Back to G's and Failure Sequence
Based on the factual findings regarding both C-GNDY and N174BK, it looks like the forward VS spar failed first, just above the doubler that ties into the HS. As the VS moved aft it then broke at the aft spar just above where it ties into the bars that are used to mount both the VS and the HS. This aft movement then tears the rudder in half, followed by the lower rudder bearing being compressed and bent into failure. The lower rudder, now just attached by the control cables, flops back and forth with the cables sawing the fuselage.
As this sequence happens, ancillary damage occurs and varies depending upon many factors. Balance weight lost, rudder blown apart, and in the case of BK, left HS/Elev failure - due to a rolling moment.
The big questions I have center on the breakup speeds calculated as 234K and 220K, and the recorded/calculated maximum G loadings of 3.5 and 2.5.
So, was there a last pull that overloaded the structure that was unrecorded?
Could the speed alone start the failure sequence? The '7 rudder is offset to the left.
Flutter was discounted, but not eliminated as a factor in C-GNDY. Vans tested to 217K and the Canadians estimated that with the addition of 1 pound of filler and paint, the calculated flutter speed would be just above 250K.
It would be very reassuring if the probable cause showed a G loading in excess of 9 (or even 6). That is presumed, but not recorded or even directly addressed in either accident analysis.
What am I missing?
Best regards,
Merrill