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  1. #1
    hugger-4641's Avatar
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    Introduction to Glow Engines

    I was perusing the "RC University" link while helping a newcomer to the hobby and I noticed there was not, as of yet, any basic information on Glow Engines. Here is an article I wrote to help some of my students, it may be of use to someone else as well so I thought I would post it. Feel free to add it to the "RC University" if it is deemed worthy.

    Two Cycle Glow Engines by Gerald (Jerry) Hughes aka Hugger-4641>>

    There is no substitute for one-on-one help from an experienced person when it comes to operating and tuning a glow engine. If you really want to learn how to use one of these engines safely and properly, I highly recommend getting some help from a club or experienced modeler.>>

    This article is intended to help gain a basic understanding of how a two cycle glow engine works, how to set up the fuel tank and fuel supply system, and how to safely start and tune a basic glow engine. If you already have a basic understanding of how IC (internal combustion) gas and diesel engines work, then you will have no problem understanding the concepts discussed here. If you have no idea how a typical IC engine works, you should probably get a basic understanding of this first. A quick “Google” on “internal combustion engines” should lead you to an adequate tutorial on the basic concepts of compression, combustion, timing, and ignition for two cycle and four cycle internal combustion engines.>>

    Just like any other IC engine, in addition to compression, there are four basic things required for a glow engine to run. These are: Fuel, Air, Ignition, and Timing. Let’s briefly address these and how they are used in a two cycle glow engine.>>

    Fuel for a glow engine is a usually a mixture of Methanol , Nitro-methane, and some type of oil for lubrication of the engine. This has historically been Castor oil, but now days there are many fuels that use a synthetic oil component or a blend of both Castor and synthetic oils. These fuels are sold with different ratios of oil and Nitro (nitro-methane). Just like race cars can be modified and make use of different fuels, glow engines can give different results with different fuels. Engines that have been modified for higher compression can make use of less Nitro, while a lower compression can make use of a higher Nitro content. We are addressing the entry level RC enthusiast here, so generally, a fuel with 10% to 15% nitro content is preferred for most glow engines. Fuel with an oil content of 15% to 20% is also typical, and as said before, this can be castor, synthetic, or a blend of the two. >>

    Air is mixed with the fuel at the carburetor. The two most common kinds of carburetors used on glow engines mix air with the fuel in a slightly different way. One is called a “two needle” carb, and the other is called an “air bleed” carb. The two needle carb is the most common and most reliable of these types. As the name implies, it uses two needle valves to regulate the fuel and air delivery for idle and high rpm operation. The High Speed needle regulates the amount of fuel being mixed with the air that is drawn though the intake of the carb. This mostly controls the higher rpm performance of the engine. The low speed needle controls the idle mixture and as you might guess, controls the idle and lower rpm performance of the engine. >>

    The other type of carb is called an “Air Bleed” carb and is more common on cheaper, lower performance engines. These engines are typically found on RTF trainers. Most experienced modelers do not prefer engines with these carbs, but they are an economical entry level choice and are simple and reliable enough for most beginners to use effectively. The air bleed carb also has a high speed needle, but controls the air for the idle mixture by using a small hole in the exterior of the carb instead of using another needle to control fuel. Many “trainer” engine carbs such as the Evolution engine have locking screws or other mechanisms that prevent or limit the amount of adjustment that can be made to the idle and high speed settings. This is designed to keep an inexperienced person from making an extremely improper adjustment to the engine that would prevent it from running at all. >>

    Ignition in a glow engine is a little strange compared to the typical IC engine. A glow engine is kind of a hybrid of a two cycle gasoline engine and a diesel engine. Glow engines have a “glow plug”, but this is different from a “spark plug” in a gas engine and more similar to the glow plug used for starting in some diesel engines. The glow plug in an RC engine has a filament made of Platinum, very similar to the Tungsten filament in a light bulb. A battery or some electrical source is used to energize the glow plug for starting the engine, just like in a diesel, but once combustion occurs, a chemical reaction between the the fuel and the Platinum in the filament keeps the filament “glowing”, and the electrical source is no longer required. The fuel/air mixture is compressed by the piston as it travels towards the head, when the correct compression and fuel/air mixture is present, if the glow plug is “glowing”, then combustion occurs. Unlike a diesel engine which continues to produce combustion from compression alone, if the glow plug in a glow engine stops working, the engine will not run. Likewise, if the glow plug is working but not working properly, the engine may start, but may run erratically, may not want to idle, or may not want to run at full speed. >>

    Timing of the fuel delivery is achieved by a port in the crankshaft that is “connected” to ports in the cylinder walls, much like a typical two cycle chain saw or weed-eater engine. As the crankshaft turns, this “port” rotates past the opening in the carb at the same time that the piston has created a “vaccum” in the cylinder, causing the fuel to be pulled into the cylinder. This “timing” is not easily adjustable, so we won’t get into the details of how it works other than to say that it pulls fuel from the carb and delivers it into the cylinder. Timing of the ignition is not directly adjustable either. Ignition timing can be affected by the amount of compression, the amount of nitro content in the fuel, and the glow plug. Using the same fuel, a hotter or colder glow plug can slightly affect the timing of the Ignition, which may or may not be a good thing. The engine manufacturer will usually recommend a glow plug and fuel that is best for a particular engine. In the absence of manufacture's information, using a fuel with 10-15% nitro content and a “hot” glow plug such as an O.S. #A-3 is usually a good starting point that will run fine in most beginner level .25 to 1.20 sized two cycle glow engines. >>

    >>

    >>

    Fuel Supply to the carb is one of the most problematic areas of a two cycle glow engine. Let’s discuss the typical components involved in a basic system and the problems they can present. This may sound strange to some, but the muffler is actually the first link in the “chain” of the fuel system, following the chain from the muffler, next is the tank, clunk and pick up line, bung seal, High Speed Needle, carb fuel inlet, barrel, and low speed assembly.>>

    The fuel tank is the next link in the chain. The vacuum created by the engine is usually not enough to pull fuel from the tank reliably, so the tank is “pressurized” from a tube connected to the muffler on the engine. If this tube is not connected to the tank and to the muffler, or if the muffler has been modified improperly so that “back pressure” is lost, the fuel supply to carb will not function. If this happens the engine may not run, or may start and run briefly and then die. Another common mistake is to accidently switch the “pressure” line and the “pick up” line. The “pressure” line must be connected to the muffler. The “clunk” and “pick up” line must be connected to the High Speed needle valve. If these are switched, fuel will not flow properly. The High Speed Needle may built into the carb itself, or it may be a remote needle valve assembly attached to the firewall or elsewhere. Either way, the High Speed needle is next in the chain after the fuel leaves the tank through the clunk and pick up line.>>

    Fuel is “pulled” or “pushed” (which ever works best for you to think about it) from the tank to the High Speed needle through the “pick up” line and “clunk”. The clunk is basically a weight with a fuel tube connected to it that allows fuel to be “drawn” from tank no matter what position the tank might be in as related to the ground. If the clunk is installed properly, the plane can be right side up, inverted, or anywhere in between and the clunk will fall to the same area of the tank as the fuel, thus fuel flow is not interrupted during maneuvering. I should clarify that this may not be true if the plane experiences a prolonged “nose down” attitude. Most clunks and fuel lines stay in the rear portion of the tank and are not flexible enough to fall completely to the front portion of the tank. In a prolonged “nose down” attitude of the plane, the fuel can fall to the front of the tank where the clunk cannot reach, thus fuel supply can be interrupted. For this to happen, you would have to make a very prolonged dive from several hundred feet up, but it can and does happen. >>

    The bung is the opening in the fuel tank where the pressure line and pick up line enter and leave the tank itself. This is a common area for problems. If the bung is not sealing properly you may have a fuel leak. You may also have air getting pulled into the system at this point. If you have fuel leaking, the problem is usually obvious, but many times the problem won’t show up until the tank is half empty of fuel. You can observe the fuel line to the High Speed needle valve with the engine running and look for air bubbles. If you see any bubbles you have a leak in the bung or some where in the pick up line and clunk assembly. You must correct whatever is allowing the bubbles into the fuel line or you will be wasting your time trying to adjust the High Speed needle. >>

    The High Speed Needle is the next link in the chain. As mentioned before, the High Speed Needle assembly can be attached directly to the carb or it can be a remote assembly. Remote assemblies are often attached to the back plate of the engine crank case or on the firewall of the engine compartment, and this presents another place for fuel to leak or air to enter the system. This is easily identified if you observe the fuel line with the engine running. If you have no air bubbles between the tank and the needle valve, but you have bubbles between the needle valve and the carb, then the o-ring in the needle valve is probably the culprit. A temporary test can be done by removing the needle and applying grease or petroleum jelly to the threads and o-ring area, then re-install and set the valve. If this stops the bubbles, then you know the needle valve needs a new o-ring. >>

    Setting the High Speed needle. A general rule of thumb for getting started is to open the High Speed Needle 2 ½ turns. Usually, turning the valve clockwise closes the valve and turning the valve counter clockwise opens it. Close the valve completely, then open it 2 1/2” turns or 900 degrees of rotation. This is good starting point that should allow the engine to start, but may not be the optimal setting for performance. We will discuss starting the engine and fine tuning the needle setting later. >>

    Carb fuel inlet. This is the point where fuel enters the carburetor. If the high speed needle valve is mounted remotely, then this is the point where fuel enters the barrel and ultimately goes into the engine. The barrel is the mechanism that rotates as the throttle is moved and regulates the amount of air allowed to enter the carb. If the needle valve is attached directly to the carb, then the fuel exits the needle valve and goes directly into the barrel.>>

    If the carb has a Low Speed Needle, the adjustment screw is usually located on the opposite end of the barrel from the fuel inlet. Most often it is a very small slotted screw recessed inside the barrel assembly and throttle linkage. It requires a very small flat head screw driver to make any adjustments. We will discuss fine tuning the low speed needle later, but like the high speed needle, a good starting point is 2 ½ turns open. There are a few engines, such as some Supre Tigre, engines which are left hand thread. This means that to open the needle, you must turn clockwise instead of counter clockwise. Most O.S., Magnum, Asp, GMS, and other entry level brands have needle valves with right hand threads and must be turned counter clock wise to open them. If the carb is an “air bleed” type, it will usually have a small external screw head that may have a slotted, hex, or Phillips head, as well as a small locking nut.>>

    >>

    Starting the engine. Let’s talk about safety at this point. Starting a glow engine can be dangerous even if the engine is not running yet. First of all, the aircraft needs to be strapped down securely to a starting stand designed to prevent any forward motion once the engine starts. Examples of these starting stands can be found in various threads on RC universe and other forums.>>

    Starting a glow engine by hand is commonly done by experienced folks, but to be done safely requires some habits and precautions that are best taught in person. A propeller can “kick” back during starting and do a lot of damage to fingers if not done properly. The safest way to spin a glow engine is by using an electric starter. This is basically an electric motor held in your hand and applied to the nose cone of the engine. These can be cordless, or powered by connecting to a car battery or some other external power source. But this just gets the engine spinning, more is needed! As mentioned earlier, the glow plug requires some electrical source to begin the process. The most common method of doing this is by using a “glow starter”. This is basically a rechargeable battery with a long neck that is attached to the glow plug temporarily while the engine is being started. There are two potentially hazardous situations that occur at this time:>>

    First you must apply the engine starter and remove it when the engine starts without putting any body parts in the path of the propeller. A very real danger is that the propeller or spinner could come loose or break apart during starting or right after the engine starts. If a spinner or propeller fails, it usually flies forward and/or off to one side. So, it is best to position your head and as much of your body as possible behind the propeller and reach around with one hand to apply the starter.>>

    Second, once the engine starts, you must remove the glow starter. This places your hand in a very close proximity to the spinning propeller. You must remove the glow starter carefully keeping your eye on the propeller and keeping your hand from slipping into it. I paint the tips of my propellers red or yellow to help keep track of where the arc of the blades is.>>

    Once the plane is secured and safety concerns are addressed, the starting procedure is simple:>>

    1. Fill the tank with fuel and turn on the rx and tx. Set the throttle so that the barrel of the carb is just slightly open. You should see a very small crescent shaped opening just big enough to put the head of a pen or pencil into. Make sure you have pre-set the High Speed Needle as mentioned previously, or no fuel will be able to reach the carb.>>

    2. Place a finger over the exhaust and rotate the propeller counter clockwise by hand several times until you see fuel in the fuel line to the carb inlet. Plugging the exhaust helps force the fuel into the lines quicker, but be careful not to let the prop slip or kick back on your hands. Using a “chicken stick” is a good idea for this task as well as for the next one. >>

    3. Rotate the propeller clockwise by hand until you feel some resistance, leave the prop in this position. This gets the engine back off of the compression stroke and lets the prop build some momentum before reaching compression. If you don’t do this, often the engine starter will slip on the nose cone or may just stall out when the compression stroke is reached.>>

    4. Attach the glow starter securely to the glow plug.>>

    5. Apply the engine starter and spin the engine. If the engine does not start within a couple seconds, re-check all the previously mentioned items.>>

    Once the engine does start, carefully set the engine starter aside, then carefully remove the glow starter.>>

    Now we are ready for tuning the High Speed Needle and possibly the Low Speed also. There are many threads devoted to this topic in the “Glow Engine” forum, but it will be discussed in another article titled “Tuning a Glow Engine”.>>

    Jerry
    AMA -922698 Nomal people scare me, but not as much as I scare them...

  2. #2
    downunder's Avatar
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    RE: Introduction to Glow Engines

    Just a couple of comments.

    First the para about Fuels. The basic fuel for glow is just methanol but can be mentioned that nitro is a normal additive to make a more powerful fuel.

    Second is the para on Ignition. Once the engine is running there's a catalytic reaction between the methanol (not nitro) and the platinum coil in the plug.

  3. #3
    hugger-4641's Avatar
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    RE: Introduction to Glow Engines

    Thanks for the correction!
    Jerry
    AMA -922698 Nomal people scare me, but not as much as I scare them...

  4. #4
    Moderator blw's Avatar
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    RE: Introduction to Glow Engines

    Jerry,

    Just an observation, but I don't think any Evolution glow engine is a bleed air carb type. They are all the two needle type.

    Also, the A3 plug may be a little hot for a starting plug. It's hard to go wrong with the OS 8 as a starter plug for 2 strokes, and the OS F for 4 strokes.

    Maybe to make the post more international for readers outside of the U.S. you should note that nitro is very expensive in a lot of other countries. Many RCU members use 0 to 5% nitro only.
    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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  5. #5
    hugger-4641's Avatar
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    RE: Introduction to Glow Engines

    Quite correct about the Evolution! Thanks.

    I disagree to some extent about the nitro content, but I'm very open to hearing other's experience here. Many people do use 0 to 5% nitro, as I do in one plane I have with a Rossi. But I don't think a beginner should start there. Since this article is aimed at beginners who are most likely starting out with an entry level engine like an 0.S. or Magnum (especially if I'm training them and they are taking my advice) I think 10% to 15% Nitro content is more user friendly when it comes to tuning for a beginner. Agree or disagree?
    As for the glow plugs, I have sort of the same opinion. I didn't address 4 strokes in this article, but I do use O.S -F or Fox glow plugs in them.
    However, In my two strokes, I do use #8 in the summer in most of my planes, they serve me longer than the A3's. But I find that tuning is a little more finicke using the colder plugs. So for beginners, I usually have them use an A3. Agree or Disagree ?
    Jerry
    AMA -922698 Nomal people scare me, but not as much as I scare them...

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    RE: Introduction to Glow Engines

    Depending upon the scope of your reference material you could address rust prevention in these engines.

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    RE: Introduction to Glow Engines

    Barry, this thread should really be here, http://www.rcuniverse.com/forum/forumid_85/tt.htm
    John Deere 820, 72.82 HP @ 1,125 rpm, 470.7 cu. in., bore=6.125", stroke=8.00", two cylinder. CR=16 to 1.
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    Club Saito member #5

  8. #8
    hugger-4641's Avatar
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    RE: Introduction to Glow Engines


    ORIGINAL: GarySS

    Depending upon the scope of your reference material you could address rust prevention in these engines.

    A very good topic! But ,I think maybe better addressed in a seperate article. What I was shooting for with this article is a basic introduction for people who know little or nothing about glow engines and how they work. I seem to unintentionally do a lot of P.R. for our hobby. I fly in some public places including my church and where I work, so I constantly find myself explaining how our equipment works. I also teach for a living and I've recently "hooked" a couple of my students who are also pulling some of their friends into the fun. Most of the students I get at work already have some understanding of how a car or tractor engine works, they just don't know anything about RC models.
    For the ones who are interested in electric planes and helicopters, I've been able to steer them to the E-books in the electric forum to gain some knowledge. But for glow engines, I haven't found similar resources. You can read through various threads and glean some information, but there really is not anything similar to my article that was readily availble to help answer someone's questions. So I wrote this article about a year ago and keep a couple printed copies in my desk drawer.
    I made some edits before sharing it here, but hopefully it will end up in the RC University. If that happens, then maybe someone will add an article on tuning, maintenane, rust prevention, and other relevant topics, or maybe I'll get around to it myself. I already have another article written for tuning, but no sense sharing it yet until I see how this article is received by the RC community here.

    Jerry
    AMA -922698 Nomal people scare me, but not as much as I scare them...

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    Moderator blw's Avatar
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    RE: Introduction to Glow Engines

    Jerry, I agree 100% with you on nitro, but I was pointing out that members in a large portion of Europe pretty much can't unless they are rich. Some European, Australian, etc oriented engines specify 0% nitro. Just thought the note may be appropriate if you agreed.

    I teach a small group class twice a year to fly indoor electric airplanes and helicopters. (Yeah, I know, electrics) the course was originally glow engine based, but driving and weather concerns were too problematic.

    Hobbsy has a good point about moving.
    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

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    Moderator blw's Avatar
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    RE: Introduction to Glow Engines

    This got moved as I was typing the last message. Good luck, Jerry.
    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

  11. #11
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    RE: Introduction to Glow Engines

    Hi Hugger. GREAT JOB.. I have been flying models since the 1940s. I few Super Sonic jets in the USAF. I have instructed Model airplane pilots and Air Force pilots. I have a Draft copy of my "Instructor Training Guide" and have found little interest from 2 major magazines about this subject. I have been communicating on another part of R/C Universe with many interested parties. The main reason for acknowledging your "Two Cycle Glow Engines" is it takes INITIATIVE on your part to take on a VERY IMPORTANT subject and put yourself on the Firing Line. KEEP UP THE GOOD WORK. Col. Chuck Winter
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  12. #12
    hugger-4641's Avatar
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    RE: Introduction to Glow Engines

    Thanks for the encouragement Chuck!
    I am a little frustrated that the information I'm trying to share is not readily available without spending hours reading through multiple threads. This thread will soon get buried here in this forum but maybe it will help somebody before it does. I know there are folks here with much more knowledge and experience who could do a much better job at what I've attempted, but I've been on this site for several years now and nothing has surfaced yet. I'll just keep printed copies of my article to give to my "students" until someone here gets off their can.

    I enjoyed the pics and thank you for your service! Must have been cool to fly those jets, I'm envious! I tried to enter the Marines and the Navy after high school to fly anything they would let me, but at that time, the stigmatism in my right eye was just enough they wouldn't take me as a pilot. I still have nearly 20/20 vision and great depth perception, just wasn't good enough for Uncle Sam.

    By the way, is that a Sig Komet you're holding in front of that 106?
    Jerry
    AMA -922698 Nomal people scare me, but not as much as I scare them...

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    RE: Introduction to Glow Engines

    Jerry,

    I think what you've written is worthwhile and like most things we write often needs some editing. No harm or foul remember there are many personal preferences, opinions, and techniques out there with most everyone thinking they are correct. With that said there is common ground in the use of glow engines which you have presented well.


    With a little refinement your efforts may well become a very fine resource for everyone who needs help with glow engines. Thanks for your time in doing this.


    Steve

  14. #14
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    RE: Introduction to Glow Engines

    Thanks Steve!
    You are absolutely correct. I wrote my article based on the questions I seem to get the most from the people I seem to attract to the hobby. There are definitely some personal preferences included such as my preference for 15% fuel and A-3 plugs. If I lived in Denver or the Florida coast, my experience and preferences might be different. Hopefully it is generic enough that someone will benefit, and I have no problem with some one correcting me or editing it.
    Jerry
    AMA -922698 Nomal people scare me, but not as much as I scare them...

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    RE: Introduction to Glow Engines

    Hi Jerry. The R/C airplane Im holding is my Original Designed Dart 1. I made a series of Darts and had Dart 3 published in the now defunct RCM (Picture of front pages of RCM). Can you email me a copy of your "Two Cycle Glow Engines". I would like to make copies to pass out to my students and club members. Talking about FUEL, I have traveled around the world and flown model airplanes at every base I was stationed and many times I had to SCROUNGE alcohol and Castor oil to make fuel so I could fly. I have been mixing fuel for over 50 years and there are NO SECRETS. I have transported R/C models strapped to Missiles in my fighters missile bay. In the late 1940s when racing control line speed I would go to down town NY City to a Chemical House (Store) and buy chemicals in glass 1 LB. bottles. Alcohol, Nitro Methane, Castor Oil, Oil of Merbane (Not sure of spelling)(Has another chemical name) smells like shoe polish. We would mix the fuel at the racing site so it would fresh. We never used more than 40% nitro and eventually accomplished the World Control line Speed record with our Hellrazor on 2-.016 wires. Enough RAMBLING ... Col. Chuck Winter
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  16. #16
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    RE: Introduction to Glow Engines

    Message sent Chuck, hope it's of use!
    I've been thinking about mixing my own fuel for some time now, but I'm still using a spare room in my house for my "hangar", so I'll probably wait until I get my garage built before I start buying anything in bulk. Right now I'm only using a couple gallons a month, so it's not as pressing, but in the summer when I'm going through a gallon or two a week, it sure would be easier on the wallet if I could mix my own!

    I think it's pretty cool that you were flying full scale jets and hauling models around at the same time! Everyone I've met who does fly both full scale and models definitely has a true love of flying. I kind of fit that bill myself, except the only full scale flying I've done so far is a few dozen hours in a 182. One more kid to get in college and, Lord willing, I'll be getting a 172 or a Cherokee. Been toying with the idea of a light sport like a Challenger or Kit Fox. As long as my health holds out, something's gonna happen soon....!
    Jerry
    AMA -922698 Nomal people scare me, but not as much as I scare them...

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    RE: Introduction to Glow Engines

    I'm a great advocate of uniflow tanks. Where in one's learning curve they should appear is, I suppose, a matter of opinion.

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    RE: Introduction to Glow Engines

    Hi Jerry. Here are a few pictures of F86Ds that I flew. Real and Ducted Fan (Byron) ... Got your copy of "Two Cycle Glow Engines" Thanks, I'll make copies for my students and club members. Col. Chuck Winter
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    RE: Introduction to Glow Engines

    Thanks for your efforts Jerry. I teach a great deal. In today's model aircraft world people seek information on the net a lot. Giving the new folk a good explanation of the working of the glo-engines is much needed. It is one more good teaching tool. Many now come to sites like RCU for information. Good solid usable information is the very heart of your engine explanation.
    I do have a question. Lou Penrod and Larry Posey. Two of my old buddies. Both were on the world wide team. Both men are now gone. I do miss them so. They were two very good engine men. The way you explain things sounds very much like Lou and Larry. I can not help but wonder if you knew these two men.

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    Moderator CGRetired's Avatar
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    RE: Introduction to Glow Engines

    To all that have posted here. My first impression was to move this to the glow engine forum, but I read through it a couple of times and see that there is a lot of good information that has been presented here.

    And, I am totally impressed with not only the content but the way everyone has treated each other. It seems to happen more or less in this type of thread that someone's hackles get raised and the insults begin to flow. This has not happened here and I am most impressed. It certainly makes my job as moderator much easier and pleasant when I can read through something without having to consider anything but the good information.

    I wish I could pin this one as a sticky, but Ken reminded me a while back that we just can't do that for everything that we really want to, so, hopefully, what will happen is that someone will add to it and keep it on the first page for a while.

    Thanks again, everyone.

    And, to everyone, have a happy, safe, and prosperous New Year!!

    CGRetired
    Moderator, Beginners - Pattern Forums.
    Skylark 70 - OS .75 AX; Excelleron 90 - OS 1.20 AX; Venus II - OS 1.20 AX; And, I still fly my trainer, Hanger 9 Alpha - OS .46 FX! Some electrics. Airtronics RD8000 - Spektrum DX7 - DX6i. AMA 705964.
    Semper Paratus!

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    RE: Introduction to Glow Engines

    On the question of #8 vs A3 plugs and which nitro content for beginners, I would personally suggest ammending the article to say that those choices should be based on the manufacturer's recommendations for the particular engine. If we're talking about an engine that's made for low or no nitro like a Super Tigre then it's a good recommendation to stick with that (or at least it's ok to in places where nitro is expensive). But if we're talking about an O.S. or any other engine made for the American market, starting out with 10% is the best. Same with plugs- the manufacturer designs the engine to run with a certain one, and changing it makes tuning harder.
    No kid, I said break ground and fly into the wind!

  22. #22
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    RE: Introduction to Glow Engines

    Charles, thanks for the picks! When I get my F-86 built, I'll post the picks and PM you.

    Koastrc, I didn't know Lou or Larry, but they sound like guys I would be honored to be associated with. Thanks for the encouragement!

    CG,
    thanks as well for the encouragement! Actually, I posted this in the glow engine forum first and Hobbsy or somebody moved it here. I asked for an explanation of how it didn't apply to glow engines why it should be moved here and really didn't get an answer. What I really hope will happen is you or Ken or someone will add it to the RC University link for glow engines. If you go the the RC community/ RC University/ RC Courses link, there is a good article on Turbine engines, but nothing for glow engines or electrics. There is a sticky in the electric forum by Ed Anderson that is easily accessed and provides a lot of good information, but there is nothing easy to find or readily available for glow engines that provides the information I'm trying to share.
    Jerry
    AMA -922698 Nomal people scare me, but not as much as I scare them...

  23. #23
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    RE: Introduction to Glow Engines

    Jester, I agree with you in part that there are some engines in which the A-3 might not be the best for. I will follow your advice and add a sentence to stress looking up the manufacture's recommendation. But I think as a general statement, most beginners are probably starting out with an entry level O.S. , Magnum, Thunder Tiger, etc. and in my experience, those engines are easier to tune with an A-3 and 10% to 15% nitro. It is just my opinon though.
    Jerry
    AMA -922698 Nomal people scare me, but not as much as I scare them...

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    RE: Introduction to Glow Engines

    Ok, I've had a couple people ask for the tuning article that follows my previous article, so here it is. Open to all criticism and construction! Doesn't mean I'll implement every suggestion in my original article, but I definitely want to hear other's opinions.





    Tuning a Glow Engine. By: Gerald Hughes (Jerry) aka Hugger-4641.

    >>

    This article is intended to cover basic principles and methods of tuning a .25 to 1.60 sized two cycle or four cycle glow engine. It is recommended that you understand the basic principles of how a glow engine operates before attempting to tune one. There is an article titled “Introduction to Glow Engines” that precedes this article and explains the basic components and principals of common glow engines. There are also other resources available to help understand these concepts, including the manual that came with your engine. This article addresses the most common glow engines used by beginners in the hobby, which are not generally the highest priced or highest performance engines available. Some engines have special carburetors and tuning procedures that may be slightly different from the general methods that will be mentioned here. If you can obtain the manual for the engine you have it is recommended that you do.>>

    The basic information and methods in this article can be applied to both two cycle and four cycle glow engines. Let’s start by mentioning a few things that need to be correct before attempting to tune an engine, these are:>>

    fuel>>

    glow plug>>

    fuel lines and tank>>

    throttle linkage>>

    needle valve settings>>

    >>

    Fuel- Engine manufactures usually recommend an optimal fuel mix for each engine. The brand may not be important, but the ratio of Methanol, Nitro-Methane, and lubricating oil is important. In the absence of a manufacturer’s information, a fuel with 10% to 15% nitro content and 15% to 20% oil content is usually a good place to start. The oil can be castor, synthetic, or a blend of the two. I personally prefer a blend of synthetic and castor oil since they both offer different benefits to the engine. Many engines can run on a lower or higher Nitro content or even no Nitro at all, but if the engine is designed for certain type of fuel, tuning can be a headache if not impossible when using the wrong fuel. Most entry level engines like O.S., Magnum, Asp, Thunder Tiger, K & B, GMS, and Saito, just to name a few, will run well on 10% to 15% nitro. Higher performance engines like Rossi, Jet, and Enya, just to name a few, may be designed for a higher or lower Nitro content. If so, then the manufacturer’s recommendation should be followed. Fuel should be stored in a cool, dark, storage area, and should be sealed to prevent moisture from the air being absorbed by the alcohol in the fuel. Prolonged exposure to light and air will degrade and contaminate fuel and make tuning difficult, possibly to the point of a total inability to produce combustion in an engine. If you have any doubts about the condition of your fuel, save yourself some headache and buy a new bottle of fuel. >>

    Glow plug- Engine manufacturers will also usually recommend a glow plug or a range of plugs that work best in the engine. Glow plugs are generally classified by heat range from “hot” to “cold”. An O.S. A-3 (now called a #6) is considered a “hot” plug, where as a # 8 is considered a “cold” plug. Cold plugs will usually give a longer service life and will tolerate a “leaner” fuel mixture better. A hotter plug will tolerate a “richer” fuel mixture better, but will fail very quickly if the mixture is too lean. When running a glow engine, it is better to err on the side of the mixture being too rich, so where tuning is concerned, especially during break in, a hotter plug is usually more forgiving. I usually start with an O.S. # A-3 on two cycle engines (A3 is now called a #6). Most four stroke engines will use an “F” plug, which looks just like any other plug, but has a slightly different filament due to the differences in combustion cycle of a four stroke engine. >>

    In addition to different heat ranges of plugs, there are also two different “styles” or lengths commonly used. Some engines may require a “short” style plug, where others may work with either a “long” or “short” plug. If a manufacturer specifies a “short” plug, it is likely that damage can be done to the piston by using a long style plug. Most of the engines already mentioned here will accept either a long or short plug, but this is another reason you should obtain the manual for your engine so you will know for sure. >>

    There is another common type of plug called an “idle bar” plug, which has a small bar across the end of the plug that partially shields the Platinum filament. Idle bar plugs are not usually recommended by manufacturers for the previously mentioned engines, so we will not concern ourselves with them at this time.>>

    Fuel lines and tanks- This is a common area for problems and mistakes. Let’s assume that your fuel lines and tank are new and/or in good condition. If they are not new, it is inexpensive to replace them if you have any doubts about their condition. Cracks, discoloration, stiffness, corrosion, and dry-rotting are obvious indications that tubing, metal tubes, and/or the tank need replacement. >>

    Fuel lines are easily confused and switched if one is not paying attention. The pressure line from the muffler should attach to a piece of metal tubing that passes through the bung to the inside of the tank and bends upward terminating as close as possible to the top of the tank. The “bung” is a term that is commonly used to describe both the opening in the tank as well as the rubber seal that fits in the opening and through which the fuel lines also pass. This seal must be tight and free of leaks. The clunk and fuel “pick up” line are inside the tank and connect to a straight piece of metal tubing that also passes through the bung . The clunk should be within ¼” of the rear of the tank but not touching the tank. The clunk should swing freely from the bottom of the tank to the top so as to allow fuel to be picked up in any orientation the plane might be in. From the metal tubing the pickup line and clunk are attached to, fuel tubing should be connected to the High Speed needle valve. This may be a remotely mounted needle valve, usually located on the firewall or the back plate of the engine, or the needle valve may be attached directly to the carburetor. If the needle valve is a remotely mounted assembly, then another fuel line will exit the needle valve assembly and connect to the carburetor.>>

    Installation of the fuel tank is often restricted by the design of the plane. As a general rule, the fuel tank and engine should be mounted so that the center of the bung is in line with the carb inlet. If the bung is lower than the carb inlet, fuel may not draw from the tank properly, especially as the fuel level in the tank is drawn down. If the bung is higher than the inlet, fuel may want to siphon on its own and usually results in flooding the engine. This can often cause “fluid lock” also called “hydra lock”, which occurs when the cylinder and/or the crankcase gets full of excess fuel which cannot be dispelled, thus causing the engine to “lock”. “Hydra-lock” can usually be alleviated by removing the glow plug and spinning the engine until the excess fuel is pushed out. However, the condition that caused the “hydra-lock” should be corrected if possible. Planes with engines mounted in the inverted position often suffer from this problem. If it is possible to move the engine or the tank to correct the alignment problem, then it should be done, but often the design of the plane and engine cowl limits this option. Scale and Pattern type planes are a typical example of this. Mounting the engine inverted allows the engine head to be hidden inside the cowl, which reduces drag and improves performance as well as being more cosmetically pleasing to eye. And besides, real planes don’t have a big engine head sticking up in front of the windshield, right? However, the benefits of mounting the engine inverted sometimes come at the expense of the carb inlet being lower than the fuel tank bung. The problem with flooding and hydra-lock usually don’t occur once the engine is running, but often happen during fueling and startup. Fortunately, most trainers and “novice” level planes are configured to allow proper positioning of the fuel tank and carb, sometimes at the expense of cosmetics.>>

    Throttle linkage- While the engine may be able to run with an improperly adjusted linkage, it will prevent many problems if you take the time to get this right. Several undesirable things can result from an incorrect linkage such as poor throttle control, inability to idle, inability to reach full throttle, inability to shut off the engine, and binding of the push rod, which can cause servo failure or drain the flight battery too quickly. Details will vary depending on the type of linkage and the type of plane, but it is important to get the push rod or whatever linkage you have to move freely in both directions. The articulation between the servo arm and the throttle arm is very important. You will notice most throttle arms have more than one hole to connect the linkage and also the servo arm will have multiple holes. The linkage needs to be configured so that the motion of the servo arm and the throttle arm match as closely as possible. This will usually mean installing the linkage in the throttle arm first and then finding a hole in the servo arm that matches the length of the throttle arm. I usually remove the servo arm from the servo, power up the electronics and radio, and move the throttle stick and trim lever to full throttle. I always have a voltmeter of some kind installed during set up of any linkage so I can tell if the servo is under too much strain at any given position. I move the carb barrel so it is full open and temporarily install a short piece of dowel rod or ink pen top to keep the barrel open. If the linkage was able to be installed in the throttle arm without removing it, then it should already be set properly, if not, then I move the throttle arm to the proper position and lock it down. Next I re-install the servo arm in the proper position and adjust the linkage to the proper length. When done correctly, there should be no strain on the servo at any point in the travel from full throttle to shut off. When the throttle stick is moved to idle and the trim lever is centered, the barrel should close, but there should still be a slight crescent opening in the barrel, just about big enough to stick a tooth pick into. This enables the engine to idle. When the trim lever is now pulled all the way back, the barrel should close the rest of the way. If all is done properly, the engine should idle at 2000 – 3000 rpm when the trim lever is centered, and the engine should die when the trim lever is pulled all the way back. If it is impossible to perfectly match the servo arm travel with throttle arm, I will adjust so any binding that must occur happens only at the “shut off” position and not at the full throttle position.>>

    >>

    Needle Valve Settings- Ok, now we’re down to the objective! Assuming everything else previously mentioned has been done correctly and you also read the first article, you should now have an engine that is safely secured and running. If it is idling or running at mid to low rpm, we’ll assume for the moment that the low speed needle is ok, or close enough for now, so let’s look at the high speed needle first. There are two methods for adjustment I commonly use depending on the circumstances. The better of these two is to use a tachometer to find the maximum rpm and then richen the mixture for a loss of 400 to 600 rpm. There are many inexpensive tachometers out there. I use a “Glo Bee” (about $20) because that’s what my LHS had in stock. Set throttle to full throttle, and assuming you started with the needle set at 2 ½ turns out, as mentioned in the previous article, slowly turn the needle valve in (clockwise) one click at a time until you find the maximum rpm. It is important to remember that turning clockwise closes the needle valve and “leans” the fuel mixture, and turning counter clock wise opens the valve and “richens” the mixture. (Be very careful around the propeller, take your time and move very slowly and cautiously) As you are turning the needle valve in, you should see the rpm rise until maximum rpm is reached, then it will start to drop off again. Do not let the engine run for more than a second at this setting, quickly open the needle valve back up several clicks rich until the rpm drops 400 to 600rpm below what the observed maximum was. >>

    With the second method you must use your ear as your “tachometer”. The process is similar, turn the needle valve in until you find maximum rpm then richen back up a few clicks. Here’s where it gets a little different, you must have access to the fuel line between the carb and the tank. Pinch the fuel line briefly and notice if the engine speeds up briefly then slows back down to its previous rate. If so, great, keep turning the needle valve in a click at a time and then pinching until you find the point at which the engine no longer speeds up when pinched. Quickly open the valve back up to a point where the engine does speed up again when pinched. Then open one more click just to be sure. (always better to be too rich than too lean!) It is also important to note that if you have a remotely mounted needle valve, there is often a slight delay in reaction between pinching the line and the engine speeding up, if this is the case, pinch the line a couple times in succession to verify the results.>>

    If you have a trusted assistant, you can improve this process by holding the plane vertical while making these adjustments. (keep the prop above your head!) This simulates what will happen in the air when the plane is climbing and the fuel draw is a little more strained. Also, when a plane is flying, there is more air being forced past the intake, which causes the engine to “lean” out on its own. This is why you always want to err on the side of being a little too rich as opposed to being lean. >>

    If you are getting a good transition and good high speed results, but just can’t get a high or low enough idle, there may be a throttle stop screw that needs to be adjusted. If you have the manual, check to see if it shows an idle stop screw. This screw is usually perpendicular to the carb barrel, and simply adjusts how far the barrel can be closed, which determines how fast the idle will be. >>

    If you cannot get a good transition from idle to full throttle and back to idle without the engine quitting or sputtering, setting the low speed needle (or air bleed) may be needed. This can be done using the same process as the high speed needle, except you don’t go to full throttle. Leave the throttle at idle, and use the pinch test or a tachometer to find the best setting. One big difference is that it may be impossible to move the low speed screw with the engine running. The adjustment screw is usually very small and may be recessed into the carb barrel. If you have a very long screw driver with a small enough tip, you may be able to do it without getting into the prop, but one slip will be a serious risk, so you may have to keep shutting the engine off and adjusting the screw in small increments. It is important to note that if you do have to make adjustments to the low speed setting, you will most likely need to go back and re-adjust the high speed. >>

    There are a couple in-flight tests you can do to verify your success. Obviously, you should have a good idle and a good transition from idle to full throttle. If you can do a prolonged vertical climb and fly inverted, any problems with your needle valve settings will likely show up during one of these two maneuvers. Always make a short test flight and then land and check the temp of your engine. It may sound perfect and still be running too lean while in the air. Fly one or two circuits in a normal pattern, then land the plane. Wait about one minute after shutting the engine off. If the muffler is still too hot for you to touch, you probably need to richen the mixture another click or two. If you continue to fly at too lean a setting, the engine will probably overheat and quit before you are ready, either due to the fuel vaporizing or the glow plug burning out. This can also damage the engine cylinder, pistons, and rings. If all goes well with the first flight, then proceed with a vertical climb and inverted flight test. Check the engine temp again when you land. If you have to richen more than two or three clicks, you were probably not as accurate as you needed to be with your initial needle valve setting procedure. As they say; “practice makes perfect”, don’t be afraid of trial and error, just try to limit the errors by learning as much as you can on the front end!>>

    There is also no shame in asking for help. If you’ve followed all the instructions here and are not successful, there may be a problem that will require an experienced person to diagnose. Finding a club and getting personal help is always a good plan. I don’t know when or where you are reading this article, but at the time I am writing it, RCuniverse.com is a great place to get help online. Pictures and/or videos of your efforts and problems are always helpful when trying to get online help. Many things that are hard to describe or easily missed are glaringly obvious in a picture or video!>>

    I hope this has helped you with your glow engine endeavors. At some point in the near future, I intend to follow up with an article on basic RC air frame and control surface set up. Maybe soon after that, an article on basic flight training for RC planes. Until then, happy flying to you, and feel free to contact me personally on RCuniverse if I can help in any way!>>

    Jerry
    AMA -922698 Nomal people scare me, but not as much as I scare them...

  25. #25

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    RE: Introduction to Glow Engines

    Nicely done Jerry. There are two things I think should be added. First is a short guide on how to spot an issue with fuel lines and air leaks. There are too many threads to count on RCU from guys who simply can't get an engine to tune, and I'd wager 90% of them are caused by either a damaged fuel line letting air bubbles in or a loose backplate, bad carb oring, or bad front bearing letting the engine suck air. The second is explaining that engines gain RPM in the air so setting them a little rich is actually needed for optimal power. The amount they need to be set rich is determined by the diameter to pitch ratio and how slippery the airframe is, which determines how many RPM the engine gains in actual flight. For example, my Kaos running a TT .46 PRO turing a 10x6 prop needs to be 800 rpm rich on the ground (as measured by a tach) in order to have top horsepower in the air. If I go leaner than that, I see a noticeable drop in level flight speed. However, my Ultra Stick with a ST G90 turning a 13x6 only needs to be about 300 rpm rich for optimal power. The determining factor of what the optimal needle setting is always how the plane flies, not what the tach says. Which is not to say you're wrong in how the initial settings should be done, just that it's not clear in the write up that the final test is what the plane does in the air.
    No kid, I said break ground and fly into the wind!


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