Climb Mixture

[201er]

My mechanic suggested bringing the mixture back in the climb toward best power if the CHTs allow. Others suggest following a target EGT based on takeoff EGT and maintaining that in the climb (like 200-300 ROP). So basically, what's wrong with bringing the mixture back toward best power (100ROP) in the cimb if cooling is sufficient? Seems like it would give you back some power and save gas. The POH is completely useless in this regard as it just says "Lean for smooth operation."

Also, if you have only enough surplus cooling to bring the mixture back towar best power or close/trail the cowl flaps, which of those two will give you better climb efficiency?

A) Closed cowl flaps, mixture full rich/target EGT

Open cowl flaps, mixture toward best power

[Cruiser]

You can............. but.

What is your detonation margin at 100°F ROP? Compared to targetted EGT detonation margin?

Can you provide the attention needed to maintain CHT during the very active phase of flight? This has always been the basis for Lycomings resistance to LOP ops. The pilot will screw up..........

 

You can also check John Deakin's articles on the subject. Both are on AvWEb

Pelican's Perch #64 Where Should I Run My Engine? (Part 2 — The Climb) http://www.avweb.com/news/pelican/182176-1.html

Pelican's Perch #84: Don't Set Mixture with CHT http://www.avweb.com/news/pelican/pelicans_perch_84_mixture_cht_194816-1.html

[danb35]

Quote: Cruiser

Can you provide the attention needed to maintain CHT during the very active phase of flight? This has always been the basis for Lycomings resistance to LOP ops. The pilot will screw up..........

[KSMooniac]

Target EGT method is the simplest and "safest" in terms of cooling and detonation margin for NA engines.  CHT is also a function of OAT, and trying to set mixture with it is thus not wise.

[John Pleisse]

Quote: danb35

Is climb out really "very active"? 

[Parker_Woodruff]

Target EGT. Mooneys climb pretty quick anyway, so you'll be down there in the low teens in fuel flow in a matter of minutes.

[201er]

Quote: danb35

Is climb out really "very active"?  Once past maybe 2000 MSL, I've got my clearance, proceeding on course, and still have 6000' or so to climb.

I'd have two concerns with leaning for best power.  First, the engine will definitely run hotter, and the reduced airflow available at climb airspeeds might not be enough.  Second, how would you determine where 100 ROP was while in the climb?  Lean to peak, enrich, and repeat every 1000' or so?

[Immelman]

(For normally aspirated engines)

I really like target EGT until an altitude where agressive leaning is safe. One thing I have found when climbing to higher altitudes is that target EGT actually keeps me very close to best power as I climb higher (as the max EGT possible at a given altitude tends to drop). By the time I'm north of 10-11,000', target EGT is right about 100 ROP.

[Parker_Woodruff]

what immelman said. You're leaning to begin with.

[bnicolette]

For what it's worth, I do the same thing with the target EGT in the climb and it has worked great for me. (as far as I know)

[johnggreen]

I took the on line course of Advanced Pilot Seminars, the LOP gurus, and learned a lot more than I thought I knew about the combustion event.

To keep it simple and not lecture, because I don't feel qualified to lecture, consider the following.

Your NA engine is capable of 100% power at sea level on a standard day.  Above that you are producing less than 100%.  The mixture is "set" to allow the engine to produce 100% power and keep comustion temps and pressures under control at sea level.  From the minute you leave "sea level" conditions, you are now producing less than 100% power and some mixture adjustment is desireable, otherwise you are running too rich, blowing unburned fuel out the exhaust, and may be producing even less power than that of which the engine is capable.

Hence the target EGT.  Note your EGT at full power sea level then as you climb and the power produced drops, you continuously lean to that target EGT and maintain that until you get to altitude.

One of the most important things I learned from the Advanced Pilot Seminar course was that when your power drops below the red zone, 65% or less, you cannot really hurt the engine by running TOO lean.

If you want a quick demo of how too rich actually reduces horsepower, simply go to cruise altitude, set cruise power, and leave the mixture full rich.  Then lean to best power.  You will probably see an increase in a J model of 4 or 5 knots.

OK, that's my two cents worth.  I fly a Bravo and don't fly LOP cause my engine simply doesn't respond well; i.e. loss of lots of speed and little savings in fuel.

Jgreen

[testwest]

+2 for Immelmann. The Target EGT method is what I use as well. The method is located here for those who are curious:

http://www.advancedpilot.com/downloads/targetegt.pps.zip

I am pretty sure at sea level, full rich fuel flow puts you "around" 200 deg F ROP. At least that is how Don Rivera at Airflow Performance has the RV guys set up their 180-200 hp Lycomings. Our Mooney is down for avionics right now, otherwise i would go out and check that today. It would be interesting if someone went out and checked that in flight with a recording JPI unit (put the data rate at 2 seconds, please!).

At sea level, full rich only costs a couple percent hp over what you get for best power. Keeping the target EGT at that level on climb is only very slightly worse on getting the most power out of the engine than by flying at Best Power in a climb.

But the power has to go through the prop to make the thrust to move forward and the excess thrust horsepower to climb.

And you can get that power back, and more, for free by simply flying a little faster on your climbs. Here is how, and why:

Don't climb at Vy unless something forces you to do so. Around 1.3 Vy puts you at Carson's speed, which is the basis for my proposed Vz "Best Efficiency of Climb" climb profile and procedure.

Using Benchmark, I looked at just the efficiency of the prop converting horsepower to thrust. Let's say you are in an M20J, climbing past 3000' at WOT Target EGT and 2700 RPM, making 176hp. That's about all you can make at the engine, standard day, at Target EGT. At Vy (86 knots) a McCauley C212 is about 76% efficient at WOT, 2700 rpm, 3000 feet. So you only have ~133 thrust hp available. Now, increase the airspeed to 113 knots (Vz, or about 1.3 * sea level Vy as published), leaving everything else the same. 

The prop efficiency goes to 83%! You still have 176hp at the engine, but the thrust hp goes to 146!! Now, that 13 thp increase plus a little bit, goes to overcome the increased drag of the higher speed. So the climb rate will be a "little" less. But there is still a lot of power left over for climb, and you are going much faster over the ground. And, you are burning the same amount of fuel.

That is one reason (but not the only reason) why a faster cruise climb works so well in the M20. And it is also why the old-skool 25 square full rich climb at Vy "kills climb performance and efficiency, 5 ways".

[jetdriven]

Target below 5K density altitude, then target + 50-80F if temperature allows.

[scottfromiowa]

This thread has been helpful for me.  I have attempted to lean to peak in climb and found it to NOT be easy so I have kept the plane at full rich during climb.  I cruise climb 120MPH (indicated) as this has kept engine cooler and gives a better view..and covers a little more ground.  I am at 871' and have 200HP.  Curious what others use as their "range for target EGT". Is 1200-1250 about right?  I will check, but wondered what others are using as range.

[jetdriven]

Take off on as close to a seal-level-pressure 59 degree day and note your EGT.  Ours is 1285 F.   Peak in cruise is ~1550 for reference.  Of course, Peak at 100% power is going to be more, but this is for a comparison. Depending on where your probe is your number can vary.

Anyways, note your EGT at this "sea-level-std day" whether it is a digital monitor, or an Alcor EGT.  Ours is 1285 F or 3 marks LEFT of vertical on the Alcor (we have both).    As you climb, lean to that value.  If above it, richen slightly. If below, lean slightly.  Make small adjustments, give it ten seconds to settle down. Dont be concerned with small variations such as 30 degrees.  Just get it close.

Make small adjustments, use a cruise climb airspeed, and watch your CHT. I shoot for 110 KIAS, and 330-340F on the hottest jug with cowl flaps in trail. Adding FUEL or AIRSPEED will lower that CHT.

 

On any day above sea level density altitude that "full rich EGT" is going to be lower than Target.   At 1000' or whenever you get around to it, lean to the predetermined Target EGT.  On a takeoff from higher than 4-5K density altitude, lean to target before brake release.

Above 5K feet density altitude, you can go a little leaner (hotter EGT)  than that 1285 target. It appears for us that 100 ROP is the lean limit for CHT when climbing on a warm day. Think, you are below 75% power, which is a cruise setting anyways.  Eventually, at 15K feet, there is only one mixture setting for climb and cruise.  80 F ROP.

[Cruiser]

Quote: testwest

+2 for Immelmann. The Target EGT method is what I use as well. The method is located here for those who are curious:

http://www.advancedpilot.com/downloads/targetegt.pps.zip

I am pretty sure at sea level, full rich fuel flow puts you "around" 200 deg F ROP. At least that is how Don Rivera at Airflow Performance has the RV guys set up their 180-200 hp Lycomings. Our Mooney is down for avionics right now, otherwise i would go out and check that today. It would be interesting if someone went out and checked that in flight with a recording JPI unit (put the data rate at 2 seconds, please!).

At sea level, full rich only costs a couple percent hp over what you get for best power. Keeping the target EGT at that level on climb is only very slightly worse on getting the most power out of the engine than by flying at Best Power in a climb.

But the power has to go through the prop to make the thrust to move forward and the excess thrust horsepower to climb.

And you can get that power back, and more, for free by simply flying a little faster on your climbs. Here is how, and why:

Don't climb at Vy unless something forces you to do so. Around 1.3 Vy puts you at Carson's speed, which is the basis for my proposed Vz "Best Efficiency of Climb" climb profile and procedure.

Using Benchmark, I looked at just the efficiency of the prop converting horsepower to thrust. Let's say you are in an M20J, climbing past 3000' at WOT Full Rich and 2700 RPM, making 176hp. That's about all you can make at the engine, standard day, full rich. At Vy (86 knots) a McCauley C212 is about 76% efficient at WOT, 2700 rpm, 3000 feet. So you only have ~133 thrust hp available. Now, increase the airspeed to 113 knots (Vz, or about 1.3 * sea level Vy as published), leaving everything else the same. 

The prop efficiency goes to 83%! You still have 176hp at the engine, but the thrust hp goes to 146!! Now, that 13 thp increase plus a little bit, goes to overcome the increased drag of the higher speed. So the climb rate will be a "little" less. But there is still a lot of power left over for climb, and you are going much faster over the ground. And, you are burning the same amount of fuel.

That is one reason (but not the only reason) why a faster cruise climb works so well in the M20. And it is also why the old-skool 25 square full rich climb at Vy "kills climb performance and efficiency, 5 ways".

« Last edit: Apr 13, 2012 12:01 PM by testwest»

[scottfromiowa]

Quote: jetdriven

Take off on as close to a seal-level-pressure 59 degree day and note your EGT.  Ours is 1285 F.   Peak in cruise is ~1550 for reference.  Of course, Peak at 100% power is going to be more, but this is for a comparison. Depending on where your probe is your number can vary.

Anyways, note your EGT at this "sea-level-std day" whether it is a digital monitor, or an Alcor EGT.  Ours is 1285 F or 3 marks LEFT of vertical on the Alcor (we have both).    As you climb, lean to that value.  If above it, richen slightly. If below, lean slightly.  Make small adjustments, give it ten seconds to settle down. Dont be concerned with small variations such as 30 degrees.  Just get it close.

Make small adjustments, use a cruise climb airspeed, and watch your CHT. I shoot for 110 KIAS, and 330-340F on the hottest jug with cowl flaps in trail. Adding FUEL or AIRSPEED will lower that CHT.

 

On any day above sea level density altitude that "full rich EGT" is going to be lower than Target.   At 1000' or whenever you get around to it, lean to the predetermined Target EGT.  On a takeoff from higher than 4-5K density altitude, lean to target before brake release.

Above 5K feet density altitude, you can go a little leaner (hotter EGT)  than that 1285 target. It appears for us that 100 ROP is the lean limit for CHT when climbing on a warm day. Think, you are below 75% power, which is a cruise setting anyways.  Eventually, at 15K feet, there is only one mixture setting for climb and cruise.  80 F ROP.

[testwest]

HI Cruiser

I edited my post significantly, if you could edit yours with my latest version quoted that would be great.

I have a complete friction horsepower chart for the IO-360-A* as installed in the M20J. Want a copy?

I do not have a model for a C214 prop. I would need the blade activity factor (BAF) and diameter to model it in Benchmark. There is a method to find blade activity factor by a series of measurements on the prop, it is here in the forum, just search the term "blade activity factor". Or, you could call McCauley and ask them for the number. The right person (engineer) to talk to will know what "blade activity factor" is, right off the bat. Once I have that data, modeling a C214 is trivial.

I would guess that the C214 is a little better than the C212, it is more rounded at the outer portion and should be a bit more efficient than the C212. For reference, the C212 BAF is 105, and the Hartzell BA 7497 BAF is 95. I would guess the 214 is somewhere between these.

By the way, I just did a series of comparisons of the Benchmark prop model for the Hartzell BA versus an output from Hartzell's proprietary prop modeling algorithm....Les Doud at Hartzell was kind enough to run some input conditions and gave me the results they would use as truth. (He did not share the actual program, natch.)

Benchmark had the parameters nailed, and was about 1% optimistic on the predicted thrust at all the conditions compared.