W

Walter Atkinson

Well Known Member
There are two issues concnering timing that must be considered when operating your engine. The first and the one you can't do much about in flight is the mechanical timing set by the mechanic or the designer of an EI.

The issue of concern is where the thetaPP happens after TDC. There is a general consensus that the optimum EFFECTIVE timing is at 15-16 dATDC. This is the point where the peak of the pressure curve is best placed to gain maximum mechanical advantage with the crank-conrod geometry. UNless the EI system altering timing is MEASURING the thetaPP in real time, it is necessary to use a map to guestimate the optimal timing. Frankly, this is only marginally successful. There are three ways the pilot can affect the thetaPP. RPM, MP and MIXTURE.

A slower RPM moves the thetaPP closer to TDC.
A higher MP moves the thetaPP closer to TDC.

The maximum flame speed is seen at 40dF ROP. For any given MP and RPM, 40dF ROP will result int he highest pressures and CHTs. Richer slows the burn rate a little. A LOT richer slows the burn rate more significantly. This is why we want a very rich mixture during takeoff and high-power climb. LOP mixture slow the burn rate as well and lowwer CHT and ICP as a result. This is accomplished by moving the thetaPP.

***** OWT ALERT ******

Extra fuel ROP does not cool the CHT. Extra air LOP does not cool the CHT. The CHT is altered based on the movement of the thetaPP and the resultant lower ICP which affects the rate at which BTUs are transfered across the thermal boundary layer and pushed into the cylinder head metal.

Walter Atkinson
Advanced Pilot Seminars
 
So what timing do we use?

Walter Atkinson said:
There are two issues concerning timing that must be considered when operating your engine.

A slower RPM moves the thetaPP closer to TDC.
A higher MP moves the thetaPP closer to TDC.

Extra fuel ROP does not cool the CHT.

Walter Atkinson Advanced Pilot Seminars
Click to expand...
Walter I assume lower RPM means less power, and than its correct, you can advance the timing. However you should consider MAP and RPM when talking timing, because that is power. RPM alone is not power. What do we do with this INFO?

Are you saying NOT to follow Lyc's 25 BTDC spec? In one flight we are at both high power and low power. So what do you suggest? We can't change timing in flight with a magneto. Also many of us experimentals run EI with timing that advances automatically. EI looks at MAP/RPM to control timing, not just RPM by the way. (E/P-mag has a very conservative advance option on RPM only, however most opt for the MAP sensor. All other EI use RPM/MAP only.)

Walter 25 BTDC is from certification and detonation margins. I know you have made statements that Lycoming does not know what you do. Have you done a detonation survey on a Lycoming? As you know if the power it too high and timing advanced too much, detonation WILL occur. In severe cases (pre-ignition) will happen. I recall you think detonation is OK. It may be at 45% power. At 100% power you will destroy the engine. So when you post your alternate procedures and specs, may be you could be more spacific. You throw out a fact that is correct, but don't put into context. Thanks

I would recommend to follow Lycs timing specs or use a EI you trust. If you don't believe me call Lyc customer support. I would be careful about timing advance past 25 BTDC on RPM only or at high power. Also you are vague and don't specify POWER and degrees timing. Anyone who knows engines know about timing, but what can we do with this info? We either have fixed mag timing or timing controlled by the EI.

CHT?
Again you are trying to campaign LOP operations and your Seminars, which I think is great that you are giving us your info for free. However extra fuel DOES lower egt and thus CHT. This is not a guess this comes from the Power charts Lycoming publishes.

It may be true that CHT is cooler at LOP side than the ROP side for the same EGT, (you say 40F). What differnce does it make if you are already at a cool CHT, say 360F. As long as you are below 400F CHT you are good to go. Walter you may not know Lycs and RV's but we in general don't have a CHT issue. When builders do LOP operations would not be the answer to the problem, in my opinion. CHT is not a big deal ROP and LOP. It does not really matter, but you are right, you can run cooler CHT's at LOP. Great if you can get to it with a 4-cylinder Lyc, some can, some can't. For those who can't it is OK, run ROP.

I (Lycoming) don't recommend 40F ROP ever unless below 65% power. 100F ROP is good. Not till you get below 65% power would I lean to 40F ROP. At 65% power CHT should not be an issue. You can run Peak EGT, but I don't unless down 55% power. By then your CHT is very low in a RV with a Lycoming, so LOP or ROP is a moot point when it comes to CHT.

Most RV's do not have a problem with CHT, but appreciate your info. RV's with high CHT can't be fixed with LOP operations. Do you agree Walter? I would like it if you would give Lycoming spacific data, such as % power and timing advance when you talk about LOP operations. Thanks
 
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George:

**Walter I assume lower RPM means less power, and than its correct,\**

Well, that's not all-together true. As you implied, when ROP, power (Hp) is controlled by mass airflow. RPM is *part* of that, but not ALL of it. When LOP, only FF has ANY effect on Hp being produced.. That is quite a realization for most. RPM/MP have no effect!

**Are you saying NOT to follow Lyc's 25 BTDC spec?**

No. Never said that.

**EI looks at MAP/RPM to control timing**

Yes. They do that because they cannot measure what they really NEED to measure and that is ICP and ThetaPP. So, they estimate and calculate the desired results and adjust accordingly based on some assumptions. This *can* work OK, but may be sub-optimal. Their *estimated* timing selections based on MP and RPM are necessarily incorrect when LOP. It may be, but I'm not convinced that their timing map ROP is optimal either.

** I know you have made statements that Lycoming does not know what you do.**

I have not said that. I do know that I have seen some data that they cannot have seen simply because there is only one place on this planet where it can be seen on their engine and they have not yet accepted our invitation to come see it.

** Have you done a detonation surveys on a Lycoming?**

Yes. extensively. We probably have more Lycoming detonation experience than anyone. Lycomings tend to be more prone to detonation than TCM engines. Your assumption that detonation is less harmful at low power than at high power is not shared by me.

**I would recommend to follow Lycs timing specs or use a EI you trust. **

I AGREE. Lycoming's engineering data is good and their timing recommendations are solid. I am far less comfortable with mapping that does not MEASURE the parameter that is the important parameter in detonation--ICP.

** extra fuel DOES lower egt and thus CHT. **

Well, no, but sorta, not really! The heat of vaporization of extra fuel in a rich mixture has so little effect on CHT as to make it a non-issue. CHT is reduced because the slowing of the burn rate from the richer mixture retards the EFFECTIVE timing (makes the thetaPP later). That results in lower ICP and less BTUs being forced across the thermal boundary layer and into the head metal. Please let me know if I need to further define EFFECTIVE timing. We must be on the same page there or there will likely be misunderstanding.

**What differnce does it make if you are already at a cool CHT, say 360F.**

Excellent question. It can matter. The ICP can still be high, even with low CHTs. Take the boundary condition of a not rich enough mixture on takeoff out of Barrow, AK. You can destroy the engine and still have very low CHTs.

**As long as you are below 400F CHT you are good to go**

I don't disagree, but we kinda like 380 as a max operational CHT. No real argument, though.

I have nothing against ROP opertaion. I recommend it when appropriate. I know from detailed research that we as pilots have tended not to run rich enough when we run ROP at power settings above around 60-65%. If you run ROP, get rich enough--how much richer depends on the power setting.

**RV's with high CHT can't fix that with LOP operations.**

CORRECT. That is a baffle issue. It should be corrected.

George, with all due repsect, in less than 48 hours, you've put a lot of words into my mouth that not only did I not say, but with which I disagree. These are interesting topics worthy of factual discussion. If I am less than clear, please ask for clarification, but please do not put words into my mouth. I can screw that up on my own with no help at all! :)

Walter
 
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ThetaPP

fodrv7 said:
Forgive me Walter.
What is ThetaPP.

Pete.
Click to expand...

Pete, it would be more understandable as Theta PP, and it's the angle (Theta) from Top Dead Centre (TDC) at which Peak Pressure (PP) occurs: ie peak Internal Combustion Pressure (ICP). Optimally, to get the best mechanical advantage at the crankshaft Theta PP should be around 16 degrees after TDC.
 
No words, just questions

Walter Atkinson said:
George, with all due respect, in less than 48 hours, you've put a lot of words into my mouth. Walter
Click to expand...
No offense I am just asking questions Walter, not putting words in your mouth; trying to fill in the gaps between what you did say. No need to be adversarial.

Q: How do you measure ICP (in a plane)?
(I looked for the ICP gauge on the panel and missed it. :D All we have Walter is RPM/MAP in the cockpit to determine power in an ATMO engined plane, in the plane, not a test cell. Let's keep it practical and relevant to flying not the lab.)

Comment: You are correct we don't agree about leaning at high power.

Q: So to be clear, you say you can't detonate an engine at high power (ICP) and lean mixture? (not sure just asking)

My answer: You can damage and engine with aggressive leaning at high power (over 75% pwr) and you will not even know it. An engine monitor will not tell you. We agree to disagree. I have seen burned (detonation damage) pistons, and the Lyc engineer I talked to also agreed, excessive leaning at high power. This is echoed by John Schwaner, Sacramento Sky Ranch. May be I'm putting words in your mouth; you don't really give spacific power settings in your discussions. A lean mixture can burn so rapid (detonate) under the right conditions (high power), the boundry layer will be lost. Now Walter to be clear this takes nothing away from LOP if done properly. I am sold on LOP if done properly.

Thanks for the info. That's all I need. I have to figure out how to get my O-360-A1A EGT delta less than 50F. I'll try the crab heat and throttle closing idea you mentioned. Hope it works. I'll let you know.

BTW: A Lycoming rep. has been to your seminar, I know I talked to the guy on Friday and he mentioned it. You say you have data that Lycoming does not have! Cool what kind of data is that. I thought Lycoming had test cels and state-O-art instruments. I would like to know what you have, can you share? Is it a ICP transducer? Sounds like interesting testing.
 
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<<No is no need to be adveserial Walter.>>

??

<<Q: How do you measure ICP?>>

Pressure transducer in the cylinders. On a highly-instrumented engine test stand in a labratory. The 1,000+ who have been through the APS classes have seen it. It's impressive.
 
For a bit more info on the engine test facility, here's a link.

http://engineteststand.com/

In particular, the link on that page about Carl Goulet is interesting.

The data graphs are difficult for me to understand, and I only get it when one of the gurus there takes the time to explain what each of the lines/graphs/numbers is measuring.

It is state of the art. I would not be surprised if this is the finest aircraft piston engine test facility in the world.

As a result, they are discovering many things which contradict what has long been held as truth. That's why, in my view, there are very few engineers -- no matter who they work for (Lycoming or TCM) who really understand this stuff.

As for looking for the ICP gauge on the panel, that's a good question, and leads to a concept worth understanding. No, there is no ICP gauge . . . yet. I have seen one, and it is elegant.

But (and this is critical), through education, we use surrogate gauges. If you know which engine settings and readings produce higher ICPs, you don't need an ICP gauge. You substitute.

For instance, we do the same thing every day, using the EGT as a way to set up the engine. We don't really care what the EGT is for its own sake The actual number means nothing. We are concerned with CHT, but cylinder head temperature changes slowly. EGT readings react quickly.

So, we substitute. We perform engine management via EGT (because it reacts quickly), using the knowledge we have that a certain EGT will generate a certain CHT.

Once we set the engine up with the EGT (ROP or LOP), we then monitor the CHTs to make sure we are getting what we want for the really important parameter.

When a pilot understands the correlation and connection between EGT, CHT, ICP, Theta PP, what detonation and pre-ignition really are (rarely understood by pilots or mechanics and many engineers), and perhaps most importantly, how to interpret engine problems through the engine monitor, the pilot can operate the engine safely through a much wider range of options.

A quick example. This week I will replace the spark plug in the number six cylinder, running off the left mag. It checks perfectly during a ground runup. It fails, however, during an in-flight, LOP, mag check. I know what to look for, and it tells me this spark plug is on its way to failure.

Also, you can spot a leaking exhaust valve with the engine monitor, if you know what to look for. We are not using an exhaust valve gauge, but substituting something else.

I'm not an engineer, nor a mechanic. Walter (though he may not tell you) is an A&P and has a ton of ratings, including ATP, CFII, and experience in a lot of interesting planes.

One does need the proper equipment (engine monitor) and knowledge. I have flown LOP at wide open throttle for every minute of cruise over the last 7 years. I average about 300 flight hours a year. Most of those flights have seen the engine running at 85% power for the entire flight.

I do like to fly fast, save fuel, and be kind to the engine. I'm doing all three.
 
85% ???

"I have flown LOP at wide open throttle for every minute of cruise over the last 7 years. I average about 300 flight hours a year. Most of those flights have seen the engine running at 85%"

Tom,

Is that a typo???

John
 
John: I'm guessing you are asking if running at 85% power is a typo.

No. I typically run the engine at 81% to 88% power. My typical flight is 4 hours, but sometimes 6 hours before fueling.

Note, that I fly a turbonormalized engine, so I can maintain 30 inches MAP. Otherwise, I would not be able to run at these settings.

CHTs are usually 320 to 350 degrees F. This can only be done with a well-setup engine, a multi-cylinder engine monitor, and knowing what you are doing. The internal cylinder pressures are low. The CHTs are low. The mechanical advantage (angle of crank/conrod/etc.) is close to optimal.

In reality, it's a procedure which reduces pilot workload. Pretty much "set and forget" mode.

(I should note, also, that even with this turbonormalized engine, I could not keep up with the two Harmon Rockets I flew formation with in Sedona last spring. Watch for the video on TV this summer. Those suckers are FAST!)
 
85% ???

Tom,

I thought that LOP was only recommended below 65% power? What kind of work do you do with the t-bone? What a cool machine!

John
 
John:

LOP is not limited to running below 65% power. What is commonly said, and is true, is that below 65% power (really, it's 60% based on more recent data), you can set the mixture anywhere you want, and there is little or no chance of harming the engine.

Above that power setting, you need to know what you are doing. As power increases, you need to run the engine either farther LOP, or farther ROP. Either is okay, but you don't want to be where (unfortunately) many POHs recommend -- 25 to 50d ROP. I usually run at 70 to 100d LOP.

My T-Bone is normally aspirated, so I can't get these numbers in it.

I run these power settings in a turbonormalized A36 Bonanza. That's what I was flying formation in.

We were shooting high definition video of the RV-8s in front of the red rocks at Sedona, on a beautiful winter morning. It will run on the weekly TV series Wings To Adventure, on The Outdoor Channel. Beautiful planes. If only I didn't have to carry so much stuff!
 
Beautiful Sounds

Tom,

When I wasa kid in San Diego, a Twin Bonanza used to take off every weekday evening from Montgomery Field carrying bank checks to LA. What a wonderful sound! Second only to the Mallard that would come in two or three time a month.

OK, so the 85% is WOT at about 5500 feet. Why do you cruise so low, at such high powersettings? Not trying to be argumentative, I just can't picture it!

John
 
John:

It probably was a typo. I think he meant 87% power, not 85%. We fly the same engine and aircraft types.

For the last eight or so years, at a rate of over 300 hours per year, I've been operating my engines at 87-90% power in cruise as a matter of routine. It's a 300 Hp TNIO-550. I generally have my engine producing between 260 and 270 Hp in cruise with CHTs under 370 (yep, I have a very good baffle set-up based on the data gathered from about five years of intensive research into baffle design).

There are several hundred of these engines being routinely operated in this manner with outstanding success.

Here's a measured data FACT that might surprise you.

Tom and I, along with the hundreds of others who are doing this are doing so with the engine operating under less stress than someone who is operating their engine at 75% power according to the OEM's mixture recommendations.

About four years ago, we had one of these engines that had been operated this way since the breakin and at 1000 hours with nary a jug pulled, the engine was disassembled and inspected by an independent shop. Their first question was why were we asking for a tear-down on an engine that appeared to have less than 100 hours and second, the report was that the engine was still within NEW limits. Not Service limits; NEW limits. The engine was then reassembled and run about 200 hours past TBO with no further issues.

Walter
 
John, I do not fly the T-Bone at 85% power.

I do fly my Bonanza that way, and I go high for most flights.

The plane likes it (as do I) in the mid to high teens. 16,000 and 17,000 feet are great. No one is there. I'm doing 200 knots TAS running 70d LOP, with almost 7 hours of range. It's cool, smooth, and quiet up there.

The T-Bone is for carrying more folks, making cool sounds, and having fun.

It's also for sale. <grin>
 
85% power at LOP

Tom and Walter,

Those are incredible claims. I am impressed. But is this not contrary to your earlier posts on max power output for LOP? What do you figure you detonation margin is at these power settings?

John
 
"Those are incredible claims."

Not really. Just everyday fact, and quite common and accepted by those running the TN Bonanzas. I'd be happy to take you up in the plane to see how it's done. It will become even more common when the turbonomalizing system is ready for the Cirrrus.

I'm sorry, but I don't remember saying anything about max power settings LOP.

Detonation margin: I better let Walter handle that one, but it's one of the reasons why we run FAR LOP at these power settings.

The operating procedures for these engines is interesting, but a bit too long to post here. For those who want to see how it works: http://www.taturbo.com and click on "Turbo Operation."

Note that the HP figures (derived from fuel flow) are specific to the compression ratio of the IO-520/550 engines (8.5:1). It is different for other compression ratios.

And, at this point, I'm on the ragged edge of my knowledge/understanding of mechanical/engineering stuff. Walter will correct my mistakes, I hope.
 
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George:

**Q: How do you measure ICP (in a plane)?

It should not be far off that such a gauge will be available. I'm doing the flight tests for such an instruemnt in five days. It's not really necessary, though. If one has a thorough understanding of the "Five Landmarks to Understanding Piston Engine Management" and their relationships, you do have the proper instrumentation already available. If one cannot draw reasonable reproductions of a mixture sweep set of curves from full rich to idle cutoff of EGT, CHT, ICP, HP, and BSFC from memory, this discussion will be rather perplexing and possibly at an impass.

**Q: So to be clear, you say you can't detonate an engine at high power (ICP) and lean mixture? (not sure just asking)**

The assumption that high ICP equates to high Hp is mistaken. (There are those pesky five Landmarks and their relationships again.) MEAN pressure relates to torque which relates to Hp. Peak Pressure relates to durability, not Hp. Your misuse of the term "lean mixture" is the problem here. LEAN mixtures are almost impossible to make detonate. Not-rich-enough ROP mixturesc can detonate easily. Remember in an earlier post I said that the most detonation-prone mixture was 40dF ROP? That's not a lean mixture. (See below for more explanation on the misuse of this terminology.)

**You can damage and engine with aggressive leaning at high power (over 75% pwr) and you will not even know it. An engine monitor will not tell you.**

The DATA does not agree. I have spent the last years dissecting a LOT of engine monitor data for a lot of pilots and mechanics and detonation and pre-ignition DO show up on an engine monitor. You DO know it--if you know what you're looking at.

Let me throw you another curve. I've made several flights where the mixture NEVER got ROP at all. We took off at full rated power, LOP and made the entire 4 hour flight never being ROP--ever. These wereproof-of-concept test flights to prove that a Full Time Lean Run engine (FTLR engine) is possible and actually desirable. FF at takeoff to produce 300 HP is 20.1 gph. Be aware that telling someone that something is impossible when he's already doing it successfully can result in later embarrassment and crow-eating. (BTW, I've eaten enough crow as I've learned from the data that I can tell you, it tastes a lot like Spotted Owl.)

**I have seen burned (detonation damage) pistons, and the Lyc engineer I talked to also agreed, excessive leaning at high power.**

That is a common mistake... again based on the real data, detonation has been erroneously blamed for this destruction for decades.

**A lean mixture can burn so rapid (detonate) under the right conditions (high power), the boundry layer will be lost.**

That is absolutley incorrect. You may be calling a rich mixture that is not rich enough, a *lean* mixture. If THAT is what you are saying, then, OK, but that is a bad terminology. 50dF ROP is not a lean mixture. It is a rich mixture that is not rich enough at high power. A LEAN mixture is a mixture that is lean of peak EGT only. There are no lean mixtures ROP. It is very, very, very difficult to get a LEAN of PEAK mixture to detonate. It is very EASY to get a not-rich-enough ROP mixture to detonate. Please do yourself a favor and look at the entire mixture sweep curves of CHT and ICP. You will quickly identify your misunderstanding due to the improper use of the terminology. Not-rich-enough (?leaned?) ROP mixtures are VERY prone to detonation.

** I thought Lycoming had test cels and state-O-art instruments. **

In 1960, maybe. Not when compared to the Carl Goulet Memorial Engine Test Facility.

Walter
 
John:

By measured data, the detonation margin at 90% power at 70-80dF LOP is significantly wider than it is at takeoff power, full rich. It's simply not an issue worth wasting a lot of bandwidth over.

Here's the bad part. This has been clearly understood for over 50 years. It got lost when the flat engines wouldn't run smoothly LOP and we quit running engines LOP as SOP.

A friend of mine, 100 year old Captain John Miller said in 2003, "I bought my first Jenny in 1928. I've run every piston engine I've ever operated LOP since." He retired from the airlines in the sixties and he flew his own Bonanza into OSH in 2003--solo, at age 97--and LOP! He operated the TC-18 variant of the R3350 for 80,000 hours, LOP. That's 20,000 hours, four of 'em at a time! The guy is no neophyte.

(The only thing I've flown four at a time has been the two-speed blowered, turbosupercharged 1830s on the B-24 bomber. I've wrenched on the B-29, but not yet flown it. I'm a piker compared to Captain Miller. I'm just a lowly ATP, S&MEL&S; CFII, MEI; and A&P who taught myself how to fly helicopters and has flown 58 different types of aircraft from J-3s to the DC-3, C-46, and B-24. I'm a bozo. John Miller is the real thing. However changing an R-2800 with one other guy on the C-46 might qualify me to say something about big engines. They are a pain in the butt. <g>)

Walter
 
TCM Warranty Policy

Walter,

Couldn't help myself.....I called a Continental Tech Rep. He was absolutely incredulous when I mentioned those power settings. Didn't mention anybody's name, but did tell him it was GAMI injector equipped. Here's what he said:

1. GAMI has a good product, BUT.......
2. At least one set of cylinders come to him every day for warrany, 7 of 10 are from a GAMI equipped engine.
3. Exhaust valve failures are the most common complaint, bore and ring problems second. Described cylinders as "burnt up"
4. He said the first thing he tells them is "Go see GAMI for your warranty". Doesn't ruleout warrany, but it places the burden of proof on the customer to prove operational techniques didn't cause the problem.
5. He said, in no uncertain terms that LOP produces less power, slower airspeeds, and if done below 65% probably causes no harm. He thought improper operation, dirty injectors, bad plugs or mag timing and ill-maintained injection pressures were the cause of cylinder failures.

He also said detonation is very rare in Continental engines.

A very interesting conversation. I love this stuff!

John
 
John:

LOL! This always happens. It's predictable. I was wondering how long it was gonna take for the "this is what a TCM Rep told me" post to show up.

I know the VP of Customer Service at TCM. He attended the APS class. We were on a common program not long ago and he agreed with everything I said that day and said so aloud, to the group of Lancair Pilots. It would be very helpful to him if you could give me the name of the Tech Rep who is giving such absurdly incorrect infomation. That TCM tech rep knows less about this than the members of this forum. He shoul hang out here and learn something. To wit:

**2. At least one set of cylinders come to him every day for warrany, 7 of 10 are from a GAMI equipped engine.**

Well, there are 16,000+ sets of GAMIjectors out there and there are one heck of a lot of TCM engines with Valve Disease from poor QC. They fail no matter how they are operated. Besides, if that's the case, why is TCM now selling their own copies of GAMIjectors calling them "tuned injectors?" And how does he explain the TCM TSIO-520BE which is PROHIBITED from being operated ROP in cruise? ONLY LOP on the TCM TSIO-520BE--by LIMITATION.

**3. Exhaust valve failures are the most common complaint, bore and ring problems second. Described cylinders as "burnt up"**

TRUE. From poor manufacturing techniques. This all started the first week of Feb., 1991. They *say* they have fixed it, and I'm hopeful, but the early data is not encouraging.

**4. He said the first thing he tells them is "Go see GAMI for your warranty". Doesn't ruleout warrany, but it places the burden of proof on the customer to prove operational techniques didn't cause the problem.**

Respectfully, if his boss finds out he said that, he will be selling French Fries.

**5. He said, in no uncertain terms that LOP produces less power, slower airspeeds, and if done below 65% probably causes no harm. He thought improper operation, dirty injectors, bad plugs or mag timing and ill-maintained injection pressures were the cause of cylinder failures.**

[snip]You would probably, by now, guess that each of those [snip] statements can be refuted with data. It can. I don't have the time. I go faster LOP! 90% power, LOP is faster than 75% ROP-- on less fuel! He's got some holes in his understanding. Besides, none of what he listed has anything to do with mixture management! [snip] Quickly, one at a time:

improper operation -- yep, being not rich enough ROP will ruin one.

dirty injectors-- Yep, that has nothing to do with mixture technique except that a partially plugged injector LOP cause LESS harm! ROP it can induce detonation from being not rich enough.

bad plugs-- yep. nothing to do with mixture.

mag timing-- yep, nothing to do with mixture.

ill-maintained injection pressures-- yep, nothing to do with mixture.

**He also said detonation is very rare in Continental engines.**

That is true for the NA TCM engines. Almost can't make 'em detonate as long as the engine is conforming, the timing correct, and the fuel is of the proper octane. On the TC'd engines, they, too are hard to make detonate, but a determined pilot can screw one up!

This is sooooo funny. I'f seen that same post crop up on at least a dozen other forums and in every case, it gets debunked as just, plain, uninformed drivel--most recently by the VP of Customer Service at TCM! [snip]
Walter
 
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TCM Warranty

Won't give you his name, nor did I give him yours. I talked to him about 2 hours ago, and I can prove it prove it if necessary. The conversation was based on your claim of 87% power operation, not 65% LOP.....I think I made that clear in my earlier post.

As I previously stated, he didn't criticize the GAMI product, only stated that misapplication of LOP procedures and inadequate maintenance were at fault in many warrany claims. He didn't deny qc problems at TCM, and said that many cylinder claims were ultimately paid, inspite of questionable ops.

I know there were some valve manufacturing problems, and I think some of their older cylinders are soft, but both are certainly aggrevated by questionable procedures.

John

John
 
LOP %Power

I hope that I am not diverting this thread, but I am trying to understand how to determine % power when all of the operating variables are known: MAP, RPM and Fuel Flow. None of the Lycoming curves supplied with my engine (O-360-A1A w/AFP fuel injection) show the relationship of all three.

Put another way: If I want to run at 75% power, at 50F LOP, what combination of MAP, FF and RPM would give me that?

OR​

If I know that at 24"/2400, 8.0 GPH results in 50F LOP, What % power am I getting?

Are there curves or spreadsheets available that gives this information?

Ben Beaird
Plymouth, WI
-6A Flying 140 hrs
 
Ben:

If you are LOP, only fuel flow matters.

If your engine has 8.5:1 compression pistons, use the number of 14.9 as your multiplier.

14.9 times the fuel flow, in gallons per hour, gives you the horsepower.

Divide that HP number by the rated horsepower of your engine, and you have the percentage.

For instance, if your fuel flow was 8gph, in a 200-HP engine, you would be at 59.6 percent power. ONLY if running LOP.
 
Ben:

When ROP, Hp is affected only by mass airflow. Large changes in Fuel flow have very little effect on the Hp generated.

When ROP, the formula for estimating the % Hp is:

100 - ((max RPM/100)-(RPM/100) * 2.5) + ((max MP - MP) * 3.5) = %Hp

Notice there is no fuel flow part of that equation. Only RPM & MP.


When LOP, the formula for estimating the % Hp is:

CR constant * Fuel flow = Hp produced
further: Hp produced/rated Hp = % power

Notice that MP and RPM play no part.

The CR constant is determined by the BSFC(min) of the engine. That is primarily determined by the compression ratio. For example, the multiplier for a standard NA TCM engine with 8.5:1 CR is 14.9. For the 7.5:1 CR engines, the mulitplier is 13.75. It's not linear and I do not have a chart for all of the possible values. I'm disinclined to calculate them all just for this post! I hope you understand.

Walter
 
Lop %hp

Thank you Walter & Tom. I think I understand. Although it's not intuitive.

If I establish a LOP fuel flow, when I want more speed (power) and add MAP &/or RPM to get it, it's not those parameters that is increasing power but only the resultant increase in fuel flow that comes with an increased MAP or increased RPM.

Is this correct?

Ben Beaird
Plymouth, WI
-6A 140hrs
 
max map

Walter, thanks for all the information. I don't have the Lycoming 0320 manual with me. Where do I find the Max MAP for a Lycoming 0320 160 HP. Playing with the data I have at home, I am backing out 29.4 inHg. Is that anywhere close? Thank again, John.
 
Walter Atkinson said:
100 - ((max RPM/100)-(RPM/100) * 2.5) + ((max MP - MP) * 3.5) = %Hp
Click to expand...

How is "max MP" defined? Max available MP at sea level? Sea level pressure? Units in inches of Hg, I presume, or millibars?


...NA TCM engine with 8.5:1 CR is 14.9. For the 7.5:1 CR engines, the mulitplier is 13.75. It's not linear and I do not have a chart for all of the possible values. I'm disinclined to calculate them all just for this post! I hope you understand.
Click to expand...
I completely understand. However... :rolleyes: Is there a reasonable formula that we can play with?
 
LOP %HP Spreadsheet

I just developed a simple Excel spreadsheet. I'd insert it if I new how.

If I understand correctly, for any LOP fuel flow the HP is equal to 14.9 (for 8.5:1 compression ratio) times the GPH. The result divided by the rated HP (180 in my case) gives the %power.

By crude extrapolation, I would guess the multiplier for a 9:1 engine would be around 15.7.

Ben Beaird
 
Compare to Lyc chart...

Interesting Stuff! I just pulled out my favorite chart from the Lycoming O-360 Manual - Figure 3-34 "Fuel Flow vs Percent Rated Power". It's my favorite for two reasons - One, I can actually read it, and Two, it has only a single line, so I can understand it! :p

There are two things I note that are relavent to the discussion:

1) The line is basically linear from 45% to 73% power - then the shape gets wild! I am sure that some young math whizzes could curve-fit it to an equation, but I'm interested in the low end for now anyway...

2) When I calculate this line from the equation Fuel Flow x 14.9 = Power, I find that for any given % power, the Fuel flow from the equation is a consistant 0.2 gph below the line on the chart. I guess this tells me that I can beat Lycoming's recomended minimum fuel flow by that amount if I run LOP.

This is really interesting to me, because when I lean by ear, with reference to my EGT's, I have found that when everything settles out, I do run just a little below the chart value and the engine is running nice. This is a carburated O-360-A1A.

What is also interesting is that in the Lycoming table, the non-linear shape of the curve is ABOVE a straight-line equation value at higher power settings, yet the linear equation given above is going to keep the same slope, so the delta between the table and the equation is going to be higher (actually by a lot!) at power settings above 75%.

I'm not making any claims or drawing real-world conclusions, just making observatioons from the equations and the table. I find this discussion fascinating, because it seems to confirm what I am seeing with my engine. I'm still not sure I am daring enough to try leaning the carbed engine that much at power above 75% - but then I always fly x-country above 8,000' anyway, so I guess it isn't an issue - right?

Walter, if you've got any insights on this, I'd be happy to learn more - thanks for your contributions so far!

Paul
 
Paul:

The most important thing in your post is that above 8000 feet, it doesn't matter what you do. That's absolutely true.

As far as the Lycoming chart is concerned, these are of limited value unless they state what the mixture is for the data points. Sometimes they do that and sometimes they leave that off. Based on your report and based on what I know to be Lycoming's historical recommendations, I'm guessing that chart is using peak EGT as the reference mixture. No way to know for sure, though, unless it's SAYS so. Some charts wil b based on Best Power. For example Beech used 25dF ROP as their reference. Why in the world they deicided on that is a puzzlement!

(head-shaking mode)

Walter
 
Effective timing and EI

Walter

An earlier question reposted. My, and many other EI systems provide for up to 40 degrees advance at high RPM and low manifold pressure. The question is, would you expect the optimal LOP mixture (to realize the optimal theta PP) to be shifted farther into lean territory, say 50 to 100 degrees LOP or would it stay close to the 10 degree LOP figure often sited?

I am inclined to guess I should run a bit further LOP, which would slightly retard the effective timing, putting theta PP at about the same point as a slightly LOP mixture and 25 degrees advance.

I mentioned large natural gas fired compressors in an earlier post. Part of the tune-up process involves setting the fuel air ratio. This is done by observing a combination of excess oxygen in the exhaust (up to 12 percent!) and real-time, graphic observation of combustion pressures versus crank position on a laptop. Some of these engines are relatively old designs being pushed to work harder and cleaner so it is pretty critical that peak ICPs and theta PP are as prescribed. 12 inch bores and low speed so detonation is also a real possibility if we miss the mark. When running 3000 hp, missing the mark also costs a signifcant amount of fuel. Thought you might be interested in another application of the same "technology".

Duane Zavadil
N678BT
 
Duane:

Whooooee, you're rigth! Those slow speed, high pressure engines are a bear to control AND maintain emissions goals You're always on the ragged edge and when one of those goes, I'll bet it's quite a show.

As for your other question, it's impossible to guess without measuring where that map is placing the theta PP for real. I just don't know and any guess I would have would be a WAG, but you have all of the right ideas. The proof of the pudding would be the CHT change. That's the probelm I have with timing maps. They are an educated guess and do not take mixture, the BIGGEST factor, into adequate account as far as I can tell.

I just don't have a clue what the answer to your question is without measuring it. Sorry. The scary part is that I don't think the people who drew the map have any better idea than I do. As far as I know, they haven't run these on a pressure-transducer equipped test stand.

From my perspective, this is an important question that needs an answer. As a matter of fact, it's not the only important question on the subject of EIs that is still unanswered.
 
Experimental Vs. Beech Bonanza

Walter Atkinson said:
I have seen some data that they cannot have seen simply because there is only one place on this planet where it can be seen on their engine and they have not yet accepted our invitation to come see it.
Click to expand...
That's interesting, because when I talked to Lycoming on Fri that was exactly the same thing they said. Apparently you have an invitation to see their data, you don't have, but, as I was told, you do not want to see their data. I am just the messenger.

Walter Atkinson said:
**Q: How do you measure ICP (in a plane)?

not be far off....such a gauge (ICP) will be available....flight tests for such an instrument in five days. It's not really necessary, though.....thorough understanding of the "Five Landmarks to Understanding Piston Eng Mngmt" & their relationships, you have proper instrumentation already. If one cannot draw reasonable reproductions of a mixture sweep set of curves from full rich to idle cutoff of EGT, CHT, ICP, HP, and BSFC from memory, this discussion will be rather perplexing and possibly at an impass.
Click to expand...
Walter try me. I have a masters in engineering , built engines and flown pistons for years. I like to try. Teach me to draw a "reasonable reproductions of a mixture sweep set of curves from full rich to idle cutoff". I'm your student. Please share, I'm genuinely interested. I'm just a dumb pilot now, but like you said, you don't think pilots are too stupid to figure it out.

BTW, measuring ICP, that was a rhetorical Q. What can a PILOT do with ICP. Ans: Nothing. Your point, ICP measurement is not available via a gauge but can indirectly be estimated. Agreed, usually Lyc drivers est. ICP by percent power using MAP/RPM. By not leaning above 75% we get a margin to detonation.

FYI: real time ICP has been available for some time: http://www.tfxengine.com/hardware3.html

In old days of airlines, pilot's where taught the fuel line diameter, but they realized years ago, it's not critical knowledge. What's important are repeatable procedures, that the pilot can use to keep an engine within limitations, for worst case scenario.


Walter Atkinson said:
I just don't have a clue what the answer to your question is without measuring it. Sorry. The scary part is that I don't think the people who drew the map have any better idea than I do. As far as I know, they haven't run these on a pressure-transducer equipped test stand.
Click to expand...
That's the most eloquent statement you made to date, you don't know, w/ out measuring it. That's why we fly with "extra" margins provided by factory procedures? It's a safety net. How about you do "experimental" Lyc dyno tests with EI.


Walter, please, more details in your examples. A low compression radial is not a RV with a Lyc: high compression pistons, tight cowl, free flowing RAM air intake, low restriction exhaust and electronic ignition (w/ adv). A Bonanza is not universal. You Beech guys get excited about getting 18gsl/hr. RV's go faster on 1/2 the gas, so your data needs "normalizing" for RV builder/pilots. [snipped]

I'm protective of RV'ers. I am a professional instructor, and giving partial info "teases" concerns me. I appreciate theory, but everything I read, you offer no cautions, warnings or negatives. [snipped] Your detonation explanation omitted lean mixture as a prime reason for detonation. [snipped]

I am not anti-LOP, just pro safety. Tell the whole story or none. You keep talking about data but see no 4-banger data, 5-landmarks or mixture sweep curves. [snipped]

An alternative to LOP - FLY SLOWER, at lower power, ROP. There's nothing wrong w/ a little O235/O320/O360 RV, ROP with NO eng monitor. It works, simple, safe and fun. That's what RV'ing is. I see a culture clash w/ your teachings, more than technical ones.
 
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Impressive Post

Great post, George! Thank you for taking the time to point these things out. I think the perceptions of RV LOP are coming back toward the center.

John
 
**That's interesting, because when I talked to Lycoming on Fri that was exactly the same thing they said. Apparently you have an invitation to see their data, you don't have, but, as I was told, you do not want to see their data. **

Hmm? I'd love to see it. NO ONE from Lycoming has offered that to me. Let me know who this is so I can contact him. The only folks I have had conversations with were the new head of engineering and the new VP and the chief engineer. We had a meeting at OSH last year.

It's important to give Lycoming a break here. They've been pretty covered up with their crankshaft issues and this is VERY low on their priority list.

I've seen a lot of Lycoming's data. It's a shame that their verbal recommendations are not in harmony with their own data.

**Teach me to draw a "reasonable reproductions of a mixture sweep set of curves from full rich to idle cutoff". I'm your student. Please share, I'm genuinely interested. I'm just a dumb pilot now, but like you said, you don't think pilots are too stupid to figure it out.**

Oh, they're not dumb at all. We've taught over a thousand students to draw those graphs from memory and understand the relationships between them. Go to <http://www.advancedpilot.com> and go to the TECH page. Download the articles by John Deakin. The Landmarks Graphs are in that material. One could also get all of the detailed explanations of same from the Online course offered at the same website. Four of the five traces are directly from TCM, Wright, P&W, and Lycoming data. The trace that is missing is the ICP trace. That info was generated from The Carl Goulet Memorial Engine Test Facility. Others have not published that data if they have it.

** I just wanted to know what a PILOT can do with ICP. Ans: Nothing. Your point, ICP measurement, not available via a gauge, can indirectly be estimated. Agreed, usually Lyc drivers est. ICP by percent power using MAP/RPM. By not leaning above 75% we give ourselves a margin to detonation. **

That statement indicates a lack of appreciation of the distinction between MEAN pressure and PEAK pressure.

**FYI: real time ICP has been available for some time: http://www.tfxengine.com/hardware3.html**

Yes. It's been very expensive, not viable for large scale commercial purposes, and only until recently has the sample rate been such that really good detonation measurements at very high sample rates have been available.

**That's why we fly with "extra" margins provided by factory procedures? It's a safety net.**

And a very poor net it is. The factory recommendations do not result in "extra margins" like one might assume.

Your assumption that all of the top-level knowledge is found within RV efficianados is admirable, but it may not be as accurate as you think it is. While the RV crowd is trying a lot of new things, some of it is truly experimental with little hard data to back it up.

**Your detonation explanation omitted lean mixture as a prime reason for detonation. **

That's because LEAN mixtures are NOT a detonation risk. PERIOD. Please review the terminology I detailed earlier. LOP mixtures have wider detonation margins than ROP mixtures. PERIOD. I fear you are misusing the terminology. I already tried to clear that up. I guess you missed that post.

**I guess I've got to take your course?**

No. But, it would help you clear the fog.

**FLY SLOWER, at lower power, ROP. **

That's an option. It has only one downside. Low power ROP is dirty. It fouls plugs and ring lands and leads to higher maintenance costs.

I tried to upload a copy of the Landmarks Chart, but it wouldn't go. If you will e-mail me directly, I'll be happy to send it to you.

Walter
 
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dmaib said:
Wow!! I always know that when gmcjetpilot chimes in, I am hearing from the smartest man on the planet!"
Click to expand...

Guys, give George (and others) a break, he is well read on all things aviation and when he does have on opinion he can AFAIK always back it up with one ore more references to 'solid' industry or research data. If you think he's never in doubt it is probably because he read something from Lycoming, Vans or NACA that he is repeating AND probably verified in practice.

It would appear that Walter is bringing some information that runs contrary to popular percieved understanding of engine operation. I have noticed that as Walter slowly gives us more and more detailed tidbits of data (and Doug makes threats :) the tone has changed from Walter being an idiot threatening the RV community with dangerous recommendations to one where he is being asked/begged to teach us what he knows...

chuck
 
Thanks will do

Walter Atkinson said:
I tried to upload a copy of the Landmarks Chart, but it wouldn't go. If you will e-mail me directly, I'll be happy to send it to you. Walter
Click to expand...
Yes agreed. Thanks Walter, will email you. Info will be appreciated.

I am just getting caught up on the GAMI site publications. I am re-reading George Braly;s back to the future articles. I just have to figure out where to mount those GAMI injectors in my O-360-A1A Lyc. :rolleyes:

The articles reinforce my opinion not all engines are cut out for LOP ops. I am OK with not operating LOP. I would like to, but if you can operate LOP it's a benifit. If I had a plane with a TCM TSIO-550, I would have the GAMI T-shirt, hat and key chain.

My only lament is I am committed to my Carb, because my MA-4-5 is all shiny, new. To switch to FI now in the hopes to improve my potential for LOP ops is just not financially justified (about $3000). However I am pleased to hear one RV'er got LOP operations with a carb 320 I think. As I said there may be some air box magic I can do to "control" or trim the balance between jugs along with slight closure of the throttle. However we have to fly the new engine first to see what going on.
 
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George:

I sent you the Landmarks chart by e-mail. Feel free to post it here. The Back to the Future articles were written quite few years ago and we have learned quite a bit since about improving the engines that first presented difficulties. The TCM IO-520WB on the Baron remains a tough one. We know why and how to fix it but the STC is a ways from getting done (other, more pressing isues). There are none of the Lycomings which are still unmanageable (as far as I know).

One issue is that TCM made a significant mistake in the intake plumbing design resulting in the occult transfer of fuel from cylinder to cylinder being fairly predictable, BUT the mistake is very consistent and makes most of them easy to address.

OTOH, Lycoming's intake plumbing and the occult transfer of fuel is not consistent from engine to engine and initially it made the answer to fix them more elusive. The answers are known and the fixes are known, but when George wrote the Back to the Future article, we were just starting to work on the Lycomings. That was a while ago.

Walter
 
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