Onewinglo
Active Member
Guys I suspect we are overcooling our RV-8 engine and suffering with excess cooling drag in the process. We built and installed a nearly leak free plenum.
The James Cowling exit area appears to be huge in comparison to the inlet area. The 2 round inlets total 33.6 square inches and the exit measures 84.2 square inches. We plan to reduce the exit area during the condition inspection in January, but the question is how much? Is there an inlet/exit area ratio that we can use as a starting point?
I did a test flight to collect a little data as follows:
RV-8 CHT and Oil Temp Test
Climbed out at 100-110 mph WOT to 8000' DA, Surface OAT 23c. Full fuel with 1 pilot at 170 lbs.
Max CHT as #4, 3, 2, 1 (oil cooler is behind #4)
355, 319, 292, 286
Max oil temp 168
Level at 8000' DA, 2500 RPM, OAT 13c, leaned to 7.5 gph resulted in:
Max CHT as #4, 3, 2, 1
297, 273, 278, 272
Max oil temp 168
Indicated/true AS in mph 166/187
WOT at 8000' DA, 2850 RPM, same lean position, 11.4 gph:
Max CHT as #4, 3, 2, 1
333, 306, 318, 311
Max oil temp 170
Indicated/true AS in mph 192/216
150 hours on the engine / airframe; First flight - January of 2017
Superior O360XP with 9:1 pistons and Phase 3 camshaft, Slick mags; Vetterman 4 into 2 exhaust, no mufflers
James cowling; Cato 3 blade composite FP prop; Grove airfoil gear; Wheel Pants and all fairings in place
Bottom line, I have never seen a CHT > 360 at any time, even the heat of a Louisiana summer.
The James Cowling exit area appears to be huge in comparison to the inlet area. The 2 round inlets total 33.6 square inches and the exit measures 84.2 square inches. We plan to reduce the exit area during the condition inspection in January, but the question is how much? Is there an inlet/exit area ratio that we can use as a starting point?
I did a test flight to collect a little data as follows:
RV-8 CHT and Oil Temp Test
Climbed out at 100-110 mph WOT to 8000' DA, Surface OAT 23c. Full fuel with 1 pilot at 170 lbs.
Max CHT as #4, 3, 2, 1 (oil cooler is behind #4)
355, 319, 292, 286
Max oil temp 168
Level at 8000' DA, 2500 RPM, OAT 13c, leaned to 7.5 gph resulted in:
Max CHT as #4, 3, 2, 1
297, 273, 278, 272
Max oil temp 168
Indicated/true AS in mph 166/187
WOT at 8000' DA, 2850 RPM, same lean position, 11.4 gph:
Max CHT as #4, 3, 2, 1
333, 306, 318, 311
Max oil temp 170
Indicated/true AS in mph 192/216
150 hours on the engine / airframe; First flight - January of 2017
Superior O360XP with 9:1 pistons and Phase 3 camshaft, Slick mags; Vetterman 4 into 2 exhaust, no mufflers
James cowling; Cato 3 blade composite FP prop; Grove airfoil gear; Wheel Pants and all fairings in place
Bottom line, I have never seen a CHT > 360 at any time, even the heat of a Louisiana summer.