Oil consumption

[kmyfm20s]

I knew separators needed to be positioned properly so I went over to the MSC on my field and looked at other Ovation that had them. I believe its a factory option because there is a place provisioned for them on the baffling. Mine was in the same position as every other one. Mine could have been clogged or dirty causing the problems but things didn't seem correct, instead of figuring out the problem I just removed it. I will be curious to see if there is a difference in my oil samples.

[PTK]

2500 is normal cruise rpm. I do note it seems to use more oil when using higher RPM but the trip takes longer at lower rpm so I do f see any reason to cruise at low RPM.

I think the oil shears down to a thinner viscosity with more hours on it so it uses more then.

I think there are some more very compelling reasons to run lower cruise RPM in addition to oil consumption.

Increased propeller efficiency by producing more thrust

Maximize engine efficiency by allowing it more time to extract more useful energy from combustion rather than dumping it prematurely out the exhaust. Higher RPM generates higher EGT which equates to more wasted energy.

Friction within the engine varies with the square of RPM. So a small RPM reduction goes a long way to reducing friction.

Lower friction also helps lower CHT.

I lean towards (pun intended!

[jetdriven]

All those sound great but the airplane, depending on altitude, appears to burn less trip fuel and less hours on the tach at 2500 and even 2700 RPM. If cruising below ~2450 RPM is more efficient, I haven't seen it. The speed drops off faster than the fuel flow

[chrisk]

A simple reading of my POH indicates a lower RPM gives better fuel economy. 

[kmyfm20s]

My POH attribute .1gph per 100rpm for the same power settings.

[jetdriven]

Then explain this, the same 9.3 GPH.

2200 RPM 147 mph

2500 RPM. 152.5 mph

2700 RPM 154 mph

Use the data set at the bottom, below the line. The one above was too lean at 2700 RPM.

Below around 2400 RPM the speed falls of faster than the ff. similar to going leaner than 50 LOP.

My POH Also says lean to roughness then enrich slightly for climb.

[kmyfm20s]

POH list it as % power not speed. Prop efficiency comes into play with RPM and there for you figure out your economy from speed and FF.

[kmyfm20s]

Then explain this, the same 9.3 GPH.

2200 RPM 147 mph

2500 RPM. 152.5 mph

2700 RPM 154 mph

Use the data set at the bottom, below the line. The one above was too lean at 2700 RPM.

Below around 2400 RPM the speed falls of faster than the ff. similar to going leaner than 50 LOP.

My POH Also says lean to roughness then enrich slightly for climb.image.jpg

 

You list RPM, FF but not MP. with MP being constant your increasing power with rpm. To be the same power you need almost 1" MP for every drop of 100 rpm

[jetdriven]

It was full throttle the entire time. It was also still slower the lower the RPM was. A turbocharged airplane like yours I think you have a bit more flexibility with MP.

I'm just a skeptic that lower RPM is more efficient. Efficiency is NMPG and true airspeed.

[ArtVandelay]

It was full throttle the entire time. It was also still slower the lower the RPM was. A turbocharged airplane like yours I think you have a bit more flexibility with MP.

I'm just a skeptic that lower RPM is more efficient. Efficiency is NMPG and true airspeed.

Lower RPM should result in less friction losses

Lower RPM means it's using less air for a given fuel flow which means you have to re-lean between changing RPMs, lower RPMs required to be leaned a little more, less FF, less HP.

And then there is the timing of the ignition, I assume it's optimized for max power at 2700 RPM