Hot plug, cold plug

I just checked with my plug supplier (Merlin). Your 1st question

>Somebody please tell me again...The hotter the plug, the
>richer the needle for the same RPM (?)

is correct. The Fireball is a colder plug. In order to get the same RPM, you had to lean it out. It was not igniting the richer mixture as well as the Thunderbolt.

Last season Gerry Meyer borrowed a LA46 from Alan Hahn and we helped him set it up. We had the same experience with the larger venturi plus a tongue muffler. Tons of 4-cycle power (no break) at the expense of fuel consumption. We ended up with a smaller venturi (forgot size) a stock muffler (more backpressure) and 5% Nitro. It turned a 12 x 5 Graupner (cut down to 11.5 or 11) in a nice 4-2 break on about 4 oz of fuel. Ask Gerry Meyer for the exact prop size and fuel consumption. I also gave him a Merlin 'hot' plug to run in it.

Will you be at the Milwaukee contest on Father's Day? I will have a supply of plugs along. The ones I'm running are about the hottest I've found for my Fox35ABC. Plus I'll have some 4-stroke plugs, which seem to run well in some Schnuerle ported engines. I'll give you a couple to try.

Fred

But...Why would a colder plug give you a earlier break? Because of the leaner needle?

If its breaking at 10:00 area, say on a loop, wouldn't that give you more power then a engine with a richer needle that hardly breaks?

Scott

ps shorten lines by 18-24"

Here's the way I like to think about plug heat.

Along with other variables, (specifically: compression ratio, nitro content and (if appropriate) pipe length) plug heat controls the ignition timing of the engine. A hotter plug, more nitro, higher compression or shorter pipe (within the tuning range of the pipe) all will "ADVANCE" the timing or cause the mixture to burn earlier in the compression cycle. The reverse is obviously true.

This is just like advancing or retarding the timing on your car. Within reason, advancing the timing will increase power and retarding it will decrease it. Beyond a certain range, of course, bad things happen in either direction. retard it too much and ignition won't take place. Advance it too much and ignition starts too soon and knocking and extreme heat build up result...and, of course, power is shot.

Specifically, I tune the various components so that I get no loss of RPM when the battery is removed. You've probably noticed that, if the revs drop when the battery is removed, you can regain the desired RPM by leaning out the mixture. What you get then is the same revs at a leaner mixture and a greater tendency to switch to two stroke ops. Using a hotter plug, more nitro or higher compression (either by reducing head shims or, if pipe equipped, shortening the pipe to increase the rebound wave inducted into the combustion chamber) will allow the same RPM to be maintained at a richer mixture with less tendency to break. An additional bonus is that torque and power will be greater as well.

So, the answer to your question is; yes, a likely result of a hotter plug will be a later break as long as the additional heat doesn't advance the ignition timing excessively.

Like all else in stunt, it is a delicate balancing act and will change as atmospheric conditions change. Don't get put off by that, however, once the proper plug is selected any changes necessary to optimize engine run for different atmospheric conditions is usually accomplished by juggling the nitro content and/or the head shim.

Easier yet, if you're sport flying tune your set-up so you get no loss in revs when the battery is removed and don't worry about the fine tuning unless the rev loss shows up unexpectedly.

Ted Fancher

p.s. Keep the bees out of the venturi regardless of the plug heat range!!!

According to reports from informed sources who must remain anonymous, the villainous creature was secreted by Paul Walker's special CIA division in a secure location somewhere aft of the drive washer and forward of the uniflow exit, camouflaged by a film of nine year old castor residue and dust bunnies. Upon a precisely timed, laser guided signal, since determined to have emanated from the vicinity of P.W.'s toolbox/beeHQ, said special agent, utilizing the latest in miniaturized pitons, crampons and spitoons, stealthily advanced up (remember the Final Edition was inverted at the time of the attack) the backplate, around the cyliner walls, carefully avoiding the blistering inferno of the pulse pounding P.A. .61 header and, upon reaching the summit of Mount Venturi, through him/herself into the abyss...a suicide terrorist's ultimate fantasy.

Alas, the last laugh was mine. Instantly recognizing the nefarious act for what it was--an insane attempt to prevent your hero from displacing P.W. from atop the heap--I alertly stuffed the valiant war bird to a safe but ignomineously inverted touchdown amid the soft embrace of the clover carressing the edge of the runway. Modest damage ensued but, although the battle was lost, the war is yet to be won. The Final Edition lives on! Woebetide any further would be assaulters from the nether regions of the Northwest. A similar fate awaits them and their ultimate demise is not a matter of if...only of when!

Or something like that.

Ted

Well, no, not exactly. There is, however, an unrelenting bouquet of squashed butyrate grapes lingering in the vicinity of the late lamented Nobler smushing.

Think that might be the culprit?