Hi
Fantome,
The DH86 sounds a bit of a nightmare. It seems to have been basically lacking in directional stability, and one wonders how many accidents may also have been engine-failure related.
http://en.wikipedia.org/wiki/De_Havilland_Express
The fitting of auxiliary fins (DH86B) would have improved directional stability in symmetric flight, but I wonder if they also needed to enlarge the rudder.
Its post-war equivalent, the DH114 Heron, was a rather a nice aeroplane, with a similar power-to-weight ratio. It had 4 Gypsy Queens @ 250HP, compared with the DH86's 4 Gypsy Sixes @200HP, but the Heron was a monoplane. The Heron1B had fixed L/G and a MTOW of 13000lb, compared to the DH86's 10250lb. (The Heron2 had retractable L/G, and the Heron2D had fully-feathering propellers to achieve Performance A standards. Don't recall the Vmca.)