Originally Posted by
Control Eng
If that force was due to impact by the HS and/or pivot assembly, it is inconceivable that the frame would not be totally distorted.
I take your point re this. As I'm seeing it up to now, the HS goes down, the lower edge of the HS pivot attaching lug striking the connecting pin/bolt/casting which connects the two halves of the 'sandwich'. This causes the pivot mounting to twist around the HS pivot, with aerodrag on the HS causing the lower pinion to push backward onto the APU cone, twisting the lower supporting frame with it. What you then have is the length of the pivot mount sandwich prising away the APU cone at the lower end below the slot, the two halves of the sandwich exerting equal force on the inner and out edges of the APU cone surround frame on both sides.
The key to why the surround doesn't distort could be in the alignment of the cone attachment lugs at the top - they are vertical - so as the pivot mounts force out the lugs at the bottom, the top end opens up like a hinge.
Having said all that though...