flybikedave
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I recently purchased a RV9A and am experiencing high CHT (475+). Single probe on #4, behind which is oil cooler. Would greatly appreciate advice comments. Will cowl flaps be needed?
475 is so grossly high the first thing to look at is to confirm the inst. indication is valid.
475 is so grossly high the first thing to look at is to confirm the inst. indication is valid.
I recently purchased a RV9A and am experiencing high CHT (475+). Single probe on #4, behind which is oil cooler. Would greatly appreciate advice comments. Will cowl flaps be needed?
Unfortunately, this advice is contrary to the mechanics of the downdraft cooling system seen on most Lycomings. Entry air flows from the top, and the baffling makes sure that the airflow stays in contact around the circumference of the cylinder and head picking up heat, finally discharging at the bottom. Proper baffling is particularly important in an air cooled engine to ensure equal cooling around the entire cylinder. I believe the scheme you have come up with throws a LOT of air at the lower fins, yes, but at the expense of the top. Yes, there is indeed a shallow spot on the head at the front of #2 and the back of #3 which blocks airflow, but that has been discussed and solved ad nauseum on this forum. It’s unlikely your modification will result in damage, but before people blindly take your advice it’s important to point out the downsides of possible asymmetric cooling.I encourage anyone building an RV with a Lycoming engine to leave about a 1/2 inch of open space between the into of the baffle ramp and the forward cylinder or even better create a smooth curved, as I did at the cylinder/baffle interface...............Carl
Like others have said 475 is dangerously high, easy things to check in preferred order...I recently purchased a RV9A and am experiencing high CHT (475+). Single probe on #4, behind which is oil cooler. Would greatly appreciate advice comments. Will cowl flaps be needed?
A lot of RVs actually have a dam on #1 and #2 to force more air to back jugs. The RV-9A kit comes with these dams...I recently was asked to market an RV-6-A for a friend. When I flew the aircraft to my hanger to detail and test all functions, the cylinder head temps peaked at 425 degrees on climb-out. I decided this would be problem, I must address before sale to an unsuspecting buyer. I got to work cutting the front baffle ramp so I could remove the white latex caulk that the owner had mistakenly applied thinking it would, in his words "force more air into the cylinder cooling fins". I cut way the ramp left and right and created a smooth bend into the entry point of the cooling fins. ON the first test, I knew I had solved the problem! The cylinder heads peaked at 375 degrees on a full throttle climb-out at 90 knots on a 92 degree day.
The latex caulk turned out to be only part of the problem. The Vans designed baffling is much to tight agains the smooth forward face of the Lycoming cylinders restricting cooling air to cylinder #1 and #2 cylinders. As can see on the photo, the entry of cooling air is much enhanced to the open gap between the cooling fins and the air now follows a nice curve down into the bottom fin area. I encourage anyone building an RV with a Lycoming engine to leave about a 1/2 inch of open space between the into of the baffle ramp and the forward cylinder or even better create a smooth curved, as I did at the cylinder/baffle interface...............Carl