Leaning and Engine Performance (split topic)

[GAHorn]

Come on now Geoge, look outside of your paradym!

First off, you are starting off all of your calculations using the imaginary number of 145 horsepower. Even if our airplanes were new, how many of them would have exactly 145 horsepower?

Second, I have never seen a pilot looking at the trees, whip out his calculator or chart and say, "OK, I have 122 horsepower, that will do it!". Owners practice and know their airplane and it's capabilities. Renters look at charts and they are either not allowed by the rental agreement or they just don't know the airplane well enough to go to tight places.

Cessna was probably required by the regulations to provide charts. Even with interpolation for the different atmospheric conditions we fly in, the charts would have a hard time accomadating all of the different ways airplanes are maintained, fuel quality, prop nicks, tire sizes, etc, etc. Those same charts say it takes 3 times as much runway to land than it really does.

It's like the accountant that eventually comes to believe that the real reason every one is there at the corporation making widgets is to help him count the widgets, not to make them. Those charts are just documentation George, you don't have to defend them. Take a survey and find out how many owner pilots refer to them.

Whoa, Joe! I don't have to defend the charts. They're FAA Approved Data!
145 isn't imaginary. It's a fact, based upon FAA certification of mfr'r data that if your engine turns 2700 rpm it's making 145 horsepower! (and if it's only turning 2250 static it's making 118 hp, etc.)
"Second": The pilot is required by regulation to determine his required takeoff distance prior to flight, and the data to do that is in the FAA Approved Flight Manual. If the airplane meets it Type certificate, is in airworthy condition, and is operated according to the recommended procedure...then it will meet the charted data. It's the reason we follow airworthiness standards when maintaining our airplanes.
Lastly, with regard to your observations regarding "owner" experience with their airplanes and "prop nicks" and "3 times as much runway": The airplane is to be maintained according to it's maintenance schedule and FAA regulations therefore if there are any "prop nicks" etc they'd better be within the specifications or the airplane will not meet it's performance data (the owner/operator is req'd to keep the airplane airworthy according to such requirements) and "owner experience" is a relative term. As is "3 times the rwy required" an anecdote, without factual basis....it's your commentary...not a proven fact based upon flight testing.
The aircraft performance by FAA definition is documented using "average" pilot technique as proven by the factory test pilots who certified the aircraft's performance. If an owner is especially adept, or personally more familiar with his aircraft or uses special operating techniques then he may exceed (or fail to meet) the published, approved data.
If you are looking at trees, then you'd better whip out your charts and confirm the takeoff data before you start the roll. Not only are you required to do so by regulations, it's also prudent.

[N1478D]

"Those same charts say it takes 3 times as much runway to land than it really does. "

George, that is what I said that you apparently did not read! Do you take as much runway to land as the charts predict?

Surley you don't believe everything the government prints, do you? FAA certification of mfr'r data, what in the world does that mean? It's just people doing the same job day in and day out. Somebody does not come along behind them and say, "Hey, we tested these engines and they are only putting out 137 horsepower at 2700 RPM." And just because a pilot is required by regulation does not mean that all of the pilots are doing it. FAA Approved Data for hundreds of airplanes coming off of the assembly line on different days with different vendors involved in supplying the parts? Was the data developed during the manufacturing of each airplane, or was it developed prior to the start of manufacturing? A homebuilder who builds his airplane, and then tests and makes his own charts off of his flight tests of that airplane would come closer to having accurate charts.

I would bet that there are many pilots who have never even looked at those charts, besides the ones who don't use them.

[GAHorn]

Joe, I addressed your "3 times" comment pretty vividly. I don't know why you think I didn't read it. Perhaps you're not comprehending what I'm writing in my efforts to assist you to understand aircraft performance.

Let me assure you, the data in the charts is not fiction. It's the documented performance the factory demonstrated and the FAA certificated the aircraft to be capable of under the conditions stated using average pilot technique.
If you got your airplane to stop in 1/3 the distance the charts say, then you've done something different than average pilot technique or you've done it under atmospheric conditions or aircraft weight etc differently than the approved data stipulated (or both.)
When aircraft are evaluated for certification of performance data, they are evaluated under two major categories: Gross Data and Net Data. Gross data is the performance the entire fleet is expected to meet if maintained in accordance with established criteria, while Net Data is the performance guarantees that the worst example of the fleet will meet if maintained under the same criteria, and I believe Net Data is the published data in the charts for light aircraft. If your particluar aircraft beats the charted data then that's not a problem. But certainly a pilot should not attempt critical flights that cannot be expected to perform within the charted data.
In any case, it's legitimate data that should be consulted and be familiar to any pilot who intends to operate the aircraft.

If as you say, "I would bet that there are many pilots who have never even looked at those charts, besides the ones who don't use them."...then I feel those pilots are not practicing good, safe operating practices and/or they are simply choosing to be ignorant. Aircraft performance is a major subject area that all pilots are required to be taught and practice, and it's an area of Practical Flight Tests that examiners can usually rely upon to flunk a weak applicant that the examiner feels needs to take additional instruction.
I don't believe your observation is typical but if it is then perhaps aircraft performance, particularly Cessna 170 Performance, should be offered by TIC170A as a seminar item?

(BTW, ...if you can land your airplane in 1/3 the distance that the charts say, then you're pretty hot! On a standard day, at sea level, the charts for a B-model show a landing distance of 1140' passing over a 50' obstacle at 67 mph, with actual ground roll being only 458'. I'd like to see someone demonstrate to me that the charts are 3 times more than actually necessary.)

[mvivion]

George,

I understand that induction air modified by carburetor heat is warmer. That is precisely the point. My point was that warmer air provides better atomization, and more even distribution of fuel in the induction system. Thus, by using partial carburetor heat in cruise flight, you can actually smooth out the egt's of the engine, which is what you should be using as a reference for leaning the engine. By producing more even distribution and more complete atomization of the fuel, you can run the airplane on less fuel, making the same cruise speed, by being more efficient.

It is important to note that you should not try this without full instrumentation, but it works. It is a technique that a fellow named Lindberg used in part to fly long distances.

As to digital guages, some folks probably don't like GPS or flat panel displays either. So what? Doesnt' mean that others shouldn't take advantage of technology.

And, by the way the EDM 700 provides a graphic and a digital display. If the single digital display makes you crazy, switch it to the outside air temp, and it won't flicker. Mine doesnt flicker in any case.

Finally, the EDM 800 instrument provides horsepower for even our engines nowadays. It weighs a massive 18 ounces. Total. It also provides six point egt/cht, fuel flow, fuel remaining, fuel used, fuel to destination, carburetor air inlet temp, etc, etc.

So, you don't need to buy DC-6 instrumentation for your 170.

And, it is nice at times to know what percentage power you are using, for reference, if nothing else.

As to performance charts, my airplane relies on the same Cessna charts, even though it has more horsepower. They guarantee you it will perform at least as well as a lower powered airplane.

Put Vortex Generators on your airplane. They do change the performance capabilities of your airplane, but there are no performance charts provided with them, so what do you do there? The manufacturer simply demonstrates for the FAA that they don't deteriorate performance, and that's good enough. We're left with an airplane which may significantly out perform the book numbers, yet we aren't going to try anything the stock book says isn't within the operating parameters of the stock airplane?

Maybe that's the conservative answer. As to a stock 170 being able to perform to the standards Cessna published fifty years ago, I wouldn't bet teh farm on it. There are a lot of things that will deteriorate the performance of an airplane that DO NOT make the airplane unairworthy. Those are the ones that'll hurt you.

It is not accurate to state that ANY airplane that does not, on a given day, meet the performance figures provided by Cessna in the POH is not airworthy. If that were true, a LARGE percentage of the fleet wouldn't be airworthy. All the POH says is that your airplane, operated with average pilot technique, should have performed to those standards the day it was test flown at the factory. After that, there is no recurring requirement to document or demonstrate performance. Ever.

Your statement is somewhat correct, though, in that a properly maintained aircraft should come pretty close to those performance standards. If not, there is probably something unusually wrong, beyond normal wear. But those standards aren't an absolute benchmark, that we must test to, and certify as unairworthy any tired old airplane that can't make it there.

Mike Vivion

[GAHorn]

I erred previously during a senior moment. I mis-stated the Owner's Manual recommended leaning procedure.
The recommended procedure (from Section III, Operating Details) actually is: "At any cruising altitufe, adjust mixture control for best rich power by pulling knob out until maximum rpm is obtained with fixed throttle; then push control forward toward "full rich" until rpm starts to decrease. Readujust for each change in power, altitude, or carburetor heat."
Notice that technique is for "best rich power".
The technique I posted earlier was equivalent to "best lean power" and for the life of me I am presently unable to locate the document I found it.
At power settings 65% or below (see the cruising performance charts) that technique should result in maximum mpg and minimum fuel burn without injury to the engine. It is: Lean until maximum rpm is obtained, continue leaning until the first sign of rpm loss occurs, then enrichen until max rpm is re-obtained.
How did I get that error past all you guys?
============

Thanks, Mike. No implication was intended to indicate that performance charts are an airworthiness standard. They certainly are not. They are simply the best data available to predict the performance of an airworthy aircraft.

Lindbergh also used parachutes to abandon aircraft on top of undercasts. (And got lost. Even circled fishing boats to shout "Which way Ireland?")
Seriously, I've never heard he used partial carb heat to improve fuel atomization. I believe he used it purely for anti-icing purposes (which curiously made his partially iced carb run smoother. And if you do run with partial carb heat, you should have proper instrumentation. Not necessarily an EDM (Lindy didn't have one either),...but a carb air temp gauge. And re-leaning in order to recoup the loss of power experienced from the application of continuous carb heat in cruise is good operating procedure (and prescribed in Section G of the Operating Check List of the Owner's Manual.) But heating up the carb air to make it less dense so one can lean even further is getting the cart before the horse in my opinion.)

The EDM 700 is a smart gauge. The literature is impressive as well. There are some reknown experts who would take issue with JPI's claims and logic however when they claim (in support of their instrument) "If you lean to the hottest, some cylinders will be too lean of peak, and could cause detonation" It's been pretty well argued that LOP does not cause detonation and in fact that LOP ops actually prevents detonation. The farther LOP one leans the cooler the cylinder runs... not hotter. In fact, the wide variations of our engines would likely encourage the cylinders which run richer than the "first" to peak...to be more susceptible to detonate! (Admittedly, our engines are unlikely to experience detonation, and the EDM gauge should immediately indicate that to an attentive pilot.)
The bigger question in my mind is: With the well-known wide variations in the C145/O300 induction system (the the relatively wide differences in each cylinder's mixture) then how does one operate LOP? Or if you prefer, 25 degrees rich of peak? Which cylinder do we operate that close? And what does that do to the remaining cyls that cannot be brought to the same exact mixture setting?
If leaning the engine in accordance with their claims/gauge and it's operating recommendations can save over $2K in a Bonanza (a fuel injected engine mind you) then how can that expectation be applied to our engine installation which cannot be so accurately leaned despite the instrumentation? (Their own Manual points out that carbureted engines may have cyl-to-cyl differences in EGT of 120-150 derees! We need digital gauges to measure that?)
I believe leaning to best rich power using simple rpm like the Owner's Manual recommendation is more cost effective and likely just as good a job as can be done without the expense of buying a micrometer to measure the hatchet cut.

The per-cent HP readout is cool on the EDM 800. But note that it requires the necessary inputs from manifold pressure and rpm. And also note their manual states: "Displays percent of rated HP OR RPM depending on pilot programming." My question is: Why (other than for entertainment purposes) do we need to have an otherwise unnecessary and expensive guage read our rpm and convert it to %HP when we have a chart that has already done it for us at no cost?

In another example of overkill, they state (with regards to their graphic CGT display): "CHT is displayed by a missing segment and
should be interpreted as follows: a missing
segment corresponds to the CHT in 25 F°
increments, starting at 300°F at the bottom. In
the example shown here, the CHT is 350°F. If the EGT bar
is lower than the missing CHT segment, then the CHT will
be indicated by a single isolated lighted segment."

Now, it just so happens that the illustration they give actually has CHT delineations of 50-degree increments....not 25 degrees. And while on that subject,...I can't help but wonder why we need to spend a lot of money to get a digital gauge that only claims at best to display accuracies only within 25 degrees! That's digital? The 50 year old original (analog) Cessna gauge is calibrated to 12.5 degrees!

In my opinion, It's a toy. A cool one though. (GPS will at least let us find Ireland.)

[doug8082a]

... growing weak....
.. eyes... glazing over....
.. must find....... new... topic...

(thud) ZZzzzzzzzzzzzzzzzzzzzz

[GAHorn]

[GAHorn]

Well, this old F--t got a refresher course from and even older F--t by the name of Dick Lemmon (aka blueldr) via email, in which he corrected my failing memory regarding BMEP gauges.
"The BMEP (Brake Mean Effective Pressure) gauge reading with the RPM and a "constant" number will give you the horsepower on the propeller shaft. The "Induced" horsepower less the pumping losses and accessory load is what is left for the prop, the Brake Horsepower. The Induced Horsepower is the limiting factor on the engine, So the more accessory power you use off the rear of the engine , the less available to the prop. For example, a DC-6 ran five less BMEP on the outboard engines because of the cabin superchargers driving off the rear."

Thanks, Dick! And I suppose those outboard superchargers put out quite a bit of hot-air?

[mvivion]

George,

You seem to consistently miss the point of the post: The point of my post was simply that you CAN even out the EGT's to MUCH closer than 120 degrees IF you use carburetor heat as an aid.

The EDM instruments can be equipped (and should, in my opinion) with a carburetor air inlet sensor.

Combine those attributes, and devices, and you CAN run the engine more efficiently, if you choose to. Then again, you can run it at full rich, as well, and you won't hurt my feelings at all.

My comments on the EDM 800 and its horsepower percent calculation were simply in response to your comment that this was only a DC-6 function, with a gauge that weighs a bunch and is antiquated.

I too see no particular value to the percent power calculation function of that gauge, but it's available.

As to manifold pressure, every engine has some. Not every fixed pitch prop equipped airplane has a gauge to measure it, but you can sure put one on your 170 if you like.

Mike

[GAHorn]

I don't miss the point at all, Mike.

Consider this comparison:
An airplane on a cool day at low altitude VS the same airplane on a hot day at high altitude. Which engine will make more power, and which airplane will perform better?
Adding partial carb heat makes the engine induction system believe it's a hot day at high altitude. That's why it must be leaned further, in order for it not to be running overly rich in that artificially created high density altitude.
Where can we find information that will make a valid comparison of the output of the same engine in each operating condition?

Take the example a step further: A pilot so eager to wring the last vestige of performance out of his engine (in other words, one likely to try your suggested technique) would likely be the kind of pilot that will also have consulted the performance charts and determined the optimum altitude to operate his airplane, and would discover that altitude is the same (or very nearly the same) as the altitude that lets him operate at full open throttle (in a normally aspirated engine such as ours.)
Notice that will result in a specific RPM with a fixed pitch prop, and notice that RPM produces a particular amount of power.
Raising the density altitude of that engine artificially by increasing carb inlet air temperature will result in a loss of power, which cannot be reclaimed by adding throttle. It will not be made up by "equalizing" EGT's because the RPM is the sole measure of power output in a fixed pitch installation. Also, any reduction of fuel burn is a direct precursor to the resultant loss of power.
Consider the mechanical carb air box: With full cold selected, ram air enters the air-box chamber and is deflected directly upward toward the carburetor throat by a butterfly valve. Application of partial carb heat reduces the ram air effect by presenting a progressively horizontally positioned valve. Now the engine sucking air from two opposing directions which nullify each other, portions of which even are dumped downward into the lower cowl to escape back to atmosphere. The loss of the ram air effect costs engine performance due to a loss of velocity. (Another reason the mixture must be further leaned from the cold position...because less air is actually being consumed.)
I believe there may be some merit to your suggested technique in arctic climes, but not where most of us operate. The entire induction system of our engine installations is located downstream of the heated cylinders in a warm if not downright hot environment. The mixture control already allows us to lean adequately to alleviate overly rich mixtures.
Engine makers are eager to promote the power output of their products, and would likely jump at the opportunity to recommend operating techniques that might measureably improve the performance of their engines. Are there any engine makers that recommend the regular operation of their engines with partial carb heat for the purpose of increasing engine efficiency?

[mvivion]

George,

Your logic train is all accurate, however, the point is that the fuel savings by leaning with partial carb heat applied is greater than could be explained by a simple increase in density altitude at the carb inlet, and a consequent decrease in horsepower.

Oh, and the guy who introduced me to this concept is John Deakin. I think he operates out of Texas, a true arctic climate.

This isn't my technique, and I emphasize that it can and should only be used with full instrumentation.

The point is to allow every cylinder to make the SAME HORSEPOWER, or as close to that as possible, which then allows you to lean more aggressively before you experience engine roughness, which is simply one cylinder receiving too little fuel to function right, hence less hp, and rough engine. Even out the distribution of fuel and air and it makes for a more even leaning, which means all cylinders approach their leanest at about the same time.

This is essentially what GAMI injectors are designed (and proven) to do for you in a fuel injected airplane, and that is all they do: even out the fuel/air ratios among all the cylinders.

Yes, you make less horsepower when you lean aggressively, but this isn't a procedure intended to make you go faster, it's designed for fuel economy. I do realize that the horsepower changes in this case.

There are lots of reasons we have all these controls in our aircraft. I'm not looking forward to FADEC, personally.

Mike

[GAHorn]

Capt. Deakin is a person I have a lot of respect for, and I think he's done a lot to illuminate some of the darker, less understood areas of engine operations in general aviation.
But I'm convinced that his theories and advice are most applicable to fuel injected engines with constant speed props (along with accurate instrumentation, as you also point out.) Of course, fuel injected engines don't have carburetor heat, although some may have air induction heat systems. Most have only an alternate air source.....which is not actually/purposely heated. (And most such systems also result in a loss of ram-recovery when this technique is applied.)
I've never seen Capt. Deakin address the issue of loss of ram-recovery due to the air-box/carb heat valve design however, and while warmer air certainly may assist fuel atomization*, I've never seen any comparative data that proves power losses are avoided by the technique without additional throttle....which becomes either a vicious circle or a dead end.
If, as you say, a loss of power is acceptable, and "smoothness of operation" is the primary object, then the technique seems much less objectionable to me.

*-Aside from the well-known range of correct-proportions of fuel-weight VS induction air weight relationships (a relative constant)... I must admit I'm curious as to why it seems logical that warmer inlet air is preferable to cool dense air as it regards solely to "fuel atomization" in multi-cylinder distributions. The amount of fuel droplets that get "vacuumed" up into the induction airstream is a direct result of carb/venturi design and mass-flow. In other words, in any given volume of induction air, there will be a proportionate amount of fuel sprayed into the airstream. The only thing that might improve efficiencies is the complete vaporization of that fuel before the combustion event. By the time that fuel air mixture reaches the inside of the cylinder's compression stage of a hot, running, 4-cycle engine, (having already turbulently passed by the intensely hot intake valves, guides, and chambers) it must surely be as vaporized as it's might ever get whether or not the air it's carried in began it's journey through the system at 30 or 130 degrees.
It'd be an interesting experiment to set cruise power, and watch the HP readout of the EDM gauge (properly calibrated with manifold pressure inputs) after the mixture was re-leaned but before the throttle was re-adjusted after applying partial carb heat. I'll theorize the HP will decrease on a fixed pitch prop.

Mike: "This is essentially what GAMI injectors are designed (and proven) to do for you in a fuel injected airplane, and that is all they do: even out the fuel/air ratios among all the cylinders."

Yes, and that's an intersting point. If it's so important to get fuel completely "vaporized" prior to it's entry into the cylinder (the theoretical reason to use partial carb heat)....then how do you suppose those fuel injectors, GAMI or otherwise, work so well..... considering that they inject liquid fuel droplets directly into the cylinder with virtually no vaporization at all?
All the hgh-performance engines are designed very purposefully to get as much COLD air pumped into those cylinders as possible. Turbocharged engines even go to the extra-expense and weight penalties of adding intercoolers specifically to cool that compressed air back down before it's allowed to get to those cylinders....where raw fuel is sprayed into them.
I thnk this an interesting discussion.

[jrenwick]

A couple of years ago I heard a talk given by Darryl Bolduc, a widely respected engine overhaul shop operator in the Twin Cities. He was discussing leaning technique, and how to avoid mixture settings that lead to exhaust valve deterioration. He said that at higher power settings, this is a matter of making sure no cylinder is running in the range between max power and peak EGT, where the CHT is highest. If the EGT spread between cylinders is large, it will be hard to get them all running efficiently while keeping all of them away from the peak CHT setting.

He told a story about overhauling an engine that had gone to TBO with no sign of valve burning. (I think he said it was an O300, but I wouldn't swear to it.) He thought this was very unusual, so he quizzed the owner about his leaning technique. It turned out the owner consistently used carb heat while leaning, because that helped equalize the EGT readings. (I guess he wasn't leaning for peak power.) Bolduc said he believed the application of carb heat helps equalize fuel distribution; I don't recall that he mentioned vaporization, but maybe better vaporization is the means by which distribution is improved.

He also cautioned, as has been said several times in this forum, that this should not be done without reference to a carb temperature gauge, so that you're not warming the intake air just to the point where ice can form.

This all seemed to make sense to me. I'm still learning to use my fairly-new engine analyzer, and I haven't yet seen this effect of carb heat on the EGT spread, but then I haven't really spent much time looking for it, either, partly because I don't have my carb temperature probe installed yet. I'll probably post something if I learn more about this.

Best Regards,

John

[mvivion]

John,

I too have heard Darryl speak on this subject, and my interpretation of his dissertation is the same as yours.

George, I didn't mean the point was to even out the egt's, I said the point of the exercise was to run more efficiently. To do so, you need to even out the egt's. A minor point, but an important one.

Anyway, this isn't one turkey in Alaska talking through his hat. It's an interesting phenomenon, and worth experimenting with. I didn't buy it at first either.

I sure don't agree with everything John Deaken states either, by the way. But, his information is worth taking out and experimenting with. There are some interesting and useful bits in there.

Mike

[GAHorn]

I think I see your strategy now, Mike. I think it goes like this: "Let's see now, ...If I can get George curious enough about this, then he'll feel compelled to try to prove the point....and the only way he can do that is to have good, digital instrumentation....and then, after he has that EDM 800 installed....of course he'll fall in love with it, and he'll have to admit I was right all along! Yeah! That's the ticket!"