nigelspeedy
Well Known Member
I normally use the Target EGT climb method, but until recently only did it because I had read about it. So I set out to quantify the difference between climbing full rich and climbing progressively leaning the mixture to maintain the same EGT I see at sea level.
The climbs were from 3,000' to 10,500' so a difference of 7,500'. They were done back to back in the same area in quick succession so weather and aircraft weight were pretty close. I flew a constant 120 KIAS for the whole climb, with wide open throttle and 2500 RPM. I had been flying for about 20 minutes prior to beginning the test so engine temps were normal before beginning each climb.
The full rich climb had an average rate of 1286 fpm and used 1.5 gallons of fuel. The fuel flow slowly reduced as altitude increased (as per Dan H's explanation in his recent Kit Planes article) and the EGT steadily reduced as well. The CHT increased to a max of 325F in the initial part of the climb then reduced to 300F. At the end of the climb I leveled off and leaned the mixture to determine how ROP the engine was at altitude, turns out it was about 300F ROP.
Repeating the climb but this time progressively leaning to maintain 1200 - 1250F EGT (what I see at sea level with WOT, 2500 RPM and Mixture full rich) I saw an increase in average climb rate to 1345 fpm (~4.5% increase), fuel used decreased to 1.1 gallons (0.4 gallon saving or 26% reduction). The CHT in this case steadily increased to a maximum of 375F. EGT remained ~constant as I progressively leaned a little every thousand foot or so. At the end of the climb I leveled off and leaned the mixture to determine how ROP the engine was at altitude, turns out it was still about 100F ROP.
Graphs of Rich then Target EGT are shown below.
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Full Rich Advantages: Easy, set and forget on takeoff. Lower CHTs.
Full Rich Disadvantages: Takes longer and burns more fuel.
Target EGT Advantages: Faster climb rate, less time and fuel used in getting to altitude.
Target EGT Disadvantages: Slight increase in cockpit workload cross checking EGT/CHT and fuel flow. Higher CHT, although in this case still less than the often touted 400F recommended maximum, could be a problem if cooling is marginal or the weather extreme.
If things are not too busy the target EGT climb method seems like an acceptable compromise to get a useful performance and economy increase. For your consideration.
Cheers
Nige
The climbs were from 3,000' to 10,500' so a difference of 7,500'. They were done back to back in the same area in quick succession so weather and aircraft weight were pretty close. I flew a constant 120 KIAS for the whole climb, with wide open throttle and 2500 RPM. I had been flying for about 20 minutes prior to beginning the test so engine temps were normal before beginning each climb.
The full rich climb had an average rate of 1286 fpm and used 1.5 gallons of fuel. The fuel flow slowly reduced as altitude increased (as per Dan H's explanation in his recent Kit Planes article) and the EGT steadily reduced as well. The CHT increased to a max of 325F in the initial part of the climb then reduced to 300F. At the end of the climb I leveled off and leaned the mixture to determine how ROP the engine was at altitude, turns out it was about 300F ROP.
Repeating the climb but this time progressively leaning to maintain 1200 - 1250F EGT (what I see at sea level with WOT, 2500 RPM and Mixture full rich) I saw an increase in average climb rate to 1345 fpm (~4.5% increase), fuel used decreased to 1.1 gallons (0.4 gallon saving or 26% reduction). The CHT in this case steadily increased to a maximum of 375F. EGT remained ~constant as I progressively leaned a little every thousand foot or so. At the end of the climb I leveled off and leaned the mixture to determine how ROP the engine was at altitude, turns out it was still about 100F ROP.
Graphs of Rich then Target EGT are shown below.
Full Rich Advantages: Easy, set and forget on takeoff. Lower CHTs.
Full Rich Disadvantages: Takes longer and burns more fuel.
Target EGT Advantages: Faster climb rate, less time and fuel used in getting to altitude.
Target EGT Disadvantages: Slight increase in cockpit workload cross checking EGT/CHT and fuel flow. Higher CHT, although in this case still less than the often touted 400F recommended maximum, could be a problem if cooling is marginal or the weather extreme.
If things are not too busy the target EGT climb method seems like an acceptable compromise to get a useful performance and economy increase. For your consideration.
Cheers
Nige
