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Modern vs. Vintage Fuels and Oils

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    Modern vs. Vintage Fuels and Oils

    I was watching some documentaries about Trans Air Link flying out of Miami back in the early 1990s:

    …the narrator mentioned that because of the lower octane fuels available (in 1991), they stopped using high blower and ran lower manifold pressures than they did back in the 1950s.

    Which makes me wonder: if we follow the PMDG tutorials and the POH provided, are we running the DC-6 in the sim according to the limitations of the higher octane fuels from ~1950 that it was designed for? If so, would we need to do anything differently to simulate using the commonly available fuels today?

    On a related note, I remember reading about diluting the engine oil with fuel to help deal with the cold, as well as rotating the hub to break up “congealed” oil (yikes!). Would this apply in 2021? As I just sold a car still running smoothly after 200,000 miles on 5W-20 it made me wonder if modern multigrade oils with winter ratings were used on these engines, or if even modern “straight weights” were dealing better with the cold than the stuff they had when these planes were built?

    Matt Smith


    I'm pretty sure the DC6's used 130/140 octane avgas. Did not verify though. What you could do is run down to NAPA and buy a container of Octane booster. LOL LOL. In all seriousness though. 115/145 is still around in limited production quantities. However running on low boost only sure sounds like a good idea. The PMDG POH reflects I believe original fuel grade performance. I could be wrong though.
    Regarding the oil. It's an interesting question. Not sure how the engine behaves with a multigrade synthetic over a straight weight mineral. Or if the engines would even like a synthetic inside. Given all the functions the oil has in these radials. It might be that the mineral is the only option and in such a case, diluting still needs to be performed. Everts would be the ones to ask regarding this. :-)
    First Officer Boeing 777 - Xander Koote


      Good question. The AF dash-one provides performance data for both 100LL and 130/140 fuels. It does not have a limitation on blower use with respect to fuel in use. The POH includes performance tables at the end of that section that are by a current operator of the DC-6, and I'm certain they are using modern fuels. Too bad we don't have the engine analyzer in the simulation, it'd be interesting to play with.

      I had a BMW parked overnight in a detached garage at a home I had in Omaha, on one of those cold clear January mornings. The oil cavitated in the crankcase and I aborted starting the engine. I placed a 100W trouble light next to the oil pan and when inside for a cup of coffee. I was probably using 5W40 oil. Yup, multigrades can turn to heavy syrup too. Viscosity is tightly dependent on temperature.
      Dan Downs KCRP
      i7-10700K 32GB 3600MHz 2080Ti


        Hey Matt

        I do not know enough about fuels but I can go through oils

        So the trusting thing about 'how things used to be' vs 'how they are now' in aviation - especially piston engines (Diamond Aircraft Excluding), is that they really have not changed that much. My expertise is in helicopters, but the Lycomming 0-530IO that we have in our R44RII is [sadly] very similar to the ones rolling off the production lines back in 1950's

        Engine Oils on the other hand have progressed light years. Gone are the days where oil would turn into honey. Their viscosity stays relatively stable and can protect the engine in -20' cold as well as +30' heat. In 2021 adding AvGas to oil is big no-no, it breaks down many of the properties of the oil. It has never been a good thing, except of course, shitty oil is still better than sludge, thus the lifehack.

        There are two oils that primarily used in 'regular aviation piston engines' through its life cycle. Mineral (aka straight, aka Redband, aka a whole bunch of names), and Single Grade Ashless Dispersant Engine Oil (or just W100Plus as this is what most people end up using)

        When the engine is brand new the aircraft is put on straight, mineral oil. After oil consumption is normalised it is then put on W100[Plus] Single Grade Ashless Dispersant Engine Oil. During this time we ask our pilots to pull maximum power (5min/Cont) wherever possible. This is to help the engine wear in and is also the reason that the mineral oil is used. Basically the cylinder walls have imperfections (low and high spots) and we need the rings to have small limited amount of metal to metal contact with the walls them perfectly shaped with the rings. W100+ has very high film strength which is resistant to rupture. Thus the rings will have a hard time abrasing the walls of the cylinder. Secondly the temperatures of a new engine are usually very high. The additives in W100Plus can glaze the piston and go inside the little crosshatch grooves in the walls. This will result in high oil consumption, more heat and a poorer performing engine. High power settings come with high combustion pressure which forces the piston ring out to rupture the oil film

        Now above can be different for engines that are force inducted, but the overall fundamentals are the same

        TLDR - Oils have progressed in the last 70 years about as much as computers. If you put 'the best' 1950's oil into your modern car you will be likely buying a new one in no time at all - also wrote all this on my phone so excuse the autocorrect and the terrible writing. Hopefully everything made sense
        Last edited by nikoel; 18Oct2021, 10:21.
        Niko Eltarenko
        3900x OC @4.45Ghz - RedDevil 6900XT OC @2850mhz - 64GB - Hyper X16 NVME RAID


          Thanks for the replies gentlemen! I know it has no real bearing on the sim but this stuff still fascinates me
          Matt Smith


            Originally posted by nikoel View Post
            Hey Matt
            TLDR - Oils have progressed in the last 70 years about as much as computers. If you put 'the best' 1950's oil into your modern car you will be likely buying a new one in no time at all - also wrote all this on my phone so excuse the autocorrect and the terrible writing. Hopefully everything made sense
            I'm not an expert, but I did work as a contract engineer in petrochemical plants for a couple of decades and engineered the installation of several viscosity measurement equipment ranging in use from asphalt to motor oils. Trust me, the temperature has a direct and fundamental impact on the viscosity of all "thick" fluids. The Aeroshell 100WPlus has a pour point of -21C.... this is where the oil no longer flows as a liquid. It has a wide range of viscosities over an operating temperature range of 40C - 100C (195cSt - 19.96cSt).

            I'm fairly certain that Evert's has oil dilution procedures in effect that are used in extreme cold conditions when engine heaters are impractical or not available.

            Although not related, before my industrial career I was in USAF logistics, my last assignment in a combat communication unit. Every year we deployed to Fairbanks AK in the winter for the Brimfrost Exercise (big multi-service military training exercise); except for one year when temps dropped below the pour point of kerosene/diesel fuels. We didn't bother going.
            Last edited by DDowns; 18Oct2021, 17:52.
            Dan Downs KCRP
            i7-10700K 32GB 3600MHz 2080Ti


              For cold weather operations it's quite interesting to watch the series "Ice Pilots" which focuses on Buffalo Airways up in the Northwest Territories of Canada and their collection of vintage propliners. It gets so cold up there they they routinely wrap up the engines in blankets as soon as they shut them down and I think I remember one episode where the crew of a DC-4 or C46 got stranded because they had issues with the heaters or something and they couldn't even turn the engines over by hand.
              Last edited by FrontSideBus; 19Oct2021, 18:12.
              Mark J Jones.


              • DDowns
                DDowns commented
                Editing a comment
                Ice Pilots is a great series. Seen them all.