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IO 360 M1B FF at T/O full power

As a data point I just went down this road with a Glasair II, Superior IO360/CS and silverhawk FI. Customer complained of high CHT during climb with associated higher than normal EGT's (1300 + T/O), FF in 14 GPH range, airplane had this issue since new.

The shop that checked the servo said it looked like it was flowed for a 320, after calibration customer can now do unrestricted climb, CHT down by 50 deg, FF in the 17 GPH range, EGT's in the low 1200's.

BINGO!!!!

This is EXACTLY what I suspect is happening. What is more i have found this exact same issue on an Avstar setup as well. It is only in recent times. If anyone cares to search my posts there are some other threads with this same comment.

Thanks a heap Walt...... some days it feels like being a solo pioneer :eek:
 
David
I recently purchased an RV6A Superior O 360 A1A C/S, Lasar Ignition, and I am having C/H temps of 420+ on take off. We have tried everything we can think of without success. Fuel flow seems the final option (14.5 GPH Full Throttle) , I need some advice on where to get the right info on diagnosing the problem. I live in Albury NSW.
 
Email sent :)

Unfortunately finding the right people is hard, closest to you is in Adelaide.

Call me as per email.
 
Just putting my datapoint out there.

2000 ft DA this past Saturday and I saw 16.8 gph
 
Follow up to this thread.

My concerns about recent delivery (last 2 years maybe??) engines having far too low a fuel flow are continuing to be proven. This is for Precission and Avstar by the way.

The last week or so I have seen similar results to those in this thread and when the FCU was removed and sent to Andrew Denyer at Riverina Airmotive in Adelaide, he found the flows low.

Once set to the correct flow, which is the upper end of a small tolerance, and reinstalled, the very next flight, all the flow, EGT and CHT numbers were exactly as I predicted.

You can't argue with the laws of physics, they apply equally to all men and machines (except the F22 :D).

So guys, if you have data showing anything different, get it fixed.

Happy to take questions or offer guidance if you think yours is affected by this.
 
Once set to the correct flow, which is the upper end of a small tolerance, and reinstalled, the very next flight, all the flow, EGT and CHT numbers were exactly as I predicted.

You can't argue with the laws of physics, they apply equally to all men and machines

Let's consider the physics. Enriching increases burn time, which moves the point of peak cylinder pressure some additional degrees after TDC, which in turn lowers CHT. Same effect (delay) for very rich or very lean.

David, I assume you have seen unedited GAMI data. When running the trusty 540 dyno mule, 100 additional degrees ROP moves peak pressure how many degrees?

BTW, just to be clear, I'm asking specifically about the 540 at WOT. We've already seen the generic school chart:

2hya421.jpg
 
Flying all day today and that will take a fair amount of time digging through some files. Remember in the several (maybe 10's) thousands of hours of dyno work, I have only a few to draw direct data from.

The next point is the engine, matters not. The fuel does not know who made the cylinder or piston. Which 540 do you want???? ;)

I gather you are actually wanting to know the Delta for an extra 100dF ROP from a properly set up Vs a not rich enough engine? If so I can probably just surf through some data and look for a sample close to that.
 
I gather you are actually wanting to know the Delta for an extra 100dF ROP from a properly set up Vs a not rich enough engine?

Yes. Let's illustrate the physics, the actual reasons why adding fuel lowers a problem CHT. Retarding peak pressure is one probable contributor, the question being how much contribution as compared to other factors.

The generic school chart doesn't indicate peak or stoich, and it is generic; not sure the values can be taken as specific values. Some actual data (F/A ratio vs pressure peak in degrees ATDC) from a cylinder similar to the majority of RV installs would be nice. Given it's the foundation of APS engine management philosophy...
 
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Retarding peak pressure is one probable contributor, the question being how much contribution as compared to other factors.

It is the retarding of the peak, that means a lower peak value that is the factor.

If you want some values I can pick some off the dyno run for illustration purposes. I am out of town again today...sorry for the delay!

Given it's the foundation of APS engine management philosophy...

No. It is the foundation of the science. Long before APS was around.
 
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OK, Just had some time to look at various engine runs and no this is not your IO360 or 320 in the majority of RV's but the science is the same. It was a 540 set to 30" though.

I did bit of interpolation and when it all boils down to it the spread from around full rich to say 75-100 ROP was in the order of a Delta thetaPP of 5 degrees, but most importantly the greater the degrees the bigger the effect as the volume is not directly proportional.

In other words the first 2.5 degrees of change with increasing mixture has an effect but the next 2.5 degrees has a much bigger effect.

The points of the data I used were at power settings (ROP and constant) and fuel flows that varied in the range of 15-20%.

I am refraining from issuing specific data points as all that will do is start a riot with arguments over this setting that setting this engine that engine. It matters not.

What it did demonstrate to me however the picture above is not just generic and is rather accurate! :)

Bottom line is this. If the full power fuel flow is not enough, fix it! :)
 
....the spread from around full rich to say 75-100 ROP was in the order of a Delta thetaPP of 5 degrees....

So, would it be fair to say that increasing fuel flow in the full rich but not-quite-rich-enough case would only retard thetaPP maybe two degrees at most? Interesting, but not unexpected. As you say, the school chart is pretty close; it says thetaPP response to mixture change is minimal on the rich side of peak, as compared to a significant response on the lean side.

I'd suggest other factors are more likely to be the root of the temperature reduction with mixture richness. Here's a chart from Taylor's "Internal Combustion.." The c and d curves are from NACA data circa start of WWII, mean combustion gas temperature at two measurement points. They're from two different papers, at different times. At the top I've translated F/Fc into more conventional labels.

It would appear that moving from stoichiometric to best power to full rich (15:1, 12.5:1, and 10.7:1) makes a very large difference in heat load applied to the head.

2m63hcm.jpg
 
So, would it be fair to say that increasing fuel flow in the full rich but not-quite-rich-enough case would only retard thetaPP maybe two degrees at most?

Dan, unless I am misunderstanding your statement, I suggest that in the case of where a mixture is ideal full rich at takeoff power and reduced back say 10%, this has a more significant effect than the next 10% getting leaner. As for two degrees at the most, well that is not insignificant if that is what you are suggesting.

In other words, the last extra dose is what matters the most. To start splitting the numbers up it was something like this, roughly, from full rich to

As luck would have it, so you are pretty lucky, George Braly sent me some data from fuels testing this morning. And what do you know? :) x100

The exact question you are asking has its answer hidden within! Now I am under NDA's so I cant publish it here but the data I can take from this confirms what I have said previously. This is from certification testing and can be relied on. The data collection was for completely different and unrelated purposes and the answers yielded are a serendipity of this.

The recent Avstar and Precision FCU's have had under-flows around 15%, and the data points I have of ThetaPP are tabled below which reflect this range. These are averaged over a few runs and cylinder to cylinder variation is to be expected and also from one sample to the next can be a bit of variation, so please anyone reading tis, these are fuzzy numbers that vary by the milliseconds (about 20 times a second) so be careful how you read this.

This is comparing full rich to FR-10% and FR-20% of flow and the % of ThetaPP compared to the previous position.

CYLINDER Delta TPP-10% Delta TPP-20%
C1 >> 88.45 >> 92.50
C2 >> 85.00 >> ----
C3 >> 89.40 >> 95.25
C4 >> 90.55 >> 97.30
C5* >> 97.85* >> 99.10*
C6 >> 92.70 >> 95.50

* this cylinder has an anomaly that could easily be explained by the pressure sensors and the fact this one has been deliberately subjected to a lot of abuse. In any case it shows a similar trend, but beware the raw data.

Interesting parameters here are the EGT values at each point represent a full rich, 1250-1320dF range using a standard 8.5:1 compression ratio engine. Assume this to be about 250-300dF ROP mark. The -10% flow figure was yielding around 70-75dF higher, so about 225-175dF ROP, and the -20% flow was about 150dF higher or about 150-100dF ROP. The ThetaPP shift overall was around the 2.5 to 3 degree range, a little less than the observations I made during less than ideal examples to extract data. Remember this stuff bounces around all the time so no hard numbers, fuzzy averages. Mid you these are not leaned off as much either, so lower changes of TPP are to be expected.

Interesting that if you compare this fresh data from the dyno today, the indicators I have been using to determine who has enough flow and who does not is validated. The concerning thing is that for as long as any of us can remember, Lycomings have flowed well, and TCM not. Now TCM publically declare a bit more would be nice, and Lycoming are shipping variations. Who the heck would know??

I hope that has been as fun for everyone as it was me in collating and delivering the data.

Last point, the thermal transfer is affected by the boundary layer, the higher the pressure, the smaller the layer, the more transfer.
 
..I suggest that in the case of where a mixture is ideal full rich at takeoff power and reduced back say 10%, this has a more significant effect than the next 10% getting leaner.

Tend to agree, but remember, here we're considering the why.

As for two degrees at the most, well that is not insignificant if that is what you are suggesting.

I am suggesting the insignificant shift in thetaPP is not enough to be the sole casual factor underlying the cylinder head temperature drop in the region richer than Lycoming's published minimum fuel flow.

Yes, that particular 10% richer does indeed have more effect...due to several combined factors, one being reduction of mean combustion gas temperature.

This is comparing full rich to FR-10% and FR-20% of flow and the % of ThetaPP compared to the previous position.

CYLINDER Delta TPP-10% Delta TPP-20%
C1 >> 88.45 >> 92.50
C2 >> 85.00 >> ----
C3 >> 89.40 >> 95.25
C4 >> 90.55 >> 97.30
C5* >> 97.85* >> 99.10*
C6 >> 92.70 >> 95.50

Percentage reduction of thetaPP is a bit obscure...heaven forbid we should see the actual peak pressure point in degrees ATDC. However, if we accept the curves on the school chart as accurate (blue curve, full rich peak at 16 degrees ATDC), then full rich less 20% flow only moves the point of peak pressure 10%, or 1.6 degrees.

(Throw out high and low, average the other four values = 90.275%, making the shift 9.725% of 16)

BTW, the column labels are switched.
 
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No the column labels are correct.

The -10% column id full rich flow x0.9 and the second column is FR flow x0.8, and as I have said the first reduction of fuel flow moves Theta PP more than the next ..... think about it for a minute. ;)
 
No the column labels are correct. The -10% column id full rich flow x0.9 and the second column is FR flow x0.8, and as I have said the first reduction of fuel flow moves Theta PP more than the next ..... think about it for a minute. ;)

The -20 column is expressed as a percentage of the -10 column? Please excuse me....lets recompute.

Again drop the high and low, average the rest, assume 16 degrees @ full rich per the school chart. The first 10% flow reduction moves peak pressure 1.6 degrees and the second moves it an additional 0.7.

Conversely, if a particular setup is 10% leaner than your ideal full rich, adding that additional fuel only retards the point of peak pressure 1.6 degrees, perhaps 2 degrees if it was 15% too lean?

Your previous statement was 2.5 to 3 degrees for 20%. Works for me. Shall we consider it quantified?
 
I'll take that as a yes, so returning to discussion...

..I suggest that in the case of where a mixture is ideal full rich at takeoff power and reduced back say 10%, this has a more significant effect than the next 10% getting leaner.

Agreed; the data is clear. Could you quantify the above ideal full rich in terms of A:F, F/A, or F/Fc please?
 
We have tested this exact config.

I am trying to find what is the anticipated fuel flow (or range) for an IO 360 M1B (Van's) with C/S hartzell and Precision FI. Full throttle / full rich during take off and initial climb near sea level. Thanks

Airhead,

Hey I checked with the braintrust here at Titan Engines concerning your question and this is what I found:

"Measured fuel flow for the same engine, same prop, under near sea level conditions. 16 -18 GPH."

Hope that helps.
 
Relentless, 16-18 is a BIG range, have the TITAN folk measured the Internal Cylinder Pressures on the Dyno at 16GPH at full rated power?

It sounds like 16-18 is a throw away line, a rough statement, even if it is just within a manufacturers range, and I bet they would much prefer the 17.5 range if they set it up and saw the data. ;)

It is a bit like saying spark plug gaps 0.016 - 0.028", when really they should be 0.016 - 0.018" if you get what I mean.

Until you see the data, everything else is just an opinion.
 
I bet they would much prefer the 17.5 range if they set it up and saw the data.

Please tell us why...and show us the data so we don't mistake it for opinion.
 
No, I get sick of going over the same thing and I have trouble deciding whether to waste more time on this or not. Plenty of data been provided already, all of which is all in harmony with the physics, which you seem to accept.

....when the FCU is set up properly by those who have the data and spec's which I do not have readily at hand is why you expect to get around 17.5GPH.

As for data.......I have seen enough of late with one IO360 and one IO540 (stock engines) in the last two weeks alone, who have had ridiculous take off CHT's and low fuel flows yet when the FCU is sent to a qualified repair shop and corrected everything data wise reflects what it should. Data enough. This validates the correct flows set up with the correct data, yields the expected result. The repair stations have it, 99% of pilots would not understand it if they saw it anyway, you would and most would not, but I still do not have it at hand and not going to spoon feed it to you. Go ask a good servo overhaul shop for the manuals, they do cost a few thousand dollars to purchase.

Bear in mind also, the BSFC if you want a unit of measure varies from some engines to others, i.e IO550 Vs TNIO550, both 300HP, so printing a specific here could be the misleading thing to do. But you can calculate that just as easily as I can. I bet for an IO360/540 it is around 0.57-0.58 which is the right range. For a TIO540J2BD it is 0.68-0.72 and say a TSIO 520 is 0.66-0.68 so it is horses for courses.

Bottom line if your CHT's are high and your fuel flow is way too low, fix it.

EOM
 
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26.8 Hg and 2700 RPM, 100F induction air, a lot like conditions climbing through 1500 MSL on a hot day. This is a detonation check run for an IO360A, slightly de-rated with 20 BTDC timing. However, it would be mighty close to Bob's M1B. Note the 105 lbs/hr (17.5 gph) fuel flow....way off at the bottom right.

8xvlzo.jpg


Yes, dumping fuel will lower CHT. Here, 17.5 wouldn't hurt anything, other than probably not making rated power. If the installation won't make rated power, an overly rich mixture to control CHT is a rather poor crutch. There are other choices. For example, a slight timing retard would net the same thetaPP shift (at no operating cost) if you figure that little shift is the full explanation. And let's not forget installation and baffling.

Consider rated power and BSFC. Lycoming cooling air requirement charts are all calibrated to 0.50 BSFC or less...in other words, full rated power. The chart spells out the minimum flow necessary to cool it. Just keep lbs/sec above the right hand lines. Again, this comes with no operating cost.

ienmeb.jpg


I've done a lot of work on cooling. Most readers assume that top speed is the reason, but in reality it's more about the Vans mantra, balanced performance. I get to use all 210 down low for speed, or slow climb, or every bit MP will allow at altitude, because at 100-200 ROP (ballpark 12:1, best power mixture) I am never CHT limited. Heck, I've never broken 400F, ever. Admittedly, not everyone is willing to do the work, or like the classic certified installation, is unable to make modifications. In which case, we drag out the old monkey-see, monkey-do...make it rich as six feet up a cow's butt. It's the only choice.

Bottom line? An overly fat mix is a cure for an airframe issue. The engine does not require it.
 
An overly fat mix is a cure for an airframe issue.

Define "overly fat" please? Seems like you are introducing a red herring opinion into the debate.

As an expression I agree. In fact I agree with most of what you say, you are a clever guy, but you are insinuating that less than the the correct (OEM data) fuel flow is all right so long as you keep the CHT down. This sounds like one of Mike Busch's flawed arguments on just remain below 380 and all is good.

Dan an overly fat mixture will drown out HP that is for sure, and on a certified airframe you cant fiddle as much (STC improvements notwithstanding). However sub optimal fuel flow could be offset by timing, true, however the pilot will now complain about inability to run LOP smoothly like before.

Just because you keep the CHT down, does not do anything for the ICP, it remains the same, in fact it gets higher as the volumetric efficiency improves with a cooler cylinder....but we are splitting hairs so let's not worry about that.

Bottom line is this......Get your fuel flow correct, timing correct, everything else correct and this ensures the correct combustion events and hence ICP. Then assuming this is good get your baffling and airflow correct, and I defer to your expertise in this area, and guess what......no CHT problems. Many folk here on VAF suffer from this last problem, the lack of fuel flow problem seems to be only just appearing in engines built in the last 1-2 years, not before.

My reading of your post above is suggesting that if you have incorrect fuel flows just mask it with better cooling.

Your favourite chart above shows a BSFC of 0.57-0.58 = 160HP (for the set MP/RPM) and right on the flat line. Surely this suggests that it is not a fat overdose mixture. It starts at well over that.
 
Airhead,

Hey I checked with the braintrust here at Titan Engines concerning your question and this is what I found:

"Measured fuel flow for the same engine, same prop, under near sea level conditions. 16 -18 GPH."

Hope that helps.

Hey Relentless,

Seeing as you were able to answer that one without all the graphs n such...

How about the same engine but with a Fixed Pitch Prop turning 22-2300rpm at take off??? (CS prop turning 2700rpm 16-18gph, do I reduce GPH by the same % of Prop RPM difference?)

Thanks in advance if you can answer this?

Scott
 
Define "overly fat" please?

Richer than about 250 ROP. I'm comfortable with 200 ROP as a rich limit, but 250 isn't unreasonable.

...you are insinuating that less than the the correct (OEM data) fuel flow is all right so long as you keep the CHT down.

Correct OEM data eh? Six posts back you told a sharp manufacturer's representative that his engineers were offering a "throw away line, a rough statement". Their stated range was 16-18 GPH. You informed them that 17.5 was correct.

They're right...it's a range. When expressed in gallons per hour, as seen by users in the field, it approximates the full rich fuel requirement for a range of power output varying with sea level air density. Fuel and air in proportion; as the air supply becomes less dense, the real fuel requirement drops. The density difference between 32F and 100F is about 12%, much like the manufacturer's GPH range.

Assuming rated power (sea level, cool day, if at all), further assuming 0.58 BSFC as appropriate for full rated power (it's not, see below), then multiplying 180 HP x 0.58, and declaring 17.5 (the 105 lbs product @ 6 lbs gal) as "correct" is, at best, a double assumption.

To illustrate, I've offered a real power chart approximating hot day climb at 1500 feet MSL...the reality of observed fuel flow. 1500 is about where a pilot might settle in, scan gauges, and note the numbers. Low air density and a bit if altitude have already conspired to reduce HP, and thus the required fuel flow. If under these conditions Bob saw 17.5 GPH on an accurate instrument, he would definitely not be making full power.

Bob did get excellent advice from the folks at Precision (read post 42). They told him to do a mixture sweep and look for 200F difference in EGT from full rich to peak.

I know it must be tiresome to hear requests for supporting data, but there is so much to be learned from it. Here, I've added labels and blown up the chart for little laptops:

2hod0n7.jpg


The sweet spot for maximum performance is (as usual) 100-150 ROP. It burns 13 to 14 GPH in that range, at this point in climb. Flow will reduce further if the pilot leans to stay at 100-150 ROP with altitude gain. Doing so at 2700 RPM is detonation free. 200 ROP is a reasonable "full rich", a little down on power as expected. 100 ROP is 0.48 BSFC; note the value on the cooling chart in the previous post.
 
It's all about fuel air ratio

The origin of this thread was what fuel flow should be seen with an IO-360M1B, constant speed prop and Precision fuel injection. And the answer is, there is no correct answer because the fuel flow is based on the horsepower the engine is producing, which is effected by RPM, MAP, induction air temperature, humidity, compression ratio, exhaust system design, cam timing, ignition timing and so on and so on. For some reason people get hung up on fuel flow as the defining parameter. I guess if you have a Continental fuel injection system, that statement would be true, as the Continental system only knows how fast the engine is turning and what the position the throttle is in. The system does not know engine air flow therefore in the POH it states a specific fuel flow for rated RPM. The fuel flow will be the same if the engine is running that RPM and the throttle is wide open. It doesn?t really matter if the engine is developing 100%, 80%, 110% power, the fuel flow is the same. This type of metering system has been around a long time and I guess it?s easy to remember ?the fuel flow should be X amount period?. We get calls from customers and pilots stating, ?my fuel flow is low?, ?my fuel flow seems high?, ?what should my take off fuel flow be?? What?s the answer? Well it depends. Being that the RSA and Airflow systems meter fuel based on engine air flow consumption, their purpose is to set a fuel air ratio to the engine. So if the engine makes more or less HP the fuel flow will be different, the fuel air ratio however will be the same. With the RSA systems as well as our systems Lycoming establishes the fuel air ratio. Most of the fuel flow limits for full throttle operation are +/- 2%. That?s only a 4% total change in fuel air ratio, or for those of you that still have to have a fuel flow number that?s only a 4% change in fuel flow for the specified airflow at full throttle. To my knowledge the fuel flow limits haven?t changed in the last 40 years. And even when I was the project engineer at Bendix on the RSA product line in the late 70?s, early80?s those fuel flow limits were the same as they were in the late 50?s. So when I hear the fuel flow (correctly fuel air ratio), is lean by 20% that?s pretty far fetched. Indeed, your wouldn?t have high CHT?s with this set up. All this stuff about thetaPP and what ever is pretty meaning less to the common folk unless you have a million dollar dyno with cylinder pressure measurement and data acquisition. But the fact is (and I?m old school) that the chart that Dan shows (post 61) is right on, and the information is the same as I have from Lycoming data showing the effect of fuel air ratio to CHT, EGT, and power. We use this data in our FI 101 Class. Lycoming ran the same tests as what was shown in the listed curves (61) and basically fuel air ratio can be derived from the change (get that, change, not the value) in EGT from peak. It doesn?t matter if it?s naturally aspirated, turbo charged, 4 cylinder, radial, etc. The change in EGT relates to a specific fuel air ratio (there?s that word again). If you look at the curve you will see that a 200-degree change in EGT from peak relates to a fuel air ratio of around .086, where peak EGT is around .065. If you take the .086 fuel air ratio and multiply it by 1400 you get 120.4. That?s 120.4 PPH of fuel or 20 GPH. Guess what. The fuel flow spec from Lycoming for an IO-360A1A (200 HP) is 120-125 PPH at 1400 PPH air flow. So for all you guys that want to know if your fuel injection is set rich enough, don?t look at the fuel flow number, look at the change in EGT from peak. Of course don?t do a lean to peak test at full throttle, do it at 24 square. Even at this power the fuel injection fuel controller is linear so the fuel air ratio will be the same at WOT. Then there's fuel control for the IO-320. The Lycoming spec is 75 to 76.5 PPH at 900 PPH airflow. That?s a .085 fuel air ratio. A tick leaner than the angle valve IO-360 (1%). So when your overhaul shop tells you that your servo was calibrated for a 320 instead of a 360 and that?s why you CHT?s are hot, you can just smile and say ?is that so? (remember the limits on fuel air ratio are +/- 2%). THAT?S A CROCK PEOPLE. You can take a servo that?s set up for a 320 and bolt it on a 360 and it will work. Just like the parts list (calibration) for an IO-360 is the identical parts list for the 260 HP IO-540. The beauty of this type of fuel injection is that the system holds a fuel air ratio, that?s how your engine works, it?s nothing more than an air pump, so if you hold the fuel air ratio constant the engine will operate correctly under any power setting.
Now granted there are fuel flow settings (calibrations for certified installations) that are richer or leaner than these examples. But like Dan said the reason for that is the air-framer was covering up cooling air problems with fuel. I saw this all the time working with various airframe manufactures.

So to answer the first post in this thread, ?it depends?. Go back to the Lycoming charts and put all the ?Ifs? in there. 180 HP at .55 BSFC = 99 PPH or 16.5 GPH.

How accurate is your measurement equipment? Are you really making 180 HP? Do you have optimum cooling or is your cooling system not up to post 71. Your mileage may very.

But I can guarantee that if we set a fuel control to the specification the Lycoming provides then the fuel control is delivering the fuel it?s suppose to. If the fuel flow number is low then maybe the engine is not pulling the air to make that fuel flow number. Now you all know what that means.

OK, so a 360 turning 2300 at take off WOT. Lycoming says it?s making 110 HP (standard day air). Take .55 BSFC and you get 60.5 PPH fuel flow or 10 GPH.

Hey maybe we need to have another FI 101 class this fall. Let me know

Don
 
Don, the facts are off a flow bench that the Fuel servo's are being sent out of the factory right at the very bottom and not an ounce more of the range. I doubt you are doing this.

So you are correct, in that the flow on a 320/360 or even a 540 are being held the same. But in these cases, The same = not enough. The results are proving this.

If you do not believe me contact Andrew Denyer at Riverina Airmotive. This is a simple thing. He is seeing it on certified engines too. By the way when the servo's are set up right they flow at about 0.57-0.58 BSFC for IO360/540. Exactly where they should be.

You state that the IO360A1A should flow about 20GPH, yep 100% consistent with everything I have said so far.

The data says so.
 
Dan at high power peak EGT is higher 26.8 Vs 29.92), 250 ROP as you agree is about right for full rich at 100% power. Thats almost 0.60 BSFC closer to 0.57-0.58.

You have just confirmed everything I have been saying, everything George Braly would say, and everything the Precission Airmotive data says. If at ISA conditions, 29.92" 15dC and 2700 you should see a BSFC of 0.57-0.58, or around 17.5GPH.

You can fluff around at 1500' and whatever you want. Facts are facts and you are avoiding them. By the way your graph is an IO360 but at 26.8" not 29.92" so you are not WOT on an IO360 (180HP) with your graphs. The fuel flow point at 17.5 by rights should be off the page, and it is.

Get your facts straight. Show the 180HP graphs at 29.92/2700 at full rated 180HP so it is apples vs apples not apples vs strawberries. Otherwise you are confusing the folk who want to see the educational value.

Dan get your ducks in a row and then lets debate it. You keep asking me for data but you post graphs that are not relevant. Let me show you.

160HPgraph_zps68e58cac.png


Dan, have you spent the money yet and bought the manuals, only a few grand? Have you sat in front of a Dyno spending thousands per hour studying this exact topic yet?

You asked for data and facts. The 180 HP engine operating at 26.8" MP should be drawing exactly what you say it should, by your own graphs above, about 15.6GPH, now just advance the MP to 29.92 and ISA temp and see if the fuel flow increases directly proportional (As Don says it will) and it will be what? I will save you the calculation, 17.5 GPH or near enough.

Parade rest.
 
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Dan at high power peak EGT is higher

Have that chart too. Here's the same engine, same RPM, same dyno, same day, at 28.5" Hg and 26.8" Hg. Compare carefully. There is no practical difference in peak EGT.

9tzacg.jpg

28tkuiu.jpg


250 ROP as you agree is about right for full rich at 100% power.

No, I don't. It is richer than necessary (the engine doesn't require it), and it's too rich for max power. However, it is not unreasonable, if you can't cool it some better way.
 
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So trying to get past some of the fog of this thread leaves me still trying to learn something.
It seems that Don is saying the servo is linear.
I assume that means for safety I can lean at 60% power and then increase throttle or altitude and still have the same distance from lean of peak or BSFC.
This helps real world as most often you play a little with the throttle during a flight.
Dan, you also seem to be saying that I should check and adjust my mixture to a setting that is about 200ROP @ sea level if my cooling system will allow. Since I have a fixed pitch prop that could help give better take-off power, waste less fuel, blow less raw fuel into the oil and improve engine cleanliness.
Is there a good way to test this and should I just remember the setting on the mixture knob for each TO or is there a good way for me to adjust the Precision Airmotive servo myself?
 
Just wanted to weigh back in. After posting the original question concerning T.O. fuel flows and absorbing many of the reply’s, I went on a several week trip and naturally thought about it. On my return I decided to conduct a hanger test of timed fuel flow into a measured container vs. red cube / Dynon Skyview fuel flow reading. As I previously posted, I had very gradually adjusted my K value from the original setting of 68,000 to 72,500 based on my longer term monitoring of fuel usage (Fuel Remaining) according to Skyview with actual fuel added over about 50 flying hours. At the time I was questioning my relatively low (15 gph ) reading at full power takeoff (and initiated this post) I had arrived at a K value (72,500) which very closely matched the two.

Without boring you with the test details, when I conducted timed flow tests (using a adjustable valve on the end of the fuel line at the servo input), at multiple flow rates, into a container with known volume, I discovered that in order to get these results to match I had to reset the K value back to 68,500. I’ll call these constant flow tests. With my initial K setting of 72,500, I found that the actual measured constant flow rate was about 12% higher than the Dynon fuel flow was indicating during the test. Therefore, I kept repeating the test (again, multiple times at different fuel flows ranging from 5 to 20 gph) and adjusting the K value downward until matching the two.

Doing the math, my 15 gph readings at takeoff appear to have been in reality closer to 17 gph. (My plane has been in the paint shop since just after flow test)

I can’t explain why the longer term fuel consumption “computed” by the Dynon does not more closely match the short term constant flow. However, I can understand why it would be possible for the highly variable power settings used during my testing period, which were rarely just “x-country like” flights, might introduce this difference, which I will point out leads to a conservative value for Fuel Rem, and would be acceptable if you reset the Fuel remaining at frequent top offs. In fact, I may leave it there and just always know I have a bit more fuel in the tanks than Dynon is showing me. However, I will always continue to monitor and record actual v.s. computed usage.

I will look for ways to improve CHT’s, but a bit of power management about 800 into the initial climb out seems to keep temps into acceptably conservative range (for me), and certainly way below Lycomings specs. My cruising CHT's have never been an issue, always being below 380.
 
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Fuel Flow Limits

All I?m saying is that the fuel flow limits established by Lycoming that are to be used when calibrating RSA servos are +/- 2%. That puts the fuel air ratio at .086 to .089 for most of the 4 cylinder and 260 HP 6 cylinder Lycoming?s. So David, what you are saying is that Precision is setting the fuel servos to the lean limit on the new parts flow sheet and this is failing operation on the engine. I may point out to you that Lycoming has Service fuel flow limits that are deemed within their parameters for detonation and cooling. These fuel flow limits are +/- 6% and that puts the fuel air ratio to .084 to .095. Even with a .084 fuel air ratio, it is about 180 degrees F rich of peak, which is still rich enough to keep the engine happy. Running 250 rich of peak is putting the fuel air ratio around .091 to .092, which is out of the rich limit for new parts calibration. I guess I am curious why supposedly your shop is finding so many servos from Precision set out of the lean limit. We are using the same limits your guys shop uses and we do not get rejected servos from the field. It just seems strange that being lean 2% from the mean on the new parts fuel flow limits would cause a problem.

Basically on most RSA-5?s the fuel curve is pretty linear from 8 GPH on up. That means if you set the mixture at altitude and the fuel flow is above 8 GPH then increase the power (RPM or MAP) the fuel flow will increase but the fuel air ratio will remain the same (not touching the mixture control). So the amount of EGT ROP would remain the same. With fuel flows less than 8 GPH, WOT; the fuel mixture tends to go richer. This again is a function of the fuel curve that Lycoming prescribes for these units.
 
My recent experience as a data point-

I recently changed out cylinders on my 180 HP IO-360 with a Bendix mag and an LSE electronic ignition. I used ECI with ECI 9:1 CR pistons and porting by Lycon. I immediately saw high CHT's on what had previously been a very cool running engine. I reset timing back from 25 BTDC to about 23 BTDC. Some small improvement was seen in CHT's. After rotating the mag drive gear 180 degrees I was able to get 20 BTDC. CHT's improved somewhat (slower to go high and a tighter spread) but high CHT's (425 F or so) persisted at full power during takeoff and climb out.

I was seeing 17.5 GPH during this period. After talking with Don, I did the peak to full rich check and was getting about 150 degree deltas. My T/O numbers were 17.5 GPH and EGT's about 125-145 degrees ROP.

After much thought, more reading and more thinking, I sent the RSA fuel control down to Don with a request to richen the F/A ratio. Kyle called me immediately upon receipt and said that the control calibrated exactly where Lycoming said it should and if I richened it, I would be going off the norm. We discussed it further and went with about a 10% richer calibration.

After a few quick flights, it appears that I am now getting 18.8 GPH at full rich T/O and seeing EGT's 200 degrees ROP. CHT's began their slow post takoff climb and I figured "here we go again", but they leveled nicely at 380 degrees during full power climb, about 50 degrees lower than before.

For my particular engine (9:1 and ported) the extra fuel seems just the ticket. I sense better WOT power although that is subjective until I can run some reliable 3 leg speed tests.

This fuel flow would now seem more commensurate with the 190+ HP I was expecting and seemed not to get.

Thanks Don and Kyle, excellent service including taking the time for a nice discussion about fuel controls in general and my personal situation in particular.

I think that this all supports the general points made in this discussion.

I still contend that many who are suffering from high CHT's need to look very critically at timing, fuel flows and cooling system. Having one out of three right may not be enough to achieve acceptable (less than 400) CHT's.

Great discussion and so much to learn here!!! Thanks all.
 
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Two other quick points -

I have the often maligned Hall effect triggering option on my Lightspeed Plasma II. One advantage to it is the timing is infinitely and easily adjustable with this unit as opposed to the crank fire sensor which, to my knowledge, is difficult to adjust.

In addition to setting the WOT fuel flow, Don's guys also correctly set the idle fuel flow. As he has posted, there is now no need to lean during idle/ground ops. Thanks again Don!!
 
To clarify post 81. The fuel flow limits I have been referencing are for ?stock? compression and magneto ignition. I haven?t seen fuel flow limits for modified engines. In that case we do as the customer specifies understanding the ramifications of just setting the unit rich as they request. Most of the time the stock settings work fine as they are, typically the settings are set a bit rich. I do not know if Lycoming has done detonation and cooling tests on all the combinations of compression ratios and ignition systems available in the homebuilt world. Obviously modifying the stock configuration gets us into the ?experimental? part of what is required for the fuel curve. Still the basic physics prevail. You start cranking more HP per cylinder than the cylinder was designed to handle, and maybe the cooling fin design is not quite adequate, or as Dan stated the cooling system has to be optimized for these engines to operate correctly with the existing cylinder design. We saw this type of phenomenon on the M-14 engine when it was hopped up. In fact as far as I know, there are no published fuel flow curves for the Silver Hawk parts lists. I haven?t seen them, but maybe they exist somewhere.
 
Don,

In reply to your question above, the last of the FCU's that have been sent to Riverina Airmotive, the flow was 119PPH at the test reference airflow.

This is clearly out of spec as a new unit should be at least 124. It has been sent out to the customer now at 131 PPH I believe.
This one was an Avstar, the last one a Precision Airmotive. Numbers in the 10-13% range are what we are seeing as the required increase.

For anyone else watching this thread, think about this. If you had to choose, would you take a max flow rate FCU or a min flow rate or even a half way flow rate FCU?

Remembering that you can always make the max rate FCU flow less at will, but pushing as hard on the red knob as you can you can't make a min spec flow more. ;)
 
I?m assuming you are re-setting these units for experimental use. In that realm you can do pretty much what you want. We even calibrate RSA-5?s to run ethanol for some RV group in South Dakota. The flow specs you are referring to I believe is test specification 11263-01. This flow spec. is used on RSA-5 servos that are installed on IO-360B series, IO-360A series (angle valve engines) and IO-540C (260 HP) series engines. Per the spec the fuel flow at 1400 PPH airflow is 120.0 to 125.2 PPH fuel flow. As a note the Service limits for this setting are 117 to 132.8 PPH. As a PART 145 Repair Station we have to set the units we overhaul to the new parts limits (120-125.2). Since our existence as Repair Station in 1997 and previously while employed at Bendix, we have never had a fuel controlled returned for lean operation in any of the applications this servo is used in the certified world. We use pretty much the same limits (fuel air ratio) for setting our experimental units (FM-series). This too has worked quite well with only the ocasional re-cal like what was described in post 82. We generally have more cases of rich operation than lean, which I suspect, has to do with inlet configurations on these experimental installations. The limits for this fuel control were established in 1961 when the fuel control was certified and they are still serving us (in the US) well.

Limits are limits, and 119 are out of the new parts limits. Likewise 131 is way out of the rich limit for new parts and is near the rich limit for the Service limits. Maybe I need to check with Wilshire Engineering in Sidney, to see if he is experiencing the same lean operation you are. Again if these instances are set for experimental installations all bets are off.
 
Don,

The majority of new units will be installed and if out of limits on the low side, never detected. People do not know how to pick it.

I guarantee unless one of these units ends up in an aircraft with an EMS, and someone who knows what they are looking at, they will be none the wiser.

If you ask around you will get very few if any responses. This does not mean they are all set correct.
 
David,

Maybe you and you associates need to purchase all your new and overhauled fuel controls from Airflow Performance.:)

I see an opportunity in your area.
 
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