GLOW PLUG TEST

I needed to break in my new PA-75, so I decided to take the time to test some of the new glow plugs that I had found at the local hobby shop and on the Internet.  The PA 75 is so powerful that there has been some concern keeping the fire lit on cold days in hard corners on smaller .61 and .65 props (like I prefer to run).

It was my guess that it would just take a little trial and error to find the right cold weather plug for the Big Monster.

The subject of hot plugs is a common one in CLPA flying, as the need for running rich can make for some interesting fuel, pipe, engine compression, venturi, and plug combinations.  Basically, there are few plugs that really fill the need for fire when we are running the engines very rich, and many poor runs can be caused by simply having horrible fire.  Poor fire can effect the overall power, tank shim, and most definitely consistency from run to run.

I devised this simple test.

Set the engine at running temperature, and open the needle until it stumbles and quits.  Not very scientific, but it gives a very good indication of which plug is burning "clean" at rich settings.  There were interesting results to be sure...

First movie is the test run of the Sig 4 cycle (click the picture)

The next movie is the test run of the OS Max "f" (click the picture)

You will notice that the Sig and OS Max 4 cycle plugs, considered to be extremely hot plugs stumbled and eventually died when the needle was opened.  Notice ESPECIALLY that there was definite point in the needle where the engine just "fell off the pipe" and went to the basement.  There was a lot of surging and stumbling after opening the needle below 9500 RPM (watch the test stand jumping).

The Sig plug was the coldest performing plug of all the ones I tested.  The OS Max "f" plug was fairly typical, not to say it did not perform marginally well for overall fire, but was nothing exceptional.  It was comparable to most medium range plugs including the OS Max #1, the Thunderbolt RC idle bar, the Merlin Hot, and the Magnatech #3.  These plugs would probably be real good choices for hot weather flying.

The next two movies are of the test runs of the Merlin Ceramic 4 Cycle (click the pictures)

This plug was pretty darn impressive, and did what I was looking for.  The engine never really stumbled at all, even at the richest setting I could achieve.  I know it is hard to tell from these videos, but the 4 cycling of the engine remained very smooth even down to 8000 RPM, without any real stumbling at all.  The response was more like a throttle.  The only plug that was comparable was the Thunderbolt 4 cycle, but I believe I want to re-test, as the temperature had changed about 10 degrees by the time I tested this plug.

More later.

GZ-

P.S. Check out Brian Eather's cool new muffler.  The little one is shown.