Cruise settings

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cessna lover

Cruise settings

Post by cessna lover »

when i get to cruise altitude i set the Manifold pressure to 23 inches and i set the RPM'S to 2,300 and i get a cruise speed of 172 is this a realistic setting or am i flying this to hard? this one is for you Scott since you fly the real 6229P :D

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Scott - A2A
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Re: Cruise settings

Post by Scott - A2A »

There are only three ways to over stress a Lycoming 540 / prop combo that I can think of:
- Running it above its redline
- Overheating
- Running above max manifold pressure for a specific RPM

Keep in mind this is assuming a proper mixture and not something very lean, like lean of peak.

The Lycoming 540 in the Comanche can run max throttle at 2400 RPM all day long as long as the engine doesn't overheat. No overheating, no issue. At 1800RPM, for example, 25" manifold pressure is the limit. However, keep in mind colder weather makes more power so in cold weather so maybe use 24" as my limit for 1800RPM in the winter. Also some props come with their own limitations, for example, an RPM to avoid for extended periods.

My favorite RPM for our Comanche is 1900RPM and full throttle at 4.5k or above. It's the most efficient cruise power that motor can make (1800 is actually more efficient but for some reason the engine in my Comanche prefers 1900).

Scott
A2A Simulations Inc.

cessna lover

Re: Cruise settings

Post by cessna lover »

thank you for getting back to me. i think on my next flight i will try that combo and see if that will work to. i was at 6K feet with those power settings. is there a level at which she likes to cruise at? i know it's not pressurized so you can't take it very high.

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Scott - A2A
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Re: Cruise settings

Post by Scott - A2A »

4.5-7.5k are the best altitudes for fast, efficient cruises for any normally aspirated combustion engine. Flying at the lowest altitude you are comfortable with full throttle will result in the fastest cruise speeds.

In my Comanche 250, at 1900 RPM I climb until I see about 25" at full throttle. And then pick the closest altitude to that.

Scott
A2A Simulations Inc.

cessna lover

Re: Cruise settings

Post by cessna lover »

Scott - A2A wrote: 27 Oct 2021, 15:48 4.5-7.5k are the best altitudes for fast, efficient cruises for any normally aspirated combustion engine. Flying at the lowest altitude you are comfortable with full throttle will result in the fastest cruise speeds.

In my Comanche 250, at 1900 RPM I climb until I see about 25" at full throttle. And then pick the closest altitude to that.

Scott
ah ok thank you. i did a flight yesterday i was at 7.3K because of terrain clearances. but i got 22.5 manifold pressure and 1,900 RPM'S and got about 165 knots. :D

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