Is Bell testing a multi-fenestron?

[CTR]

The math is not that simple

Dangermouse and Riff Raff, the math is not that simple, or the whole requirements story.

First, loss of tail rotor control on most FAA certified helicopters is not classified as catastrophic, requiring 1E-9 probability of failure. Loss of tail rotor control is typically classified as hazardous, requiring only 1E-7 probability of failure. For Part 29 certification, the cyclic and collective controls however a catastrophic classification is correct.

Second, the Bell 429 is a Part 27 certified helicopter. For Part 27 certification flight controls a FEMCA is not required. However it is required under Part 29. I admit for new and novel technologies this is a gray area.

Third, the analysis you are providing as a reference is for a screw EMA actuator. You can delete the screws from the probability analysis. Additionally bearing failures are easily mitigated by use of redundant bearings or bushings, along with a sensor to detect primary bearing failure. So the probability of a dual simultaneous bearing failure is not even worth considering. Finally, main reason screw actuators are not used in aircraft primary flight controls is the difficulty in mitigating the common mode jam failure of a single screw. Configure two or three actuators in parallel, one actuator jams the assembly. Configure two or three actuators in series you end up with a very long actuator.

This is a big reason the Bell EDAT makes sense. In the event of one jammed fan, the remaining fans performance are not impacted.