UnPossible
Well Known Member
Hey -I am struggling a bit to figure out where my missing ~10 knots are. I now have around 60 hours on my RV-7A. All of the wheel pants/fairings are in place.
My plane has an Aerosport IO-375 with the 8:1 pistons and is rated at 195Hp. It has a P-mag and one slick Mag.
The prop is a "blended airfoil" Hartzell constant speed prop
As far as I can tell, the engine appears to be running well / smooth with no issues.
Below are Van's numbers for 180 and 200 HP RV-7A's at gross. I extrapolated out the expected cruise speed for 195 hp to be in the neighborhood of 175 kts
Cruise [75% @ 8000 ft]
180HP = 197mph / 171 kts
200HP = 204 mph / 177kts
195HP = 202mph / 175 kts
Last night I went flying to check my speeds. My weight was somewhere around 1600 lbs. With the density altitude around 1500 feet, I climbed to 6500 feet, left the throttle wide open and leaned it out a bit(but stopped leaning well before any power reduction was felt).
The G3X calculated the % power to be ~75-76%. The prop was set at 2600 rpm. Fuel burn was around 14 gallons per hour.
I used the autopilot to fly a box pattern at the 4 primary compass headings.
My calculated true airspeed was indicated at 166 kts. When I averaged the GPS derived ground speeds of the four headings, I came up with 167.5 kts.
Now 167 knots is not way out of the range of expected speeds, but I am a bit suprised that I am not at least making the speed expected of a 180HP plane.
Does anyone have suggestions/a check list I could use to try and determine why I seem to be a bit slow? I normally cruise at 145 -150 kts at around 8gph, so the missing 10 kts on the top end aren't that big of a deal, but I'd still like to figure it out.
Thanks for any help,
Jason
My plane has an Aerosport IO-375 with the 8:1 pistons and is rated at 195Hp. It has a P-mag and one slick Mag.
The prop is a "blended airfoil" Hartzell constant speed prop
As far as I can tell, the engine appears to be running well / smooth with no issues.
Below are Van's numbers for 180 and 200 HP RV-7A's at gross. I extrapolated out the expected cruise speed for 195 hp to be in the neighborhood of 175 kts
Cruise [75% @ 8000 ft]
180HP = 197mph / 171 kts
200HP = 204 mph / 177kts
195HP = 202mph / 175 kts
Last night I went flying to check my speeds. My weight was somewhere around 1600 lbs. With the density altitude around 1500 feet, I climbed to 6500 feet, left the throttle wide open and leaned it out a bit(but stopped leaning well before any power reduction was felt).
The G3X calculated the % power to be ~75-76%. The prop was set at 2600 rpm. Fuel burn was around 14 gallons per hour.
I used the autopilot to fly a box pattern at the 4 primary compass headings.
My calculated true airspeed was indicated at 166 kts. When I averaged the GPS derived ground speeds of the four headings, I came up with 167.5 kts.
Now 167 knots is not way out of the range of expected speeds, but I am a bit suprised that I am not at least making the speed expected of a 180HP plane.
Does anyone have suggestions/a check list I could use to try and determine why I seem to be a bit slow? I normally cruise at 145 -150 kts at around 8gph, so the missing 10 kts on the top end aren't that big of a deal, but I'd still like to figure it out.
Thanks for any help,
Jason