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Engine Break In and First Flight

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  • #16
    I did a little searching on VAF, and some of them talked about paying for test cells, and one said somebody had made a "ground cooling duct" to run the engine on the ground. No other elaboration so I did some you tubing of various flavors. Dyno's, test cells, Lycoming, airboats, etc.

    I might be overthinking how hard it is too break the engine on the ground. A few of the dyne's had fan fed duct, but most simply had some flavor of scoop sitting above the engine directing the prop blast down through the cylinders. Sort of like a big hood scoop. I would estimate most were 4-8 square feet of opening facing the prop. Lycoming had one of the simpler ones where they said they run their new engines in for 1-2.5 hours.

    A lot, or maybe most, airboat look like they run with nothing but the bare engine. A few had an extremely simple venturi effect updraft setup for cooling. Just a flat piece of sheet metal on top of the engine with tabs cut and bent up. The air flows over, and suck a little air from the bottom.

    The picture of Lycomings' test cell is attached. Quality isn't that good as it is just a screenshot from youtube.

    It may not be rocket science to at least seat the rings on the ground.
    Attached Files


    • #17
      The nice thing about testing on your own plane is not only simplicity, but you get to put some time on your installation, not just the engine. The only thing that would not be tested would be your ducting and cooling exhaust exhaust. You get to watch the instruments and see when the rings seat, and that is it. Not test flying simultaneously.


      • Chewie
        Chewie commented
        Editing a comment
        I just saw this, sorry for being redundant!

    • #18
      Originally posted by svyolo View Post
      Stuff deleted...

      I am pretty sure an RV-8 wouldn't want to fly around at 205 mph for the airplanes first hour of flight either. This can't be a new issue.
      When I test flew my RV-8 with a 0 timed IO-360 I was at 100% for the first couple of hours. I left off the wheel pants to give me some drag, but still zipped around at 175 kts !


      Maule M5-235C C-GJFK
      4 Seat Bearhawk #1078 (Scratch building)
      RV-8 C-GURV (Sold)


      • #19
        My understanding of Engine Break in theory. (warning, I have no experience, just book knowledge)

        ....a new cylinder wall has been honed and has a microscoipic peak/valley scratches that form a cross hatch pattern. The break-in mates the compression ring to the cylinder wall and wears those microscopic peaks into plateau's.

        Increasing the pressure between the Ring and the Wall seems to be the goal at break-n. The highest Internal Cylinder Pressures are attained at high power settings, which increases outward pressure on the compression ring against the cylinder wall. My vision..... "Its a dirty Job, get it done quickly to avoid glazing!" Results of a well done break-in are low oil consumption for the life of the engine.

        Low Power reduces the pressure between the ring and cylinder wall.

        A common failure is the hills/valley being filled in with carbonized material from combusted oil residue that builds up, glazing the cylinder walls. The result in a smooth cylinder wall and high oil consumption. Its cylinder walls, replacement of the rings, then re-do the break-in. I've wondered if the high pressure is what scrapes this contaminate off before it cooks/hardens.

        Whee. Higher power settings are attainable If you did your engine runs in single digit temperatures. Your density altitudes would come down a couple thousand feet. If CHT are elevated at Best Power mixture during break-in, richen it up.

        I wonder how the re-honing cost compare with a $1000 test stand run. I have no idea, jus thinking out loud. It Might be worth the risk.

        Bengelis has a drawing of an engine test run shrowd in his book "On Engines" or "Firewall Forward".
        Brooks Cone
        Southeast Michigan
        Patrol #303, Kit build


        • rodsmith
          rodsmith commented
          Editing a comment
          You describe the process very well. Besides the cost of rehoning there is all the work involved in removing the cylinders. Plus re-installing and getting everything properly torqued again. This is something I am really anxious to avoid.

      • #20
        Originally posted by rv8bldr View Post

        When I test flew my RV-8 with a 0 timed IO-360 I was at 100% for the first couple of hours. I left off the wheel pants to give me some drag, but still zipped around at 175 kts !

        Brooks, You seem to have a good understanding of the process now how do we make it happen on a unproven airplane at a higher elevation airport?

        Removing cylinders is a big deal; removal of all the stuff, installation of the torque plates, cylinder and ring work, re-installation. Lots of room for error.

        I'm probably making a bigger deal out of engine break in than I need to. Minimizing ground running and running the engine as hard as safely possible will likely be adequate. I guess we will find out.

        Thanks everyone!

        Scratch Built 4-place Bearhawk. Continental IO-360, 88” C203 McCauley prop.


        • #21
          I've shared my test flying procedures on here before, I think. Here's a link to the short version we used recently, following our rebuild:

          Refer to pages 7 and 9 for the most relevant information.

          Here is the original full plan, and I mean FULL... This was for the original first flight.

          Refer to pages 11 and 12 for the most relevant information.

          Note the original plan was written without the benefit of hindsight. The second iteration was under a different context, the plane we already well understood and proven.
          Last edited by Battson; 02-13-2019, 03:24 PM.


          • #22
            Thanks Battson! Just today I downloaded your POH, guess I'll have to pirate your flight test plan too.
            Last edited by whee; 02-13-2019, 03:26 PM.
            Scratch Built 4-place Bearhawk. Continental IO-360, 88” C203 McCauley prop.


            • #23
              Originally posted by whee View Post
              Thanks Battson! Just today I downloaded your POH, guess I'll have to pirate your flight test plan too.
              I would rather people spent their time building Bearhawks than creating mundane (but important) documentation. Share and share alike!


              • #24
                I can attest to being very nervous flying behind my first airplane engine overhaul.. especially since the instrumentation was oil temp, oil pressure and a bayonet probe on number three. Plugs out of the top holes...spun the engine until the oil pressure came up..used lycomings mineral oil and STP mix to assemble. Installed the plugs. Fired up...ran for about a minute. Checked for leaks. Blasted off. Full throttle...had to keep full rich...I don’t like a CHT meter with just one bayonet probe. Kept CHT below 450. 10 minutes...landed and reassessed cooling issues..airplane had 3k hours plus..but less than 300 hours on an owner built cowl.. modified the cowl outlet...made it bigger. Used a quart of oil during the first hour..probably blew it overboard. Oil level at a quart from full for the next couple hours, may have used 1/2 quart. Doesn’t use oil now...cylinders had unknown hours on them. Log book said they were new 300 hours before the engine had to come down due to bad vibration. They were not new...exhaust seats had three was at the edge of the valve face. One cylinder required the shortest push tube available from Lycoming...a dash 10

                Next time...I’m going to build a big hood with a nice arc towards the back to mimic in flight airflow.

                My rule of thumb after an overhaul on a Diesel engines. Start...check for leaks and noise. Button everything up. Then if no truck dynometer.. try and drive the engine through the brakes.. I was a dealership journeyman diesel mechanic... did many, many overhauls...just one come back...and that was a blower seal on a silver 6V92TA. Took a week to fail.

       did not have a CHT meter until I installed one at overhaul.


                • #25
                  Sorry if I missed a mention above, but there's an article in Kitplanes Dec 2018 by Michael Leigh on ground engine break-in.

                  He brings up some good points of why to break-in on the ground, using your airplane as the test stand (with proper cooling and ducting of course).

                  - you can break in before you do the taxi tests, which are by definition low-load tests that seemingly contradict the engine manufacturer break-in process
                  - you get very familiar with your engine, it's operation, sounds, vibration, pressures, temperatures etc etc and the worst thing that can happen is you have to shut er down.
                  - obviously less risk involved vs unproven engine + unproven airplane tested together at once

                  It's a compelling idea.
                  Scratch building Patrol #275
                  Hood River, OR


                  • rodsmith
                    rodsmith commented
                    Editing a comment
                    Thanks Mark, I missed that

                • #26
                  A couple of my take aways from all the sources I read about engine break in and 1st flights.

                  Guy takes off on his first flight/new engine. CHT's are through the roof. Lands. Modifies his cooling system................What I read is that new engines generate a lot more heat until the rings seat. Lots of metal to metal contact between rings and cylinder wall. After they seat, CHT's go down 25-50F individually as they seat. Did the cooling system need to be modified?

                  Older certified planes had little in the way of engine instrumentation, but the cooling system was certified. Put a new engine in, takeoff, and run the heck out of it and you were blissfully ignorant of the individual CHT's. Sometimes too much information isn't a good thing.

                  But homebuilts have homebuilt cooling systems, so that is a variable. High CHT's and rising on the first flight? Poor cooling system, or just the engine breaking in normally?

                  Depending on where you live there is another problem. Whee said he lives at 6500'. 75% power is around 8000', on a standard day, and Idaho gets pretty hot in the summer. Even on a standard day would you want to test fly a whole flight at 1500 agl ? On a hot day he probably can't generate 75% on the ground.

                  I haven't seen the Kitplanes article but I will look,


                  • #27
                    The break in of the O-360 on my Patrol went about as badly as one could imagine. I initially installed an electronic ignition system that I'd had prior good experience with. The one on the Patrol had serious issues. Lots of ground running. Most was un cowled. I think I had 3 hours on the engine before the first flight. It was pumping oil so badly there was actually oil seeping from the exhaust system joints. I didn’t have much choice. I ended up pulling the ignition system and installed a Pmag (which is amazing!).
                    On the first flight, I never pulled back from 2700 rpm. CHT’s ran near 400 and oil temp was quite high. I spent a little time making a cooling lip and tightening up the baffling. By the third hour, CHTs were at or below 350. I ended up replacing the vernatherm to help oil temp.. As the engine broke in, oil temp came down.
                    Nearing 100 hours now and all temps are good. Oil consumption is about a qt in 10 hours, which is great in my book!

                    I offer up this information to ease the worries about a textbook break in. Sometimes you just have to do your best.



                    • Bcone1381
                      Bcone1381 commented
                      Editing a comment
                      Real Life experience is better than book knowledge!

                  • #28
                    I read the article, his article is in agreement with what was written here. He did a lot of fabrication, and from other examples I have seen, it might be easier than that, especially since we already have a pressure cowl built. I think either using the pressure cowl, or a scoop, seems easier.

                    The only issue I see with the scoop is if you have the top half of the cowl removed, I am not sure how the lower cowl will respond to the prop blast. Maybe no problem.

                    Here are a few pics of test stands.

                    Attached Files


                    • #29
                      Here is a screenshot from the article. Michael custom built two cowls, and attached a coupe of leaf blowers to them. I can post a link to a free link to the article, but I am not sure if putting copywrited material is against forum rules.

                      I will try to find a different design that I saw, It was a sheet metal shroud, with what looked like a 12" scat hose feeding it from above. I think you could just make a cheap upper cowl flap, and feed the air in through that, using the pressure cowling on the airplane. The basic spec is 1/4 PSI, but you also need the correct flow rate. Lycoming supposedly specs a mass flow rate for cooling for each engine, but I haven't been able to find it yet. I will keep looking. If anyone knows the number, or where to find it, it would help.

                      If 1/4 PSI is enough to drive the cooling flow, I don't see why you couldn't create that Delta P from the bottom, instead of the top. Attach a duct to the bottom of the cowling, seal the upper cowling with some duct tape, and draw air from the bottom.

                      Doing a really rough calculation a different way, and I am not at my place where I can measure my cowl intakes, I think the volume flow rate seems to be a few thousand CFM. You can get a blower in that range, in 12" diameter.
                      Attached Files


                      • jaredyates
                        jaredyates commented
                        Editing a comment
                        Posting a link to where they have the content published on their site is always fine. Posting the content itself is less optimal, even if it is currently available publicly. If they were to make it unpublic on their site, and it was also posted here, then that could be a problem. By posting a link to where they have it published, we are preserving their ability to control whether it is public or not. I think of it this way... If someone wants the information in that article and is not a kitplanes subscriber, we don't want them to be able to come here and get it for free instead. For me this is mostly about respecting the viability of what is perhaps the most important publication for our hobby. It's doubtful we'd ever hear anything from them either way.

                    • #30
                      FWIW, Here is a link to a book that I had purchased about flight testing a homebuilt aircraft. I bought the book and it is well worth the money: