CGRetired

My Feedback: (1)

I had an interesting thing happen to me this weekend. First of all, the weather here in the Northeast (southern NJ) was absolutely perfect for flying both Saturday and Sunday. Sunday was especially nice with temps in the low 80's, low humidity, and bright sunshine with just about no wind all day long. Great RC day, that's for sure.

Anyway, I was getting my Venus II ready to fly. It has an OS 1.20 AX for power. I started it up but when going to full throttle to set the fuel flow, well, with the glow driver connected, it would be just fine. If I disconnected the glow driver, it would go to full throttle, stay there for a moment, then sputter and die.

I played with it for a few minutes until the 'club pro' came over and helped me out. Well, after he listened to it for a while, then did a few adjustments, he told me to swap out the glow plug. I only had some OS-8's in my field box so I took one out of the package and replaced the one that was in the engine, which was an OS-F.

Well, I was very impressed with how that not only fixed that problem, but the engine ran supurbly after that, much better than it had been running in the past. Like many people, I guess, I assumed that if it ran after disconnecting the glow driver, well, the plug was probably good. Not so, I guess, and I learned something this weekend.

DS.

Montague

Yep, I had almost the exact same thing going on yesterday in an Evolution .45. The tipoff there is that the engine runs fine with the glow driver on. Same problem though, it would run slow fine, and if you got it to full throttle with the driver on, it would stay there, but if you ran it up with the driver off, it would "miss" and often stop. In my case, it didn't always stop, just about half the time.

Oh, and in my case, the old plug would light up on the glow lighter as well. Just becaue the plug is glowing a bit, doesn't mean it's "good". In my case, the element down inside the plug was glowing, but about the first turn of the coil wasn't lighting up like the rest, and compared to a new plug, you could see how less of the element was glowing.

CGRetired

My Feedback: (1)

Yeah, good point.

I had been noticing that this engine ran sort of crappy at times before, like the last time I flew that particular plane about three or four weeks ago. It even sounded poor while flying. Yet, after the glow plug swap, it ran so much better. Smoother, more even, and even sounded like it had more power, which it did. I took it on a straight climb at half throttle then went to full AFTER I entered the vertical climb and the thing accelerated, and kept going (until I pulled back and did a 'stall' (hammerhead) turn).

Great thing to remember for the future. Before the swap, it would run like it was running very rich, but it wasn't.

DS.

Montague

Interesting. You also changed the type of plug? You're now using an F plug, and what did you have before?

It's possible you had a plug that was too cold or too hot before, and now you have a plug that just matches your engine/fuel/prop better. The wrong plug will cause the ignition timing to be off, either too soon (too hot a plug) or too late (too cold a plug). It's like driving your car with the igition timing off, and the difference you get with a good tuneup.

(if you want absolute peak power, you can actually change plug models and use a tach to check the RPM, you'll find the plug can make quite a difference for some engines)

bruce88123

He said that he took out an "F" and put in a #8 this time. If you were asking what he had before the "F", I don't know. Isn't the "F" meant more for 4 strokes?

Montague

Ah, right, I mis-read the post, and wasn't clear about the plugs at first.

The F plug is a 4-stroke plug, it's hotter than most, since 4-strokes need the plug to maintain the heat through the non-firing stroke. Used in some 2-strokes, it can cause pre-ignition, which would result in all kinds of bad things. But some 2-strokes like the hotter plug. I think the OS 8 is a mid-range plug. So I think it's likely that the plug change also retarded the ignition timing a little bit.

CGRetired

My Feedback: (1)

Yes, I removed an OS-F and put in an OS-8.

Whatever it did, the engine definitely runs much better than it did before. That combination for that plane works.

DS.

Jim C.

wow, that is weird! I had to replace mine yesterday also. Although it has alot of time on it. I couldnt get the engine to run right like you said after you take the driver off. I just replaced it and it ran like a champ.

MinnFlyer

My Feedback: (4)

I smell a conspiracy by the Glow Plug Conglomerates

Jim C.

you know it! I have been flying for 10 yrs, and that was like the 2nd one I ever had to change like that.

checkmate91

Friend had a similar thing at our club on Sunday. A couple of hours fiddling with idle jet etc, change of plug and this "so and so of an engine that never ran properly" ran like a dream! Definite lesson learned there...

bigedmustafa

My Feedback: (2)

The O.S. #8 is a Medium Hot plug for 2-strokes. The F-type plug is a hot plug for 4-strokes, but it will run fine with most engines that will normally use the #A3 Hot plug for 2-strokes. The F-type plug is fairly pricy because it has a thicker coil than a typical plug. It's designed to hold heat longer, which is ideal for 4-strokes.

Why is a thicker coil more expensive? Most glow plug coils contain a bit of platinum, and even tiny amounts are costly. After a while, even F-type plugs will lose enough catalytic materials from their coil that they are no longer efficient.

The next time you're out at the field and you're enjoying some aerobatics, try not to think about all of the platinum that you're vaporizing!