jjconstant
Well Known Member
?Problem? or ?Feature?
My #4EGT is wildly erratic on the high side after start-up, during taxi, run-up and takeoff and a little bit erratic on let-down. It is so erratic (200-500* higher than other 3EGTS and varying by hundreds ever second) that I have been comfortable that it was not the actual EGT but rather an electrical issue. After level off in cruise, all 4 egts are stable and believable.
In chasing down this problem someone asked if I had tried turning off the Alternator field. I stupidly ran the EGT harness and the bus feed lines through the same hole in the firewall. I tried the test and when I turned off the alternator field in the run-up area, not only does #4 EGT drop to much closer to the others, it goes past and shows lower by a hundred degrees rather than higher by many hundreds. When I get established in cruise and pull the field breaker, it shows a bit lower than the others.
It seems that what #4 EGT is showing is a temperature that is being affected by the charging output of the alternator--wildly higher than others when charging but minimal affect in normal cruise after charging start-up drain. When the alternator is offline it appears to show the current drain on the battery--a bit lower than others, dependant on load. So it appears to be showing current flow into and out of the battery.
When I built the electrical system I decided to put the ammeter doughnut on the line between the battery and the bus bar, rather than between the alternator and the battery. It now appears that, in a way, I have both due to the behavior of #4 EGT.
Knowing this, the question is am I comfortable not having good EGT4 reading on take-off and climb-out. None of the rentals that I've flown had intrumentation anywhere near this good...and I've kind of answered it in that I'm flying it like this...
So...do I fix the ?problem? or do I leave it and enjoy the now-understood ?undocumented feature??
Jeremy Constant
RV7A 90 hrs
My #4EGT is wildly erratic on the high side after start-up, during taxi, run-up and takeoff and a little bit erratic on let-down. It is so erratic (200-500* higher than other 3EGTS and varying by hundreds ever second) that I have been comfortable that it was not the actual EGT but rather an electrical issue. After level off in cruise, all 4 egts are stable and believable.
In chasing down this problem someone asked if I had tried turning off the Alternator field. I stupidly ran the EGT harness and the bus feed lines through the same hole in the firewall. I tried the test and when I turned off the alternator field in the run-up area, not only does #4 EGT drop to much closer to the others, it goes past and shows lower by a hundred degrees rather than higher by many hundreds. When I get established in cruise and pull the field breaker, it shows a bit lower than the others.
It seems that what #4 EGT is showing is a temperature that is being affected by the charging output of the alternator--wildly higher than others when charging but minimal affect in normal cruise after charging start-up drain. When the alternator is offline it appears to show the current drain on the battery--a bit lower than others, dependant on load. So it appears to be showing current flow into and out of the battery.
When I built the electrical system I decided to put the ammeter doughnut on the line between the battery and the bus bar, rather than between the alternator and the battery. It now appears that, in a way, I have both due to the behavior of #4 EGT.
Knowing this, the question is am I comfortable not having good EGT4 reading on take-off and climb-out. None of the rentals that I've flown had intrumentation anywhere near this good...and I've kind of answered it in that I'm flying it like this...
So...do I fix the ?problem? or do I leave it and enjoy the now-understood ?undocumented feature??
Jeremy Constant
RV7A 90 hrs
