Some info on bob/inertia weights fitted to Spitfires.
It was first trialled in the prototype MkIII, then a MkII
From everything I've read the reason it was fitted was that lots of pilot's were writing off airframes by overloading them. Bent wings were a bit of a reccuring theme. Caused in the majority of cases by pulling out of a high speed dive or too tight a turn.
In June 41 it was decided that all Mk V's should have inertia weights fitted.
3.5lb for a VA and 6.5lb for a VB
After RAE trials it was decided that all the following marks must have the 6.5lb weight fitted. Mks F VI, PR IV, VI and VII, Seafires I and II.
No weights needed for Mks I and II and V's, provided that with the browning only wing the rear oxygen cylinder was removed, and with the cannon wing the oxygen cylinder, signal discharger and IFF radio were removed.
In '42 a VB Merlin 45 (BM589) did handling and stability trials with special reference to pull out from dives and tight turns. Tested with and without 6.5 lb inertial weight. (This after reports from pilot's who did not like the inertia weight). The outcome was that it was suggested that the inertia weight only be fitted into aircraft (V's) with the Rotol prop.
The inertia weight was quite unpopular: Hornchurch reported "All pilot's are beginning to complain" Biggin Hill " Condemned for making Spitfire difficult to land and reducing manoeuvrability" Kenley "Did not notice effect of the weight but opinion of the Spitfire was in general, low" Tangmere "Do not care for the the device"
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