IO 360 M1B FF at T/O full power

[DanH]

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.



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.



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.

[RV10inOz]

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.

[Rhino889]

Originally Posted by Relentless

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

[DanH]

Originally Posted by RV10inOz

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:



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.

[Don at Airflow]

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

[RV10inOz]

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.

[RV10inOz]

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.



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.

[DanH]

Originally Posted by RV10inOz

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.

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.

[MarkW]

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?

[Airhead]

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.