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  #11  
Old 12-04-2007, 11:28 AM
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gmcjetpilot gmcjetpilot is offline
 
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Default Pay back in two to never years

Quote:
Originally Posted by petehowell View Post
Steve, Not to muddy the water, but I think many carb engines can be run LOP if they have dual EI with advance. It requires some futzing, but that becomes second nature after you do it for a bit.
OK I'll bite.

What does the EI w/ advance have to do with it?
What kind of futzing did you do to make it work?

Not doubting just asking. I do think its possible for some with Carbs to run LOP and for some, never possible. Individual and normal variation from cyl to cyl can cause this inability to run LOP. Ignition in my opinion is not a player or a very minor one, its all fuel and volumetric issues. A carb just blows a wet fuel mix in a hole and you hope the cylinders suck-up the needed fuel/air mix to run LOP, all about the same time the other cylinders are running LOP. I don't think ignition has much say so and you really can't vary the ignition to "tune" for LOP. Balanced cylinders makes an engine more accepting of LOP ops, which is mechanical and hard to change. I also say LOP is WAY OVER BLOWN. You can run LAMAYCG (lean as much as you can get) just fine and save lots of fuel. FI has the ability to compensate for unbalanced cylinders may not even balanced flow but imbalanced flow to compensate.

One Gent whose post I read on VAF could not get his engine to run LOP before a rebuild to save his life, but he could run LOP after he had the engine rebuilt. He had his cylinders custom flow balanced. If you think about it, a Lyc is like 4 separate one cylinder engines that share a crank an induction plenum. Each jug can vary. Unless you can "tune" your fuel flow to each cylinder's individual needs accurately, you will not run LOP with a carb. It's not about even fuel distribution but individual tuning to each cylinders needs. However if you balance the cylinders on the bench, that can be half the battle. FI has more ability to customize and tune fuel and compensate for variations between cylinders, whether they are flowed or not.

Also LOP has taken on mythical importance. LOP has been around forever. Lyc says lean to rough and than enrichen to regain smooth ops. What do you think that is? Well it may not be LOP but peak just slightly ROP. The difference in LOP and PEAK is not that much fuel savings. LOP loses power at an ever increasing rate, meaning slower airspeed. You really want to SAVE fuel? Pull the black knob back and fly slower; fly closer to long range L/D speed. I know Avweb is persuasive with their gospel, but my gosh, they make it sound like they discovered the holy grail of aviation.

How do you tune a Carb and induction of LOP? So you fly and see one cylinder is rich, one is super lean and stumbling and the other two are about the same and in between. WHAT TO DO? There should be some way to bias the fuel to/away from individual cylinders even with a Carb, by futzing with the plenum or induction runners? Any IDEAS? With the C-182 you can move the carb heat around and play with the fuel flow and get LOP ops. Of course LOP with hot air is less power. Again just pull the throttle back and fly slower with "LAMAYCG".


LOP 1 to 2 gal/hour less? No
As far as fuel savings I'm not buying 1 to 2 Gal and hour, sorry AlexPeterson. May be in a IO540 you might get +1 gal less per hour. The real savings is about 0.5 or 0.75 gal per hour at best. Lets not forget you can LEAN with a Carb right up to as lean as you can get for smooth operations. The difference between LOP and LAMAYCG - LEAN AS MUCH AS YOU CAN GET is not 1 to 2 gal hour. May be lean from full rich to LOP is 1 to 2 gal an hour. Also what people don't count on with LOP is lower power = slower airspeed, so you add TIME to your flight and more fuel burn. There's no free lunch, but you can LEAN and fly economically with out LOP. Avweb has made this a big deal, however this is OLD NEWS. If you are below 75% power and all temps are in the green, you can fly at PEAK, per the Lyc manual. All the happy talk about HOW WOUNDERFUL LOP is and how COOL your engine will run is great but semi-trivial; the reason its cool is because you're LOSING POWER. All this techno talk about combustion pressure is fascinating but you want to lower your combustion pressures and FF, throttle back, lean the heck out of it as much as you can get and FLY at slower air speeds. As far as efficiency, LOP is goodness IF YOU CAN GET IT. I like to date supermodels and own a winning Westminster purebred show dog, but you see what my dog looks like. You should see my girlfriend looks like. You might as well get a constant speed prop and drop the nose gear if you are into efficiency, both of which have impact on efficiency as much or more than FI.

If you want to save fuel, Carb or FI, throttle way-way-way-back and fly at say 120 mph TAS, and lean as much as you can for smooth ops (provide a tail wind, flying faster with a headwind is better right). PER LYC: Lean to rough and than enrichen to regain smooth ops. That is anything from LOP to near peak. No engine monitor is required. So this LOP stuff is NOT NEW, just over hyped. It's still important and its cool to balance your FI's injectors, no doubt. If you have FI its almost a free lunch, why not do it. But it should not be the only reason to go with FI. There are other reasons to go FI today.

PAY BACK MATH?
As was said too many variables; still the math is easy. Now how much do you fly fully leaned in the magical LOP zone? Well mostly in cruise. Your ability to flight-plan trips, pick altitudes, throttle back and lean aggressively save's as much or more than FI can. If you're lazy and fly WOT at full-rich, it doesn't matter what's blowing fuel into your engine. From my estimate, assuming $5/gal, 150 hours a year, 50% cruise w/ lean-O-peak (0.75 gal less than peak) is about $280 a year, less if you just putz around local doing touch-n-goes. Assume 100% of your 150 hours/yr is LOP ops, than $560/year. So it could pay for itself in who knows? I don't think you need an Excel spread sheet to calculate pay back. In theory it will pay back at some point. If gas goes to $10/gal, YEA think of the money you will save! (joke, sad but true).

MY reason I'm suggesting FI today
The temporary (I hope) suspension of Carb production by Precision Airmotive Inc. throws a monkey wrench in the works. If I was buying today I'd go FI, even though I love Carbs. Some people are afraid of FI because its an unknown to them, like tail-draggers or constant speed props. FI set-up is a little more involved and there are operational "procedures" or techniques with FI, but they're easily understood & learned. I'd get FI if buying today, simply because its in production from three different companies, and the one manufacture of Carbs has stopped making parts because of product liability insurance cost. Yes, Kelly Aerospace makes parts, but I don't think they can make all new assemblies outright, as far as I know, just OH parts. If a used engine with a Carb fell in my lap, I'd use it with out hesitation. You can convert to FI but that is expensive. If you're buying a new engine, now is the time to go FI. Forget the cost of the PUMP FUEL savings. Your spending $60k on your plane a $600 fuel pump is a show stopper? FI can't get Carb ice which is nice (can get snow / sleet blockage). FI is "better" technically from a fuel metering standpoint, and the acquisition cost difference is not that great any more.
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Last edited by gmcjetpilot : 12-04-2007 at 12:38 PM.
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  #12  
Old 12-04-2007, 12:33 PM
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AlexPeterson AlexPeterson is offline
 
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Default

Quote:
Originally Posted by gmcjetpilot View Post
OK I'll bite.

SNIP

LOP 1 to 2 gal hour less? No
As far as fuel savings I'm not buying 1 to 2 Gal and hour, sorry AlexPeterson.

SNIP
George, there you go again! I am just reporting what real life fuel burns are with airplanes flying next to me. I can't vouch for their fuel flow accuracies. But, I have compared fuel tickets when we fly cross country together. So, the data is accurate.

What is missing is that the peak egt spread, in terms of fuel flow, on many carb'd engines is 1 to 2 gph. This surely seems hard to believe, but we have data on several local planes to prove it. So, when we turn the red knob out until the engine starts to run rough, we have caused one cylinder to start missing, or putting out enough fewer horsepower to cause engine roughness. But, the richest cylinder is still very rich at this point. The richest cylinder(s) must remain rich, or we drive the engine into a rough running area.

This offset does not only matter when running LOP. This is true also when the leanest cylinder is at peak power, or say around 150 ROP. That means other cylinders are much richer than that. So, forgetting the LOP/ROP part of this, you are running four different mixtures, only one of which is where you would like it. Either way, efficiency suffers.

Take careful data of egt for all cylinders vs total fuel flow. Start way rich and slowly lean it until it runs rough, taking data of all four (or six) egt's (and you might as well get cht's) vs total fuel flow. Pausing about a minute for each setting is prudent. Try to stop at every .1 or .2 gph. The spread will vary a lot with throttle settings, but one can determine what is called the GAMI spread with this. There are several real life graphs posted elsewhere on this site.

As you said, there are carb'd engines which run well on the lean side of things, but they seem to be the exception. In any case, LOP aside, different mixtures mean more fuel burned than necessary.
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  #13  
Old 12-04-2007, 04:00 PM
ninerhawk ninerhawk is offline
 
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Default Converting cowl, carb to FI

Am still toying with the idea of converting my as yet unordered Lyc. 320 engine to FI. I have in my inventory an as yet uninstalled lower cowl for the Lyc. carbed 320. Vans has a list of items to be swapped in the appropriate kit. It includes the recommendation to modify the cowl by purchasing from them a scoop designed for the 360 and installing it, in lieu of returning or swapping out the original cowl. Has anyone performed this surgery on their cowl? How difficult or time consuming was the conversion of the cowl for a Lyc. 320 from carb to FI?
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  #14  
Old 12-04-2007, 04:17 PM
jmartinez443 jmartinez443 is offline
 
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Default

Wonder if you realize that Precision has halted production on carbs due to the cost of insurance.
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  #15  
Old 12-04-2007, 04:55 PM
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Quote:
Originally Posted by jmartinez443 View Post
Wonder if you realize that Precision has halted production on carbs due to the cost of insurance.
....and another company has already said that it will buy the line....
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  #16  
Old 12-04-2007, 05:07 PM
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AlexPeterson AlexPeterson is offline
 
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Quote:
Originally Posted by Ironflight View Post
....and another company has already said that it will buy the line....
Something to keep an eye on is if the actual division of the company, the building and mainly the people, are being bought or just the rights? Big difference.
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  #17  
Old 12-04-2007, 06:14 PM
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Walt Walt is offline
 
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Default LOP and ignition

Ignition does make a difference, I was told that the hotter spark as well as the more advanced timing is the key. I can tell you that with one LSE I could do LOP a little, with dual LSE I can lean further and maintain smoother operation longer.
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  #18  
Old 12-04-2007, 06:20 PM
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Default

I am not a motor head and don't have my engine yet but intend to go FI. But some observations.

-If carbs are so good why is the only company making them stopping and only one company going to fill the vacuum.

-If carbs are so good why do all autos today run with FI?

For me being in a cold wet climate the FI is the way to go, no more carb ice. If buying new I think the prudent thing to do is go FI, even though there might be some higher cost. With what may happen to aviation fuels in the future I think FI may become a must, not sure I am no expert. However, you can't argue with the simplicity of carburated engines. BTW this is the best part of VAF, the flow of ideas and opinions.

Debate on!
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  #19  
Old 12-05-2007, 12:00 AM
Pirkka Pirkka is offline
 
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Question Ellison throttle body injector

This has been interesting thread. And to keep it interesting I wish to make a question about Ellison's throttle body injector. (http://www.ellison-tbi.com/) For me, it seem a lot of money so is it as good as it claims to be? It sure solves some problems like flying acrobatics without FI but would you see that it saves fuel and therefore would step between carburettor and FI?
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  #20  
Old 12-05-2007, 03:36 PM
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gmcjetpilot gmcjetpilot is offline
 
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Default Nicely done

Quote:
Originally Posted by AlexPeterson View Post
George, there you go again! I am just reporting what real life fuel burns are with airplanes flying next to me. I can't vouch for their fuel flow accuracies. But, I have compared fuel tickets when we fly cross country together. So, the data is accurate.

What is missing is that the peak egt spread, in terms of fuel flow, on many carb'd engines is 1 to 2 gph. This surely seems hard to believe, but we have data on several local planes to prove it. So, when we turn the red knob out until the engine starts to run rough, we have caused one cylinder to start missing, or putting out enough fewer horsepower to cause engine roughness. But, the richest cylinder is still very rich at this point. The richest cylinder(s) must remain rich, or we drive the engine into a rough running area.

This offset does not only matter when running LOP. This is true also when the leanest cylinder is at peak power, or say around 150 ROP. That means other cylinders are much richer than that. So, forgetting the LOP/ROP part of this, you are running four different mixtures, only one of which is where you would like it. Either way, efficiency suffers.

Take careful data of egt for all cylinders vs total fuel flow. Start way rich and slowly lean it until it runs rough, taking data of all four (or six) egt's (and you might as well get cht's) vs total fuel flow. Pausing about a minute for each setting is prudent. Try to stop at every .1 or .2 gph. The spread will vary a lot with throttle settings, but one can determine what is called the GAMI spread with this. There are several real life graphs posted elsewhere on this site.

As you said, there are carb'd engines which run well on the lean side of things, but they seem to be the exception. In any case, LOP aside, different mixtures mean more fuel burned than necessary.
That is good info. We can disagree like gentlemen, thanks. I'm just saying to define the 1 to 2 gal hour you have to define all other parameters. If one plane is going 10 mph slower it puts FF in perspective. May be the other plane was running 150F ROP. My point is you can LEAN to the MAX of smooth ops with a CARB'ed Lyc with out restriction or fancy engine monitor or FI. It may not be as good as LOP but than how much? I'll be honest I don't know first hand data, but based on what I read and Lycoming data, I've come to my conclusion, good, ugly or wrong. Just looking at Lycs FF/HP/CHT/EGT chart below; it does not look like much FF diff between peak EGT and LOP. LOOK down at specific FF curve, bottom left. Specific fuel goes up if you deep into to LOP. (Specific - FF per HP. LOP ops causes HP to nose dive as the power curve shows.)

You can see the difference between peak and LOP specific fuel, not much. Granted if you have some large EGT spread on one, two or three of the other cyl's, running ROP, they are burning more fuel. However even up to +60F ROP, the FF does not really change radically. Now get into 100-175F ROP you do burn more fuel but you also make peak POWER. Econ per LYC is peak EGT.

I know +60F is peak CHT, but if your at low power and its in the green, its in the green, which to me is under 400F. You should avoid 40-60F ROP unless at real low power if you can. Richer or leaner is cooler CHT clearly from the data.

This has been written in stone for decades and how and why Lyc makes the recommendations they do. LOP is not recommended except for the Malibu big turbo 540. From a practical stand point 150, 160 or 180HP engines get smaller fuel savings than a 540 running LOP. Still with FI, balanced injectors and an engine monitor, why not run LOP. Fuel is fuel and money.

I still say 2 gal/hr is a lot to claim for LOP with a little 180HP engine. That is what, 15%, 20% or 25% savings? That pegs my too good to be true meter. 1 gph, OK, I'll buy that at an extreme, if you're comparing it to running well over peak EGT on the rich side. Bottom line 1 to 2gph is a big spread even per your est. Is it 1 or 2? To be fair overall LOP savings are hard to nail down, too many variables.

The big Continentals is what Avweb knows and really writes about. It does pay to run LOP on those big engines running 20 gph, where just 5% is 1gph. Also many Continentals have FI that don't compensate for altitude like our mass airflow FI. Even Carbs compensate fuel mixture to a degree as you climb, but not so with most FI on Continentals. So getting busy with the mixture control on a Continental is a must to save lots of fuel. It applies to small 4-cyl Lycs as well, just the savings are smaller. Even if our savings is 0.5 or 0.75 gph its well worth it in dollars. I just don't want people to be bamboozled or mystified. Since the time they where a student pilot in a C152 leaning to rough and than moving the mixture control in a scooch, they may have been running LOP or peak unknowingly. How many GA planes even have one channel EGT? The rough and make is smooth lean method takes no time or fancy instruments. There's something elegant about that. Clearly LOP, FI and 16 channel engine monitors is BETTER, but I just don't want to overstate the advantage.

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Last edited by gmcjetpilot : 12-05-2007 at 04:20 PM.
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