JonJay
Well Known Member
A question came up in another related post but I thought I would start a new thread. The question related to CHT spread and performance.
I wanted to solicit some feedback from the vast network of all knowing RV folks.
My original thought was that CHT spread did not affect performance. However, this may not be correct when it comes to climb performance or the ability to sustain a climb before power reduction and/or attitude adjustment is necessary to deal with a CHT limit.
My EMS data indicates that CHT's are pretty consistent through climb and cruise. The hottest cylinder is always the hottest, the coldest same... I checked multiple flights at different times of year and this rings true with my set up.
Now, lets assume a spread of 20F (an acceptable number) at a high elevation airport, on a hot day, at gross, with obstacles ahead. If your CHT limit is set at 425F (set it at whatever you like), and you are taking action when a cylinder nears or reaches that limit, one or more other cylinders are still below that limit.
Assume that we have done all we can with our cooling system, baffling/plenum, exit, louvers, whatever, so we know we have the maximum amount of cooling possible, we are leaning properly, etc...
If we where able to redirect cooling air from the coolest cylinders to the warmest cylinders, moving the cooler ones up and the hotter ones down, we would be able to sustain our climb longer before any one cylinder reached its limit. Ideally they all reach the limit in roughly the same time.
If we stretch our CHT spread out farther, climb performance or the ability to sustain a climb suffers even more. It was suggested that 50-60 degrees spread might be acceptable. If any of the above makes sense, that kind of spread could be very limiting in climb performance.
So, can we conclude that CHT spread does affect performance?
I wanted to solicit some feedback from the vast network of all knowing RV folks.
My original thought was that CHT spread did not affect performance. However, this may not be correct when it comes to climb performance or the ability to sustain a climb before power reduction and/or attitude adjustment is necessary to deal with a CHT limit.
My EMS data indicates that CHT's are pretty consistent through climb and cruise. The hottest cylinder is always the hottest, the coldest same... I checked multiple flights at different times of year and this rings true with my set up.
Now, lets assume a spread of 20F (an acceptable number) at a high elevation airport, on a hot day, at gross, with obstacles ahead. If your CHT limit is set at 425F (set it at whatever you like), and you are taking action when a cylinder nears or reaches that limit, one or more other cylinders are still below that limit.
Assume that we have done all we can with our cooling system, baffling/plenum, exit, louvers, whatever, so we know we have the maximum amount of cooling possible, we are leaning properly, etc...
If we where able to redirect cooling air from the coolest cylinders to the warmest cylinders, moving the cooler ones up and the hotter ones down, we would be able to sustain our climb longer before any one cylinder reached its limit. Ideally they all reach the limit in roughly the same time.
If we stretch our CHT spread out farther, climb performance or the ability to sustain a climb suffers even more. It was suggested that 50-60 degrees spread might be acceptable. If any of the above makes sense, that kind of spread could be very limiting in climb performance.
So, can we conclude that CHT spread does affect performance?
