Dauphin Build / Fenestron Gearbox

We are going to jump ahead quite a bit, as I did not take photos of about 3 months of sanding, patching bubbles, sanding again, sanding more, and then really sanding.  Did I mention sanding?  Oh, then there was more sanding...  I would work on this for 5 hours per day, and after two weeks of work, people would visit my garage and say: "Gee, you haven't done any work on your helicopter!"   

For those of you who don't already know, a Fenestron is a shrouded tail rotor of a helicopter that is essentially a ducted fan. The housing is integral with the tail skin, and, like the conventional tail rotor it replaces, is intended to counteract the torque of the main rotor. 

Anyway, this is where Bryan came to the rescue.  I needed to couple the Vario gearbox for the Fenestron fan to the standard Align Torque Tube. Bryan made a number of custom parts for this assembly, we replaced the Pitch ring with one that fit the original Vario part. This requires two shoulders on the ring, one for the bearing, and one for the nut to seat. This was made pretty much "caliper to lathe", so there was no diagram. The actuator arm was made to replace the Vario one, and fit the bellcrank. The mounting plate for the bellcrank support arm is just a square of aluminum, drilled to fit the end of the gearbox, with a relief to prevent rotation, and a mounting hole.


The Align boom is larger than the Vario, so a thin sleeve must be made to make up the difference in diameter . A shoulder on the sleeve prevents it from sliding up the Align boom. The Vario gearbox connector 49/56 is disassembled (remove the pin and slide off the articulating connector) and reassembled with a machined part that has been made to accept the Align Torque tube.



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