Using the Carenado Bonanza F33A by Carenado enhanced by the excellent and must have REP plugin by Simcoders, I will quickly explain why it is better for the engine.
I will not enter details about how an engine works but basically it needs a given ratio of air to fuel mixture in order to properly work. The higher the altitude of the plane, the less oxygen is present. This means that during cruise, we need to lean the engine (i.e. bring less fuel to the engine via the red mixture lever) to compensate for the lowest amount of oxygen at the altitude the plane is flying.
But how should we lean?
I already wrote an article talking about leaning depending on the cruise power setting in this section of the blog. To summarize, we can lean either Lean of Peak LOP which is when reaching the EGT peak (maximum Exhaust Gas Temperature obtained by looking at the EGT gauge and leaning via the mixture lever until the gauge shows the maximum EGT value), we continue to lean until a certain amount of degrees is lost from the EGT peak.
Rich of Peak ROP is the opposite: once the EGT peak is found, we need to enrich again until a certain amount of degrees is lost from the EGT peak.
The graph below gives nice rules of thumb to apply a correct leaning process depending on the % Maximum Continuous Power vs ROP/LOP.
One can see that when running ROP, one needs to be between 100°F to 200°F ROP vs between only 0°F (i.e. EGT peak) to 60°F LOP depending on the power setting.
And here is why:
Consider that we are flying at 4,000 ft MSL in standard atmosphere with a plane weight of 3,100 LBS.
We have found the EGT peak and because we are running at 71% of power, if we want to fly ROP, we need a minimum of 125°F ROP. Which means 125°F below the EGT peak (by enriching again from the EGT peak). In these conditions, we will consume 15.5 US gals per hour at a true airspeed of 169 KNOTS. The EGT will be 1158°F and CHT (Cylinder Heat Temperature) of 344°F.
Now let's consider running the engine LOP. So again based on the power setting, we need a minimum of 25°F LOP so let's set it and see what are the results on the other engine parameters.
We will consume 12.5 US Gals per hour at a true airspeed of 165 KNOTS. The EGT will be 1262°F and the CHT will be 327°F.
Conclusions:
Even though running 125°F ROP means 125°F cooler Exhaust Gas Temperature than the Peak, the CHT is higher than when running 25° LOP. Why is CHT important? Because this is the CHT that determines the health and life time of your engine. The higher the CHT the worse for the engine.
So running 25°F LOP will result in 17°F cooler Cylinder Heat Temperature and will save you 3 US Gals per hour of flight while sacrificing only 4 KTAS.
Basically when running ROP, the power is higher and the excess of fuel serves to keep the engine cool (reason why if altitude permits, we always climb when the engine is running at full power with the mixture fully rich to ensure the best cooling conditions during that phase of flight). But it means that the spark plugs can be fooled due to residues of not totally burned fuel.
Running the engine LOP, results in lower power and lower CHT by matter of fact. Much less risk of spark plug fooling and a significant economy of fuel and therefore a higher endurance.
So what's your choice? I know mine: LOP!
PS: the values in the graph are the parameters I recorded from a test flight with the Reality Expansion Pack by Simcoders for the F33 Bonanza and waiting for the engine to stabilize its CHT before actually recording the data. The cowl flaps were fully closed.
TIPAH
Comments