Lean or Rich & How to Determine

[jax88]

I've read the threads concerning running these aircraft LOP or ROP, the associated performance, possible advantages/disadvantages, and the conclusion I keep coming to is that I need to figure out how my M20F likes to fly.  To that end, can some of our experienced M20F owners tell me how best to determine the optimum cruise settings for my '75 M20F?  I have only the original temperature gauges, and in the 20+ hours I've flown in the aircraft, I've found it somewhat difficult to find anything other than a general peak EGT.

My procedure has been to establish straight and level at cruise altitude, full throttle, back the RPMs down to book settings for the observed MP, and then start leaning the mixture ever so slowly while watching the EGT as part of my scan.  As expected, there is a slight delay between the movement of the mixture control and the indication on the EGT guage.

And while we're at it, what's the best way to determine actual fuel burn?  In my brief experience, it seems the lack of precision in the fuel guages forces me to estimate, which I've been doing by topping the tanks at the end of each flight and doing the simple calculation of gallons burned divided by time flown.

I suppose I'm leading myself toward the purchase of some type of device that will help me obtain a more detailed picture of engine performance.

Any advice would be appreciated.

[danb35]

An engine monitor and a fuel flow instrument would both be good investments.  For leaning, try full throttle, 2500 RPM, and lean until you just feel the plane slow down--that should put you around 40 LOP.

[Lood]

Personally, I would never attempt any LOP operations without an engine monitor. Running LOP requires good knowledge on the subject and you have to be able to monitor all temperatures very closely. I usually fly my M20F WOT, between 75 - 100 deg ROP, 2400 rpm and have an average fuel burn of 10 gal/ hour over the last 2+ years. Whether you have a fuel flow computer installed or not, do yourself a favour and empty your tanks one day. Then fill them with say 5 gal at a time and make yourself a dipstick that is specifically calibrated for your airplane. This way you will always know exactly how much fuel you have in the tanks and in a situation where your airplane sat quiet for a long period, you'll find that the dipstick is even more accurate that the feul flow computer.

[Immelman]

Agreed about the engine monitor being requisite for LOP.

Also, in an NA airplane you will give up speed - significant speed - going LOP if youre over, say 4000-5000' MSL.

[GeorgePerry]

Quote: jax88

I've read the threads concerning running these aircraft LOP or ROP, the associated performance, possible advantages/disadvantages, and the conclusion I keep coming to is that I need to figure out how my M20F likes to fly.  To that end, can some of our experienced M20F owners tell me how best to determine the optimum cruise settings for my '75 M20F?  I have only the original temperature gauges, and in the 20+ hours I've flown in the aircraft, I've found it somewhat difficult to find anything other than a general peak EGT.

My procedure has been to establish straight and level at cruise altitude, full throttle, back the RPMs down to book settings for the observed MP, and then start leaning the mixture ever so slowly while watching the EGT as part of my scan.  As expected, there is a slight delay between the movement of the mixture control and the indication on the EGT guage.

And while we're at it, what's the best way to determine actual fuel burn?  In my brief experience, it seems the lack of precision in the fuel guages forces me to estimate, which I've been doing by topping the tanks at the end of each flight and doing the simple calculation of gallons burned divided by time flown.

I suppose I'm leading myself toward the purchase of some type of device that will help me obtain a more detailed picture of engine performance.

Any advice would be appreciated.

[danb35]

Quote: Immelman

Also, in an NA airplane you will give up speed - significant speed - going LOP if youre over, say 4000-5000' MSL.

[Immelman]

Quote: danb35

If you lose over about 5 kts, you're probably leaning more than you need to.

[rgaines]

I recently reviewed Lycoming manuals on this issue and they do seem to look favorably on LOP operations.

[Cruiser]

Yes, Lycoming's official position is against LOP operations, but not because of the physics. It is because they fear the pilot will make mistakes in managing the engine controls. They never say what exactly the problem would be IF the pilot did these things (also undefined) but nevertheless they do not recommend LOP.

I believe this is changing, Lycoming is now saying (unofficially) that LOP is OK. When and if they makes it the written word is anyones guess.