The De Havilland DH106 Comet 4 was the final development and stretched fuselage version of the Comet series. From the tragic setbacks of the early Comet 1’s, De Havilland put all the lessons learned into the larger and more powerful Comet 4’s. Initially brought into service by BOAC in 1958, to inaugurate jet passenger service on the North Atlantic route (and to beat Boeing and their 707), the aircraft still had too few seats for the burgeoning traffic and it was found to be better suited to the hot and sometimes high elevation runways of Africa and the Far East. The Comet quickly became the aircraft of choice for many of the carriers on the African and Asian routes, continuing in service until the 1970’s.
Powered by 4 Rolls Royce Avon 524 or 525 engines the Comet 4 had a cruising speed of 500 mph at an altitude of 30 -39,000 ft. The range with a maximum payload of 106 passengers was 2820 miles.
The Model and its construction.
Wingspan: 15′ 3″
Length: 16′ 3″
Weight: (dry) 105lbs
Wing area: 37.4 sq ft
Power: two, JetCat 120 turbines
Construction started in October 2001 and was a joint project between John, and son Steve. Acting as a two man team, but located in different parts of the country, it was agreed that John would build the fuselage and tail components and Steve, the wings. Each would construct as much of their respective parts as possible before mating the wing centre section to the fuselage centre section. While this may initially sound a recipe for error it actually all went smoothly. The critical part was in ensuring that the dimension between the wing spars was exactly the same as the mating fuselage formers.
Fuselage pieces, part sheeted. Note the relatively small work area. Are the pins in the map where they plan to display the finished model?
Here is the model assembled with the construction of the centre section highlighted.
To ease construction and subsequent transportation, the model was designed to be broken down into a one piece centre-section that carries the engines, fuel tanks, undercarriage and most of the radio with detachable front and rear fuselage sections and outer wing panels. The tailplane halves were also made detachable. The main components are all less than 6ft long and will comfortably fit into a medium sized van.
Traditional balsa and ply, construction methods were employed. The spars were made from cypiras. The entire model was sheeted in 1/8″ balsa and then covered in fibreglass cloth. Cellulose white primer was applied prior to the finishing coats of Japlac enamels. A final topcoat of Aerokote gloss fuel proofer was applied overall.
The model was completed and test flown in May 2004, it had taken 2 1/2 years to build, but there had been some quite lengthy inactive periods during that time.
With an access cover removed, one of the engines can be clearly seen.
Main battery and radio board.
One of the design objectives was to be able to assemble and disassemble the model quickly (this seemed to be important knowing the vagaries of the British weather). The wings panels each have two projecting aluminium tubes which slide onto corresponding tubes in the centre section. When the wing panels are slid into position the electrical connections make via multi-pin plugs and sockets. The wings are then retained by two cap screws. The fuselage sections are joined by seven cap screws per section accessed through (non-scale) hatches in the lower portions of the fuselage; again the electrical connections automatically make when the sections are screwed together. The tailplane halves slide onto aluminium tubes and are retained by elastic bands passing through the fuselage. Having had quite a lot of practice now in putting the model together they can do it in about 10 minutes, that sounds good, but you can still get very wet in ten minutes.
Another design objective was for a slow flying (and landing) model. It was reasoned that if the model could land slowly the complication and weight of brakes could be avoided and hence the model could be built lighter, which would help it to land slower!
The radio installation follows the now standard large model practice of having two receivers each having their own (4.8 volt) battery supply. Separate (6 volt) power supplies, as well as backers, are provided for the servos these being driven through opto-isolators. A further battery supply (12 V) is included to power the four, 35 W halogen landing lights.
The model assembled with construction completed, awaiting finishing.
Discussing the completed model.
With a power to weight ratio of just under 1:2 the Comet is more than adequately powered. The model will fly for 15 minutes on 10li of fuel. The take-off run is relatively short and the climb-out good. Aileron response is adequate but not exceptional so it’s best not to fly in very windy weather. The model though has surpassed expectations – we were hoping for a realistically slow flying and stable aeroplane and have not been disappointed. With a model airliner there are not many manoeuvres that can be put into a flying repertoire if realism is to be retained. Fortunately the low weight enables the Comet to be cruised around at low speeds and low angles of bank, just like the real thing. On calm days, landings can be accomplished with the nose held high off the ground until the speed has decayed – now that does look realistic and has made the whole project worthwhile!
During 2004 the model has flown 22 times and visited Bruntingthorpe, Cosford, Woodvale, the British Nationals at Barkston Heath and Hucknall where it was awarded the Rolls Royce Merlin trophy.
The model about to touch down. (Cosford 2004)
Retracts and oleos Unitracts. 110lb allows one retraction.
Radio accessories SM Services.
Fibreglass Materials Fibretech.
Only the grass gives this picture away as being of a model. (Cosford 2004)
Finally, on the runway ready for another flight of this awesome model.
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