Double Star Classic 40
                        by Derek Pickard   

          Derek Pickard tests the latest replica engine and finds a superb upgrade on a top selling traditional 35.

         The Double Star company in the little-known country of Moldova in Eastern Europe makes its living manufacturing specialist competition engines, mainly team race 2.5s. Recently it moved into western markets with its replica of a Tigre 60. When reviewed, that version was found to be of excellent quality and top performance and it was obvious we'd all be hearing more about this engine maker.

        Keen to back-up on the success. Double Star has now turned its attention to the Fox 35 and given that all-time favorite the top treatment. The Classic 40 is the same size as the Fox, weighs the same and bolts into the same mounts; but there the similarity ends as this is no ordinary replica, this is a total up-grade and the specification is as excellent as the quality.

       Within the exterior dimensions of the Fox 35. Double Star has used contemporary AAC liner-piston technology which, together with a bigger bore and stroke, enlarges the capacity out to a 40 without any penalty in weight. The result is a 15% increase in cubes which with less piston/liner friction results in a performance gain of at least 20% in output.

       Make no mistake about it this Classic 40 is a lightweight, compact, full 40 stunt motor. The fact that it fits straight into Fox 35 mounts is a bonus. This is the lightest 40 dead serious stunt motor on the market and the performance is excellent.

       Suddenly all those fantastic ships of the 1950s and 1960s which were flown with a Fox 35 years ago, but appear to be underpowered by today's standards, can now be taken out of storage. Dropping in a Classic 40 gives them a new lease of life as this motor can pull a bigger prop to hold better line tension in the wind while not worrying about the plane size and weight that bothered the 35.

Because of this retrofitting facility, the market for this new compact Double Star is huge.

       The specification of this new 40 is a weight of just six and a half ounces, a bore and stroke of 21.2x18.5mm. 274 thou venturi .138 degrees exhaust timing, 120 degrees transfer timing. 36-45 degrees shaft timing and an 8:1 compression in a hemi head. Against thai the Fox 35 is slightly smaller with 20x18 bore and stroke with under 7:1 compression 130 degrees exhaust timing. 110 transfer timing and 45- 35 shaft timing. Those numbers, together with the iron piston, mean it needs around 10% nitro and 25% castor oil to give a slightly lower power performance.

       The materials applications side of the Moldovan engine is impressive with a bushed main shaft bushed conrod with oil holes, bridged ports with expansion slit just below the exhaust window and an AAC piston bore where the alloy liner is chrome plated and well matched in expansion to the high silicon alloy piston. Two thou bore taper is used and the top of the piston is taper-relieved by one thou.

Running-in takes about 15 minutes and 20% castor oil is plenty. Also 5% nitro is about right with the stock compression. Adding more nitro does further improve output but it should be done in conjunction with a head shim.

       A well made needle with a long smooth taper is used that complements the engine's stage of development to give precise settings right through the rev range. Starting and setting this engine is a delight. In operation, a 11x5.5 prop proves best and the test plane was a stock Thunderbird Mk I. This had been originally built for a Fox 35 but needed a lot of nitro to fly the 54 ounce model. Subsequent swapping to a Merco 35 saw the plane's performance improve but the final switch to the Double Star Classic 40 answered all the plane's dreams.

      The classic Tee-Bird now flies as beautiful as it looks. The new 40 can be easily set to a classic 4-2-4 stunt run which handles the bigger prop effortlessly. More importantly, the plane is much better in the wind.

To respond to the obvious question of: "How good is this new 40 when set against the six 40s compared last year?" The answer is I can confidently state the power is at least that of a modified OS FP40 and as good as the Stalker 40 but behind Lew Woolard's modified Fox 40 ABC TBR. But the biggggg advantage with this Double Star is the light weight compact size and the fact that it bolts straight into a Fox 35         plane taking the same muffler. Those pluses certainly put the new engine well up the ratings to be at least equal second in the conventional 40 stunt engine ratings. Praise indeed.

Conclusion:  Double Star's business approach of taking a proven stunt engine, developing it further and adding the latest metallurgy makes an excellent product. The highest recommendation.

Adding head shims to cure the run away only cuts power even more.