Help researching 1961 Electra crash

[Concours77]

Originally Posted by G0ULI

Concours77

I can envisage a situation where a developing whirl mode might cause an incorrectly assembled aileron cable to break. The vibration and flex of the wing adding just enough stress to part a misassembled joint.

My experience involved other than standard “flex”. The wing was “twisting”, in spiral fashion.

Since all aircraft wings are designed to flex, often by several feet at the wingtips, the designers would have taken this into consideration when planning the control cable run for the ailerons. They would assume in their calculations that everything was assembled correctly and in good condition.

Yes, but there are no cables in the wing. Rods, running in sleeved ball bearings. Aileron Trim is by cables, I believe.

You propose a plausible mechanism as to how the aileron cable broke when it did, but the root cause was still incorrect assembly and ajustment by the ground engineers.

Well, the cable did not break, it separated at swage/connector/turnbuckle. CAB claim the cable parted at the forward junction block, between the turnbuckle and the pulley carriage.

As far as the flap and aileron experiment is concerned, I believe that it was conducted to ensure that neither part could significantly interfere with the other. I don't think it was conducted to see if whirl mode was more likely at certain power settings as a series of experiments had already been carried out to determine the cause of the two previous whirl mode accidents where aircraft lost their wings. Then there is the question of whether flap would reduce the ability of a disconnected aileron to return to a neutral position in the slipstream. Clearly in this case, the ailerons remained displaced, so it was important to determine why this happened. I believe that it was determined that the ailerons were held in place by residual hydraulic pressure from the boost system. Once the control cable separated, the valves would have remained at their last commanded position.

By “significantly interfere” is your meaning aerodynamic interference (Which would have been known, via wind tunnel testing in design) or mechanically, flap fowling aileron at inboard pocket rib? The scar found on the aileron would represent evidence of my theory, that the aileron flap “joint” was closed, due fouling of flap in its track, or aileron due to separated hinge?

With boost active, the Ailerons, Rudder, and Elevators return to neutral without stick deflection, by design. It’s in the manual. This is how we know the cable did not separate; had it separated, the aileron would have returned to neutral (without damage present). Boost ON or OFF. Ailerons do not need a reversal command to return to neutral.