mountainride
Well Known Member
I have an RV-14 with the standard IO-390 A3B6 that has been running fantastic. I am really impressed by the Van's team getting the cooling just right for an aircraft without a cowling flap. Just enough cooling for hard climbs and pattern but not excessive drag in cruise. My CHTs will sit in the low 300s in cruise during the summer at the altitudes I normally fly at in Colorado (7-15K). In a shallow 175 kias descent with 16 inches of MAP in I have trouble keeping them above 300. In fact with the 5 inch oil cooler modification my oil generally sits on the vernatherm at 185 unless its a summer climb. However if I do a ROP VY climb my chts would rise to the high 300s and oil lower 200s maybe even higher if I didn't add some airspeed like I normally do.
I can't help but think if I could remove some of the cooling drag in cruise to bring my CHT's up to ~350, I would gain some performance. My idea was to remove the bump out on the original RV-14 lower cowl, glass it flush and install the cowl door design for the new EXP engine. The cowl flap would go in the cowling instead of the tunnel (where my single exhaust stack exits) I already have the push pull cable installed for cabin control. From what I can tell there are not any clearance issues. I would basically just be reducing the exit area which to my understanding has the biggest effect on cooling drag.
I don't think I would add the operational complication of a cowl flap or wear from running 40 degree hotter for a knot or two but the gain of 5-10 knots would be worth it. What do folks think of the idea or value of a modification like this?
I can't help but think if I could remove some of the cooling drag in cruise to bring my CHT's up to ~350, I would gain some performance. My idea was to remove the bump out on the original RV-14 lower cowl, glass it flush and install the cowl door design for the new EXP engine. The cowl flap would go in the cowling instead of the tunnel (where my single exhaust stack exits) I already have the push pull cable installed for cabin control. From what I can tell there are not any clearance issues. I would basically just be reducing the exit area which to my understanding has the biggest effect on cooling drag.
I don't think I would add the operational complication of a cowl flap or wear from running 40 degree hotter for a knot or two but the gain of 5-10 knots would be worth it. What do folks think of the idea or value of a modification like this?