From time to time I have folks contact me about cooling issues on a Sonex. Tom Huebbe from Missouri has a Sonex and has experienced high chts for some time. This past winter he pulled his heads and added some fin extensions, his email with the results:
Hi Wayne, Tried to download the pictures I have from my wife's digital camera, but something is screwed up with her camera so I will try to take some more pictures and get them to you. In the meantime here are my results: To begin with I have been flying my Sonex since 2006 and have about 350 hours on it total time. Have been having problems with high CHT's and oil temps. since day one. I had been flying behind VW's since early 80s' but all in single place, small engine airplanes, 1600 cc and 1835 cc and never had any problems with high CHT's or oil temps. Had about 1300 hours in those two planes---no issues. I am sure because they were small engines and not hauling around much weight. With the Sonex is it quite different especially with two people aboard. My engine is a 2276, 94 mm cylinders, and 82 mm crankshaft using an Aerocarb. I also tuned the engine using my son's wide band fuel/air meter and verified the timing on both ignition systems. I also verified my CHT sensors using two other digital thermometers so my CHT temps I read are quite accurate. My sons and I also measured the pressure in the cowl using a manometer. We tried just about everything to try and bring the temps down to no avail. I have always measured the CHT the same: under the spark plug right up against the head so I am always comparing apples to apples. Typical flying day is: start up cold and taxi to take off which can be 1/4 to 1/2 mile depending on which runway to use. CHT's will be up to 350F by the time I do runup and ready to fly. Take off and climb at 90 MPH and by the time I am turning downwind the CHT's are already above 400F heading for 450F. I cannot get to pattern altitude without the temps going above 450F. I then have to level off and reduce power and wait until the temps get down below 400 F and then try to climb some more. Have to do step climbing to reach cruise altitude. Oh, also my airport is here in Missouri, 440 MSL. I usually end up cruising at at 2500 to 3000 ft. altitude because it takes so long to climb. After I reach cruise altitude I then pull the power back to cruise at about 22-23 inches M.P. and then my CHT will very sssssslllllllooooooooowwwwwwllllly fall to 360-370 F. I know this is too hot because my old planes never did this and the VW's I raced years ago never ran over 280F cruising and 310F racing very hard. We always thought anything over 360F was getting hot and never wanted to run over 380F.
Now, new results with the fat fins we welded on: Taxi forever and never get above 280F. Takeoff and climb at 80 mph W.O.T. till reaching pattern altitude and do not get above 376 F tops. Also, left and right heads are now ALWAYS within a couple of degrees of each other. Never did that before either. When I pull back to 22-23 inches of M.P., and go into cruise flight, CHT's will pretty quickly fall to 290-300F and stay there.
This is with two people aboard and near gross weight. As I said before this is measured under the spark plugs not way out on the fins someplace which will make you THINK you are running cool all the while you are toasting your heads. The engine now runs just as cool as my little engines did. Just need more fin area to dissipate the extra heat the bigger engine makes. It is well worth the effort to not cook the heads with all the associated problems a person will run into running such high temps.---regardless of what some "experts" may tell you is acceptable to run.
This may not be as good as your results, but each plane is very different. And, I had to work within the confines of the cowl I already have.
I am now a happy camper.
Regards,
Tom
Congratulations Tom! When we get some pictures I'll post them for folks to see.
Wayne
Hi Wayne, Tried to download the pictures I have from my wife's digital camera, but something is screwed up with her camera so I will try to take some more pictures and get them to you. In the meantime here are my results: To begin with I have been flying my Sonex since 2006 and have about 350 hours on it total time. Have been having problems with high CHT's and oil temps. since day one. I had been flying behind VW's since early 80s' but all in single place, small engine airplanes, 1600 cc and 1835 cc and never had any problems with high CHT's or oil temps. Had about 1300 hours in those two planes---no issues. I am sure because they were small engines and not hauling around much weight. With the Sonex is it quite different especially with two people aboard. My engine is a 2276, 94 mm cylinders, and 82 mm crankshaft using an Aerocarb. I also tuned the engine using my son's wide band fuel/air meter and verified the timing on both ignition systems. I also verified my CHT sensors using two other digital thermometers so my CHT temps I read are quite accurate. My sons and I also measured the pressure in the cowl using a manometer. We tried just about everything to try and bring the temps down to no avail. I have always measured the CHT the same: under the spark plug right up against the head so I am always comparing apples to apples. Typical flying day is: start up cold and taxi to take off which can be 1/4 to 1/2 mile depending on which runway to use. CHT's will be up to 350F by the time I do runup and ready to fly. Take off and climb at 90 MPH and by the time I am turning downwind the CHT's are already above 400F heading for 450F. I cannot get to pattern altitude without the temps going above 450F. I then have to level off and reduce power and wait until the temps get down below 400 F and then try to climb some more. Have to do step climbing to reach cruise altitude. Oh, also my airport is here in Missouri, 440 MSL. I usually end up cruising at at 2500 to 3000 ft. altitude because it takes so long to climb. After I reach cruise altitude I then pull the power back to cruise at about 22-23 inches M.P. and then my CHT will very sssssslllllllooooooooowwwwwwllllly fall to 360-370 F. I know this is too hot because my old planes never did this and the VW's I raced years ago never ran over 280F cruising and 310F racing very hard. We always thought anything over 360F was getting hot and never wanted to run over 380F.
Now, new results with the fat fins we welded on: Taxi forever and never get above 280F. Takeoff and climb at 80 mph W.O.T. till reaching pattern altitude and do not get above 376 F tops. Also, left and right heads are now ALWAYS within a couple of degrees of each other. Never did that before either. When I pull back to 22-23 inches of M.P., and go into cruise flight, CHT's will pretty quickly fall to 290-300F and stay there.
This is with two people aboard and near gross weight. As I said before this is measured under the spark plugs not way out on the fins someplace which will make you THINK you are running cool all the while you are toasting your heads. The engine now runs just as cool as my little engines did. Just need more fin area to dissipate the extra heat the bigger engine makes. It is well worth the effort to not cook the heads with all the associated problems a person will run into running such high temps.---regardless of what some "experts" may tell you is acceptable to run.
This may not be as good as your results, but each plane is very different. And, I had to work within the confines of the cowl I already have.
I am now a happy camper.
Regards,
Tom
Congratulations Tom! When we get some pictures I'll post them for folks to see.
Wayne
