect in this respect. Or we can go back to the good old spraybar or a tangential wick, or other arrangement that introduces the fuel well away from the venturi wall.

As an experiment, a venturi insert of conventional design was made to fit the JAK 09 engine. It has four jets located at the spraybar level, a bell-mouth inlet and 45 degree chamfer below the jet area.

The original choke size of 2.7mm dia. was retained.

The new venturi’s effect on running characteristics was remarkable. The surging problem was eliminated and (perhaps because of its less restrictive shape) the custom venturi added around 600 RPM with the larger prop sizes.

Furthermore, the ability to get a consistent setting essentially cured the chronic vibration at higher speeds. This allowed the engine to show its true potential and peak power of 0.35 BHP was realised in the 20,000 – 23,000 range.

The engine ran very sweetly with the Seryogin prop spinning at 23,000 RPM, presumably just as Mr Kalmykov intended. The performance data presented are from tests with muffled engine and custom venturi insert.

The JAK 09’s torque levels are typical for a good 1.5cc diesel. The curve shows a nearly linear drop from 21 oz-in at lower speeds to around 15 oz-in at 23,000 RPM. It was not possible to test the engine beyond this speed, as the next calibrated prop could not safely have its hub drilled out to accommodate the 8mm dia. prop nut spigot, nor was there sufficient length on the crankshaft for a conventional hex-nut.

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A switch to glowplug

The test engine was supplied with an alternative head that accepts a Nelson glowplug. It was a simple task to switch heads for an instant conversion to glow power.

With no instruction as to fuel type, it seemed reasonable to assume that F2D fuel with 10% nitro methane content might have been intended.

Operation in glowplug mode was very straightforward. Starting was easier than the diesel and the engine was quite insensitive to mixture adjustment. Again, the tachometer was useful for seeking out peak running speed. The Nelson plug survived the test session unscathed.

In comparison to the diesel, performance was inferior at the lower and higher ends of the speed range, where torque was significantly down. However, the JAK 09 glow can keep up with its diesel cousins in the 15,000 to 18,000 RPM range.

Conclusions

A check of the engine after testing showed all to be in perfect order. There was no appreciable change to the “fits”, which bodes well for a long life (providing no dirt gets inside). Some carbon build up was evident, suggesting that attention to detergent additives or other means of keeping the engine cleaner inside would be a good idea.

In its as-delivered form, the JAK 09 did not entirely live up to expectations. There was a nasty mixture surge that made high speed running almost impractical. By sheer good luck, a substitute venturi of different shape cured the problem, allowing the engine to show its true potential. Perhaps the test engine is an exception, but if others exhibit the same symptoms, then a relatively simple solution is at hand.

The JAK is a real fuel miser. Especially in diesel form, you get a lot of running from a half-litre of fuel.

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Half-A combat is a one model per bout event. So for practical purposes, most people choose a nylon propeller. The JAK 09 registered a little over 16,500 RPM in either glow or diesel form, with Graupner or Taipan nylon 7x4 props. That should realise most of the engine’s potential in the air and place the pilot at a significant advantage over almost any other engine currently in use. A F2D prop, as suggested by the manufacturer is probably the smallest practical size.

It may seem strange to have a muffler on board a 1.5cc diesel engine, but it really should be used. It weighs only 5 grams and this muffler does not appear to adversely affect power output or starting. However, the noise reduction is nowhere near that of modern “sport” engine mufflers. The muffled engine, running with the Seryogin prop produced a peak noise level of 97dB (A) at three metres in diesel form and 101 dB (A) in glowplug form.

The JAK 09 diesel may be an option for Half-A Team Racing. However, it is not the easiest engine to mount or cowl in a racing model.

So which is it to be – diesel or glow? The JAK 09 comfortably exceeds 0.2BHP per cc, in either form, putting it in the high performance category. The choice may come down to personal preference.

The diesel version’s ability to outperform its glowplug equivalent is probably due to the JAK 09’s modest choke area. This would be expected to restrict performance in glow mode more than as a diesel. As the current rules for half-A combat call for suction feed, huge venturis and bladder feed (although an enticing prospect) are not an option for JAK 09 glows.

Never the less, tests in the air might show that a larger choke is practical for combat and would almost certainly be fine for racing. As a point of reference, the Cox TD 09 has a 3.2mm diameter choke, giving a full 40% more area than the JAK’s modest 5.2mm2. More nitro might also give the glow version a significant boost of power.

The old days where plain bearing engines with power outputs around 0.2 BHP were competitive are probably gone. On the up side, new engines such as the JAK 09 represent good value for money and are generally superior to the oldies in all respects.

The extra power would certainly be a benefit on windy days, when the old stuff struggled. For someone looking to upgrade, or have a crack at a combat class not restricted by model design rules, the JAK 09 has much to commend it.

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This is the second generation of 1/2A planes from this maker. The first batch flew very well with a variety of power sources but none really made it shine until the Cyclon TYR engines became available.

The Test Aeroplane

On first inspection it appeared to have slight inthrust drilled in to the centre rib/engine mount causing some concern. Based on prior experience extra epoxy sealing was applied to the covering joint area around the engine mount to prevent any diesel fuel seepage, as this eats away at the foam very quickly.

A brand new Cyclon JAK in standard trim with muffler was mounted. The only modification was to mount on the inside of the engine bearers a vent pipe and connect it to the tank overflow to make filling the tank easy. All tests and flights were made with the same fuel as Maris Dislers used in his bench tests.

What a delight to fly, it required slight trimming to suit my style of flying, a very small tail weight and 4mm taller elevator horn fitted. Take off was very similar to the F2D’s, no tension for the first one to two meters then lots of tension all over the sky.

If we can get Cyclon to machine a small amount of out thrust in the engine mounts they will fly quite well in windy weather.

I made two venturis as per Maris’s description, one at 2.6mm and 3.0mm finding an improvement with each change then staying with the 3mm for the rest of the testing.

With 4 flying sessions over two weekends it was noted that it did lean out in inside turns and richen in outside turns, a needle setting was easy to find that gave a good run overall without slowing down in the outsides or crackling to much on the insides.

Prop Testing

I tried my largest F2D prop, ground rpm was 23.2K. It sounded sweet but was inconsistent in the air with a notable vibration on the control lines (Airspeed was approx 25/10). Next was a Graupner 7*4 soft prop only trimmed for balance, ground rpm was 15.8K with the comp backed off and airspeed was approx 26/10. The engine held tune very nicely and it unloaded in the air to an estimated 18K to 19K rpm.

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This was an easy set-up as the props are cheap and not likely to break in a collision with the ground. No finger protection was required as with the F2D prop, flights were handed out to anyone who wanted one, on one occasion indecision saw the model hit inverted, I simply picked it up and one bash of the prop saw it in the air again much to everyone’s amazement.

These models are constructed in the same manner as modern F2D airframes and have the same properties, strong, light and sweet to fly. Loops almost as small as F2D models are possible without too many hiccups from the suction fed engine.

These airframes will give people the ability to fly any manoeuvre provided the engine run is reasonable and I have seen many 1/2A engines with more than enough grunt to pull these airframes.

My Concerns

These models and engines meet the current rules for this event. If one was to change the set-up to inboard chicken hopper tanks, allowing much larger venturis and use optimum glass props, we will very likely see rotational speeds greatly exceeding current F2D speeds (24/10). With the event of newcomers watching having the thoughts “I cannot do that” instead of ‘I would like to try that” and start to loose existing competitors that do not have these engines.

I believe this is an entry-level event and as such performance increases should be limited. I would like to propose that a restriction of 3.0mm max venturi diameter and a commercially available plastic type propeller be used with this engine only. I would hope this is discussed at the Victoria State Champs.