Several new Super-Tigre engines are being released for 2015, including three small ones: the X.11 R/C, the X.21-RE and the X.25 RIG.
All three are shaft rotary valve, Schnuerle scavenged engines with one-piece main castings and ST Mag automix carburet-tors. The X.11, the first new small ST engine for more than twenty years, is being offered in two versions, the X.11- PB with bronze brushed main bearing and the X.11-BB which has a single ball-bearing. Bore and stroke measurements are 115 X 12.5mm, giving a swept volume of 1.789cc or .1092cu.in. No performance figures are available at present. The X.21-RE is a new 3.5cc RIC car engine with rear exhaust. Like the standard side exhaust X.21, it has an ABC piston cylinder-liner assembly but, rare in a modern engine, uses a stroke/bore ratio above unity, the stroke being increased to 17mm, while the bore is reduced to 16mm for a swept volume of 3.418cc or 0.2086cu.in. The engine is claimed to produce (fuel unspecified) just over 1.0bhp at 25,500 rpm. The X.25 R/C, seemingly a bored and; or stroked version of the standard X.21; the catalogue illustration is actually of an X.21 and no bore and stroke measurements are quoted, but the crank-shaft part numbers are the same so we would guess that the cylinder bore has been increased from 16.6 to 18.0mm, the same dimensions as for the O.S. 25FSR, which would give a displacement of 4.072cc or 0.2486cu.in. One structural difference between the X.21 and X.25 is that the latter has a conventional ringed piston running in a steel cylinder liner, instead of the X.21’s ABC set-up. Super-Tiger X.21
Our photos show a current standard X.21 in R/C aircraft form. This motor is also available, from World Engines, in three other models, i.e. in standard racing trim with a 6nun (28sq.mm) peripheral jet venturi, as an RIG car engine, or as an RIC marine engine. Like other Series-X Super-Tigres, the X.21 is essentially a high performance unit. It features the much-copied ABC (ringless aluminium piston running in brass cylinder-liner with chromed bore) set-up origin-ated by Super-Tigre designer-manufacturer jaures Garofali, a Schnuerle scavenging system and, of course, twin ball bearings supporting the crankshaft. The shaft has a 12mm main journal, a 7mm front journal, an 8mm i.d. gas passage and a large (14mm long) valve port. Counterbalancing is by means of unsealed peripheral crank disc slots. The main casting is of sturdy proportions, with a well braced front end and an offset intake to promote a tangential gas flow through the rotary-valve. The cylinder liner has a single, unbridged, exhaust port and each of the main transfer ports flanking it incorporates an angled vane to direct gas to the opposite side of the cylinder, where it is joined by the upward flow from a steeply inclined third port. The ringless piston is machined from aluminium alloy bar and the machined conrod, bronze bushed at the lower end, is coupled to the piston by a 4rnm tubular gudgeon-pin retained by wire circlips. The cylinder head has the popular bowl-and-squishband combustion chamber shape and is secured with four screws.
Super-Tigre engines strip down
manufacturers and their employers, the competition modellers . . .” who, allegedly, were responsible for the widespread loss of flying fields. So, while we did not really go along with the notion that the competition flyers were the only ones to blame for the flying site problem, we did, subsequently, try (in the January issue) to put the case for inherently quieter engines—four-strokes, Wankels and slower-revving, better silenced two-strokes. It was pointed out, for the benefit of newcomers, that a 1.5 to 2.0bhp engine is not essential and that perfectly good aerobatics can be flown on less than half the power of a modern Schnuerle scavenged .60 R/C motor and we quoted the example of people like Chris Olsen, Bob Dunham and Frank Van den Bergh who, in the past, flew championship winning performances on engines developing between 0.55 and 0.70bhp. Did we succeed in taking the heat out of the situation? Not entirely. Our defence of the quiet life prompted just one reader to reply : the one who happens to be, cur-rently, the top “top-comp-with-it” of all, namely, David. Hardaker, present U.K. National R/C aerobatics cham-pion. His letter was long, so we will omit the preamble and deal with the central issue, which is David’s argu-ment in favour of power and plenty of it. He writes .. . “There is no way that plenty of power can be an em-barrassment—only, I agree, through noise, but if power is in hand, one can afford some sacrifice towards more effective silencing. “Bob Dunham and those pioneers of his day, flew aerobatics with less power on lighter wing loadings simply because that power was as much as they could get and there was no other choice. Neither did they use silencers. “Before saying that perfectly good aerobatics are possible on less than half the power of today’s good 60s, you must take into account the present FAX schedule, a much more complex task than 12 or 15 years ago. I reckon if anyone could do today’s schedule with, say, an Astro-Hog using one of yesterday’s 45s, then that same person could walk on water. cc . . . The vast majority of British or any other aerobatic flyers use the current types of model purely because of their superior handling qualities compared to smaller or lower powered models and as such, know how to appreciate them. “However, I agree that this variety of model can be a misfit on some flying sites, purely because of nearby populated areas, but surely this is where discretion should play its part. “If progress must be made, then let’s follow full-size practice and go to the more compact Aresti type schedule where manoeuvres flow into each other and fly it with near-scale aerobatic types using larger than 60 size motors if lower revs are required.” Right. A good argument in favour of the status quo so far as the seasoned competition aerobatics flyer is concerned. But what has to be hammered home is that FAI class competition flyers comprise about one percent of the RiC fraternity. What we should all be doing is looking for ways and means of influencing development along lines that will be of benefit to the other 99 percent and this means, whether we like it or not, making model RIC flying more acceptable to the general public on whose goodwill we all, ultimately, have to depend. The alter-native is for everyone to do what an awful lot have done already: give up power models in favour of gliders. Let us look a little more closely at one or two of David Hardaker’s arguments. The latter part of paragraph one sounds reasonable, but all the evidence, so far, supports the view that competition modellers, in general, do not voluntarily sacrifice power in the interests of better silencing.
nitro rc plane silencer
We saw this in the adoption (when silencers became obligatory) of totally ineffective open-front “non-silencers”. More recently, tuned pipes have found their way onto acrobatic models, admittedly with some benefit on noise levels but, undoubtedly, chosen mainly as a means of maintaining or even increasing power output. On to paragraph two and the “pioneers”. Covering many contests in those days from club to international level in reporting (and occasional judging) capacities, we were not aware of top pilots’ anxiety, at that time, to find more power. Generally, they were more concerned with polishing manoeuvres and keeping all the hardware working properly. If, in 1961 or 1962, the FAI had de-creed that the K&B 45 or the Merco 49 would henceforth be the most powerful engine eligible, the heavens would not have fallen. We can be quite sure that FAI aerobatics would have continued to thrive and to be enjoyed by its participants. The fact is that, unlike other competition classes, RiC aerobatics has remained remarkably unfettered with regulations governing model design and engine power. In other categories, the FAT has repeatedly imposed restrictions to keep performance within bounds : for example, by reducing engine capacity (e.g. down to 2.5cc in the World Championship CIL speed class), by fuel tank capacity (as in CiL team racing) and by towline length (as in towline glider). Paragraph Three: Well, now, what a way to sort the men from the boys ! But wouldn’t it be equally true to put the question the other way round and say that, with
virtually no restrictions on design, apart from a Eke engine size limit, models have become so potent that the FAI schedule has had to be made steadily more difficult simply to mop up excess performance? As for handling qualities (paragraph four) it rather depends, one sup-poses, on whether you want contests to put the emphasis on proving the suitability of the aircraft for the task before it, or on the skill of the pilot in coping with its limitations. Paragraph Five. Where available flying sites make the currently favoured high powered model a “misfit”. The snag is that the average bod who gets bitten by the aerobatics bug will undoubtedly follow the example of the expert and will want to build and fly a high perfor-mance model. It is not much good then trying to tell him that his expert class model is a “misfit” in the club environs and that “discretion should play its part . .” What he needed to be offered, in the first place, was a viable alternative. What about a nationally or inter-nationally recognised “Formula 3″ aerobatics class that would provide a quieter, slower, club or inter-club contest alternative to the present “Grand Prix” acrobatic model? Paragraph Six. Near scale acrobatic models using larger than .60 size motors and lower revs. Fair enough. A well-muffled .90 turning slowly enough to avoid excessive prop noise and, presumably, a big wing area model flying at near scale speed. Very nice. Not, how-ever, for the ordinary club flyer who already thinks modern .60s are too expensive. Again, perhaps, this is where our Club “Formula 3″ acrobatics model would come in? .40 size engine? 12 x 6 prop? 150cc expansion-chamber silencer with 40sq.mm baffled outlet? 600sq.in. wing area? Food for thought?