Lyman
Briefly, I conclude the bogie is rotating about its horizontal plane as a result of a missing stand-off spacer.
As you requested, I looked at that picture very carefully, and yes, there is evidence of a shimmy-like oscillation in that part of the track. However, I also looked at the other pictures in the BEA report (which is the source of the Heritage picture) and I could not see any evidence of similar oscillations when the aircraft was on the tarmac.
So I have some questions for you ..
I am no expert on shimmy, but I do know that it depends on a critical relationship of feedback between tyre forces and gear structure. The tyre force/slip characteristics would change substantially when the gear moved from tarmac to grass, so why are you sure that shimmy was present throughout all the TO? The BEA certainly didn't think so. Could shimmy be present only in the grass-bound part of the roll?
By the time the FE called the #2 engine failure and fire warning and then shut down #2 the aircraft had been airborne for several seconds. There would have been no shimmy once airborne, so why do you think it such an important factor in his decision to shut down #2? Why would it trump the engine failure and fire warnings? [The debate as to whether he
should have shut down at that time is another matter]
At the time when the aircraft passed over that region (97611.5 on the BEA datum) it was at about 203 kts and had an AoA of 9 deg. One second later it lifted off, still at 203 kts but with an AoA of 11 deg. At the time we are discussing then about 80% of the weight was being carried by the wing so only 10% was on the LH gear. Since any forces transmitted to the airframe must depend on ground reaction and slip why do you think that the gear had a important effect at this point?
Shimmy, as I understand it, is a cyclical rotation of the wheels about the main leg. Again at the time we are talking about, the
aircraft sideslip was 3 deg. Allowing for +/- 3 deg oscillation because of the missing spacer that would mean the wheels oscillating between zero and 6 deg would it not? Why would the time they were at less than 3 deg not offset the time they were at more? Or in other words, why should shimmy change the
average force?
I notice that in your argument you do not mention the sideforce generated by the tyres. Have you any reason to neglect that contribution? I would think it a bigger effect than the drag and what is more it would have been acting behind the CG and giving a moment to restore the aircraft
towards the centreline.