After weeks of patient tweaking, Tuesday I finally had my Rotax and Sensensich 3-blade ground adjustable prop exactly where I wanted them. On my first cross-country traversing mountainous terrain, as opposed to following the coastline, everything was perfect. The airplane easily climbed to 4500 feet, with RPM stable in climb just above 5100, the max oil temp was 208 and cooled to 200, CHT 234, prop pitched to give about 5500 rpm on WOT, EGTs 981/1020. Finally!
But what could have happened overnight? Wed AM, setting off another cross country over low mountains, everything went to pieces. That flight, aborted, and two subsequent flights, have shown reproducibly severely degraded performance.
RPM: 5100 on takeoff, but above 1500 feet decays to 4900 and of course airspeed drops. Engine feels sluggish, but rpm recovers when you go straight and level. Never tried to push it above 2000 feet, always immediate return to airport. Engine clearly not happy.
Oil temp: Set new record highs 230-240 °F. OK, within limits but under tougher conditions earlier this week 40 degrees lower. Ain't right.
CHT climbs above 240, OK within limits but never previously observed this high.
EGT identical at t/o, but now after temps stabilize in flight there is a 150-200 °F spread between the max (1150) and the min.
No observable issues with fuel flow, pressure, etc. Made one flight with the Facet pump on, the other off, and no difference in performance. No apparent electrical system issues. OAT pretty much the same in all cases—28-30C on the ground; 22-24C at altitude.
I replaced the carb vent hoses, which are both very short, and there was no improvement.
Fuel is from the same supplier. Fuel passes through 25 micron in line mesh filters and an Andair gascolator. Carb floats, installed 24 hobbs hours ago, replaced as per SB-912-067UL R1. Carbs synched 30 engine hours ago, spark plugs have 24 engine hours on them.
I just can’t figure out why the engine performance would degrade overnight. I didn’t touch a thing! Ideas? I’m wondering if the carbs fell out of sync or something. How should I approach troubleshooting this?
But what could have happened overnight? Wed AM, setting off another cross country over low mountains, everything went to pieces. That flight, aborted, and two subsequent flights, have shown reproducibly severely degraded performance.
RPM: 5100 on takeoff, but above 1500 feet decays to 4900 and of course airspeed drops. Engine feels sluggish, but rpm recovers when you go straight and level. Never tried to push it above 2000 feet, always immediate return to airport. Engine clearly not happy.
Oil temp: Set new record highs 230-240 °F. OK, within limits but under tougher conditions earlier this week 40 degrees lower. Ain't right.
CHT climbs above 240, OK within limits but never previously observed this high.
EGT identical at t/o, but now after temps stabilize in flight there is a 150-200 °F spread between the max (1150) and the min.
No observable issues with fuel flow, pressure, etc. Made one flight with the Facet pump on, the other off, and no difference in performance. No apparent electrical system issues. OAT pretty much the same in all cases—28-30C on the ground; 22-24C at altitude.
I replaced the carb vent hoses, which are both very short, and there was no improvement.
Fuel is from the same supplier. Fuel passes through 25 micron in line mesh filters and an Andair gascolator. Carb floats, installed 24 hobbs hours ago, replaced as per SB-912-067UL R1. Carbs synched 30 engine hours ago, spark plugs have 24 engine hours on them.
I just can’t figure out why the engine performance would degrade overnight. I didn’t touch a thing! Ideas? I’m wondering if the carbs fell out of sync or something. How should I approach troubleshooting this?
