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  • IO540 Cooling & LOP.

    I've been tweaking engine cooling from a slightly different angle and wanted to post it here in case it might help others. I haven't ruled out installing cowl flaps, but I wanted to fine tune everything else first. I enjoy learning about this sort of stuff and we don't have much else to do here in NZ on the weekends, so I got to thinking about how I could get the best from the cooling setup.

    For my IO540 I used an exit area of 130 ² in (numbers that I found on the forum that seem to work very well on my engine), and I fabricated a small fiberglass lip to further lower the exit air pressure. That all worked well for the engine break-in and test flying, but I did need to refine it. Initially I have been controlling CHT's during the climb with airspeed and generally climbing with full rich mixture.

    Recently I did a GAMI spread test which is fancy way of saying that I climbed to 7000ft, set full throttle, and very slowly leaned the mixture back until the engine ran rough. I repeated his 3 times, then landed and downloaded the data. I was then able to view the graph on my computer using Savvy Aviation's free software. You're then looking to see what the fuel flow (mixture knob position) is as each cylinder hits its peak EGT. Ideally I wanted all cylinders to hit peak EGT at the same fuel flow. Actually they have a tool that checks this automatically in the software.

    What it showed me was that the #1 cylinder was running richer than the rest. This meant that when I leaned the mixture in the cruise, the other 5 cylinder EGT's were all Lean of Peak with correspondingly cooler CHT's, while the # 1 was running much hotter near peak EGT (or even on the rich side). This made it difficult to run LOP at lower altitudes because the #1 CHT was always hot while the others would run rough from being too lean.

    Airflow Performance sell individual restrictors for standard Lycoming fuel injectors, at a reasonable price, so I installed a slightly smaller restrictor (a 5 min surprisingly easy job) and repeated the test. I can now run LOP even at low altitudes with all CHT's grouped roughly even. I'll fine tune even further and will further lean both #1 and #3 cylinders now that I know how to do it. My #6 CHT still runs hotter than the rest - but for another reason (that's where the oil cooler is ducted from), but not by much and they're all fairly closely grouped now.

    Next, I realized that the original cooling lip was doing well on the cooler days, but not so much in the summer heat. No surprise there, because when I made it I simply estimated the size based on the TLAR method. I've now made a second larger cooling lip. That dropped my CHT's another 10°c and will be used during summer. It's a 5 min job to switch over (7 screws) and the original one should work well during winter.

    That leaves one last cooling aspect which is my oil temperature. With the original cowl exit lip my oil temperature is usually around 75°c - slightly lower than ideal. The larger cowl exit lip drops the oil temperature even further, but this should be negated by using it during the summer months. I do need to double check my Vernatherm setup, but assuming it is correct then I'll add a small baffle to restrict airflow into the oil cooler scat tube. This should also leave more air to cool the #6 cylinder.

    Here's the "GAMI SPREAD" results - you can see the #1 cylinder in red doesn't hit peak EGT until a lower fuel flow than the rest indicating that it was running richer than the others - it's EGT was still climbing as the others peaked.

    image_11636.jpg
    Last edited by Nev; 04-17-2022, 11:32 PM.
    Nev Bailey
    Christchurch, NZ
    Builders-log
    YouTube Bearhawk Blog

  • #2
    Nice job to equalize the fuel flow to each cylinder and help the CHT also, thanks for the input and the link to Airflow Performance. I have put a cowl flap on my Bearhawk but will use this to fine tune my injectors.

    Comment


    • #3
      I have the GAMI spread test on my to-do list. I'll be using the Savvy Aviation GAMI Lean Test.

      It was critically expressed to me that this procedure MUST be performed at an altitude high enough to indicate 65% power at WOT. Otherwise this leaning procedure above 65% power could result in serious detonation issues.

      Rob Caldwell
      Lake Norman Airpark (14A), North Carolina
      EAA Chapter 309
      Model B Quick Build Kit Serial # 11B-24B / 25B
      YouTube Channel: http://bearhawklife.video
      1st Flight May 18, 2021

      Comment


      • Battson
        Battson commented
        Editing a comment
        Or just ensure you are producing less than 65% power when you do the test? 2300 and 23" is around 65%.

    • #4
      Fun stuff Nev! Thanks for sharing. Engine operation technique discussions are right up there with short field discussions, IMO. Good stuff.

      I did the gami lean test after I broke in my engine but Continentals are not known for a well-balanced induction from the factory, thus the creation of GAMI. My spread is pretty bad and I can't run LOP very well unless I use some tricks so I pretty much never do it. You've led me down a rabbit hole of seeing if I can use Airflow injectors on my Continental which will allow me to tune the nozzles without having to spend a wad of cash on GAMIs. So thanks for that...

      Originally posted by robcaldwell View Post
      I have the GAMI spread test on my to-do list. I'll be using the Savvy Aviation GAMI Lean Test.

      It was critically expressed to me that this procedure MUST be performed at an altitude high enough to indicate 65% power at WOT. Otherwise this leaning procedure above 65% power could result in serious detonation issues.
      Opinions vary but throttle position is a subject I agree with Mike Busch on. The GAMI test should be performed at WOT and since you will spend some time at and near peak EGT you will want to be below 65% power. This can be done by climbing to altitude and/or dialing the rpm back, probably should do a bit of both.

      Personally, and this is where I agree with the Savvy guys, I run my engine at WOT all the time. Partially closing the throttle just introduces inefficiencies into the induction. If I want less power I dial the prop back. Running "oversquare" is perfectly fine and approved by the engine manufacturers; if you care you can look it up for your engine.
      Scratch Built 4-place Bearhawk. Continental IO-360, 88" C203 McCauley prop.

      Comment


    • #5
      Airflow Performance have instructions that vary slightly with the recommendation to do several tests at different lower altitudes. I hadn't thought of this and my GAMI SPREADS were all done at 7-8000ft and WOT. Yet so far most of my flying is done at 1000-3000ft so it does make sense for me check the spreads at those altitudes.

      One thing I've noticed is that if I do several GAMI SPREAD tests, they'll all be slightly different. Overall they point to two cylinders running richer than the rest, but I can get a spread of anywhere from 0 to 1.0 gallon per hour on any given test. The main factor seems to be to set the mixture rich of peak and lean it VERY SLOWLY, allowing the EGT's time to stabilize at each setting such that one sweep takes several minutes.

      I've been tracking my fuel burn - under the impression that flying higher is more efficient. For most of my career this was true, turbines burn far less at altitude. But so far with the Bearhawk I'm finding that I'm burning less fuel at low levels. Typically at 8000ft I'll get a TAS of 130kts compared to a TAS of 115kts at say 2000ft. Fuel burn is usually the same at 38-40 liters per hour (divide by 4 for gallons). It looks like it's my eye-wateringly high fuel burn during the climb that is making the difference. Up until recently I've been climbing full rich to keep CHT's in the right zone. With my new larger cooling lip, I suspect I'll be able to lean back to a more wallet friendly climb mixture. Once I've done it a few times I'll add a note here.

      For those that haven't tried flying Lean of Peak, the fuel flow on my engine when leaned to ROP is typically 55lph at 125 kts (.44l/nm) vs 38lph at 115kts (.33l/nm). That's an extra 100nm per tank along with a cleaner burning engine and no carbon monoxide.

      Each time I fly somewhere I do a quick trip plan in AvPlan first, select an altitude, and check the time and fuel burn to compare against the actual time and fuel burn. So far it's proving exceptionally accurate with the recommendation to fly low for efficiency or high for speed.

      Airflow Performance​​​​​'s GAMI spread test:
      C52E7465-FE63-4661-8895-E6B11B34C22C.jpg
      Last edited by Nev; 04-19-2022, 03:25 PM.
      Nev Bailey
      Christchurch, NZ
      Builders-log
      YouTube Bearhawk Blog

      Comment


      • #6
        I found that our carbureted Lycoming 360 yielded better cht and egt distributions if I had the throttle closed just enough to stay our of the economizer circuit.

        Comment


        • #7
          I'm a little behind on my forums, due to prepping for a move, so this is a little late...

          Battson, you are correct that operating at 65% power will virtually eliminate the chances of detonation and/or pre-ignition. That said, the GAMI Lean Test has to be done a wide open throttle (WOT) to produce valid results. GAMI specifies that it be done between 5000 and 7000 ft for normally aspirated engines (8000-10000 for turbos).

          Rob, just for the sake of recognizing the creators of the intellectual property behind the GAMI Lean Test: Neither the GAMI Lean Test nor the concept of flying LOP were created or are "owned" by Savvy Aviation founder Mike Busch (though he seems to gloss over that in his presentations). Mike himself learned about this stuff the same way I did, by attending the Advanced Pilot Seminar developed and taught by the "three amigos" (George Braly, John Deakin, and Walter Atkinson).

          Fortunately for Mike (and the rest of us), GAMI and the remaining two "amigos" (Walter Atkinson passed away recently) have chosen to be very open with all of this information, and even though they aren't real happy that Busch gets credit for their work, they are more interested in the good of GA than personal glory, and have thus encouraged the broad dissemination of the information and data they so painstakingly collected.

          For the curious:

          Flying LOP was a well-known concept even prior to WW2. It was heavily used during WW2 by both fighter and bomber pilots for extending range. The Japanese airplanes that struck Pearl Harbor flew LOP to extend their range to enable the attack. Jimmy Dolittle's "Tokyo Raiders" employed the same LOP techniques, as did most of the bombing raids deep into Germany in the European Theater of WW2. Even after WW2, during the era when "round engines" ruled the skies (DC-3 through DC-7 among others), most airlines operated their engines LOP to save on fuel cost, extend range, and reduce maintenance (minimal lead fouling issues when operating LOP)...

          Flying LOP in modern day fuel injected Lycoming and Continental engines was re-popularized initially by a series of articles by John Deakin (Google the "Pelican's Perch" article series), then picked up by General Aviation Modifications, Inc. of Ada, OK. GAMI developed the "GAMI Lean Test" to allow pilots to use their engine monitors to collect the necessary data so GAMI could deliver a set of STC'ed "GAMIjectors" (calibrated fuel injectors) that supply "balanced" fuel flow to your engine so all your cylinders reach peak EGT at the same fuel flow, greatly facilitating safe LOP operations.

          GAMI is also the company that created G100UL unleaded avgas - an STC'ed solution to the upcoming "no more leaded gas" crisis looming on the (very near) horizon. George Braly is "the man" behind both technologies, along with the Tornado Alley Turbos (TAT) that supply turbos to Bonanza and pre-turbo Cirrus owners, and actually developed the turbo package that became standard on the turbo Cirrus. His outfit in Ada operates THE most sophisticated aviation engine test cell in the world. Continental and Lycoming bring engines there to test. George is a really neat guy to talk to.
          Jim Parker
          Farmersville, TX (NE of Dallas)
          RANS S-6ES (E-LSA) with Rotax 912ULS (100 HP)

          Comment


          • #8
            Originally posted by JimParker256 View Post
            That said, the GAMI Lean Test has to be done a wide open throttle (WOT) to produce valid results. GAMI specifies that it be done between 5000 and 7000 ft for normally aspirated engines (8000-10000 for turbos).
            Well.... You can do a mixture leaning spread test at any power setting and altitude, some settings are more useful than others.

            It doesn't "have" to be done with WOT, that's what GAMI suggest in their procedure for their certified install. Airflow Performance, who made my system, have different recommendations.

            I tend to go LOP at 500ft AGL or anywhere above that, so for me, I need to know if the test gives valid results there too, as well as at high altitude.

            In my install, throttle position made next to no difference, it's the manifold air pressure which counts. I can also vary mine from closed to WOT and still get acceptable results for running LOP, and I regularly do.
            Last edited by Battson; 04-29-2022, 12:20 AM.

            Comment


            • zkelley2
              zkelley2 commented
              Editing a comment
              You have to remember the bush flying thing is still very very new to the wider audience that has adopted it(and I have a feeling it will go back to obscurity as people notice there's no reason for a 130kt airplane when they can go the same places in a 200kt airplane), and so while this all applies to any engine, they're much more used to bonanzas and cirrus looking for fuel economy, not the typical bush pilot that thinks magnetos and carbs are the be all end all of reliability and technology.

            • JimParker256
              JimParker256 commented
              Editing a comment
              Battson, can you expound further on your statement that "it's the manifold air pressure which counts" to help me understand better? I'm at a loss to understand how MAP directly relates to operating LOP...

              The Mixture controls the amount of fuel delivered to the cylinders, while the Throttle controls the amount of air (thus oxygen). Once you have more oxygen being delivered than the fuel available to consume it, adding more air does not affect the power output of the engine. Reducing the manifold pressure (by reducing the propeller RPM) has the effect of reducing the amount of air entering the cylinder, which effectively enrichens the mixture. If you're operating LOP and enrichen the mixture, you may or may not still be operating LOP, right? Depends on how close you were to that peak EGT condition?

              In the APS seminar, their recommendation was to operate with the throttle wide open (WOT) when operating LOP, and to set up the desired engine RPM before you leaned the engine. If you need to change the RPM, enrichen the mixture first, then set the RPM, then re-lean.

              I suspect we're on the same wavelength, just using different terms for it. What's that old saying about two nations divided by a common language? We Yanks usurp the Queen's English all the time...

          • #9
            Following on from the original post above, I recently purchased a 4" butterfly valve from AircraftSpruce to install in the oil cooling duct. Having installed the larger cooling exit lip, my oil temperature is now running on the cool side. I don't plan to have any cockpit control for the butterfly valve, but probably a summer/winter setting that is easily accessed beside the oil filter.

            Has anyone installed one of these before ? Any suggestions are welcomed.

            The valve is actually designed to be operated using a servo HERE. However I plan to use a simple mechanical lock.

            As an aside, for the Kiwi builders among us, when you come to purchase Scat duct, consider using Sceet Duct sourced in NZ HERE. Service was prompt and the price was right. It's used by the race car industry and the one piece I've originally installed I was very impressed with.

            I'll be replacing my existing heat muff Scat ducts with this stuff in due course.


            image_11729.jpg

            image_11730.jpg
            Last edited by Nev; 05-08-2022, 04:21 PM.
            Nev Bailey
            Christchurch, NZ
            Builders-log
            YouTube Bearhawk Blog

            Comment


            • Ray Strickland
              Ray Strickland commented
              Editing a comment
              Nev,
              I have installed a butterfly valve for my oil cooler with a push-pull cable control on the panel to adjust the valve. Works great. I run it full open for takeoff; but, once at cruise I can adjust oil temp as needed.

            • Nev
              Nev commented
              Editing a comment
              Thanks Ray. I'm going to try a spring latch to begin with. Depending on how it goes I may revert to the way you've done it. Cheers.

          • #10
            Battson, can you expound further on your statement that "it's the manifold air pressure which counts" to help me understand better? I'm at a loss to understand how MAP directly relates to operating LOP...

            The Mixture controls the amount of fuel delivered to the cylinders, while the Throttle controls the amount of air (thus oxygen). Once you have more oxygen being delivered than the fuel available to consume it, adding more air does not affect the power output of the engine. Reducing the manifold pressure (by reducing the propeller RPM) has the effect of reducing the amount of air entering the cylinder, which effectively enrichens the mixture. If you're operating LOP and enrichen the mixture, you may or may not still be operating LOP, right? Depends on how close you were to that peak EGT condition?

            In the APS seminar, their recommendation was to operate with the throttle wide open (WOT) when operating LOP, and to set up the desired engine RPM before you leaned the engine. If you need to change the RPM, enrichen the mixture first, then set the RPM, then re-lean.

            I suspect we're on the same wavelength, just using different terms for it. What's that old saying about two nations divided by a common language? We Yanks usurp the Queen's English all the time...
            You will see that the EGT and fuel flow values at peak stoichiometric mixture, varies depending on the MAP, not altitude. At the same MAP and RPM, you will always see the same numbers. So testing at WOT at 10,000ft is an expensive option compared to running the same test at sea level, with the throttle partially closed.

            The engine doesn't know whether it's at sea level of 10,000ft - it only knows what the MAP, RPM, and mixture setting are. For example, if you operate the engine at 20"Hg and 2,000PRM, at anywhere from 0 - 10,000ft, the instrumentation absolute for LOP should be the exactly same. Of course, the position of the controls will vary.

            Practically, this means you can develop LOP setting which are safe to use at sea level, for me I use 2300 RPM and 23", at 37 L/hr fuel flow. I have a check-flow at 2300 and 26" of 40 to 41L/hr. Once I have that dialed in, I know I can open the throttle all the way up to WOT, at any altitude, without the engine operating too close to peak EGT.

            The only unknown for me is the mixture enricher which takes affect as you exceed around 85% throttle from memory, however I haven't noticed any step-change in fuel flow or increase in EGT, so I have had no problems. I've never taken time to fully consider how that interplays with LOP operations, practically it seems to have no effect.
            Last edited by Battson; 05-08-2022, 06:23 PM.

            Comment


            • schu
              schu commented
              Editing a comment
              While reading through your post I was thinking that it all assumes that the fuel metering device meters fuel the same and distributes it the same regardless of throttle setting, then I got to your last sentence where you consider that.

              Given the enrichment circuit and the fact that the butterfly valve will surely affect air distribution. I plan to do my mixture spread testing at whatever throttle position I plan to operate LOP just so that the test is in the same conditions. In other words WOT.

          • #11
            Originally posted by Nev View Post

            Has anyone installed one of these before ? Any suggestions are welcomed.
            I have installed a similar valve couple years ago, as my oil temp was on the low side. It Works very well in spring and fall time to control the oil temp, but not sufficient for our Canadian winter. I control the valve with a Bowden cable. Also use it in summer at higher altitude, to reduce cooling.
            In winter, I have to restrict the exit area by about 1/3 to keep my engine and oil warm.
            BE753034-A166-4BDE-9E93-E4FC210DF128.jpg
            Mike

            Comment


            • #12
              Brilliant, exactly what I was hoping for. Our winters would be considered tropical by Canadian standards
              Nev Bailey
              Christchurch, NZ
              Builders-log
              YouTube Bearhawk Blog

              Comment


              • Aero_tango
                Aero_tango commented
                Editing a comment
                Tropical winter…I love this:-).

              • rv8bldr
                rv8bldr commented
                Editing a comment
                Personally, Michel, I think those New Zealanders should be forced to put quotes around that word..."winter". ;-)
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