Islander SE ROc
The problem with the islander (from a 'performance by numbers' scenario) was its all up weight was 'optimistic. Indeed it carried a permanent small flap setting to even achieve the rather limited SE ROC it was 'supposed' to have.
In fact selecting flap up 'again' after the normal up removed this and slightly improved the cruise (going into overdrive we called it Ha Ha).
If the engine was feathered and then motored to the near horizontal in absolutely clean air you then set 65 and waited. If/when the needle showed a supposed positive ROC, but not enough to satisfy the COA test then the speed was reduced by 1 knot and then possibly to 63 may be just enough to pass.
any sort of turbulence would see the needle drop down and therefore it was a classic demonstration of trying to squeeze a higher AUW for the brochure, but in practice one just reduced the weight to suit conditions. The actual SE handling was fine, and indeed it was basically a twin engine cub with good vis and plenty of leg room. I seem to recall a max ground operating wind speed of 45 knots was suggested due to the size of the rudder and its ability to slam against the stops which would 'twist' the mass bal on top. Like most British machines it was overbuilt and had originally been designed to use the 180 Lycoming engine not the 6 cylinder 0/540. Anyway it was lots of fun and did what it was supposed to do.