Several years ago I communicated with Van’s about the published max gross weight (1800 pounds) stall speeds of the RV-8 when I was looking at its maneuvering speed.
Van’s verified that the RV-8's flaps down stall speed (Vso) is approximately 58 MIAS/50.4 KIAS, as shown on the
RV-8's performance page.
They also verified that the flaps up, clean stall speed (Vs1) is approximately 64 MIAS/55.6 KIAS, which is shown on their “
Airspeed Indicator Markings by Model” chart as the bottom of the green arc.
But again, those are Indicated Airspeed and the new MOSAIC NPRM stall speed requirement is stated in Calibrated Airspeed (Vs1=62 MCAS/54 KCAS). So the instrument and position error at those low speeds needs to be measured to find out what the RV-8's stall speeds are in CAS for a valid comparison.