a whip stall is done by applying full power, accelerating straight and level, then pulling the nose hard up and chopping the power.
the resulting stall is quite violent.
the aircraft pitches forward until it is almost nose vertically down and recovers in a screaming dive.
it was used just once to show me a secondary stall at high speed and prove beyond all doubt that a wing stalls at an angle and not a speed.
so a whip stall is not a stall turn or a hammerhead. it is done straight forward, straight up and most certainly straight down.
dont ever do it, especially in an old aircraft. it would be a wonderful way to create a cloud of tinsel around you.