WOT/LOP question

[piperboy84]

When I get above 7k I go wide open throttle and attempt to get lean of peak with no EGT gauge, If I lean back to first sign of roughness then screw the mixture back in a ball hair, how close to LOP will be I be, or is there just no way of telling without an EGT? Should the engine be ever so slightly rough? (engine is a Lyc O-360)

[India Four Two]

with no EGT gauge

pb84,

You're dancing with the devil. Get yourself an engine monitor. It's much cheaper than a blown cylinder.

See the pictures on my recent thread:

http://www.pprune.org/private-flying...ml#post9039196

[dirkdj]

It is hard to tell in a carbureted engine. Running at peak is certainly OK at 7000ft and you can start leaning in the cruise at any altitude. Without an engine monitor and fuel-injected engine you are flying blind.
As long as your CHTs are fine and the engine is smooth, you should be OK. Do you have a VP prop?
It all comes down to the fuel-air ratio in each individual cylinder. If one cylinder is richer than another it will produce slightly more power, giving some kind of roughness. On the rich side of peak EGT, the power curve is much flatter, while on the lean side of peak, it drops off quite a bit.

Read John Deakin's articles on the subject, there is no better teacher than him. Search for "Pelican's Perch #" numbers 63 to 66.

[BackPacker]

Agree with Dirk. It's hard to tell with a carbureted engine. In fact, consistent LOP across all cylinders is hard to achieve with a carbureted engine.

When you lean until roughness sets in, then enrich until the roughness disappears, you have most likely achieved the situation where one or two cylinders are so LOP so that they're about to stop producing power (that's where the roughness came from) and the rest is peak or ROP. Maybe even well ROP.

Without per-cylinder instrumentation (EGT, CHT) and per-cylinder mixture control (for instance with balanced fuel injectors like GAMI makes) this is really the best you can hope to achieve.

I don't agree with IF2. If you are above 7000 feet and your engine temps have stabilized after the climb, going WOT and leaning should not harm the engine. Unless it's turbocharged.

[tmmorris]

Can I just check (as a hirer not an owner) that I am always safe to do as BackPacker describes and lean to roughness then enrich to just smooth? I appreciate this won't result in best power or economy but am I right that this will always avoid the danger of detonation? Some cylinders will be ROP but none will be dangerously lean?

(FWIW this is the exact leaning technique in the T67C POH I've just been mugging up on for a conversion this afternoon.)

[BackPacker]

tmmorris, you need to be careful to ensure the engine is producing less than about 70% power. At altitudes above 5000' a normally aspirated (non-turbo) cannot produce more than 70%, so you're safe there with any throttle setting. However, below 5000' you need to reduce throttle first, then lean. Your POH will have all the details.

[Johnm]

The advice in my POH for the Archer which used the O360 engine was at 65% power or less and it'll be less at 7000ft then lean until roughness starts and then enrich until smooth again. It works well in my experience.

From memory at lower altitudes 2300 RPM was a sensible 65% cruise and you could then lean in the same way, but as others have said POH is the bible.

[Pull what]

In fact, consistent LOP across all cylinders is hard to achieve with a carbureted engine.

It is in fact impossible to achieve unless you have a carb for each cylinder

[dirkdj]

I won't rewrite everything John Deakin has written but there are many 'old wives tales' around. Running leaner than peak is not dangerous in any way if the engine is smooth the CHTs drop visibly. The hottest point is around 50° ROP where you will have the highest CHTs. This is exactly where some POHs recommend you cruise. Why? Maybe the marketing department had their say (more range, more speed, less engine longevity but that is not the concern of the marketing department).

The average PPL is very much undertrained on engine management. If you are an owner, you should be extra motivated since you pay the bills for fuel, maintenance and engine care. I fly LOP or at peak since 1996 or thereabout. At the current fuel prices, the savings on fuel alone pay for a decent engine overhaul at 2000 hours with money left over for other goodies.

[tmmorris]

Sorry, BackPacker, you're right, the POH for the T67C does state at or below 75%. The power/RPM/fuel consumption table for the T67 is very confusing as it tells you what power you get for a given RPM instead of what RPM to set for a given power but I think I've worked it out in reverse!

[A and C]

Backward Graphs

Only the British could take an american manufactrers graph and turn it inside out for the flight manual............... still it could be worse they put a machine gun in a fuel tank on the Lightning !

Oh ! Tim dont forget to use the EGT gauge next time you get to fly the PA28.

[India Four Two]

Read John Deakin's articles on the subject, there is no better teacher than him.

Don't just read his articles about leaning. Read them all! A fantastic resource, full of useful information plus interesting anecdotes about his flying career, including his time with Air America. My favourite article is his description of how he nearly landed gear-up in a 747.

"Pelican's Perch" Index - AVweb Features Article

[tmmorris]

Actually A and C that's a point, presumably I could just read the O-320 manual instead... (And don't worry, I do use the EGT where fitted...)

[AdamFrisch]

Flew my Aerostar without engine monitor and LOP for over 2 years. No problem. I practice the "big pull", to get over the Peak quickly. I always cruise at power settings below 70% even though it's turbo'd. Pull until it slows down about 10kts, but before roughness.

In fact, the old-timers flew the radial old piston airliners like the DC-7 and the Connies just like this, by leaning by feel and exhaust gas color.