Hi All,

Got some questions regarding what the temperature range should be for glow engines? I worry about my engines over heating. I picked up a infared temp gauge today, but it does me no good if I don't know what temps I should be looking for.

1. Are the temp safety limits the same for all glow engines. 2 and 4 stoke?

2. Where on the engine should I be checking?

3. Should I check static on the ground or just after a flight?

Thanks for your help

Tom

There is no standard. The surface of the engine part anodized, polished or grit blasted at will change the reading from your infrared thermometer. Your best bet is to set the engine for a bout 300 rpm down from peak on the rich side. Measure your best performance (time). Then make your reading. use this as a reference point for future tuning. If you want one of the best cooling system to control heat build up try a pressure cowl. You will often see these on high performance set ups.

Your best tools are still the tachometer and stop watch!

Friends don't let friends fly nickel,
Konrad

Check these threads:

http://www.rcuniverse.com/forum/m_88...tm.htm#8808322

http://www.rcuniverse.com/forum/m_91...tm.htm#9105743

There is no problem with overheating on glow fuel, unless you are using high nitro fuel.  The problem is lack of lubrication with lean fuel mixtures.   If you convert them to gas they will operate at much higher temps without any problems, except perhaps a few with small fin areas.

There are perhaps a few exceptions to the above.  For example a Fox Stunt .35 may overheat with a lean run with moderate nitro because of its very small fin area.

I have to ask, in our glow engines isn't lubrication failure of the piston to cylinder seal a direct response to over heating?

Now the FAI F3D and AMA Formula I pylon engine have been known to actually melt holes in the piston tops[X(][:@]. But these are extreme cases of engine abuse at elevated temperatures (lean mixture settings). The two mentioned pylon engine are at the extreme nitro ranges, zero for the FAI engine and 65%+ for the Formula I engine. Nether engine will survive long without a close fitting pressure cowl.

All the best,

Konrad

hehe we blow holes in pistons all the time with 30 percent fuel.

But running at peak output rpm, with limited cooling, and it only takes a bad clunk line or loose head bolt or carb seal and you're rebuilding a motor.

Here's what we say:

It's not possible for us to give you an actual temperature or temperature range for your engine. The specific temperature is determined by too many factors. There is only one way to determine at what temperature your engine should be run. You have to run it first and then find out what temperature the engine reaches.

Make sure your engine is operating properly with the performance you expect. Use the exact setup every time...fuel, exhaust system, plug, measurement location, and so forth. If you change anything, the temperature will change. Once you have the engine running the way you want it. Take your measurement. This is your starting point. You will have to take measurements over time to find out how the weather affects it. As the air temperature and humidity change from day-to-day, the operating temperature will change. Eventually, you'll find a temperature range that you can work with.

Engine temperature is not an absolute number for setting your engine. It is only a guide, and can help alert you to potential problems. The only sure way to make sure your engine is running correctly is to see how it's running. An engine can be operating at "correct" temperatures, but not running well.

Finally, use any temperatures you read about, or people tell you, as rough information. The only useful numbers are the ones you actually measure when your engine is running correctly. If your engine is running correctly, then what you measure is correct, even if some else says it's too high or too low. Don't worry about the differences. Each engine is in a unique installation with a unique set of circumstances, so there can be wide variances in engine temperature.

No it is in direct response to a lean mixture which means less fuel, and thus also less oil. Run long enough and I suppose friction and lack of oil will cause overheating, especially in high reving racing engines. But the flame temp of low nitro fuel will not be hot enough on its own. A lean run on high nitro is another thing as the nitro can exceed the temp of gasoline, but much lower at max power.

Now, I think we are all thoroughly confused?

So are you saying that the European engines that use low or no nitro are not in danger of over heating from the alcohol flame? That the danger is from friction. Over heating in my definition is where the high temperature allows systems to fail. In the case of our engine the seal between the piston, cylinder, ring or the film strength on the rod journals. Over temp is not limited to changing of the material characteristics (size, grain structure or oil film strength).

Tom,

I do have some values of my 2 stroke 10 CC glow engines, running on 5 % nitro and 10 % synthetic oil.
Values measured with a datalogger during flight are:

Normal temperature on the ground but also during flight are between 150 (302F) and 180 (356F) degrees C,
Absolute temperature max for normal operation for me is 185 degrees C ( 365 F).
Overheating, or not acceptable for me, are all temperatures above 200 degrees C (392 F) whatever the reason is (plug, vapor lock, lean). I do have a separate detector for that.

Thermocouple.
I do measure the engine head temperature by measuring the temperature of the cupper seal washer of the glowplug with a thermocouple. See picture.
For me this is the only way to create a comparable, representative and repeatable measurement.

Maybe you can use these values to compare with readings of your instrument.
I think your indications will be much lower because I see a point temperature and not a global head temperature.

Cees

Correct, the lean condition does not cause the flame temp to rise to cause the overheating, but the lack of oil increases friction causing overheating. But as I said there are exceptions. High nitro is one because it makes its best power the richer it is, but will burn an engine up at its ideal mixture. I will add that I was refering to overheating in the context of permanant damage to parts. Of course it would be reasonable for you to consider getting hot enough to burn out plugs, or to run rough, as overheating, even if the mixture is not lean and no parts are damaged. Then in that contextthen your original thought is probably correct.

O.K. Thanks for all the replies, even though I'm more confused now than when I asked the question! LOL. I guess what I was trying to get at was. How hot is too hot. I realize two indentical engines running at their best performance could run at different temps. But all these engines are basically built out of the same materials. (I think). So, I'm guessing that they will be damaged when they reach a certain temperature. I'm not looking for the magic number. I just want to know if it's 200*F, 300*F, 500*F, or 1000*F.

There are lots of different materials used for the piston and liner, and the conrod may or may not have bushings etc. Each engine has a different tightness to it and the fuel is perhaps even more important, as some oils will simply evaporate when they get too hot.

Your engine gets too hot when it is run on the lean side of max rpm and/or when it cannot hold the rpm and sags with time. These are the things to avoid rather than a specific target temperature that you will struggle to measure correctly.

As mentioned in the threads shown above, the operating temperatures run from about 180 degrees to about 300 degrees. Measuring surface skin temperatures with a infrared thermometer can vary wildly from each measurement attempt. You have to pick one spot and use that as your reference point all the time. Surface skin temps are different from the temps on the inside. Generally, the most common measurement point is right under the glow plug, so you want to point your infrared thermometer right there at the base of the glow plug.

The surface of a engine varies a lot, from different color anodizing, different color paint, and whether it is shiny, or dull, or sandblasted gray in color. All those types of surfaces affect the temperature reading you get to measure. The best or more optimum method is to use a thermocouple, where you drill a hole in the head to place the thermocouple down inside the head at the high temperature position as close as possible. Since that isn't very practical, they usually use a washer size thermocouple and put it under the glow plug.

The reasons the temps can vary wildly, really depends on what the engine is being used for. A open engine exposed to the airflow on a sport plane being flown at 3/4 throttle will run a lot more cool than a enclosed cowled engine being used in a pylon race.

Methanol helps to cool the engine more than the lubricating oils. Nitromethane doesn't cool, so as the nitro percentage goes up, so does the heat. Also synthetic oils break down at high temperatures (they call it unzipping the molecules) an actually turn into more combustible products and instead of lubricating add to the engine's power output. Thus the peak in RPMs just before the engine seizes on you. Castor oil does eventually break down at high temperatures, but its breakdown point is higher than synthetics, also castor oil forms varnish like residues on the engine surface parts that help prevent engine seizing, at least for a little longer, but as the temps rise up, eventually it fails too. Also as the engine gets really hot, the internal parts expand fast and cause the piston to expand faster than the cylinder can. ABC engines had the odd trick of expanding and losing power when the engine got too hot and not seizing up right away. So sometimes you had a chance to back off the throttle before it locked up.

To really measure temps reasonably well, you need to use a thermocouple device and a data logger and track the engine temps while you fly, et cetera.
Now car people like to use the infrared thermometer to good effect. You run a lap or two, quickly stop and make the temperature reading, and repeat as needed.

earlwb,
I will have to question your statement about the pylon engine. Most (all that I know of) were the class allows for cowling the engine actually results in cooler operation as these cowls are set up as pressure cowls. Air flow is a lot like me, rather lazy. Air hitting a cylinder open to the slip stream would rather go around the cylinder at speed rather than slow down (pressure rise) and go through the cooling fins.

Yeah you are correct, I over simplified it. But I betcha those suckers were running pretty hot with 50% or more nitromethane in the fuel.

A few years ago, I bought one of those little infra red temp checkers...just out of curiosity.
I tested several .40 to .60 size 2 strokes and remember that they operated best in a range from about 180 to around 250 degrees F. Once they got above that, perf. dropped off a bit, and 300 degrees was borderline too hot.

My measurements were taken as close to the glow plug as possable.

There is an emissivity setting that can be changed to allow for different surfaces...that setting can effect your readings.

I preferred the performance on cough syrup (80/20 FAI fuel) and a full wave pipe.

I will say I never used a thermometer to tune my race engines. The tach and stop watch were to best tools I had at the time. Now I did use a thermometer during the development stages of the engines. (No, I didn't have these neat hand held infrared things of today.)

Again as has been said by me and others the actual reading is of little value. Tune your engine for the best performance using a tach. If you then feel the need to know the temperature take a reading at this point and record it for future reference.

http://www3.towerhobbies.com/cgi-bin...&I=LXYXK9&P=ML

All the best,

High nitro engines run cooler when operated on the rich side of peak power. That is because pure nitro has more and more power the richer it is run. In fact it cools the engine very well, so well that the nitro dragsters need no cooling, the modern engines don't even have a cooling jacket. However on a lean run the nitro may approch its stoichiometric mixture which means the flame temperature will be higher than that of the methanol. The oil does little for cooling, rather, more than remove heat it prevents it by reducing friction.

I have been flying glow engines for over fifty years. I haven't burned one up yet, although I did run my ST G21/46 hot enough to lose ring tension. That's the only time that I can recall. That's what I get for changing fuel types and then forgetting to reset the needle valve. It only cost me a new ring. Oh well.

If I came from model nitro car racing, maybe I would have the same or similar concern for overheating, but I don't. I do have an IR temp gauge, but I've never once used it on my model engines (all airplanes). No reason to do so. I hope that we can keep it that way. Don't create problems and worries where there are none.


Ed Cregger

Temps can be very deceiving. We once ran an engine on our test stand and measured the temperature at the rear of the cylinder head, where the aluminum was smooth. We used a contact probe and measured 375-degrees F. The engine was an O.S. Max .40 FP, and was running on Cool Power fuel with 10% nitromethane. We did our testing at full throttle with the mixture leaned to peak RPM. The engine would run "all day" like that. After a few hours' worth of running, we stopped and examined the engine and found absolutely nothing wrong with it. That engine was used on the shop's radio test airplane for several years before a crash into some very hard ground put an end to it.

We find that if you rely on temperatures to set an engine's needle valve, your engine will have a very short service life.

Gents,

When you manage the glow engine the way we (for me nearly) did 50 years ago you will not experience much problems, adjusting the needle valve “nose up” and you normally have a rich fuel/air ratio during horizontal flight.
Pattern flyers in the past even did mount restrictions in the carb to have more sucking pressure. Result was less difference of mixture vertical and horizontal so less variation in speed and less fuel consumption (but also less power!).
More complex it became with exhaust pressurized tank systems, two needle carbs, tuned pipes, diffuser cooling, regulators and pumps, all to give us more power or speed with the same engine.
I do still have two in flight adjustable Webra Dynamix carburetors of the past, With these we even could readjust the mixture ratio during flight.
When using pumps and pressure controllers we can peak the engine horizontal but we need more information and control of the thermal balance of the engine. For that I use data logging, not only temperature but also airspeed and rpm data logging. I think there are too much variables to find an optimum without these gadgets.
A second, more special reason for me is, I do use airspeed control, so the throttle servo is activated by the airspeed controller. I never detect discrepancies in throttle setting and lack of RPM output as result of too hot engine. The engine will die without I notice and so the Dynamix is no solution for me.
It is all our own wish to make modeling more complicate, so no “Sense and simplicity”.

Cees.

Gents,
Some pictures about engine temperature.

A new thermocouple for the Top Flite Taurus engine. Important part of electronics is the + 200 degrees Celsius detector to see if on any moment during the flight the engine head temp was above 200 degrees.
When I did run the OS Max 61 FX it did happen twice! Guess why? See picture 2 and see the carburetor!

I also can take tempreature samples during flight with a datalogger.

For the gasser I did read, the temps are the same see this post:

http://www.rcuniverse.com/forum/fb.asp?m=9995499

Cees

What am I looking at photo #2, the kinked fuel inlet line? An arrow would be helpful or some detailed text.

All the best.

Konrad