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  1. #1
    yakfish's Avatar
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    TEST: How nitro content effects RPM

    I have been doing some testing today. I really started testing so compare a couple engines I have. Then I wanted to see how much of a difference nitro content actually makes. I will add more engines later maybe. Here is what I found so far. Garmin Forerunner 301 GPS was used for the speed and I use the rc gears speed calculator to figure the RPM'S

    Engine: LRP Z.28 Spec 3
    Chassis: Mugen MBX5T
    Pipe: Jammin JP-2
    Diff ratio: 4.6:1
    Spur gear:46T
    Clutch Bell: 13T
    Tire diameter:6.5 inches compensated for "ballooning"

    Fuel: 15% nitro, 8% castor oil
    Plug McCoy MC-59
    Top Speed:37.6 MPH
    RPM: 31700

    Fuel: 30% Nitro, 9.5% castor oil (for better protection)
    Plug: McCoy MC-9
    Top Speed: 41.8 MPH
    RPM: 35200

  2. #2

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    RE: TEST: How nitro content effects RPM

    Although the oil contents are slightly different, it looks like doubling the nitromethane content resulted in an 11% increase in speed. Nitromethane results in more power, a better idle, slightly easier starting in most cases. I like the way you determine the results and it took some smarts to be able to do that. Nitromethane is probably more important in racing applications, for example, with boats, where 60-70% nitromethane is used. In fact, the nitromethane content is so high, you have to work to keep the nitromethane in solution. You can get fairly easy 30-35% nitromethane in solution. Much higher than that, and it becomes more difficult. As an aside, in some boat applications, a little Klotz Benol racing castor can protect the engine quite a bit, even at fairly low concentrations. Nitromethane is somewhat more difficult to buy now, in no small part due to the use in the Oklahoma City federal building bombing and other such events. Luckily, I can still buy nitro in 5-gallon pails and 30 gallon drums, along with racing methanol and the oils I need to make my own fuels. Glad to see someone testing the actual effects of nitromethane on performance. Then, people can determine how much nitromethane they need for fuels for their type of racing, flying and so forth. Remember than in many countries, nitromethane is not available, and in some cases, even illegal to possess, so we are fortunate to have it available for our model fuels. When nitromethane is not available, there are engines with fairly high compression ratios that run reasonably well on no-nitro fuels, that is, standard FAI fuel. Again, thank you for providing objective information about the effects of nitromethane on your engine.

  3. #3
    1QwkSport2.5r's Avatar
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    RE: TEST: How nitro content effects RPM

    There is no doubt adding more nitro will provide a lot of bonuses to the performance of the engine, but its also expensive. If I had a lathe, I'd make up head buttons and modify cylinder liners to increase the compression so I could run no nitro at the same performance levels as using a "standard" amount of nitro.

    Its hard to put a finger on just what rpm a car engine is turning. Most calculators will get you close, but a Tach is the best way to check an engine. Its too bad the crankshafts are so short on car engines, I'd like to put a prop on one mounted on a test stand and test that way. That way a Photo Tachometer will give accurate numbers.

    Edit: Yakfish - when comparing fuels like you did, you need to only change one variable at a time. The change in oil content might be skewing the results somewhat. Keep your oil content the same and change only the nitro content to have a better comparison. More oil will increase the compression slightly.
    GlowHead Brotherhood #3
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  4. #4

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    RE: TEST: How nitro content effects RPM

    No doubt, nitro adds power IF the engine compression ratio is adapted to take care of the extra fuel burnt.
    In normal engines, 15% nitro is about the upper limit. Some FAI engines are designed to run NO NITRO. These engines require a redesigned head combustion chamber if running in excess of 5% nitro. Adding shims will not quite cut the cake, because the squish zone becomes to thick. Best squish zone thickness is about 1/75 ( 1%- 2% ) of the engine stroke. The closer, the less prone to detonation.
    Pe, (www.mvvs.nl), MVVS, MOKImotor, RCexl, MTW, Xoar, Mejzlik.
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  5. #5
    Jezmo's Avatar
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    RE: TEST: How nitro content effects RPM

    This is a very interesting experiment and one I tried many many many years ago. (Yes that means I'm getting old LOL) I have always loved this sorta thing and applaud the OP for his work and interest.

    For those who may happen upon this thread, an engine CANNOT be made to make the same power without nitro as with. Some folks would have us believe otherwise. The gap can be closed somewhat by modifying the head or making new one with the proper dimensions for running methanol only. The fact is Nitro-Methane contains a very significant amount of oxygen in it's molecule chain that is available for combustion allowing more fuel to be drawn in and burned thereby increasing the available power. The stoichiometric ratio for methanol is 6.4 to 1 and for Nitro-Methane it's closer to 1.7 to 1. Looking at the numbers it's easy to see that much more fuel can be packed into the cylinder for more power when using higher percentages of "Nitro". Yes the engine MUST be properly setup for High Nitro percentages in order to make use of it but make no mistake an engine set up and tuned properly and running high amounts of Nitro WILL be significantly more powerful than one running straight Methanol.
    Spektrum DX8i, DA DLE SuperTigre OS FOX Saito Enya Jett TT: John 3:16

  6. #6
    downunder's Avatar
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    RE: TEST: How nitro content effects RPM

    Because I don't use nitro I have no idea how much extra power an engine develops with various amounts of nitro in the fuel. What I do know is how much extra power can be realised by raising the compression to make better use of plain old methanol. Many years ago I experimented with an Enya 60X and gained slightly more than 20% extra power by raining the compression to 13.5:1, further increase gave no more rev rise. A few weeks ago I made a new head button for my Enya 61RE which raised its compression from the standard 8.8 to 12.4 which gave a rather surprising 26% increase. It'd be interesting to know how much nitro would be needed to get a similar increase but it's too expensive for me to try.

    I might add that the only direct comparison I can make is with my son's car engine. I convinced him to use the same fuel we use for flying (80/20 all castor) and after a few races we raised the compression to 13.4 and his car then had identical performance to others using the same engine in the same car but with 25% nitro. His would also run 8 minutes to a tank compared to 6 minutes for the others.

  7. #7
    Sport_Pilot's Avatar
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    RE: TEST: How nitro content effects RPM

    Doubling the percentage will almost double the torque and less so the horsepower but only if the compression ratio and glow plug heat is adjusted for the increased power.  However even if you doubled the horsepower you will not double the speed because the drag increases to the square of the speed.
    Glow Head Brotherhood #15

  8. #8
    yakfish's Avatar
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    RE: TEST: How nitro content effects RPM

    ORIGINAL: Sport_Pilot

    Doubling the percentage will almost double theΒ*torque and less so the horsepowerΒ*but only if the compression ratio and glow plug heat is adjusted for the increased power.Β* However even if you doubled the horsepower you will not double the speed because the drag increases to the square of the speed.
    I haven't figured out how to measure horse power and toque yet (with just a GPS and a calculator) but I am more interested in the rpms anyway. I don't think the difference is anywhere near double though. The power was barely even noticable, but it would be interesting to see those numbers. I could hear the difference in RPM. but from a stop the power seemed almost the same with both fuels.

    Next I need to remove a shim and see how it runs on the 15%

  9. #9
    Sport_Pilot's Avatar
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    RE: TEST: How nitro content effects RPM



    Reread my statement..



    Doubling the percentage will almost double the torque and less so the horsepower but only if the compression ratio and glow plug heat is adjusted for the increased power.
    Obvioulsy you cannot easily change the compression ratio, and can only change the glow heat in steps. So the actual performance increase will not likely be close to double, and could be nothing.

    Glow Head Brotherhood #15

  10. #10

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    RE: TEST: How nitro content effects RPM

    You can slightly change the compression ratio, by removing or using thinner shims, or by redesigning the head. You can also vary performance by the heat range of the glow plug, by using fairly dry methanol for better performance. That said, American hobbyists use very high nitromethane fuels overall. For example, I do not generally use 30% nitro fuels for my Saito engines. It does not make sense to me to double the expensive nitro to get a few hundred more rpm. Competition pilots will use every advantage they can, and a few hundred rpm may well make a difference in competition. I can tell you early on, I could burn a hole in the top of a rat race piston as fast as anyone flying that day. Early trials with fuel were largely trial and error, with emphasis on error. Out of those times came some excellent fuel formulations. A lot better than adding oil of mirbane (nitrobenzene), propylene oxide, acetone, you name it. If it burned or added oxygen, it was fair game. For combat and rat race, we were able to mix our own fuels and after awhile, those fuels worked really well. My general (generational?) view is that many modern fuels are a bit high to very high on nitromethane and a bit short on the amount and/or quality of the oils used. I read a lot of mostly advertising hype about the wonderful "additives" or additive packages added to fuel and am reminded that some of our best fuels in the late 1950s were simply methanol, Klotz Techniplate oil and nitromethane. Alternatively and especially control line flying, AA castor oil or Benol racing castor work well and are still in use today. Castor has the rather unique property of building chains at high temperatures, and stick really well on lower engine parts, giving protection at fairly high temperatures. This old fuel dinosaur has 34 formulations for boats, cars, airplanes and helicopters. Most model hobbyists will not mix their own fuels and there are a few very good fuels out there. My early training was in chemistry and I loved to mix my own fuels. If it gives you any hint, my first chemistry set at age 12 included (REALLY!), potassium nitrate, powdered charcoal AND yellow sulfur in the SAME chemistry set. I guess many of you can figure out the first thing I made from this set as a 12 year old. Nearly singed off my eyebrows! They no longer sell this particular chemistry set. Something about product liability I would guess. Anyhow, enjoy your cars, boats, helicopter and airplanes. Anything this much fun surely must be illegal. :-)

  11. #11

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    RE: TEST: How nitro content effects RPM

    You can slightly change the compression ratio, by removing or using thinner shims, or by redesigning the head. You can also vary performance by the heat range of the glow plug, by using fairly dry methanol for better performance. That said, American hobbyists use very high nitromethane fuels overall. For example, I do not generally use 30% nitro fuels for my Saito engines. It does not make sense to me to double the expensive nitro to get a few hundred more rpm. Competition pilots will use every advantage they can, and a few hundred rpm may well make a difference in competition. I can tell you early on, I could burn a hole in the top of a rat race piston as fast as anyone flying that day. Early trials with fuel were largely trial and error, with emphasis on error. Out of those times came some excellent fuel formulations. A lot better than adding oil of mirbane (nitrobenzene), propylene oxide, acetone, you name it. If it burned or added oxygen, it was fair game. For combat and rat race, we were able to mix our own fuels and after awhile, those fuels worked really well. My general (generational?) view is that many modern fuels are a bit high to very high on nitromethane and a bit short on the amount and/or quality of the oils used. I read a lot of mostly advertising hype about the wonderful "additives" or additive packages added to fuel and am reminded that some of our best fuels in the late 1950s were simply methanol, Klotz Techniplate oil and nitromethane. Alternatively and especially control line flying, AA castor oil or Benol racing castor work well and are still in use today. Castor has the rather unique property of building chains at high temperatures, and stick really well on lower engine parts, giving protection at fairly high temperatures. This old fuel dinosaur has 34 formulations for boats, cars, airplanes and helicopters. Most model hobbyists will not mix their own fuels and there are a few very good fuels out there. My early training was in chemistry and I loved to mix my own fuels. If it gives you any hint, my first chemistry set at age 12 included (REALLY!), potassium nitrate, powdered charcoal AND yellow sulfur in the SAME chemistry set. I guess many of you can figure out the first thing I made from this set as a 12 year old. Nearly singed off my eyebrows! They no longer sell this particular chemistry set. Something about product liability I would guess. Anyhow, enjoy your cars, boats, helicopter and airplanes. Anything this much fun surely must be illegal. :-)


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