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.
Thank you for your mail.
8 years ago, at the begining of the RC turbine few customer tried to
faster and faster.
At this time, BVM was the only one to fly very fast with a ducted fan
As soon as the JPX turbine was born, people wanted to fly faster than
So we develpopped the Starjet, first with a JPX T240, and later with a
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
remember what type (some were made in UK, some were US). None of them
At this time is was funny to do this as they have a limited thrust
kg thrust) and all the same engine, so same diameter, smae fuel tank,
fuel capacity. So we all have the same limit made by a ratio thrust /
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
"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
was flown by Mark Leavsley). Of course speed was much higher, and I
Mark was the faster one, close to 500 km/h in diving. But it was not
interesting as now there is no limit."
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
is no speed limit. We are able to design a plane to fly at 700 or
without big problem. We already do this for UAV customers. The new
will not be the thrust or the airframe, but how to see it. If you fit
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.
is very very dangerous. That's why nobody try it again now.
I hope to have answered to all your questions
Eric RANTET / Aviation Design president
ZI le chenet - 91490 MILLY LA FORET - FRANCE
tel : int+ 33 1 64 98 93 93
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
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.
So when I open the JPO homepage (www.jetpilots.org) 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?
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?
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