I get a lot more reliable run from lower nitro fuel with a higher compression head.  More power, too.

I decided I was going to experiment, and made a high-compression head to take short glow plugs.  I got it high enough compression that without extra gaskets I could hear the detonation on regular fuel.  That's a great head for flying on the same fuel that I run in my fuller-sized planes, but if I put 'regular' 25% nitro fuel in the tank it turns into a machine for burning out glow plugs!

          I've done extensive experimenting with all types of plugs for the TD. I can say the Cox 1702 high compression plug is good a bit pricy and the duration is poor. I run 35%-40% nitro daily. I use no less than 3 shims when using the high comp head. Tim stated it perfectly the plugs are going to get destroyed. Remember, higher nitro , more shims. The Merlin plugs work very well, although without enough shims the engine becomes over compressed and very hard to start. These plugs can require 4-6 shims. The Merlin plugs are very economical and work well assuming you have the proper head clearance with shims. The Glo Bee plugs work well if you can find them except reliability falls off real fast with these, you either have a good one or a poor one. These seem to make the engine run faster than any plug I've ever used. There is 2 types of Glo Bee plugs, the racing style and the sport. The racing looks just like the head shape of the Cox high comp head. The sport has a very shallow trumpet like sphere to it. I've had to use as many as 7 gaskets with the sport type. I would try and avoid the Glo Bee plugs just due to the complications and unavailability. The Galbreath Nelson head is a very good alternative. The conversion head is about $15 while the plugs run you another $5. These work excellent and require additional shims about 4 of them. The plugs are more forgiving to lean runs and are very durable. The major draw back is the larger plugs base which requires a different clip. I use a large alligator style as opposed to the Cox style on a 6' lamp cord. This works well. Don't use old glow plug shims as they're already crushed and will cause the head to come loose constantly. Tuning with the shims takes a bit of patience but pays off in the end. I use smaller props than what I typically used when I was first learning. I used to use the old faithful 6x3's, I now use mainly 5x3's as I found the APC 5x3's to work very well for me. The drawback is price. Those props can be as much as $4 a piece. The Cox 5x3 is still available through Xenalook from Canada. These work well and can be purchased in bulk. There are 6x2 Cox props as well. There are a variety of APC props to suit your needs. The APC 5.7x3 is an excellent all around prop. You just need to experiment. Ken

I lidke the Merlin plugs too.  For use with a reed Cox engine, I would use 3 to 5 gaskets to control the compression.  If the engine tends to stop and just bat back and forth, it is overcompressed.  Otherwise, reduce the number of gaskets until it will only just run right.  For short duration free-flight, you can use very high nitro.  For CL stunt, I would not go over 15% nitro and a minimum of 20% oil, preferrably half castor, half synthetic.

Adapters for conventional plugs are fine for sport flying, but not for competition use.  They cost power and reliability.  The problem is that the shape of the combustion chamber is totally ruined by the position of the plug and the threads that are exposed to the combusion chamber.  Also those plugs seat at the top of the threads, so who knows what the compression ratio is?  By substituting a Merlin Glowbutton for the regular plug in a Brodak MK 1 .049, I gained 1500 rpm and the run was MUCH more stable.  The Nelson head added ANOTHER 1500 rpm beyond that!  These changes turned a casual sport engine into a competitve tiger!

My standard setup for 1cc stunt is the AP Wasp .061 engine, modified with the Jan Holuszko (do a search for his contact info) venturi and Merlin glow button with 1 or more extra gaskets, depending on the Nitro and prop I am using.  Other than that, the engine is totally stock and turns about 21000rpm on the ground with an APC 5.5x2.5 prop.  My new model, the Sky Streak (search again) is actually going too fast on 48' lines.  I will cut the Nitro down to 7.5%, and may try the 6x2 prop to make the speed liveable.

I have attempted to post this pic, but too large, so I'll try again!  This is my White lightning and I finished it with Rustoleum rattle can over light silk span.  It weighs 10.05oz with the TD .051, 3/4 oz tank, and I would like to know if this is too heavy.  I will build a second one now that I have learned a few things, and I will follow your advice Bruce, and use dyed tissue instead of "weight in a spray can."  I would also like advice on wood selection for the wing because I seem to have some small twists in mine. Hope it will fly okay-if not I will let my grandsons use it for another trainer.
Thanks guys,
Steve

Sorry for posting in the wrong place, I had tooo many tabs open and not enough coffee.
Steve

That's okay Steve, I enjoyed reading the old thread about my favorite little engines. Maybe the Mods will move it to 1/2A.
Nice plane. And, no, 10.5oz is fine for a Tee Dee powered plane, it should burn up the circle pretty well. As for the wood question, I'll defer to our more skillful builders.
Rusty

I have two TeeDee 049s with the Galbreath-Nelson head used in free flight. One has the same plug I installed in 1998, hundreds of flights on 35% nitro fuel. Seems indestructible if the glow igniter voltage is kept within limits (IOW don't burn out the plug!). Don't use any extra shims. I think over time (even a short time) this comes out as the least expensive AND best performing option.