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Most of my flying involves cross country legs, to reach whatever destination I'm headed to. I spend a fair bit of time watching the ASI and engine instruments on these long cruises..... I thought I would share a few performance observations.
Cruising lean of peak:
Running 23" and 2300, we are consistently seeing 115 KTAS burning 37.5 L/hr (10 gal/hr) at around 5000-7000 ft density altitude. At 10,000 ft that goes up to 120 KTAS running around peak EGT for the same 37 L/hr.
That engine setting puts us around 54% or 57% power, EGTs are about 10*C (roughly 20*F) lean of the peak, depending on the ambient conditions and altitude. That is pretty close to the ideal fuel-air mixture at 10k ft, just slightly lean. Indicated airspeeds is more like 108 KIAS depending on the day.
With those settings, the engine temps on my install run about 160*C (330*F) in winter, and 175*C (350*F) in summer.
Incidentally, at sea level we see around 108 KTAS running the same 37 L/hr lean of peak.
Cruising rich of peak:
I don't do much of this, but at 23" and 2300 we tend to see around 125 KTAS at the same 5000-7000 ft density altitude. For that extra 10 kts airspeed, I am burning 55 L/hr (14.5 gal/hr). At higher altitudes there is less benefit as the engine runs out of air. For 23" we hit WOT around 7000-8000 from memory, depending on the day. We do get a noticeable ram air effect with our engine's intake system.
Depending on the day, that is usually high 60's % power. EGTs will be sitting around 50*C rich of peak (100*F).
The engine temps are much hotter as as a result, about 20*C hotter at around 185*C (360*F). On a really hot summers day, the engine can push 195*C (380*F) and I like to open the cowl flaps around that time, which costs me a few kts airspeed.... I set my redline at 400*F.
We have been slowly running the engine hard and harder, lean of peak, doing cylinder inspections in between by borescope. We started with a limit of about 21" and gradually moved up to 23". We've seen nothing so far which worries us at all after 270 hours running. I'll probably start trying 24" and 2400 LOP like some other guys are doing (Gavin I think you were?) Of course as we increase the power we need a larger safety margin from peak EGT.
About the only time I run rich is to keep up with other aircraft who are running rich [e.g. C180] when we're doing formation stuff.
Cruising lean of peak:
Running 23" and 2300, we are consistently seeing 115 KTAS burning 37.5 L/hr (10 gal/hr) at around 5000-7000 ft density altitude. At 10,000 ft that goes up to 120 KTAS running around peak EGT for the same 37 L/hr.
That engine setting puts us around 54% or 57% power, EGTs are about 10*C (roughly 20*F) lean of the peak, depending on the ambient conditions and altitude. That is pretty close to the ideal fuel-air mixture at 10k ft, just slightly lean. Indicated airspeeds is more like 108 KIAS depending on the day.
With those settings, the engine temps on my install run about 160*C (330*F) in winter, and 175*C (350*F) in summer.
Incidentally, at sea level we see around 108 KTAS running the same 37 L/hr lean of peak.
Cruising rich of peak:
I don't do much of this, but at 23" and 2300 we tend to see around 125 KTAS at the same 5000-7000 ft density altitude. For that extra 10 kts airspeed, I am burning 55 L/hr (14.5 gal/hr). At higher altitudes there is less benefit as the engine runs out of air. For 23" we hit WOT around 7000-8000 from memory, depending on the day. We do get a noticeable ram air effect with our engine's intake system.
Depending on the day, that is usually high 60's % power. EGTs will be sitting around 50*C rich of peak (100*F).
The engine temps are much hotter as as a result, about 20*C hotter at around 185*C (360*F). On a really hot summers day, the engine can push 195*C (380*F) and I like to open the cowl flaps around that time, which costs me a few kts airspeed.... I set my redline at 400*F.
We have been slowly running the engine hard and harder, lean of peak, doing cylinder inspections in between by borescope. We started with a limit of about 21" and gradually moved up to 23". We've seen nothing so far which worries us at all after 270 hours running. I'll probably start trying 24" and 2400 LOP like some other guys are doing (Gavin I think you were?) Of course as we increase the power we need a larger safety margin from peak EGT.
About the only time I run rich is to keep up with other aircraft who are running rich [e.g. C180] when we're doing formation stuff.
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