MT Propeller w/IO-550 - Low Cruise RPMs??


Hi all, I've been trying to get smart on my MT propeller and I've had a few discussions with MT Propeller USA and they say there is no RPM exclusion for cruise. Have any of you with the MT Prop/IO-550 combo explored to see what low RPM gives you and what the tradeoff is? I typically fly 7,500-12,500' LOP and set max MP and 2400 RPM. I've played with 2500/2550 and lose a few knots, but the noise drop is worth the speed penalty.  

Have any of you explored 2100-2300 RPM? If so, what did you see for speed and noise?

harrelson's picture



I have an MT 3 blade prop with an IO-550N with 10:1 pistons in our IV. While it is true that MT has no RPM exclusion for cruise, Continental does recommend no lower than 2300 RPM for cruise with this engine. It has to do with the counterweights. I generally cruise at WOT LOP and 2300 RPM at 11,000 up to 18,000. At 11,000 my TAS is 210 knots and my fuel flow is 10.9. The economy just get better as you climb higher. 



Lancairmikees's picture

I have a IO-550-N ES but a

I have a IO-550-N ES but a Whirl Wind prop. I usually set rpm to get 65% power, then go LOP. Between 7500 and 9500 I see 175 kts and 12.2 gph. It ends up being about 2350 at 6500 and 2500 at 9500. If you are seeing a vibration/noise issue, you might want to try a prop balance and or maybe a set of Lord mounts. 

Thank you for sending the SB

Thank you for sending the SB link. That is very helpful. The MT prop is smooth between 2400-2700. The SB answers my question as to the lower limits of the engine, regardless of prop. Thanks everyone.