Aerospatiale SA-2 (42069 alternate)

 


If you're not familiar with the name, that's the helicopter from the Avatar movie. I like exotic-looking machines, and I've been thinking of building it for some time. I thought it might make a good alternate model for 42069 since the tracks can be inverted to make the wings. I figured I might need 108-110 tread links to have 2 inverted rings that don't have too much tension, and 42069 has... 108 of them. The coincidence was to good to let pass.
I've used conv-barman's great Avatar Helicopter design as reference for the general shape and some of the functions, but overall it's radically different, especially the inner structure. I've spent over 150 hours on the design alone.

This alternate model uses close to 90% of the parts, and is fairly large: approx. 60x60cm. Note that it is not for beginners.

It comes with several features:
  • The propellers can be rotated with a knob, which also drives the V8.
  • There's a joystick to alter the propellers' rotation plane, but unfortunately the wings turned out to be too heavy for that mechanism to work. However if the wings are supported with something, then it works a bit. It can also be done manually.
  • The entire wings can be tilted to and fro using a knob (the most difficult thing to implement by far).
  • Two side cargo bays with spring-operated doors can hold the 4 canisters from the original model.
  • Rear cargo bay bridge-door can be lowered to the ground with a knob.
  • Cabin doors can be opened using levers.
  • Manually-operated winch & extension arm.
  • The landing skids have suspension.

However, the wings are heavy and extend far away, so they put a lot of stress on the parts that support them. It's probably better not to have the model standing for a long time without some kind of support (example included as appendix in the instructions using extra pieces).
On the good side, thanks to the tilt function, the wings' respective weights are working against each other, so don't affect the main structure much.

If you decide to build it, you'll see that a differential is used to drive the propellers. If you're wondering why, it's because tilting wings with gradually block the U-joint of the higher wing, so a differential is needed to decouple both wings in order to prevent blocking everything.

Instructions were quite tedious to make: figuring out a proper building order and handling of all the weird part angles, which demanded a lot of time and consideration.


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