Muffinman, tis the trouble with finding information on the net, no such thing as Vtos, stick with the Vtoss
The FAA definitions follow
V A design maneuvering speed
V B design speed for maximum gust intensity
V C design cruising speed
V D design diving speed
V DF/ M DF demonstrated flight diving speed
V EF the speed at which the critical engine is assumed to fail during takeoff
V F design flap speed
V FC/ M FC maximum speed for stability characteristics
V FE maximum flap extended speed
V FTO final takeoff speed
V H maximum speed in level flight with maximum continuous power
V LE maximum landing gear extended speed
V LO maximum landing gear operating speed
V LOF lift-off speed
V MC minimum control speed with the critical engine inoperative
V MO/ M MO maximum operating limit speed
V MU minimum unstick speed
V NE never-exceed speed
V NO maximum structural cruising speed
V R rotation speed
V REF reference landing speed
V S the stalling speed or the minimum steady flight speed at which the airplane is controllable
V S0 the stalling speed or the minimum steady flight speed in the landing configuration
V S1 the stalling speed or the minimum steady flight speed obtained in a specific configuration
V SR reference stall speed
V SRO reference stall speed in the landing configuration
V SR1 reference stall speed in a specific configuration
V SW speed at which onset of natural or artificial stall warning occurs
VTOSS takeoff safety speed for Category A rotorcraft
V X speed for best angle of climb
V Y speed for best rate of climb
V 1 the maximum speed in the takeoff at which the pilot must take the first action (e.g., apply brakes, reduce thrust, deploy speed brakes) to stop the airplane within the accelerate-stop distance. V1 also means the minimum speed in the takeoff, following a failure of the critical engine at VEF, at which the pilot can continue the takeoff and achieve the required height above the takeoff surface within the takeoff distance
V 2 takeoff safety speed
V 2min minimum takeoff safety speed
It's interesting that in the regs (design criteria for Part 23 and 25 aircraft) there is no such thing as Vfo mentioned. Only Vf and Vfe. Where does this Vfo get mentioned? Flight manual?
To airaholic, the official FAA definition of Vfe is maximum flap extended speed, and the answer to
"can partial flap be extended above vfe?" the answer is a resounding NO. Follow your particular flight manual. The Vfe may vary depending on the amount of flap - Chieftain for example, 162 kias up to 25° of flap, then 132 kias to 40°