New Pulse Jet Dude

[Mark]

I should say the ~1/8 inch gap is about the most you can get with the 1/4 32 plug. I like to break the side electrode off to get a bigger spark on those tiny plugs. I've had them get wet from too rich a starting method, or just a bit of dirt or corrosion from use over time, and you have to clean them to prevent the spark from crawling instead of arcing or making a feeble spark.
Here's a few smaller ignition toys I have but I like my Model T buzz coils for most things because you can run them for hours on end experimenting and they're always there for you. If I shorten the gap to a 1/4 inch on the second unit it makes a very feeble spark, almost like a piezo sparker.
http://www.youtube.com/watch?v=d33_Fhgy5Dg

[Heli-NuBee]

Would it be better to remove the electrode from the 1/4" spark plug or to replace the 1/4" spark plug with a a larger CM-6 size spark plug and then remove the electrode from that plug?

[Mark]

You could just gently bend the side electrode up gapping it more, the gap is mighty small from the factory on the 1/4 32 Rimfire plugs, seemingly like a razorblade thin gap and the center post/electrode is oh so tiny too. Really, I think they are made more for little piston engines and not pulsejets. It should work fine, no need to go to the 10mm. As long as you can hear it buzzing and are getting pops, that's all you need. I have that plug on my smaller Japanese-made Tigerjet engine, I took out the really cheap one it came with and put in a 1/4 32 Rimfire. It starts fine with that. You can take the Japanese plug apart/disassemble it by unscrewing the parts in fact and the insulator although a hard white ceramic is slightly bent/curved -not even straight, talk about workmanship!
In some ways I think the German videos I have seen with the up-the-tailpipe ignition device is best because it's simpler and there only when you need it. But for very tiny jets it would be too intrusive, perhaps interfering with the starting. Different circumstances, different methods.

[Heli-NuBee]

OK, I changed the spark plug and she fired easily. Maybe that was the problem all along. We will try for the maiden flight tomorrow.

[Heli-NuBee]

OK, here is the good - The sport jet engine that Jet Bill (JB) built for me is awsome. Now that I changed the spark plug, it starts easily and makes great power. If anyone is interested in a pulse jet engine you may contact JB at: http://jetbillproducts.com/ Also good, the engine survived the crash and the fuel system and radio componets are also OK.

[Heli-NuBee]

OK - here is the bad - the flight only lasted a matter of seconds and the plane crashed - we are not sure if there was a radio problem or if the wing loading was just too high - I had one of the best RC pilots on the westcoast on the sticks so I don't think that it was pilot error. See the very short video here: http://www.youtube.com/watch?v=grS6U8-fsEc

[Heli-NuBee]

OK - here is the ugly - pictures of the broken airplane:

[Heli-NuBee]

OK today was disappointing, but I have learned a lot from this experience and I am even more determined to successfully fly pulse jet powered aircraft. I have ordered a kit that should be much better suited for pulse jet power. I will start a new thread for the build once I get started. I think, with what I have learned, the next airplane will be quite good.