Running LOP

Re: Running LOP

Walter,
You referenced "10?C"--not sure what you meant?  My gauge doesn't even have temp. markings, only blank lines and a movable pointer to help pinpoint peak.
Bob

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Re: Running LOP

Walter,
Sorry--you said "carb temp" and I was reading it as EGT.  But I don't have carb temp either--I thought that was for spotting carb ice??

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Re: Running LOP

Bob:

The carb temp gauge reads the temperature just behind the venturi in the carburetor--the coldest point in the system.  As it turns out, in cabureted engines, the F:A ratios are significantly affected by the temperature of the air.  At about 10 degrees C on the carb temp gauge (it seems in most 182s) the fuel is best atomized and vaporized to give the best F:A mixtures to all cylinders.

I have run a number of 182s LOP very smoothly using the technique of attaining a carb temp of 10 degrees C.  I have reports from many others who have had the same success.  Whether you run ROP or LOP, the engine runs smoother like that. The engine likes for all of the little engines (cylinders) to make the same horsepower!

I discovered this technique reading the very fine print in a 1935 Pratt & Whitney engine operators manual.  (Yeah, I know...  I need a life.) It has worked in every carbureted engine I have tried it on.  The optimum temperature seems to be different from engine to engine, carb to carb, and airframe to airframe, but once found, works rather well.

Walter Atkinson
Advanced Pilot Seminars

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Re: Running LOP

Walter,

Do you lose much of the available horsepower by adding heat to the inlet air?  I would think that it's only an issue if you approach the service ceiling of the airplane.  For climbs at max power, I assume you go back to the ROP operation with full throttle.

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Re: Running LOP

Walter, radial engines have at least one cylinder in the upside down position which would allow oil to seep past an upside down piston's rings.  Horizontally opposed engines have their cylinders located above the oil sump.  Oil will not leak down past rings on a horizontally opposed cylinder engine.  It will simply drain to the sump, except for oil in the rocker box which may drain past a valve guide and into they cylinder.  (Worn intake guides will also allow oil to drain into the intake induction system, and then to the induction system drain valves and drop onto the ramp or hangar floor a few minutes after shutdown.  If you see oil dripping from the small induction system drain valve tubes, it's due to worn intake valve guides.  Usually your exhaust guides will be worn just as much or more.)
  The oil which drains past valve guides and into the cylinder will puddle at the lowest point in the horizontal cylinder....which is usually the lower spark plug well.  That plug will not fire until the oil is burned off.  Running the engine only on the mag that fires the lower plugs (some engines are so set up that one mag fires upper and one mag fires lower plugs) will result in a very rough running engine due to the misfiring oil-soaked plug.

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Re: Running LOP

*Do you lose much of the available horsepower by adding heat to the inlet air? *

A little.  Not much.

* I would think that it's only an issue if you approach the service ceiling of the airplane.  For climbs at max power, I assume you go back to the ROP operation with full throttle*

Yes to both.

Walter Atkinson

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Re: Running LOP

George:

Thanks. On a nine cylinder radial, here are four cylinders which have the possibility of oil draining past the rings as you describe.  I have noted that oil in a horizontally opposed engine can sit along the lower side of the cylinder and *could* leak on into the combustion chamber.  Now that I think about it, although *possible*, I agree that that is very unlikely!

Thanks.

Walter

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Re: Running LOP

I'm just getting back into flying after 30 years of inactivity and one of the first thinks I read was the Feb. 2004 AOPA Pilot, which included Steven Ells' article on APS's seminar and featured the LOP concept.  Although a complete novice on this stuff, the article was very readable and made perfect sense.  However, the next thing I read was the POH for the 77 C182Q I have started flying (with an instructor) to get through my biannual flight review.  It says in no uncertain terms: "OPERATION ON THE LEAN SIDE OF PEAK EGT IS NOT APPROVED".  With this provision, operating LOP would seem to void any engine warranties, possibly insurance coverage and is clearly a violation of FAR91.9(a) "...[N]o person may operate a civil aircraft without complying with the operating limitations specified in the approved Airplane or Rotorcraft Flight Manual, markings, and placards, or as otherwise prescribed by the certificating authority or the contry of registry."  My instructor is pretty dubious too, although he hasn't seen the article yet.  Has CESSNA changed this operating limitation for 182's?

Keep up the good work, your patience is admirable.  I didn't have any trouble following the discussion and I haven't been in an airplane for 30 years!

I plan to buy an older 182 as soon as I pass my flight review and attendance at the APS Seminar is going to be one of my first "road trips".

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