Grateful for your thoughts on the speed of an Ovation II that I had the pleasure of flying today. She was retrofitted with a FIKI TKS system and has VGs installed. 310hp upgrade with the Hartzell prop.
Flying at 9,500' at 55% power, our TAS was 156kts whereas the POH says it should have been 170kts. I'm wondering whether the TKS system plus the VGs would explain such a disparity between the book figure and our actual true airspeed or whether there might be some other issue to consider, such as rigging, etc.
Just in case I have messed up the calculations:
- 9,500' pressure altitude (FL95)
- OAT: -2 celcius
- Fuel flow: 10.2 GPH (LOP)
- TAS calculated by averaging ground speeds heading N, S, E and W.
- As we were LOP, I calculated power as 55% by multiplying FF (10.2gph) by 14.9 to get actual HP and using 280hp as the denominator for the percentage power (the TAS/pwr tables assume a 280hp engine rather than 310hp). Manifold pressure was set at 20" and RPM at 2,400 but, LOP, I don't believe this makes a difference.
- Goes without saying: flaps and gear up, speed brakes retracted! 2 guys up front and only about 25 gallons in the tanks. Smooth and clear air.