Cruise Power

[MarinMooney]

I read an interesting article by Bob Cromer discussing cruise power settings.  I had never heard his advocacy of using full throttle for cruise. The flight manual shows a lower setting.  Is this technique a generally accepted procedure?  

 

Thanks,

Steve

[druidjaidan]

Would love to see what you read.  It depends on your altitude.  If you're cruising at below 4 or 5k or so and WOT you're in for a bad time running the engine well above 75% power burning a ton of fuel for no real gain and putting extra stress on your engine.  On the other hand in a normally aspirated Mooney up above 6 or 7 thousand you'll WOT (and ram air open) will start dropping below 75% rated so it should be obvious that you can (and should) run WOT.

[Hank]

I've found in my C that it is better to pull back the throttle just enough to make the MP needle move, which turns off the full-throttle enrichment circuit. But first I verify against the Performance Tables that I'm high high for that MP and 2500 (<75%); this is generally 6500-7000 msl.

For low level short trips and sightseeing, I generally run 23"/2300, but can add one more to either; my preferred mid-level setting is 22"/2400, and again I can move either one step higher.

Then uel injected Mooneys do quite well running full throttle, set RPM and pull the mixture back to LOP. Now that I've done induction and doghouse work, I can sometimes almost reach 25° LOP but I haven't played there much (no engine monitor, just the factory single EGT & CHT gauges).

[carusoam]

Bob Kromer Is a pretty reliable resource.  As an engineer, He used to work at Mooney...  He wrote some respected articles for MAPA.  Each article was model specific.  They may be 15 years old and may be a bit aged...

Is this what you are referring to?

Best regards,

-a-

Follow-up: Hank is a well respected M20C pilot and engineer with recent up to date details...

[Bob - S50]

MarinMooney

You fly a C with a carburetor which will be a bit different than me since I fly a J which is injected.  I usually cruise at 2500 RPM and either 22" or WOT whichever is less.  That gives me the magic number of 47 (RPM + MP) which is right around 65%.  However, if I'm descending into my destination, I usually descend at 2000 to 2200 RPM and 15 to 20" of MP.  I just leave the RPM set that way until I push the prop control forward for landing, even if I end up cruising for a few minutes while entering the pattern.

However, I believe John Deakin recommends that those with a carburetor bring the throttle back ever so slightly to improve fuel distribution due to induced swirling in the intake manifold.  That is supposed to increase the likelihood of being able to run LOP.

[jlunseth]

Steve we don't know the Kromer article you are looking at (there have been several).  Maybe you could post a link.

A well accepted way of flying today is WOTLOPSOP, standing fort Wide Open Throttle Lean of Peak Standard Operating Procedure.  The throttle is left full in, in a Normally Aspirated aircraft, and the fuel flow is used to regulate power output.  Once the engine has been leaned out until it is lean of peak (last cylinder hits peak EGT), then fuel flow governs power rather than MP.  Shad will probably be on here in a bit and can tell you more about how it is done in an NA aircraft, I use LOP in my aircraft all the time but it is a turbo so the technique is different in some ways.

[MarinMooney]

Thanks for all the input!  I greatly appreciate all the time and effort put in to help a new Mooney pilot.

I have a 1963 M20C with an O360 engine.

Yes.  Bob Kromer seems to be very well-versed in Mooney specifics.  Here is the link to the article I read:  http://www.mooneypilots.com/mapalog/cruisepower.html

[jlunseth]

That's a pretty old article.  The work done by the GAMI/APS people and others in the last decade has made clear that the peak EGT and 50 ROP settings are about the worst place to run an engine if you are over 65% HP.  Under 65% you can run it anywhere you like.  But at 50ROP and 75% HP the Internal Cylinder Head pressure is very high.  I have been to the APS seminar in Ada and watched the data from an engine running on their test stand.  The ICH graph line is not only high, it is "spiky," meaning it has short duration sharp upward spikes indicative or predetonation.  Other than the old POH's I don't know anyone who advocates running at 50 ROP and 75%, or at peak EGT and 75%.  The one setting in that old article that is valid, is the 50 LOP setting.  That is easy on your engine.  The carbureted engines don't always run LOP very well though.  Once you are at an altitude where the engine won't exceed 65% HP you can do anything you want.

Email Shadrach or Hank, they are much better with NA LOP settings than I am.