What’s so great about Glow Engines?

In the early days of model airplanes, there were control line planes and free flight planes, and a model plane engine ran on gasoline.  It had a battery and a coil to make a spark.  This was way before my time.  When RC became the next big thing, the glow engine came with it.  For the next five decades or so, glow engines were synonymous with model airplanes.  I have spent most of my time in the RC hobby during the golden age of the glow engine, which today has given way to the electric motor.

Now that electric power has overtaken glow power in popularity, I’ve noticed that newcomers to the hobby tend to treat glow engines with suspicion, and I’m pretty sure this attitude is encouraged by long-time RC pilots. It seems weird to me that most of the guys who spent decades having a ton of fun with glow engines suddenly can’t say anything nice about them.  It’s as if we all got old and decided that noise and oil were just too much trouble, so the new guys shouldn’t bother with it either.

As you might have guessed, I’m not one of those guys.  I’ve been playing with glow engines since 1986 and I still think they are super cool.  If you are just now getting into the hobby and you are being steered away from glow engines, you might want to think again.  Glow power still has some advantages over electric, and it’s still a lot of fun.

Whenever the glow vs electric question arises, the first point that always comes up is ease of use.  With a glow engine you have to carry fuel, pump the fuel into the tank, stick a battery on the glow plug, start the engine, tune it, and then when the flying is done, wipe the oil off the plane.  With electric power you just plug the battery in and fly.  But when the battery is dead, you have to wait while the battery recharges.  Meanwhile your flying buddy with the glow engine is simply pumping fuel for 30 seconds and then flying again…. and again and again.

But the electric pilot could fly over and over if he brings enough batteries, right?  Well, that leads us to the next point that I always hear, which is the cost issue.  Everybody has heard by now that glow fuel is too expensive, so you would be better off flying electric models.  But what about those extra batteries?  They cost money, and so does the fancy charger to charge them.  Also, LiPo batteries sure seem to have a high attrition rate.  You could compare the cost of glow fuel to the cost of ongoing battery replacement.

I think you have to weigh these two points against each other and decide if you want to buy a bunch of extra batteries and charge them all at home, or if you want to deal with oil and a little bit of extra field gear.  To me it looks like a toss-up.  You probably thought I was going to say that glow engines are better because I like them, but I can see how you might take a critical look at the options and choose either one based on logic.  Both have conveniences and inconveniences, plus extra costs.

This leaves only the most important factor, your personal preference.  To me, the RC flying hobby is about three things.  There’s aeronautical engineering on a hobby scale, there’s cultivation of piloting skills, and there is the enjoyment of mechanical equipment.  I think all model airplane pilots are into the first two to at least some extent.  Some of us are also very much into the third.  I really enjoy looking at and using model engines, but I’m sure some people do not.  I’m also sure that a lot of RC newcomers would enjoy running model engines, and I’d hate for them to be warned away by older RC pilots because they are “just too much trouble”.  For guys like me, engines aren’t trouble that gets in the way of flying a plane.  They are a big part of the fun.

Now that you’ve read this, a bunch of other people are going to tell you to stay away from glow engines because they’re too much trouble.  I don’t want to put myself on the opposite side of that argument just for the sake of argument.  I would rather give an analysis of when glow engines have an advantage over electric power.  Glow engines have generally been available with throttle control in .10 size and up.  For smaller models there are unthrottled .049, .020 and even .010 engines.  These engines were manufactured in the millions by the Cox company from the 1960s to the 1990s.  Cox 049 powered planes were very common in those days because they could be built and flown very economically.  Cox engines run full bore for about three minutes until the fuel runs out, and then they have to land.  They were generally used to power sport planes in the 30 to 32 inch range, trainers in the 36 to 42 inch range, as well as gliders around 2 meters.  Cox engines run at very high RPM, and the propellers are not very efficient at those speeds, but they get the job done and they are a lot of fun.  Electric power is a reasonable choice to replace the Cox engine because you can choose your voltage, your RPM per volt, and your propeller size.  These advantages result in a plane with more power, and longer flight time.  Also, electric motors have throttle control, and you can get decent speed controls, motors and batteries in this size range for about $7 each on ebay.  Given the low fuel consumption of tiny engines, the cost advantage probably goes to glow in this size.  So you can choose the better performance of electric or the sheer excitement of an unthrottled, screaming little engine.

Above about .10 size the performance advantage of electric starts to disappear, and when you get to medium size planes in the .40 range the only way electric has any performance advantage is if you cough up a load of cash for the really good equipment.  For me personally, .049 engines are the only thing I would even consider replacing with electric, and Cox engines have a special place in my heart so I still use them half the time anyway just because they’re cool.

If you’re a new RC enthusiast and you are intrigued by glow engines, go ahead and give them a shot even if your flying buddies are warning you away.  They’re a lot of fun.  If you want to learn more about them, I have a friend who has a really good youtube channel with engine videos where you can learn to buy, repair, maintain, and run both 2 and 4 stroke glow engines.