Ken Ryan |
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| Bristol Belvedere Build - | ||||
| DESIGN: |
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| The Bristol Type 192 Belvedere was a British twin-engine, tandem rotor military helicopter built by the Bristol Aeroplane Company . It was designed for a variety of transport roles including troop transport, supply dropping and casualty evacuation . It was operated by the Royal Air Force (RAF) from 1961 to 1969. | ||||
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| After a visit to the national Helicopter Museum in March 2009 I couldnt resist having a go at building this helicopter as it looks good and is unusual, here is a picture I took of the museums restoration project - | ||||
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| DESIGN: | ||||
| The basic idea of the design was to use the Trex600E shaft drive system as the drive to the front rotor with the rear rotor driven by a powerful electric motor and 10S 37V battery. Myfirst step was to draw a complete 3D model of the Trex600 frame and rotor head assembly. Once complete I found a very basic set of 3 view plans on the Internet of the Belvedere and imported it to the CAD programme, from this I could get the basic layout of the design to scale, this showed I needed to use a Trex700 tailboom to get everything in the correct location - | ||||
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It took 6 months to develop the design constantly changing to get the right mix of lighweight, strength and correct operation. One of the later decisions was to dump the idea of driving the forward rotor using the 600's tail drive mechanism, instead I went for direct drive using bevel gears from the mainshaft, this had a lower risk of stripping gears due to the load placed on them by a 1350mm Rotor as opposed to a much smaller tail rotor. At this stage then the dimensions of the helicopter are -
The prototype design now looks like this - |
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The chassis main strength comes from the Trex600 tail boom case combined with the Trex700 tail boom. When assembled this forms quite a rigid structure that doesnt easily twist, however it is important in a large tandem for the structure to be as rigid as possible so in my instance I have included two more components. Firstly a 20mm square alloy tube running the length of the helicopter. This does two jobs, it provides a mounting point for the undercarriage and through bulkheads attached to the tube and carbon side frames provides a measure of ant-twist particulary so at the rear of the helicopter. The tube is crossed drilled to make it a light as possible Secondly 2.5mm thick carbon fibre side frames provide mouting support for batteries and electronics and hold the mainshafts securely parallel to each other and offer anti-twist support. These components can be seen below - |
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The drivetrain consists of a rear mounted electric motor driving a Trex600 helical main gear of 188 tooth. Attached to the same shaft is a 24 tooth 1.5 Mod bevel gear fixed in place with grub screws against a flat on the shaft. This in turn drives a 16 tooth pinion gear giving a ratio of 1:1.5. The pinion has a bore of 8mm and is fitted to a transfer shaft running through the Trex700 tailboom in the same manner as the standard Align tail blade torque shaft drive. The shaft runs in the standard torque drive bearings but the shaft itself is both longer and thicker walled than the Trex700 torque drive shaft to cope with the load of the front rotor. The initial motor is of a higher capacity than the standard Trex600E motor, a Kontronik 45-08 - 800 rpm/V 45A motor providing a high degree of torque. Power will be from a 5000Mah 10S 37V battery through a Castle creations 85HV ESC, this combination should give enough power for the rotors but I may reduce the Mah of the battery after testing as at 1.3Kg the 5A battery is quite heavy. The drivetrain can be seen below - |
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