T.O.C. 1978 in Las Vegas, Günter Hoppe presents his Cranfield A1 for the first time during the aerobatics competition and finishes in an excellent 6th place among the world’s best R/C aerobatic pilots. In 1981 Günter Metterhausen presents this model as a kit in the well-known Metterhausen quality. Ralph Müller, one of the best R/C specialist authors at the time, published his report on the CRANFIELD A1 in the July 1982 issue of ‘Modell’ magazine.
Here is Ralph’s test report at the time:
The CRANFIELD A 1, specially developed in England for modern performance aerobatics, has been available as a kit from Günter Metterhausen for some time. Günter Hoppe used this construction successfully for the first time in Las Vegas and achieved a fourth place with it. Since then, this model has become increasingly popular, especially since the RC 1 X class was established in Germany about two years ago. There are now several such competitions with increasing numbers of participants. The flying style of the X models differs considerably from that of conventional RC 1 low-wing models, not only because of the size of the aircraft, but also because the need to fly turning manoeuvres brings it closer to the style of manned aircraft. flying.
You can no longer correct between the individual figures with impunity (as in RC 1), as this would result in points being deducted. The X programme is more difficult and more interesting to fly than the current F3 A programme. RC 1 X models may weigh up to 10 kg according to the regulations, the engine displacement is optional. This means that larger models than the CRANFIELD can be used, and some pilots do so, but the question of propulsion is still a problem. Two 10cc engines mounted on a gearbox would probably be ideal for a model with a span of approx. 2.5 metres, but the noise development would probably exceed the permitted limit of 85 dB. In addition, the two motors, which have to be adjusted separately, are relatively difficult to bring to absolute synchronisation.
The whole thing is of course easier with a 15 cc engine, where the resonance tube can also be integrated without difficulty due to the size of the models provided for this purpose. The kit supplied by GM-Modelltechnik is very well made and the individual parts are pleasingly light. The two wing halves (polystyrene, balsa planked) are ready sanded, the V-shape is sanded. Cut out the shaft for the aileron bellcranks and attach the bellcranks to the already installed Bowden cable. The grooves for the undercarriage mount are fitted, the undercarriage is also included in the kit. The tailplane and rudder are included in the same design, the white coloured fuselage is extremely light and without visible pores. The canopy and engine cowling, a GRP moulded part for the fuselage-wing transition and the cover for the aileron wells in the form of deep-drawn parts complete the kit together with a 3-sided view and the drawing of the head bulkhead. The CRANFIELD is not a model for beginners, so I can save myself the trouble of going into the individual construction stages.
The only thing to note is that everything fits together fantastically well, and the person who wants to build this model will have glass fibre, epoxy resin and the necessary tools in his or her craft kitchen anyway. The OS 90 FSR with mixture adjustment is installed in my CRANFIELD, the resonance tube is integrated, the wing and tail unit are covered with thin paper and the entire model is sprayed with acrylic paint. The model built in this way weighs 5.2 kg, and with a foil covering you can certainly save 200 g. However, as it turned out when flying, the weight is ideal, the CRAN FIELD has enough vapour and is very quiet. The desire for a retractable undercarriage does not even arise, nor is it necessary to integrate the tube, as the models of this manufacturer used in competitions are all flown with an external tube and made a convincing impression, as they were awarded top places. Integrating the resonance tube caused some problems, as a GRP tube had to be built for the tube, as well as two GRP parts (small tubes) for the exhaust and cooling air.
Because of its size, I doubled the rudder, while all the other control surfaces were attached as normal. So far there have been no problems with the fixing screws (M6 nylon), they are completely adequate. The engine fits almost completely under the bonnet, only a circular hole was cut out for better cooling and easy access to the glow plug. The resonance tube is mounted twice in the tube. At the end of the tube a bulkhead was resin-bonded in, which has a hole in the centre corresponding to the diameter of the end tube of the resonance tube, and in the middle the resonance tube is mounted with a bulkhead.
The trick here is that the bulkhead is connected to the tube with two self-tapping screws and is only fixed to the tube with a few drops of superglue. This means that I can pull the tube and frame completely out of the GRP tube after unscrewing the two screws. To prevent the whole thing from rattling, you should avoid “throw fits”, clean and precise work is essential here. Of course, a conventional manifold could no longer be used with this arrangement, so copper pipe angles were purchased from the DIY store, a flange made from steel, everything installed, aligned and brazed. Despite the additional GRP tube installed in the fuselage for the resonator tube, there is enough space for the receiver system.
However, you should keep the servos and the receiver as far away from the tube as possible, as this prevents heat problems. A 1200 mAh receiver battery was placed next to the 500 cc tank so that it was as far forward as possible. The correct centre of gravity can be achieved in this way without adding lead, provided it was built light “out the back”. The CRANFIELD has inserted ailerons, which requires (and is also intended by the manufacturer) a deflection of the linkage (Bowden cable) in the wing.
Of course, care must be taken to ensure that the rudders remain as free of play as possible, and under no circumstances should deflection levers that differentiate be used. A perfect solution would be ball-bearing deflection levers, but unfortunately I haven’t been able to find any. My model is fitted with normal plastic deflectors, the rudders have a small amount of play, but this has not had a negative effect so far. It would probably be worse if the control surfaces were difficult to move, because then a correct neutral position is no longer guaranteed, which would result in unnecessary corrections. It is therefore essential to ensure smooth movement. Flight testing After various difficulties with the motor – it didn’t really want to go, as it was a brand new model – it was possible to take off after the throttle and full throttle running and the transition had been adjusted correctly. For me as a “three-legged flyer”, taking off with the two-legged undercarriage was unusual and not exactly pleasant.
However, once the glider was in the air, it was surprisingly easy to keep it on course after a very small adjustment to the aileron trim. The flying behaviour is fascinating, the CRANFIELD flies slower and more sedately than my conventional low-wing aircraft. Although the model is slower than its smaller brothers, it allows a constant flying style and has sufficient power reserves to fly vertical manoeuvres cleanly. The resonance tube still needs to be tuned precisely, it’s a bit too long at the moment. I fly around nicely at first to get used to the machine, but when the “oat stings”, I try a four-time roll. It works perfectly, and the CRANFIELD only needs a little rudder deflection to fly cleanly straight in knife-edge flight. I can already tell that the model flies in a very balanced manner. I look forward to landing on our rather small field with some trepidation, but the headwind supports the landing approach, and the first landing The CRANFIELD A 1 with its unconventionally shaped canopy is undoubtedly a beautiful aircraft. Of course, care must be taken to ensure that the control surfaces remain as free of play as possible, and under no circumstances should deflection levers that differentiate be used. A perfect solution would be to use ball-bearing deflection levers, but unfortunately I have not been able to find them anywhere. My model is fitted with normal plastic deflectors, the rudders have a small amount of play, but this has not had a negative effect so far. It would probably be worse if the rudders were difficult to move, because then a correct neutral position is no longer guaranteed, which would result in unnecessary corrections. It is therefore essential to ensure smooth movement.
Flight testing
After various difficulties with the engine – it didn’t really want to, as it was a brand-new specimen – it ran to our complete satisfaction, without a headache. Well, that went quite well. On the second take-off, I demolished the GRP three-blade propeller because the wind had shifted and there was no pull at all during the roll-in phase. The resulting upside-down position was impressive. A new propeller fitted, full pull, throttle applied and the RC l-X model took off in a three-point take-off. Of course, this only went so smoothly because the rather strong wind was now coming back to the runway just right. Otherwise, you have to be careful with this kind of fun, as the expected stall can lead to considerable demolition of the model.
I try to fly the complete X programme, but I have difficulties with it because the turning manoeuvres are completely new to me. You have to fly very precisely to keep the corrections to a minimum. With the given model size, it is of course possible to place the figures further away and thus, due to the greater distance to the pilot, also increase the angle at which you want to fly (imaginary window) or extend the flight distances. However, this is a matter of practice and can be mastered through training; the CRANFIELD has all the prerequisites for successful competition flying.
Text: Ralph Müller
Images: Guenter Hoppe, Klaus Dettmer, Siegfried Hanke, Erich Gilik
