A few days ago I tested a theory I had about using carb heat during a Vy climb to help increase cooling efficiency: The basic premise is the engine increases exit area by pushing lower plenum air through the engine during combustion and out the exhaust pipe (which normally accounts for a decrease in exit area).
My first test didn't work out so well and I though maybe I was getting some blow-by at the FAB/cowl inlet junction. Turns out I just didn't run the test very well.
Today I ran 6 consecutive climbs from O-8000ft PA during a WOT, Full Rich, Vy (110MPH) climb with my exit flap open. The odd runs 1,3,5 were with Carb Heat Off. Runs 2,4,6 were with Carb Heat Full on. CHTs, OAT, Elapsed Time were recorded at T/O and every 1000ft PA. The data for each of the 3 different cofigurations was averaged and plotted as shown below...
Of note: OATs were within 1 deg for all runs to altitude.
The Avg CHTs at T/O for the Carb On conditions were purposefully higher (by 5-10) than the Carb Heat off conditions.
Rate Of Climb was 100 fpm less during Carb Heat On runs with RPM about 40-50 lower as well.
Results:
No only is the engine cooler with carb heat on but Average CHTs peak nearly 600 ft sooner (even though climb rate is slower). Any thoughts?
My first test didn't work out so well and I though maybe I was getting some blow-by at the FAB/cowl inlet junction. Turns out I just didn't run the test very well.
Today I ran 6 consecutive climbs from O-8000ft PA during a WOT, Full Rich, Vy (110MPH) climb with my exit flap open. The odd runs 1,3,5 were with Carb Heat Off. Runs 2,4,6 were with Carb Heat Full on. CHTs, OAT, Elapsed Time were recorded at T/O and every 1000ft PA. The data for each of the 3 different cofigurations was averaged and plotted as shown below...
Of note: OATs were within 1 deg for all runs to altitude.
The Avg CHTs at T/O for the Carb On conditions were purposefully higher (by 5-10) than the Carb Heat off conditions.
Rate Of Climb was 100 fpm less during Carb Heat On runs with RPM about 40-50 lower as well.
Results:
No only is the engine cooler with carb heat on but Average CHTs peak nearly 600 ft sooner (even though climb rate is slower). Any thoughts?
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