Recently I received the following letter in my mailbox. With the kind permission of the author I am publishing it here without any omissions, but will also take the liberty to comment it. Since the Google editor seems to insist on destroying the habitual alineation of arrows on the left hand side of this page, I will use quotation marks and stipled lines instead.
"Dear Sir,
Thank you for your mail.
8 years ago, at the begining of the RC turbine few customer tried to fly faster and faster. At this time, BVM was the only one to fly very fast with a ducted fan model. As soon as the JPX turbine was born, people wanted to fly faster than BVM. So we develpopped the Starjet, first with a JPX T240, and later with a JPX T260. With 6 kg thrust, it flew at 400 km/h at level flight, without diving (mesured with my plane with military radar in french test center) Some customer flew it fasted in diving. Few radar was used, but I don't remember what type (some were made in UK, some were US). None of them were FAI registered. At this time is was funny to do this as they have a limited thrust (maxi 6 kg thrust) and all the same engine, so same diameter, smae fuel tank, same fuel capacity. So we all have the same limit made by a ratio thrust
/ drag / fuel capacity"
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When it comes to racing one another, it is the athletic performance of the competitors one wants to compare. For that reason, it is desirable that the competitors compete under about the same conditions (even in formula 1 races). But speed records are in great part also technological triumphs, so an equality of technological circumstances among the competitors (or competing machines) does not make sense here.
------------------ "As soon as AMT developped a new type of engine (AMT Pegasus), cutomer imediatly fit this new engine in old plane : BVM bandit and our Exocet (one was flown by Mark Leavsley). Of course speed was much higher, and I think Mark was the faster one, close to 500 km/h in diving. But it was not so interesting as now there is no limit."
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There always exist limits in everything. And in this case, should there not exist any technological limit, there will at least exist a human limit of flying (and seeing) ability.
------------------ "Now turbine are smaller and smaller. Thrust is higher and higher. So there is no speed limit. We are able to design a plane to fly at 700 or
900km/h without big problem. We already do this for UAV customers. The new limit will not be the thrust or the airframe, but how to see it. If you fit an autopilot, there is no limit. If you use binocular, there is no limit. If you just use your eyes to fly it, either you see it and can can fly faster than an other one, either you loose it and you will crash it. But it is very very dangerous. That's why nobody try it again now.
I hope to have answered to all your questions
Regards
Eric RANTET / Aviation Design president ZI le chenet - 91490 MILLY LA FORET - FRANCE tel : int+ 33 1 64 98 93 93 snipped-for-privacy@wanadoo.fr
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"
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It is certainly true that radio jets are starting to touch an upper ceiling in terms of controlability with classical methods of model aircraft flying.If we would disregard the time it takes for acceleration and deceleration with throttle lag, a radio jet flying at a constant 300mph could (theoretically) cross a visibility circle with a radius of - let´s say - 1400ft (427m) in 6.36 seconds (at a distance of 1400ft a Starjet has an angular size of 14.25arcmin.(length) x
13.00arcmin.(wingspan). For comparison, the full moon has an angular diameter of 30arcmin.).
But do these three options which you have mentioned above (autopilot, binoculars and naked vision) have to be mutually exclusive, i.e. are they "either or" options? I don´t believe so.
Already today radio jet flying has become the high tech option of aircraft model flying. Radio jets do not only have brakes on their wheels, but they have electronic devices (ECU´s) interfering in and modulating the commands which the pilot sends to the motor and shutting off the motor in case of a failsafe, some of them have gyroscopes steering the rudder during takeoff, and some of them even have a telemetry system including altimeter and GPS.
So if full scale jets often have to fly with computer assistance, why shouldn´t the same thing happen to radio jets? With all of the surplus power supplied by the micro turbine, what reasons would there speak against a few aditional airborne microchips and more sophisticated gyroscopes (sort of an auxiliary autopilot) which could autonomously return the jet towards the radio control in case of being comanded to do so by the pilot or in the case of loss of radio control? Radio jets were never meant to be cheap.
Some people might say it wouldn´t be fun to fly a radio jet with an auxiliary autopilot. Some people might prefer to risk busting a model worth various thousands of Dollars every time they try to probe its - or their - limit. But I could imagine that in the future the flying of high tech model aircraft would sometimes be like walking a tightrope - with an electronic safety net strung below. Why should, in the case of radio jets, it forever be obligatory to crash one´s aircraft in the case of loss of control? At any rate, I doubt that it will ever be a good idea to fly radio jets within a - let´s say - 2 mile (3km) radius of any settlement or major traffic route.
Of course, the attempt to fly a speed record in a straight line with the help of an autopilot has little or no point, so in this case its use should be invalidating the attempt. But this might well be different with the attempt to fly a speed record in a closed circuit as a purely technological endeavour, i.e. as a sort of an "electronic control line" speed record.
But aside from such dreams about a possible future: Radio jets are very expensive, and they require the flying skills of an experienced model aircraft pilot. These factors by themselves should be able to eliminate inept jerks from the ranks of radio jet pilots. And a radio jet which crashes with its turbine shut down by the failsafe routine of an ECU is less of a fire hazard than a model aircraft with piston motor, since kerosene is much less flamable than the fuel of IC engines.
Airplanes, big and small and regardless of their propulsion system, have the propensity to sometimes fall from the sky. So where are the statistics which demonstrate the higher danger, which stems from radio jets? As of right now, all of the flurry around radio jets appears to be based on nothing but (paranoid, I would say) speculations.
It doubtlessly is a very timely idea if, under the new circumstances we are having today, the AMA is trying to guarantee a high degree of proficency among the radio jet pilots it insures. But when the AMA tries to "resolve" the new situation by imposing a 50lb (23kp/220N) combined thrust and 200mph (322km/h) speed limit on radio jets, it appears to me like hanging crucifixes and garlic against the evil spirits of the future. Actually, I believe that this future will come with or without the AMA trying to prevent it. And in the case of a
200mph speed limit, there will just be a lot of wild radio jet flying.
By the way: In Australia they still have speed events on jet meetings. See
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So when I open the JPO homepage
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an see their motto "Focused on the Future" it makes me wonder: What kind of future are these people focusing on, if any? One that is equal to the present? The introduction of micro turbines on the scene less than 10 years ago meant the advent of high tech model aircraft flying. Could it be that this development has already ended up in a dead alley today? The JPO at least appears to be not doing anything to prevent this. Or what has one to think about a double-dealing position paper in which on one hand the speed limit is accepted on the mere grounds of being "inherently safer" than no speed limit, but then on the other hand it is advised against the installation of speed sensors for reasons of them alledgedly being unreliable or even a nuisance? Basically, they also seem to think that the current developments in model aircraft flying can be brought under control by limiting regulations only. Would they be talking differently, if the "auxiliary autopilot" envisioned above would already exist on the market? Or are they perhaps just trying to be politically correct?
Peter Holm
First footnote: As far as I know, all of the contemporary micro turbines still remind of the homemade origin of the KJ-66, with their more cylindrical than annular flame holders of highly non-aerodynamical shape with their flat fronts and their obviously very uneven air influx into the flame holder (straight air path to the outer wall, Z-shaped airpath to the inner wall). But today next to all of the micro turbines are sold ready-to-fly, and are produced in series by means of tools that are more sophisticated than those available to the average homebuilder. Nevertheless, in contrast to the great variety of construction concepts among full scale turbojet engines, all micro turbines are still built in basically the same manner. So I, as a non-engineer, sometimes wonder about what would be the effect of mounting two instead of just one compressor wheel (both on the same axis). That should not increase the diameter of the turbine. And with more pressure one could build a more complex diffuser, which in turn would make possible the construction of a more aerodynamical flame holder with an even air influx from all sides, thus increasing the air throughput through the engine. With increased pressure it would perhaps even be possible to build a smaller combustion chamber. And if there is a higher air throughput and greater pressure in the combustion chamber, why not mount three turbine wheels instead of just one (all on the same axis)? If this should produce a heating problem for the turbines, an airbleed from the compressor for cooling them might increase the maximum diameter of the turbine (if the combustion chamber can´t be made smaller with respect to the turbine diameter) .
Now this might be just a dream of a non-engineer, but am I the only one here who would like to see how such an engine would perform if mounted on an adequate airframe?
Second footnote. Micro turbine rotors ought to be good candidates for being the fastest rotating things on earth, with the SimJet 700M going at 3300 revolutions per second (200.000rpm). The only things I know which can rotate as fast are microsecond pulsars (ultradense, superfast rotating stars which are made up entirely of neutrons and are produced by supernovae).