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  1. #1

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    Why are helicopter glow engines so smoky????

    Why are helicopter glow engines sooooo smoky????? I just love smoky glow engines...........but are the heli pilots just simply running very rich with their glow engines??? Is that very rich heli engine tuning deliberate to avoid destroying the glow engine on a lean run??? Looks good to me though when the heli pad is fogged up with the smoky glow exhaust. Larry.

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    RE: Why are helicopter glow engines so smoky????

    ORIGINAL: larrysogla

    Why are helicopter glow engines sooooo smoky????? I just love smoky glow engines...........but are the heli pilots just simply running very rich with their glow engines??? Is that very rich heli engine tuning deliberate to avoid destroying the glow engine on a lean run??? Looks good to me though when the heli pad is fogged up with the smoky glow exhaust. Larry.
    When you only have one engine keeping your model airborne, but no wings to glide with should your engine quit, you must do things differently - because helicopters do not glide in the event of a deadstick.

    Burning extra large amounts of nitromethane not only increases horsepower, but it also increases engine running reliability. While nitro is a liquid, its true benefit is in providing extra oxygen to burn with the alcohol component of the glow fuel. Since we are now not only flowing fuel to the engine through the spray bar assembly, but also oxygen in the form of nitromethane, we must also richen the mixture significantly. Hence, the smoky exhaust.


    Ed Cregger
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  3. #3

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    RE: Why are helicopter glow engines so smoky????

    NM2K,
    Thanks for the quick reply............your analysis is right on..........I love those heli's when they blanket the heliport with the lingering thick smoke from their exhaust. Larry.

  4. #4
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    RE: Why are helicopter glow engines so smoky????

    "but also oxygen in the form of nitromethane, we must also richen the mixture significantly. Hence, the smoky exhaust. "

    I always thought nitromethane gave oxygen as a byproduct of being burned.
    \"Keep it clean and not too lean\" Duke Fox

  5. #5
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    RE: Why are helicopter glow engines so smoky????

    The 50 size helicopter engine is constantly turnig about 17.000 RPM , and that alone will give more smoke than an airplane engine maybe running 12000 at full throttle.
    Planes move quite quickly away from the exhast smoke when flying, so you dont notice it as much as a helicopter hovering.
    Also, the prop on a plane is blowing away the exhaust, deluting the smoke

    Im still a newbie in helis, and I only use 10% nitro in my raptor 50.
    The other guys at my field use 20-30%, and they sure smoke more than mine does, so high nitro content also makes more smoke for sure.
    Sonnich Johannesen

  6. #6
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    RE: Why are helicopter glow engines so smoky????


    The oils used in Heli specific fuels tends to be higher in nitro and oil content, and viscosity. I know someone who flies Helis and he runs 23% synthetic oil in his fuel. He has said its also a bit unconventional to set the needles on a heli. It seems to be common for helis to have no castor in the mix, so that lends to the smoke as a portion of the lubricating oil also burns. Synthetics tend to smoke more in my experience.
    GlowHead Brotherhood #3
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  7. #7
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    RE: Why are helicopter glow engines so smoky????

    The fuel has 23% thich synthetic oil. That is why they smoke so much. Nitro has nothing to do with it or you would not be able to see AA fuel dragsters and funny cars on the drag strip without a cloud of smoke behind them.
    Glow Head Brotherhood #15

  8. #8
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    RE: Why are helicopter glow engines so smoky????


    ORIGINAL: Sport_Pilot

    The fuel has 23% thich synthetic oil.* That is why they smoke so much.* Nitro has nothing to do with it or you would not be able to see AA fuel dragsters and funny cars on the drag strip without a cloud of smoke behind them.
    The nitro itself doesn't cause more smoke, true, but the richer mixture that comes with 20-30% nitro means you're flowing that much more oil at a given time. So in a way it contributes to more smoke indirectly.

    At least that's how I see it anyway.
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  9. #9
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    RE: Why are helicopter glow engines so smoky????

    That reminds me of a flight I had a few months ago with my CL stunter and it's .61 running in a 4 stroke with 25% oil (mostly castor). The breeze dropped completely so it was dead calm and the exhaust blanketed the entire field like a fog .

  10. #10
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    RE: Why are helicopter glow engines so smoky????

    Top Fuel runs 90% nitro.

    I would want a higher percentage of castor in an enclosed engine that typically runs hot during hovering.
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  11. #11
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    RE: Why are helicopter glow engines so smoky????

    Nah we run synthetic, 90 percent of heli guys don't want to deal with the messy pipe that castor makes and the good heli fuels are safe.

    So everyone pretty much pieced it together.

    1. Enclosed engine only gets cooling from the fan and the fuel (oil specifically) so its got to run richer.
    2. Most heli fuels contain 20% or a bit more oil.
    3. Most heli guys fly 20 to 30% nitro so you have to run richer still so you get more oil and more smoke.

    Some places make LS or low smoke fuel for helis but most of us don't mess with it.
    Andy - Helicopter Forum Moderator
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  12. #12
    Moderator blw's Avatar
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    RE: Why are helicopter glow engines so smoky????

    I'd just clean up the mess afterwards. No problem. Helicopters are dirty anyway. Full scale ones are.
    The ultimate responsibility of pilots is to fulfill the dreams of the countless millions who can only stare skyward...and wish.

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  13. #13
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    RE: Why are helicopter glow engines so smoky????

    Hey Barry, Andy might recognize this issue. OS Hyper 50 engines are notorious for eating bearings. When I bought my first one I decided to run nothing but fuel containing a blend of Castor/Synthetic. That engine is still running 7 years later and more important, it's never had a bearing replaced. Go figure. There have been all kinds of "Tricks" for keeping the bearing alive including the famed "coke can" mod. Most say it doesn't work although a few at our club swear by it. For me I'm sticking with the Castor blend at 24% thank you very much. It's way too easy to clean the brown mess on the pipe with a crock pot and antifreeze LOL.
    Spektrum DX8i, DA DLE SuperTigre OS FOX Saito Enya Jett TT: John 3:16

  14. #14
    Moderator blw's Avatar
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    RE: Why are helicopter glow engines so smoky????

    I agree that the mess is much worse than with airplanes. You get oil on the skids, tail boom, and tail rotor. It probably sticks to rotor blades and everything else.
    The ultimate responsibility of pilots is to fulfill the dreams of the countless millions who can only stare skyward...and wish.

    "It's a new day for Auburn" - Gus Malzahn

  15. #15

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    RE: Why are helicopter glow engines so smoky????

    I've put a few heli engines on planes and found that when they are running at their best, they do leave more of a smoke trail than their aero engine counterpart. Heli engines are ported for high power, somewhere between a sport engine and a ducted fan engine. An OS or YS 91 heli engine makes a boat lode more power than an OS 95 AX, and at full throttle* the heli engine also uses almost twice as much fuel to do it, hence more smoke. Also, a lot of guys run 30% which means the needle must be opened up more than if it were on 15%. No free lunch for power.

    *Keep in mind that most heli's hover at about half throttle and can fly in forward flight with even less throttle.
    Oooh eee oooh ah ah(the crowd) ting tang walla walla bing bang!(the plane crash)

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    RE: Why are helicopter glow engines so smoky????

    ORIGINAL: blw

    It probably sticks to rotor blades and everything else.
    Yup, just be sure to wipe down both blades and not just one. Big time shakes![X(] What happens when someone distracts ya.
    Oooh eee oooh ah ah(the crowd) ting tang walla walla bing bang!(the plane crash)

  17. #17
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    RE: Why are helicopter glow engines so smoky????

    Yea, the hypers love eating bearings and the mods are bs.

    I run Byron Rotor Rage 30% (all synthetic) and haven't done a bearing since I ditched Cool Power and or Magnum.
    Andy - Helicopter Forum Moderator
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  18. #18

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    RE: Why are helicopter glow engines so smoky????

    why not have a better setup for cooling the heli engines, run less oil which will let ya make more power. Heli's have always had the engines run hot so they increaded the oil to help keep the engine alive. the added oil decreased the amount of power the engine makes so they had to increase the nitro to make up for the power loss.

    now for you guys that are good at making your own stuff and designing it you should look at a better cooling the engine. running a bigger cooling fan isnt the way to go as most should know when you compress the air as its doing on a heli the temp of the air goes up. they have tried tighter and tighter clearences on the fan and engines to make run cooler as the engines have gotten more powerful. instead of blowing air over and around the engine it should be pulled acrossed the engine. as you create a negative pressure from sucking the air the tempature of the air drops. This principle is how Air conditioners work on real airplanes. they take hot (400 degree) air and expand it. when this is done the temp drops to around 20-30 degrees.

    So once you get a better cooling setup on the engine you can run less oil and less nitro and still make the same power. this would be less mess on the heli...... oil in our engines doesnt burn so the more oil you have in the fuel, the less space in the chamber you have for alcohol, nitro and air to burn.


    the extra oil accounts for the extra smoke. one caution though DO NOT use the indication of smoke as the correct mixture setting. i hear many guys say " it cant be lean because i can see smoke coming out of the muffler" lol.


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  19. #19
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    RE: Why are helicopter glow engines so smoky????

    My Vario 4 stroke sucks air through the cooling fins.......its about over 20 years old now

    http://www.youtube.com/watch?v=DMO1_U7PUao
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    Sonnich Johannesen

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    RE: Why are helicopter glow engines so smoky????

    SJN no problems with heat either.....
    AMA # 126183
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  21. #21
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    RE: Why are helicopter glow engines so smoky????

    Heli Fuels with 23% oil content are running low viscosity oils that are much thinner than the oils typically used on a fixed wing engine.

    The thinner oil burns faster, hence the increased oil content and subsequent smoke.


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