Chocal-Bauer Modellbau launched a new aerobatics model at the Nuremberg Toy Fair in 1979.
Leopard -The design is by my old friend Rolf Schuler. He increasingly flew this aeroplane in F3A competitions in southern Europe. He worked closely with the Bauer Modellbau company, later known as Chocal.
Test report from 1979: There are people who claim that today’s RC-I models look exactly the same. In principle, that may be true, but when I saw the ‘Leopard’ hanging from the ceiling with its landing gear retracted at the Bauer Chocal / Schwäbisch Gmünd stand at this year’s Nuremberg trade fair, I was thrilled by the elegant lines of this model. The long, slender fuselage clearly sets the Leopard apart from today’s standard RC-I models. The tailplane with negative dihedral gives this racy-looking model the total ‘jet look’, so to speak.
I received my copy of the ‘Leo’ in a huge box, which was padded with lots of foam rubber, and I impatiently unpacked the individual parts. Two neatly crafted wings and tailplane halves, to which the leading edge, aileron trailing edge and wingtips still had to be glued, the fuselage, a plywood plate with the formers printed on it and a small construction plan with a detailed description came to light.
The neatly crafted epoxy fuselage weighed 430 g without the engine mount unit, and both tailplane halves weighed 60 g. So far, so good. However, I was a little surprised by the hardness and weight of the square timber for the leading edge and wingtips, as well as the trailing edge ailerons, the latter weighing in at 98g.
If you follow the well-written instructions, the construction is quick, and due to the available space, it was particularly fast for me. The greatest amount of work was required to plane and sand the surfaces and tail surfaces to work on the wingtips and leading edges. The hard wood offered me tough resistance, and after this process was finished to my satisfaction, I was literally ankle-deep in wood shavings, ‘sweat of my feet’.
Naturally, a retractable landing gear should be installed in the Leopard. After years of dealing with mechanical landing gears of all kinds, I decided on the American Rhom-Air landing gear. Installation in the model is not difficult, but it should be done differently from the instructions. Instead of the usual two hardwood square timbers, I also use a half-rib. A landing gear mount consisting only of two timbers will not withstand the rigours of flying in the long term, since the two timbers are only resin-coated in polystyrene and then tend to become loose.
.
The installation of the tailplane caused a bit of a headache, because the slender, oval fuselage could not be placed in a jig because of insufficient side surfaces, and the suggestion in the assembly instructions to screw the surfaces to the fuselage and then align the tail did not meet my expectations either.
It is now generally accepted that the elevator control surfaces should be linked separately, which undoubtedly has the advantage of allowing the same to be set separately. However, this type of linkage also causes problems, since the two rudder horns must be located exactly at the same point, otherwise you get differentiated deflections.
Furthermore, you need the push rod for the linkage, which did not seem ideal to me with the long fuselage, since it was difficult to mount the push rod in the centre of the fuselage. I am extremely fussy when it comes to linkages, so I came up with an idea.
Instead of the push rod, I glued in two bowden cable tubes, which, after the rear glue joint had dried, were tensioned with the help of a rubber band and then glued together on the transverse support board in the fuselage. After the whole thing had hardened well, I pushed two 1.5 mm spring steel wires into the bowden cable tubes, bent one of them so that it lay neatly against the other, pushed a piece of brass tube over it and soldered everything together, including the associated fork head. Attention! Solder neatly, otherwise you have built in a perfect crash. The rudder was linked with a standard bowden cable.
After the model was ready for the shell, it could be stretched and painted. In this regard, everyone has their own ideas. Personally, I think that a motor model should have a synthetic resin paint job, and that’s why my leopard was sprayed. The installation of the RC system with 6 servos, 5 of them are in the fuselage, must be carefully planned, otherwise you will run out of space, especially since the pressure vessel for the pneumatic landing gear and the control valve have to be accommodated in the narrow fuselage.
So, let’s get started. The built-in Rossi 60 FI engine emits its throaty roar and is adjusted to maximum speed by hand on the ground, which can be corrected in flight as required using the RC nozzle needle adjustment. My helper, Peter Erang, puts the Leopard on the runway, I confirm all the rudders again and give full throttle. With enormous speed, the edge of the unfortunately only 25 m long asphalt runway comes closer and by lightly pulling on the elevator stick, the model rises into the blue sky. Forced by a thermal bubble, I have to correct the flight path with the aileron and immediately feel the brutal reaction to this small stick deflection. Caution is advised here; the aileron deflection must be kept small, whereas the elevator requires a little more. At a safe altitude, the stall behaviour is tested, and the machine is starved to the point where the Leopard simply tips forward and picks up speed. Extremely surprised by this, I prepare to land and with far too much speed, the model touches down on the runway and rolls into the short-cut grass. The speed of the model gives it an amazing gliding angle and it is easy to misjudge when flying directly towards it.
The control surfaces are adjusted, the tank is filled and off we go again. Today, for a change, the sky is blue and the ‘Leo’ makes its way through the air. The elevator is now OK, the aileron is still a bit touchy, but that’s the way it is at the moment, and I start flying rolls. The flying qualities amaze me more and more. It is incredible how such a neat roll can be ‘conjured up’ with such an enormously slim fuselage. The 4-time roll is a particular delight; only a little rudder support is needed in the knife-edge position. Apparently, the mass distribution of this machine is accurate to a millimetre. In the loop the Leopard breaks to the right and now something has to be trimmed, if necessary, adjust the elevator blades slightly to the left.
The Leopard is a racy and, above all, very fast model for the experienced pilot. It is an awesome flyer that can do just about anything you can imagine. There is no doubt that this machine was designed from the outset for competition use and, with its jet-like appearance, represents a very good alternative, at least visually, to the RC-I models commonly used today. The kit is of today’s usual standard, but unfortunately the price is not exactly low, especially since small parts such as aileron linkages, control horns, bowden cables, etc. have to be purchased separately. In my case, the wood for the wingtips and leading edges was outrageously hard and heavy, but this may have been an isolated case. Within a week the model was ready for construction, without the need for a ‘night shift’ or the ‘fairy godmother’ of the house to make a fuss.
Technical data:
Wingspan: 1.6 metres
Fuselage length: 1.44 metres
Flying weight 3.4 kg (I think it was more)
Engine: 10ccm
Text: Ralph Müller
Photos: Burkhard Erdlenbruch
