The Glow Engine (Model AIrcraft Engine)

[Konrad]

As there is a bit of local interest in the golden area of the glow engine. Unfortunately (or fortunately) glow is dead, so there really is little chance for folks to actually experience the joy and/or frustration of high performance glow engines. Heck, with the demise of Sanye Engines I don’t think there is much in the way of sport glow engines. I think OS Engines are still sold but I never really found these suitable as sport or performance engine*. This leaves the secondary (used) market. As I was heavily involved with the glow engine, I actually built the engines that won the USA NATS in 1989**, I thought I’d try to use this thread as a way to spread my "Pearls of Wisdom” .

I’d like to set some back ground. First I’m not a historian or even an enthusiast for the glow engine. So if you have any insight as to what were the driving forces for what happened at certain times in the development of the model airplane engine please feel free to post. As a machinist and engineer I’m focused on the hardware and this will be the focus of my discussions. I do like to learn what were the market forces that drove the OEMs to make the decision that they made. So please do post what you know.

Now what I don’t want to see are posts like brand “X” is the best thing since sliced bread without a detailed explanation as to why. Conversely I don’t want to read that brand “Y” is junk again without a detailed explanation. I would like these observations to be objective rather than subjective.

While I did say I wasn’t a historian we need to realize that long established brands such as Fox, K&B, Super Tiger, Thunder Tiger, have gone through various changes over the years. These include management, design philosophies and manufacturing changes. I think it will be important to mention what era one is talking about when making broad statement about any one brand or type of engine.

Now for a bit about me as it pertains to the glow engine. I got my first glow engine in 1970 a Cox Baby Bee 0.049 (used) soon followed by a Cox Pee Wee 0.020 (new). As a snot nosed kid I was given a lot of used junk to play with. This would prove to be basis for my love of engineering as I got to see how different firms, designer solved (or didn’t) design problems. I got a reputation of being able to pull engines from the trash can and getting them to run "better than new”. Yes, I’m also know for improving things until they don’t run!

Around 1984 I teamed up with Duane Gall (latter to be an AMA RC Pylon Chairman) racing 0.15 sized Quarter Midget RC Pylon racers (AMA 422). In 1986 I was at the Rough River 1/4 Midget race where I meet Henry Nelson. He and several “engine men” where bemoaning the loss of the ST .40X for FAI F3D and AMA Formula 1 racing. From these late night alcohol infused discussion I got the crazy idea that I could make a competitive FAI F3D Pylon engine. With the help of Henry Nelson and a host of others I actually found one of my engine in the winner’s circle. This was in 1989 before Nelson introduced his FAI engine to the masses (I think Team USA had some but they weren’t talking)!

Around this time (1986) Duane Gall introduced me, with the help of Keith Shaw, to high powered electric flight (more than 7 cells). By 1993 I had all but given up on glow engine for my sport and most of my high performance models. The last glow engine I’m currently using is a Jett 426 Q500 as this is last of the glow “Sport Class” racing events.

All the best,
Konrad

*In the 80's the OS FSR was among the great sport glow motors. Today the OS engine is far too expensive to be classed as a sport engine. And as a performance engine they are lacking the proper metallurgy to compete with the old Italian Stallions of the past or the modern dedicated performance engine from boutique manufactures like Jett Engineering.

** I wasn’t on the field of battle, but it looks like the winning engine was one of my early development engines based on many Picco parts (I was a dealer for Picco back then).

 

[Konrad]

Let’s bring 2 issues with the 2 stroke engine to light. Like most engine it is best to think of them as heat pumps. Anything we can do to move the gasses (fuel air charge) and improve the burning of these gasses will improve power. To that end I take the philosophical position that I’ll gladly sacrifice base compression if it aids in the flow of the engine.

Base compression is where the crankcase is allowed to build up pressure (usually by the downward motion of the piston). This pressure is used to inject the fresh air fuel mixture, via the cylinder ports, into the cylinder and aid in the last part of scavenging the cylinder of combustion products. Some of you might have heard of the term packing the crankcase. This is what they are trying to do by lowering the volume in the crankcase. This is old school, and still works ok for open exhaust engines that don’t use a pipe. With today’s performance engine using a pipe, allowing the pipe to draw fuel from this crankcase volume has some merit. This is why today’s FAI F3D pylon engines are front rotor design as apposed to the rear rotor of my day. Front rotor motors have the added volume of the crankshaft gas passage.

And then there is the Achilles heal of all 2 stroke engines; the lubrication of the piston journals and small end of the rod journals. In a properly running 2 stroke the load on these bearing areas is always in one direction. This means that there is no opportunity for lubrication to get on (between) these load bearing areas. Compound this with the fact that there is little rotational motion here and we can’t benefit from the hydrodynamic action of a spinning journal.

These two constraints (scavenging and lubrication) will be key to the development of our model airplane 2 stroke engine.

Also in the discussion of engines please keep in mind that gasses have mass and as such have inertia. It is this inertia that is key in allowing the engine to develop its high power and in the rpm band we want.

All the best,
Konrad

 

[Hank]

Great to hear your story Konrad. Although I have been reading your posts for years and knew you had some background in making your own competition engines, I didn't know the whole story.

I started the hobby in 1974 with a 1cc model diesel engine from England. Then in 1975 got my first glow engine, a Cox 049 Babe Bee.
I flew control line in the 049 size and rubber band power until 1976 and took a long hiatus until 2006 with RC.
Most of my engines are of the humble sport types. Most of them are glow 2 strokes with a few 4 strokes.
I have a couple of gas engines on big planes and I love them them when they run well and hate them when they don't. I really think gas engines are overhyped as convenient for using gas but the complexity of their carbs and ignition are a big negative for me. Actually, most gas engines have the same ignition and carb designs, nothing unique except the engine itself. Those all look alike too, just different names and packaging. The difference would be in quality control in manufacturing.
I still think that glow engines are great as internal combustion alternative to electric, and it's not because of the "smell of nitro in the morning". But admittedly, fuel price and availability, noise, and having to fuel proof everything are a drawback.

 

[Johnnashville]

Great post about glow engines, thanks for the read Konrad.
I wouldn't say glow is dead, flew glow today along with others. (lock-down glow)
High performance glow may be dead.

 

[Konrad]

LOL,
Heck, I’m not sure I know the whole story, and I claim to have lived it!

My statement that glow is dead often gets me in trouble. When I say dead I mean there is no growth in it. Not that it is extinct and not practiced. I still love coming out with my cough syrup burners (FAI 80/20 fuel) pushing over 3 HP. It sure scares the locals! Nothing new there, even my old F5D ships scare the locals!

But glow is dead as I don’t think there are more than 2 or 3 OEMs making mass produced engine. The market place just can’t support the few OEMs we have left. OS and Saito are the two that come to mind. Of those engines that are in reach of most, it is the basic striped down LA series of engine. I don’t think this basic entry level engine is anybody's idea of an exciting 2 stroke glow engine. There are no piped timed engines with three screw auto-mixture carbs that I know of, other than in the secondary market.

I’m of the opinion that one of the best tracking and high powered sport glow engine was the 1986 Rossi 40. With her mild timing she made a great beginners engine. With her heavy crank and crankcase she could survive the early arrivals often made by beginners. And with the auto mixture carb that made tank placement much much less critical than with the airbleed OS FP of the same time frame. Just by moving down to a 9” prop one could easily release the 2 horses waiting inside her.

I’m at a loss to explain why the airbleed carb (non auto-mixture carb) is still found on engines today. Its low cost isn’t worth the performance hit!

Today would anybody in good conscience recommend a glow set up to a beginner? I just looked at the price of glow plugs and just about passed out! Should a newcomer advance past the LA Series of engine where is he to go. The next step up in the OS line appears to be the OS AX and this is priced close to that of a Jett not really a practical sport alternative. So glow is a dead end. This has been such an issue that the pylon contest board has asked Jett Engineering to make a detuned Jett engine for the entry level class of Q-500 (AMA424). As the OS costs close to the same and can’t hold up the stress of racing (nickel plating [ABL] is not suitable as a coating for high performance engines as it is a lot softer and much less tolerant to lean runs than hard chrome plating). The contest board is thinking that with the detuned Jett, guys can learn to fly the race course. Then as they gain confidence they can swap out the detuned part (carb and folded pipe) for ones spec'd for AMA 426 for very little added cost. This is using the OS AX as the cost basis. The OS can never be brought up to the performance level of the Jett and live for more than a run or two, well not keeping with the OS P&L and rod. The metallurgy of the OS just can’t hold up to the demands of racing, even sport racing.

Also telling is that Jett no longer makes injection molded cases. The investment in inventory and tooling costs is just too high with the low volumes. Heck Jett rarely has any engines on hand. Jett custom makes them from bar stock as orders are placed. While this costs more per unit, it is a lot less expensive than ramping up for volumes that just aren’t there for the glow engine.

I will try to cover all these areas such as metallurgy, carbs, timing exhaust systems, combustion chambers and cooling schemes in detail.

Yes, glow will be with us for a long time, much like chariot racing. For example we no longer see chariots like we see in Ben Herr but rather the sport lives in the form of Harness racing. Just like the chariots of old, glow has seen her heyday!

Harness racing - Wikipedia

en.wikipedia.org

John, I see you are running an OS. I'd like to ask if you have ever had the opertunity to run any of the great European or even American engines of the past. I have to admit that I was late to the game but I found the later dated (80's and later) Enya engines to be great sport engines with a strong nod to being very good performance engines.

BTW: I really liked VP fuels. The last OS I took apart was the, Surpass 70 it was very clean on the inside with little or no rust. I was running VP fuels. I don’t know what was being used as rust inhibitors but it worked well along with a religious application of after run oil (Mobil Jet 1). I can say the same for the YS 1.20 of the same time period, 2003.

All the best,
Konrad

 

[Konrad]

Gas, as in gasoline? Yep, these weed whacker engines left me cold.

Timed ignition has its strong points. For example converting a glow ignition engine to timed spark ignition often results in a rise in power of around 15%. But as you say there is a lot of weight and complexity with timed ignition. It looks like the benefit of timed ignition really aren’t realized until we get to the larger engines starting around 20cc to 30cc.

I remember when the Quadra came out. I had a large 1/4 Bud Nosen Citabria powered by a ancient Fox 0.78 cid engine. The 1/4 scale Bud Nosen Citabria was basically an oversized rubber band model (light stick type construction). A club member also had Bud Nosen Citabria but with a Quadra on the nose. But to control all that vibration and power he had to add a lot of structure to the airframe. In the end his Bud Nosen Citabria weighed over 4 time more than mine, flew like crap as it didn’t have the vertical and had a much higher stall speed. This is a classic example of diminishing returns. I don’t think it was until the Zenoah G26 engine that the weed whacker engine actually became a practical power plant for our toy airplanes.

Now I believe Enya has come out with a “very high platinum” glow plug that will actually start the ignition process with E85 fuels. Kind of the best and worst of both worlds.

The magic of glow is that in the presence of methanol platinum will glow (hence the term glow engines*). This results in a catalytic reaction between oxygen and the methanol resulting in ignition.

*I can’t for the life of me understand where the term "nitro engine" came from. I think it came from the toy car guys mimicking the term from full size drag racing.

All the best,
Konrad

 

[Hank GB Z]

My favorite sport glow engine I ever used was a K&B 40. It just worked. I never got into performance engines. Guys always gave me a hard time since it wasn’t OS.
My dad always like 4 strokes. They suited his flying style. We had an Enya Vt 240 on a proctor neiuport 28. It had ignition system and still burned glow. It was odd but man did it work great. Prime it turn on the ignition and pull through and it started.

I miss tinkering on the engines sometimes. But really electric gets me to the models I want to build.

Hank

 

[Konrad]

The K&B model 8011 0.40cid was a classic and well loved by those that had them. This engine can be identified by the small bronze front crankcase bearing journal. It also often had the Perry carb.

The latter K&B model 4011 0.40 had a better design in that it had a fully ball bearing supported crankshaft, both ends of the connecting rod were bushed and it used the Gunther Bodemann style twin needle carb. Unfortunately for us modelers, most of the 4011's were manufactured when K&B was under the management of venture capitalists and suffered many quality issues in an effort to cut down on cost.

Now a "Lee Custom" 4011 could run circles around any ringed OS 0.40. It could even give the great OS FSR 40 a run for its money and do it for a lot less money. Clarence Lee was the designer of many of the Veco engines from where the K&B 40 came from. The "Lee Custom" was basically a "blue printed" engine. Clarence would bring the clearances back to those called out in the design. He would also upgrade the engine to have Perry Directional Porting (PDP). He, Super Tiger and HB were the only engine builders to license this porting from Perry. The PDP allowed the baffle engine to scavenge as well or better than the schnuerle ported engines*. This left the baffle engine only suffering in the combustion chamber when it came to flame propagation compared to the Schnuerle ported engine. That baffle really become a problem when trying to burn the fuel properly.

All the best,
Konrad

*That baffle becomes a problem when the pipe is trying to draw fuel from the crankcase. But for most muffled engines the statement is true.

P.S.
I like methanol (even with oil in it) over petroleum any day when it comes to our toy engines.

 

[Hank]

I don't have any experience with Perry carbs. Were they good?

 

[Konrad]

Much better than the air bleeds of the time. Heck, still better than today's air bleed (non-automixture carb*). We need to define good.

But I really liked the Bodemann dual needle style carb. It was easy to re-profile the needles to custom tailer the fuel delivery throughout the whole throttle range. It was also rather easy to add in-flight mixture control (a nice a feature with tuned pipes).

I and Earlwb had a geat carb thread on the now defunct web site RCTruth. I may have to ask Earl to join me here in rebuilding much of that information. The RC carb is a huge topic in of itself. I may have to start a thread just on the carburation used in our toy engines. Understanding how the carb works goes a long way in having a reliable RC engine.

* Automixture means that the size of the fuel metering port (orifice) is proportional to the size of the throttle barrel opening. As the throttle opening changes so does the fuel metering orifice change automatically.

All the best,
Konrad

 

[Kilrah]

*I can’t for the life of me understand where the term "nitro engine" came from. I think it came from the toy car guys mimicking the term from full size drag racing.

During the time I was using those we were always told to use 10% nitromethane fuel in what would thus be our "nitro" engines probably simply because it sounded cooler than "glow" or "methanol".

 

[Konrad]

Why were you told to use 10% nitromethane, and by whom, the fuel manufacture? I wonder what is the source of this urban legend? I've heard it a lot.

A properly designed combustion chamber along with an accurate metering carb negates the need for low levels of nitro methane in a sport engine. Anything above 3% nitro in a properly designed sport 2 stroke is a waste of money. Yes, I've used 25% nitro in many older (70's and older) designed sport engines. But that was because the design of the combustion chamber and the scavenging of the cylinder benefitted from the added oxygen nitromethane carried.

Nitromethane should be though of as an oxidizer. A properly designed engine system will mix the free oxygen and methanol so that the need (benefit) for the added oxygen from the nitromethane is negated

There can be some added idle stability with the addition of 3% to 5% acetone, again much cheeper than nitromethane.

Our glow engines don't need nitromethane to run but they do need methanol (remember the chemistry between the platinum and methanol). I found calling our engine "Nitro Engine" dumb, just the opposite of cool!

Now as an engineer I have to admit I find the art of marketing rather baffling. Being “Cool” to my eye is a marketing phenomenon.

All the best,
Konrad

 

[Kilrah]

I don't know what the source was, but everyone from fellow modelers to the store I was buying my engines and planes from did. Probably started waaay before my time.
I often ran with no nitro just for price reasons - but I remember that with 10% it would be much easier to start and run more stable at idle.

Glow fuel was expensive in general and that's why anyone with a largish plane/engine wanted to use gas instead of glow.

 

[Konrad]

I'm not arguing with you, but I found that lower nitro fuels started easier than the higher nitro. More methanol to react with the platinum in the glow plug. I too found that 3% added nitro would help with the idle particularly with the older airbleed carb designs. These carbs were/are horrible at metering the fuel properly, hince the added benefit of the oxygen bearing compound "nitromethane". I also found 2% to 3% acetone helped almost as well (burned hotter to help with the binding of the oxygen and methanol at idle) and was a lot cheaper.

Yep, once you crossed the 20cc size, petrol was looking very atractive. I stayed with glow even up to my Saito 300 twin. but then this is a hobby and money is no object , my banker had other ideas!

 

[Hank]

Is acetone legal in California? That's more serious than denatured alcohol.

 

[Konrad]

One of my earliest and much loved RC engine was the 1965 Super Tiger 0.23. This was a classic with her lapped P&L and air-bleed carb. Performance a tractability were OK with the exhaust blade coupled to the carb. But when we had to use a muffler this engine became rather worthless. This was because the 1965 model of the Super Tiger 0.23 has a rather pronounced (large) sub-piston port. This is known as Sub Piston Induction (SPI). In engines were the throttle ISN'T important but peak power is important, SPI is a useful feature if the engine has an open exhaust.

Many of you might have noticed that the earlier Cox .049 allowed the bottom of the piston skirt to rise past the bottom edge of the exhaust port. This is SPI, it allows air to enter the crankcase to make up for the pressure loss from the venturi. This pressure loss in the venturi is a result of needing to draw fuel from the tank into the crankcase. On throttle equipped engines the throttle is controlling the pressure in the crankcase to limit the amount of inlet charge that can enter the cylinder. SPI bypasses the carb throttle by allowing air to enter the crankcase from the exhaust port often negating the effect of the throttle valve.

Now if the exhaust port is exposed to a muffler there is no fresh air to enter the crank case. Rather spent exhaust gasses enter the crankcase contaminating the fresh fuel mixture. This really cuts down on top end power!

In the 1970 ST 0.23, Super Tigre added some sleeve area to block the SPI from the deep under cut piston skirt. This does hamper the ability to scavenge the cylinder as it cut way down the exhaust port area and added more features to the sleeve that blocked exhaust flow. But ST knew the future was in the muffled RC engine and took the hit against their control line customers for the 1970 ST 0.23.

They also upgraded to the auto-mixture carb, which became the great Mag V. Arguably the best RC carb ever. I know it doesn’t show well but the Mag V with its superior fuel draw allowed ST to use a larger choke area than the piss poor airbleed carb found on the 1965 ST 0.23. This gained back some of the lost power lost to the elimination of the SPI feature.

Airbleed carbs, bleed air under the spray bar to kill the ability to draw fuel. Just what we don’t want at idle. At idle most engines need all the help they can get to draw fuel. But with the simple fixed orifice design of the airbleed carb manipulating the ability to draw fuel is the only way to adjust the fuel mixture strength.

With this airbleed carb ST had placed the airbleed port a bit too high in the choke body. The result is that too much air still passed by the spray bar allowing it to draw fuel. The fix was to drill a small second fix orifice bleed hole further down the carb body to ensure the air was bled under the spray bar. The OEM airbleed was used to fine tune the mixture.

All the best,
Konrad

 

[Konrad]

Is acetone legal in California? That's more serious than denatured alcohol.

Depends on your perspective. But yes it is legal to sell Acetone.

 

[Hank]

I run 15% on my smaller glow engines and my 4 strokes.
I thought you are constrained by the engine design, the combustion chamber shape for nitro content.
I do have some old Fox engines and Irvine engines that run on 5% nitro

 

[Konrad]

Sorry I'm having issues with this site uploading images and posts. It appears that there is a 90 second timer between every site action.
here is the Mag V cat's eye that didn't post earlier.

 

[Konrad]

I run 15% on my smaller glow engines and my 4 strokes.
I thought you are constrained by the engine design, the combustion chamber shape for nitro content.
I do have some old Fox engines and Irvine engines that run on 5% nitro

We are constrained by design regardless of nitro content. High nitro heads and low nitro heads are trying to do very different things when it comes to flame propagation across the piston top.

Most older Fox engines loved high nitro, "Missile Mist" was Dukes brand for 25%(?) nitro fuel. Then around 1978 Duke saw the light as to how nitro really wasn't needed particularly with his then new MK-X twin needle carb. So for most of the 80's and into the early 90's Fox set up his heads to use zero nitro fuels. This was contrary to the "advice" given by old timers and well meaning Hobby Shop personnel to use 15% nitro. Zero nitro heads have a much higher compression ratio and a much more aggressive squish band to promote better atomization (mixing of the oxygen and alcohol) of the fuel. These two feature when combined with "high" (any) nitro will cause havoc with the flame propagation across the piston.

Now at this time OS and many other OEMs were still peddling the use of fuel with same 25% high a nitro content we had in the 60's and 70's. Unfortunately for those that didn't read the manual and understand its meaning the high compression head of the Fox and many of the European (and the later eastern European) engine the use of 15% and higher nitro caused all sorts of issues. In the 90's Horizon Hobbies begged MDS to make an engine for the "USA" market (read nitro lovers). To that end MDS came out with the eight (8) series of engines. If the MDS has a "8" in its nomenclature it is designed to run with some nitro. Not as high a nitro as many would like but some nitro none the less.

Now in this time frame M.A.N. had a "Great Engine Shoot Out" article. And much to the dismay of many folks the Fox Eagle III with its "poor head" out pulled just about every other non piped 0.60 (10cc) engine. This was due to the added port area a "long stroke" engine has for any given timing and the very efficient zero nitro head.

Why so much nitro in the 4 stroke? Are you trying to keep the glow plug hot? The prechambered four cycle plug should take care of that issue. The four stroke engine does a good job of scavenging the cylinder that there is little need for the add oxygen from the nitro to help mix with the alcohol. There is at least one exception to this and that is the HP VT four cycle engine. Its combustion chamber is so poor that the use of high nitro is needed to get any power from the engine. (The glow plug is well protected, as it is in its own chamber for most of the time other than ignition).

All the best,
Konrad