On 9/12/2016 9:21 PM, Bob Kuykendall wrote:
On Monday, September 12, 2016 at 8:09:10 PM UTC-7, Bob Whelan wrote:

...I've been unable to find the "Materials Laboratory factual report."
Pointer help will be Seriously Appreciated!

The Docket Management System (DMS) has many good detail photos of broken
aircraft. It is (or should be) every detail designer's go-to resource:

http://dms.ntsb.gov/pubdms/search/hi...docketID=58737

Thanks, Bob K.


Many thanks!

Just to (sorta) complete the train of thought in my (bemused) posts preceding
this one. The photos of the release mechanism from the accident aircraft seem
to (pretty much) match my (oldish) memories of how it functions, the "pretty
much" exception being I remembered the hook retraction spring as a simple
tension spring (and not the dual-sided, probably custom-bent) coil type. It
was THAT spring force to which I referred when writing I couldn't understand
how the hook could have sensibly functioned in its absence. That force serves
dual purposes: 1) maintaining the hook cover against the back side of the
opening slot while in flight (while also allowing a back release in the event
of loss of rope tension combined with a Big Bow), and 2) (by
through-transmittal of the hook-opening-cover force) retracting the entire
hook mechanism after the pawl is released from the flat-plate/cable-hook
detent by the pilot pulling the release knob/cable.

As for the report's claimed missing pawl spring...I must be getting dense in
my old age, since I'm still puzzled by the intended function and line of force
of that implicated piece of (missing?) hardware. Using Figure 8 by way of
illustrating my puzzlement, it seems to me such a spring could either serve to
decrease or increase the pawl's contact force against the hook plate.
Decreasing the contact force would appear to be counter-productive, while
increasing it (arguably) might have served to make the incomplete contact
condition shown in Figure 9 even more likely.

In any event, my current working hypothesis is the hook likely back released
(as intended, for better or for worse) from a bow in the rope (gusty sink
being reported in that vicinity by the previously-towed pilot) at an
unfortunate/ugly towing-location, followed by loss of control. Having had two
such back releases during gnarly tows (one nearly too low to warrant an
attempted return, above head-high sagebrush, but fortunately not occurring
until later that same tow), I can relate. Whether or not the incomplete
contact condition between pawl and cable hook detent (shown in Figure 9) was a
contributor, I have no idea.

Back to the hook design - what am I missing? Thanks!

Bob W.