Missing airflow found
Posted: Sat Dec 29, 2018 3:54 am
Since converting to a 4 banger[with a pressure cowl instead of a plenum chamber] I have had doubts on my CHT temps. My single CHT originally was on no3 and EGT on the no 2 cylinder. Cruise CHT,s were around 370 deg [the no 3 cylinder] but in climb they would drop back to 320 to 340 at full power. They were new baffle seals and were sealing well .i even put a camera in the top engine bay and run the engine [idle] play back showed all good . Then fitted 4 probes and checked CHTs ,front cylinder[no 1] was 280,degs . The other 2 cylinders [2 and 4 cylinders] were around 340 degs . So many weeks of research was carried out on airflow , thermodynamics , and a heap of other big words that talk about how a airflow engine is cooled . [ I have had my knee busted and could only move around the house in great pain , so when I say weeks it’s actually months off work.] many suggestions were made by others of great aeronautical fame on my problem with the aircraft. Some said it wasn’t a problem as it was under 400 degs .
No, as there was a spread of 280 degs to 370 degs plus of cylinders bolted to the same crank case . Crank cases like to have a even spread of temperatures . There was talk of the “bradly”mod done to no 3 cylinder . But the new baffling had this incorporated. Talked to the RV guys as I have done some work for them in the past. Sealed off the high pressure areas to the lower pressure areas at the intake area and prop shalf area. No change . The intakes were changed and volutes were formed to direct the airflow more directly into the engine .some temperatures were noted that had dropped and amore even spread.
Then one night having my son ground run the aircraft as I couldn’t fly it. Brakes on and wheels chocked he went to full power . I had a LED torch aimed on the front cowl,and could see in the air intakes and to my horror the new baffle seal at the back of the engine which seals against the top cowl was blowing down leaving a great air gap. Here was a gap of about 1in just above no. 3 cylinder . Access material was cut of the baffle problem solved.
No, as there was a spread of 280 degs to 370 degs plus of cylinders bolted to the same crank case . Crank cases like to have a even spread of temperatures . There was talk of the “bradly”mod done to no 3 cylinder . But the new baffling had this incorporated. Talked to the RV guys as I have done some work for them in the past. Sealed off the high pressure areas to the lower pressure areas at the intake area and prop shalf area. No change . The intakes were changed and volutes were formed to direct the airflow more directly into the engine .some temperatures were noted that had dropped and amore even spread.
Then one night having my son ground run the aircraft as I couldn’t fly it. Brakes on and wheels chocked he went to full power . I had a LED torch aimed on the front cowl,and could see in the air intakes and to my horror the new baffle seal at the back of the engine which seals against the top cowl was blowing down leaving a great air gap. Here was a gap of about 1in just above no. 3 cylinder . Access material was cut of the baffle problem solved.