1968 M20C New Owner

[aajones5]

Wow I never knew that, once I get my EDM 900 put in I'll start flying like that and see what the difference in fuel flow is. Do you think there's a substantial difference with the extra jet turned off?

[Andy95W]

No, the mixture control still controls overall fuel flow to the engine, regardless of which jet it comes out of.

[carusoam]

They wouldn't have put an extra jet in if it wasn't a significant increase in FF.

With a fuel injected Mooney the FF is increased at FT by turning on the back-up electronic fuel pump.  Extra FF is used for cooling all moneys during full throttle T/O and climb.

The extra FF at FT is in the unusable economic range for long flights... about 2X what the leaned cruise FF is.

FF automatically is reduced as altitude and MP decreases. The need for additional internal cooling decreases with MP as well.  But, there is no automatic removal of the second fuel jet. It is a done by retarding the throttle a small amount.

Best regards,

-a-

folow-up

FF is a combination of pressure balanced by resistance.  The fuel pumps provide pressure, the mixture control supplies resistance, having two jets or one jet is the last piece of resistance in the FF equation.  Hard to know exactly what is really going on without a FF gauge. The FP of An O360 is so low to begin with the resistance to flow plays a larger part...

PP ideas only, not a mechanic.

[Andy95W]

There is a significant increase in FF at full rich mixture.  The mixture control restricts fuel flow through the carburetor to the jets. 

[carusoam]

Great aid to the conversation, Andy!

EGTs are typically set in the 300°F ROP range at T/O at SL.  Rising to 200°F prior to any mixture control change...

If you have a calibrated EGT gauge...

Best regards,

-a-

[aajones5]

Y'all are starting to lose me now, so you're saying once you lean the mixture there's no longer a substantial increase in FF even at FT?

[Hank]

8 hours ago, aajones5 said:

Y'all are starting to lose me now, so you're saying once you lean the mixture there's no longer a substantial increase in FF even at FT?

After attending a Mooney Summit and questioning Bob Kromer about this, I made one trip at WOT, leaned out like I always do, and had much higher fuel burn. In my return, I reduced throttle enough to move the MP needle abbé fore leaning, and my fuel burn was back to normal. I think the WOT trip was about 1.5 gph higher than normal; both ways were above 8000 msl.

[cctsurf]

17 hours ago, Hank said:

Leaning is pretty simple, find peak and enrich; I go 50°F rich.

Apparently, while this is the old way the POHs and our instructors taught us, it is the hardest way on the engine to run it.  It runs the pressures within the cylinders as high as we can possibly make them (as tested on highly instrumented cylinders), shortening cylinder lives.  The even older method of leaning is actually better, leaning until roughness and then enrichen just to the point of smooth operation.  This method will provide a slightly lean of peak operation on the o-360's and io-360s in these antique Mooneys we fly.  The cocked throttle can be helpful for mixture distribution, 'though it is not as necessary on these engines as say the o-470 which has notoriously bad mixture distribution.

We must also be careful to avoid seeking after that peak egt as carefully as I often have.  Running close to peak egt (as in looking for it) brings with it the almost certainty of detonation above moderate power settings.  Detonation destroys engines quickly, as in minutes...

Again, all of this is from Mike Busch's webinars, excellent information and confirmation of our attitudes for us CBs:

 

[Andy95W]

15 hours ago, Hank said:

After attending a Mooney Summit and questioning Bob Kromer about this, I made one trip at WOT, leaned out like I always do, and had much higher fuel burn. In my return, I reduced throttle enough to move the MP needle abbé fore leaning, and my fuel burn was back to normal. I think the WOT trip was about 1.5 gph higher than normal; both ways were above 8000 msl.

This is different from my experience, and I'm not sure why.  

[DXB]

10 minutes ago, Andy95W said:

This is different from my experience, and I'm not sure why.  

Ditto. 

[captainglen]

The RPM indicator should have an arc marking that shows the do not operate range to avoid a harmful harmonic vibration from the crank counterweight. The rough idle with carb heat applied is normal; apply a prolonged carb heat shot on downwind before reducing power. The primary symptom of undetected carb ice will be an uncommanded engine shutdown when the throttle is closed. After flying other aircraft it is common to flare the Mooney 2 to 3 feet to high because it is slung so low. At alpha floor (prestall) as the warning horn sounds a high sink rate develops; then it kind of plunks in. A little practice and you will begin to feel the ground effect just as you start the flare. I am sure you will love your Mooney.

[170driver]

Well, I learned something today! My cruise fuel flow has always calculated out to 10 gph or a titch below 9. I always attributed it to uneven ground when dipping the tanks. Will try backing off from wot a bit from now on & see if flow calculations are more consistent. Thanks, gentlemen!


Sent from my iPhone using Tapatalk

[apil]

New Mooney driver here as well -- congrats on getting a new bird.

On the  rpm range this graph from Vantage O-360 (that is based on Lycoming) gave me a good explanation as to "why".

 

On leaning there is definitely a ton of difference between many schools of thought and recommendations. Lycoming graphs show best power at ~150F ROP and best economy at ~25F LOP. This is generally consistent with Mooney POH leaning recommendations. Depending on OAT and humidity so far I have seen some engine roughness leaning further past peak EGT. The specific consumption difference between running at peak EGT and 25F LOP should be in single digit % so it may not be very noticeable.

 

 

 

[carusoam]

Welcome aboard Apil.

Best regards,

-a-