I believe it is all in the terminology used in the certification process and the expected flying techniques that will be applied.
V2 is in the take-off configuration , i.e. at whatever flap has been selected and at whatever weight, there will be a V2 speed. It will obviously vary through quite a range, depending on aircraft size and flap settings available for take-off. There may even be several V2 speeds for the one weight/flap configuration - from V2 min to a V2 max for so-called 'improved climb'.
Vyse - sometimes referred to as 'blue-line' speed - is quoted as just one speed, is often not variable with weight (though it could be, but certification may only require it for the gross weight case) and assumes that the aircraft has been cleaned up to flap zero.
From a pilot's perspective, experiencing an engine failure at V1, continuing through Vr to V2 should guarantee certificated performance (assuming correct handling, properly rigged airframe etc).
Suffering an engine failure in a light twin before Vyse has been reached guarantees nothing, hence often the advice to land ahead if an engine fails before reaching blue line.
Last edited by Mach E Avelli; 28th July 2013 at 07:43.