Thomas,
Point taken.
The fact that a teetering head may also be semi-rigid has nothing to do with the problem and it is not transferred to types
of head that are semi rigid but not teetering.
What I should have said was 'teetering and
UNDERSLUNG'. The diagram shows clearly how the mast can be contacted by an underslung head in some circumstances. This is the real problem with some types. A teetering head that is not underslung (if made)would not be so susceptible to the effects of Negative G as it would not be able to promote or allow mast bumping.
Coupling 1, Sparrow 0.
(Just for today of course
! )