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Flying full power & leaning ... am I missing something?


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I have just over 20hrs in my O-360 M20D with a Hartzell 3-blade. Im still trying to figure out optimal cruise settings. The fuel burn rate isn't my primary concern - right now I just want to run fast but not overload the motor's limit. I do have the '76-78 C model POH cruise data table handy to reference the %BHP. Lately I've been using 21" and 2400RPM and then leaning using my Insight G1 (flights are at 5500/6500 or 8500/9500). The POH claims 70.1BHP. Is it safe for me to be leaning at any configuration that is below 75% or was the rule 65%? According to the chart in the POH if you maintain a configuration and ascend, the BHP increases slightly.

 

So let's say at 7500 if I'm running full throttle (throttle pulled a hair back to prevent the enrichening circuit), can I lean without fear of my jugs exploding? Chart says that 22/2400 is 74.5BHP at this altitude. At 2175HRS SMOH,is my motor even putting out that much HP?

 

Also, someone here made a comment a while back in an EGT temp thread regarding my CHT's at high altitude. If my G1 shows 330 at 8500', does that mean my CHT is 330 or something else due to correction for ISA lapse rate?

 

At 8500' 21/2400 I'm getting a TAS of 152MPH.

 

 

 

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26 minutes ago, tigers2007 said:

Parsing things to make it simple (for me) to understand....

1) can I lean without fear of my jugs exploding? Chart says that 22/2400 is 74.5BHP at this altitude.

2) At 2175HRS SMOH,is my motor even putting out that much HP?

 

3) If my G1 shows 330 at 8500', does that mean my CHT is 330 or something else?

 

 

1) jugs don't explode, so you are good.  Wait... some heads have cracked because of high internal cylinder pressure caused by the stress of take-off power on extreme cold days...  helps to know the density altitude where you are.  Below sea level DA is important to know....

 

2) at 2175 hours on the engine you qualify for having the most hours I have seen published around here. Taking experience from the usual sources that don't go beyond 2000 hours, makes you sort of a test pilot in a way.

HP is a combination of FF and engine rpm. It can be measured in a relative fashion by measuring T/O distance, climb rate, and or cruise speed.  Then carefully compare back to book numbers.

If your engine has been maintained, the fuel system is working and the ignition system is working properly, you are probably still delivering the same HP that came with the plane...

Wear takes an effect, cam lobes wear, valves don't open all the way, gasses don't escape completely and HP declines...

65% HP is a bench mark used for leaning LOP. It is a place that is generally less stressful for the engine.  Leaning mistakes can be better adsorbed by the engine.

T/O and Climb are generally 100% power, declining with altitude.  Sometimes limited by your CHTs...  full throttle might need to be pulled back if you can't keep your CHTs under 380° F.  With the C's doghouse / cowl you will get CHT challenges...

 

3) 330°F is 330°F whether you are on the ground or at altitude.  If you go to Europe, use caution. Their CHTs may be given in °C.

you may find that cooling changes the higher you fly.  The air temperature decreases, usually.  But, so does the air density.  Less air molecules flowing through the dog house means less cooling going on... Fortunately you fly a normally aspirated O360.  The power is limited by the altitude at pretty much the same rate the cooling is limited... :)

See where I'm coming from?

PP thoughts only. Not a CFI.

Best regards,

-a-

Edited by carusoam
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So I think it shakes down to keeping the engine cool. If the baffles aren't perfect any type of operation is shortening engine life. Some say running it easier prolongs life. I believe you can run it right at 2700rpm, full throttle leaned to peak egt at 4000ft and after 1000 hours of that type of operation your cylinder will still meet new tolerances.

 

In my opinion what hurts engines is heat, not pressure and sitting with acidic oil. The sitting part creates surface rust which now means your nice machines surface don't slide on a thin boundary layer of oil but in rough surfaces that at any power setting grind against each other = ever heard of a engine making metal??

 

The best advice I can give is get a engine monitor and if chts can't be kept in a reasonable temp less than 380 then modify replace or do whatever is necessary until the temps are inline. 2nd fly the plane at least once every 2 weeks, preferably once a week and change oil and Filter at 25 hours if it sits longer than a week without flying. Keep acid levels in the crank case low.

 

Pretty hard to hurt a engine by running it hard but it can be cooked and rusted TO DEATH!

 

 

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Like Anthony said, 330 is 330 and if accurate then you should be fine. If you're at 65% power or less with those temps you can likely run right at peak EGT with no ill effects. Consult with [mention=11970]gsxrpilot[/mention] as he's got considerable C time and has been through the APS that's pretty much the authority on piston aircraft engine operations. Older engines can still make good power. My hope is to fly well beyond TBO too, with close monitoring.

 

 

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"2) at 2175 hours on the engine you qualify for having the most hours I have seen published around here."

I'm not wishing to boast at all, but simply state, and back this up with fact, that I truly believe engine longevity is due to flying the airplane a lot and also running lean of peak (if possible for your engine).  Of course proper maintenance and other factors obviously contribute as well.

Fact is my former Ovation had 1800 hours on the engine when I purchased the plane.  Those hours were accumulated by the previous owner in 7 years, flying LOP (lots of flying and relatively cool CHT's).

During my ownership, over 500 additional hours were put on that engine, LOP.

Oil consumption was near 14 hours per quart and compression were in the low 50's when I decided to remove the engine.

The engine was running great when removed, and continual regular borescoping yielded no anomalies along the way.

When the engine was disassembled at PowerMasters in Tulsa, the builder said he can easily identify an engine that was operated LOP over its lifetime......much, much cleaner inside he stated.  Much less carbon build up.

I realize we are not all as fortunate to be able to fly our planes this much, and again I'm not wishing to grandstand. I only wanted to provide a true example of engine longevity based on useage, with LOP operation.

 

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9 hours ago, tigers2007 said:

I have just over 20hrs in my O-360 M20D with a Hartzell 3-blade. Im still trying to figure out optimal cruise settings. The fuel burn rate isn't my primary concern - right now I just want to run fast but not overload the motor's limit. I do have the '76-78 C model POH cruise data table handy to reference the %BHP. Lately I've been using 21" and 2400RPM and then leaning using my Insight G1 (flights are at 5500/6500 or 8500/9500). The POH claims 70.1BHP. Is it safe for me to be leaning at any configuration that is below 75% or was the rule 65%? According to the chart in the POH if you maintain a configuration and ascend, the BHP increases slightly.

So let's say at 7500 if I'm running full throttle (throttle pulled a hair back to prevent the enrichening circuit), can I lean without fear of my jugs exploding? Chart says that 22/2400 is 74.5BHP at this altitude. At 2175HRS SMOH,is my motor even putting out that much HP?

Also, someone here made a comment a while back in an EGT temp thread regarding my CHT's at high altitude. If my G1 shows 330 at 8500', does that mean my CHT is 330 or something else due to correction for ISA lapse rate?

At 8500' 21/2400 I'm getting a TAS of 152MPH.

I fly a C model with the Hartzell 3 blade, a d now mostly use three power settings:

  • Low altitude (~3000 msl)--23/2300 (burger runs, flightseeing, etc.)
  • Mid level (4000-7000/7500)--22/2400
  • Travel cruise (> 8000 msl)--WOT minus enough to nudge the MP needle / 2500

To make sure I'm safe around the edges, I double check the Performance Tables which I have in my checklist booklet. Slowing down is simple, just pull the throttle back to whatever speed you want and relean.

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Hi Tiger,

The O360 is a really easy engine to run and manage. And you've got a good engine monitor in the G1. So you're all set. 

My method was to always run WOT but just off the enrichment circuit as you said. At 7500' you're not making enough MP to hurt the engine in anyway. So lean as much as you like.

When you want to go fast, you'll generally be up high, around 7500' or higher. Just run WOT and lean as you like. Down low, say below 4000' you typically won't want to be going so fast, and so pull back the throttle to around 23" and again lean as you like.  On the odd chance that you're gonna be low, but need to be fast. (I raced my C in a Sportsman Air Race once and never went over 1500') I just run full rich and full throttle.

I regularly ran my C between 10,500 and 13,500 crossing the country. WOT and leaned back to 7.5 gph. I would get 155 TAS and an easy 5+ hours of range with IFR reserves.

BTW... in the descent, I'd leave the throttle, mixture, prop, all where they were for cruise and push the nose over with trim. Just keep the ASI needle from crossing the red line and get back all the time you spent in the climb. Just know it's gonna take quite a few miles to slow down after leveling off.

Enjoy that bird...

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It's all been said before, and the LOP or ROP followers have picked their side and entrenched.  To save time (and angst), spend a few hours with an open mind on the following links  Time well spent.  I believe they cover all you need to know about engine management.

http://www.eaavideo.org/video.aspx?v=2274677932001

http://www.eaavideo.org/video.aspx?v=2534345030001

http://www.avweb.com/news/savvyaviator/savvy_aviator_59_egt_cht_and_leaning-198162-1.html

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Just now, Raptor05121 said:

Why are you guys coming off the enrichment circuit? With the mixture leaned, its not making a bit of difference in fuel flow but you are restricting the tuned intake, at least as was explained to me.

I've had it explained two different and conflicting ways to me. But from personal experience and 400 hours behind an O360, the best way for me to balance the temps, and therefore fuel flow between all four cylinders, was to back off the enrichment circuit.  At WOT, my temps were widely different, and I couldn't go LOP without roughness.  Backing off the throttle, as much as possible but without moving the MP needle, the CHT's are much closer together and I could go LOP without any roughness.

I was told countless times that a carby engine wouldn't run LOP. And I found that to be true... until I learned how to back the carb off the enrichment circuit. Then it ran LOP just fine.

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2 hours ago, Raptor05121 said:

Why are you guys coming off the enrichment circuit? With the mixture leaned, its not making a bit of difference in fuel flow but you are restricting the tuned intake, at least as was explained to me.

It's not just the enrichment circuit, it also involves the butterfly valve in the throat of the carburetor.  

With the throttle retarded a little, almost to the point of seeing a decrease in manifold pressure (but not quite), the butterfly valve is cocked over and swirls the air as it enters the carburetor.  This allows for a more uniform dispersal of fuel and better distribution to each of the cylinders.  If you throw in a little carburetor heat (very little) the fuel will atomize better and distribution will be even more uniform.  Both of these things will allow a leaner mixture while still running smoothly.

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Yes, when I bought my C, I immediately installed a G2 engine analyzer. I logged many hours giving all my attention to that analyzer while the autopilot did the flying. I consistently had one hot cylinder (it would hover between 390 and 410) no matter what I did. I worked on the dog house, baffles, etc. I also couldn't go lean without the engine stumbling.  This means that at least one cylinder is too lean while at least one other is still on the rich side of peak. I tried carb heat, and various throttle/mixture/prop combinations.

I detail my final solution in this thread.  

 

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Thank you all for the input. This fall I'm going to swap out my G1 for a G2 w/fuel flow. I'll start running her wide open from now on and see what speed improvements I get.
I noticed that at high altitudes if I pull back on the throttle, it comes back a ways before I see a response in the MP needle. And I'll also try the GSXR solution too.


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Do you have an engine analyzer? I would like to look into this some more. I've always been WOT when at alt.


Come over some time and we'll go up in my C and you can play with throttle/mixture/carb heat while watching the JPI. It's been a while but last time I tried to run LOP I was very close to getting there with three of the four cylinders running LOP but by the time I got the last one LOP I would get some roughness. I can't recall now at what altitude I did this so I want to get back to a cruising altitude around 8K and try it again. I think if I play enough with it I can probably get it. I would like to compare CHT, fuel flow, and TAS running at peak, 20 degrees ROP, and LOP if I can get there.


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When going LOP... based on my IO550 experience...

It really helps to have good:

- FF data.

- EGT data.

- Mid level altitudes... 5-7k' (70+°F LOP)

- higher level altitudes won't go as deep LOP (10-20°F LOP)

With FF and EGTs you will be able to see the second carb jet in action. The two jets are in different locations sort of.  See what happens to the EGTs when the second one is on...

 

I would have liked to share my C's data, but it didn't have an engine monitor or FF gauge...

Best regards,

-a-

Edited by carusoam
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Also, in my (and others') experience a smooth-running LOP condition is more easily achieved by tossing the massives and installing fine-wires. Even installing just the bottom four plugs makes a significant difference.


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10 hours ago, gsxrpilot said:

I was told countless times that a carby engine wouldn't run LOP. And I found that to be true... until I learned how to back the carb off the enrichment circuit. Then it ran LOP just fine.

A previous 182 of mine would run 70º LOP. Most carbs will run LOP to some degree but there is a technique to it as Paul says. Back off the throttle until the MP needle moves just a little bit. Some also require just a touch of carb heat.

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1 hour ago, KLRDMD said:

A previous 182 of mine would run 70º LOP. Most carbs will run LOP to some degree but there is a technique to it as Paul says. Back off the throttle until the MP needle moves just a little bit. Some also require just a touch of carb heat.

I tried and tried and tried, but couldn't run smoothly until after extensive refurbishment of the doghouse. Now that it seals nicely, LOP is possible.

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