back to Venice and more gondolas;
Back when aways, torque turns and pedal turns were a topic of concern, particularly with mustering use of the helicopters. Looked way too much like fun to not have issues. for the run of the mill maneuvers, the loads were not high, where the speeds were not high anyway. What passes for a torque turn or a pedal turn depends on the eye of the beholder; the manoeuver can be done at the appogee of a climb, with positive g throughout the process, and loads are low. It is also possible to whack on full pedal at cruise speed and watch the feathers fly, The machine washes speed off promptly, and, as the tail swaps with the nose, the tail starts to rise from the reverse flow over the stabilizer, and a lot of back cyclic is needed to stop the tail rising too far, but, you get to see a face planter full of dirt in front of you, including having to look up through the top of the windscreen to see the horizon. As you are reaching a cyclic control limit, the control path/TPP gets to be a big point of interest. The machine seems to sit in space for a while (like a particular scene on a Bond, James.... Bond movie with a -350) and then whistles downward in the opposite direction. The first time that one was demonstrated, I wanted to hop out immediately, as in, RFN!!. The questions that it raised on TPP clearance to the tail boom, inflow to the TRB, and pretty much everything in-between was interesting, in a morbid manner. Equally, the prior studies on torque turns and pedal turns did not appear to have covered someone doing such an extreme manoeuver. The boom takes a fair old lateral bending load for the force applied from the tail to overcome the air load of the boom and fin, with the maximum load aft of the center of the boom. K, not brilliant, but measurable. The TR takes a high blade angle in the pedal turn which was the usual way that was done except for one certain sheriffs department who were making a torque turn with a bucket of right pedal (equivalent...a euro thingy) to get the nose around smartly. from 120Kts, it was certainly entertaining. That one particularly is interesting as the change from a right pedal needed to get the nose around, to a hard reversal of pedal leads to some wild inflow angles, and some questions on what is flapping where (think "where did who go?"): with the delta-3 offsets in that case. along those lines, reversing the loads that much on the pitch links on the TR seemed to be worth a bit of a look. At that point I went off playing with the 737, so never answered the extended questions fully, but wanted to go back someday. Dunnunda, a number of funnies happened with Robbies doing mustering in the main, with the "improved single piece" pitch links shearing. Now, I think that the design of the links on a TR should not have a lot of cyclic loads being applied; they are after all a collective device only, and the only independent blade angle change arise from the built-in delta-3 hinge offset. As far as I am aware, there have been at least 3 of those sorts of failure occur, one being detected in flight with some associated antics of having a free to pitch blade... the failures may be from machining (tooling marks etc), or materiel (inclusions, embrittlement or other) but they did not. The failure was concluded to have come from the binding of the bearing due to excessive axial wer, well outside of limits. Given where they have occurred, I suspect that the TR pitch links don't like what they are seeing. The low-speed manoeuvers didn't appear to add much load, so it may be that the higher speed, higher blade angle/higher inflow is happening. Or it is just a coincidence. The reports show extensive wear of the spherical bearings, which is not a good thing. The photos show the condition of the control system...
Dunnunda had 3 of those cases... the curious point in the report relevant to mucking about in a pond over the Transvaal is:
"The factors that influence the rate of wear in the spherical bearing that attaches the tail rotor blade to the pitch link would not be expected to vary from helicopter to helicopter".
But the reports appear to come from an area where ag stuff is a common factor.
Suggestion: if you are going to use large applications of control inputs, then do good post flights and preflights.