Used to happen regularly with ST C.35's we used in combat in the late '60s - early '70s.

The thing to remember is that the platinum coil in the plug is a catalyst, and will glow dull orange in the presence of methanol with no battery connected. All it takes is the elevated temperature of a compressed charge in the cylinder and off she goes! Now, this won't happen every time. It requires the fuel/air mix to be just about perfect, and well atomized for ignition in these circumstances.

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  I have also had that happen with a Fox .35.   Same scenerio,  prime and flip over the prop once and its running



  Dalton H.

I had my Magnum XLS .36 start sans battery last July...but it was close to 100F. and I don't think I'd worry about it until it was 90F. or higher.

     I would rethink that a bit. I have had several cases of modern ABC/AAC engines that kicked - hard - even when it was gummy with oil and 50 degrees and no battery.  When it turned to TDC under the weight of the piston, in one case. It worse when it's hot but not that's not required. The piston/cylinder fits  on these engines are pretty remarkable compared to the good old days of ST46s.

      I also had your experience, at the 1993 NATs on my first official NATs flight ever.  It was oppressively hot, and the engine (40VF) started when I was choking it. No battery.  I got my hand on the spinner before it got to full crank and stopped it (which impressed Ted no end). It did it again the second time, so the rest of the week I didn't choke it before signaling.

     For safety purpose, I assume that any time there is raw fuel around, the engine can start. One of my pet peeves is guys who choke the motor, then reach under the airplane to hook up the battery without holding the prop. If it starts with your arm in there, you could be in for a serious injury. Maybe not with one pop from a VF, but with big-block motor like 61's, I wouldn't bet my life on it.

     Brett

Electrics scare me, too.

Howard,

That's why it is imperative to have a arming plug, that you plug in just before signaling the judges. This connects the battery to the ESC. When connected you get to hear the ESC play its little tune signifying how many cells are in your battery, and that it is armed. Now you can push the timer button (if the timer has a button).

On a profile, where everything is external, you would just plug the battery in, since that itself is equivalent to the arming switch

Since all this stuff is well behind the motor itself--not un-similar to a rear mounted needle valve, there is very little risk that you will put your hand through the prop.

Now when you land, if you have trained your helper right, then he/she will pull the arming plug on the plane before picking it up to carry it back to the pits. Best of all, there will be no greasy goop to cause their hands to slip and drop the plane.

So don't be afraid.

The reason I like the plug is that if the ESC is armed, I am always worried that I will bump the start button by accident.

Of course I have never had an issue with the timer "going rogue". On my timer, once it goes through a run, it will not restart until you pull the plug and replug it back in. However it is true that you can get complacent with these things.

This is something I've been curious about ever since I heard of it. Not once in 50+ years of flicking/turning over engines have I ever felt the slightest sign of one firing. Although I assume it isn't common I'd have thought that 50+ years would have been long enough for it to happen to me. This makes me wonder if it's because I've never used nitro. Now I know that nitro has no catalytic reaction but it's quite sensitive to compression ratios so possibly nitro acts something like ether in diesel fuels. This may be way off base but it's the only difference I can find to explain why I've never felt this.

To me, it seems like the Fox 35 is a particular engine that is susceptible to firing without an igniter attached. I think it may be because we tend to really get the Fox wet by choking it.

I think I have had other engines do this, but not as prevalent as the Fox 35.

I find it interesting that the engine will start while flipping it with no battery connected. But at a contest that same engine wont start no matter what you do.

Just lie at a FF contest, the plane finds every thermal around - - till you call for a timer!

I like the hardware arming plug.  I've seen people rely on timer software to keep their motors from running.  I think one should assume that a timer can jump to anywhere in its program at any time.  I don't know what goes on inside the motor controller, but I would be suspicious of it, too.  The combination is the wrong kind of redundancy: the probabilities of the two faults add.  When flying by myself, I would worry about walking from the unattended handle to the airplane after a flight.   

   If I were to be writing safety rules for electric stunt, my first act would be to require an arming plug. There's no way in Hades I would count on low-level, ESD-sensitive, logic states to keep it from starting or to do what I was expecting. I have spent WAY too much time watching low-level logic glitch from one state to another over my long career to ever trust anyone's safety to it entirely.

     Brett