zzuf,
I should have made myself clearer re certification. I was referring to initial certification by a regulatory authority. Obviously, there will often be no read across from one authority to another so an aircraft will have to satisfy the requirements at the time for issuing a type certificate.
I used the phrase 'accelerated stall' to mean a stall at greater than 1g (as per Def Stan 00-970 and Mil Specs). FAR23 and CS23 use the same phrase to mean a deceleration rate of 3-5 IAS per second - again, apologies for ambiguous phraseology. At 30 deg AoB and 75% MCP the pitch attitude will be high to achieve the deceleration but normal acceleration and IAS will be low. I have flown this test in a high powered piston aircraft under the old CAA Schedule 233 and been about 60 deg nose up with full rudder and almost full aileron, the ASI below its minimum value and still not reached an aerodynamic stall! However, normal acceleration was less that 1 due to the nose up attitude. Remember that it is pitch attitude that determines the deceleration rate, not normal acceleration.
Reduced directional stability may be mitigated by small extra fins but rarely will those compensate totally. The potential effect on stall speed is that stall characteristics may change due to the greater probability of having more sideslip present at the point of the stall, thereby resulting in a different stall speed. Rudder control strategy will have a major impact on this (eg. slipball central, zero yaw rate for wings level stalls, rudder free, rudder fixed from trim etc) because that is what will affect the sideslip at the stall. For a given cg. the longitudinal static stability may be affected by aerodynamic pitching moments from the floats, again potentially affecting pitch characteristics at the stall.
You are correct about ASI PECs affecting indicated stall speeds but it is actually AoA effects that are the cause rather than normal acceleration.
Please note that all of my points are generic and may not apply to the Beaver. Any thoughts on why different manuals have different stall speeds?
Rgds
L