TC, since there is nothing going on at the moment:
turboprop engines and and wing mounted fins so that the handling characteristics of different aircraft could be simulated without building prototypes.
I think that, since the additional surfaces did not move, they were for another purpose.
The addition of the extra cockpit, kit, and crew etc., would have moved the centre of gravity quite a way forward. This would have reduced directional static and dynamic stability (but increased longitudinal stability at the expense of increased tailplane downforce and extra trim drag).
A look at the photograph below shows that the additional appendages were aft of the C of G and thus would have increased the directional stability.
Conventional wisdom would have suggested adding the surfaces to the tailplane, in which case they could have been smaller in area. I can only assume that the tailplane was not big enough to facilitate this.
I am more than happy to be corrected if you can find more data.
Just my two-penneth.
I'll go away now.....
LM
