Warbird Information Exchange

Today I was going to fly a Bonanza over the mountains to pick up the Spitfire. The runup was fine, mag drop minimal and smooth like the hundreds of times before. On the runyway it seemed normal as I came up to full power, then at about 50 knots as I was about to raise the nose, the engine burped once, then did it again. I stopped, did another mag check and it was rough on one. Could it have fouled a plug as I sat waiting for the jets to clear before takeoff? But this wasn't just like a fouled plug.The mechanic found one plug had a completley cracked through insulator, which I had never seen before. Replacement cured the problem completley. A couple of weeks ago I was about to fly a show in the Spitfire and had a rough runup on one mag, later found to be one fouled plug. I had done a very short 18mile flight and with that and a long taxi, I guess the plugs never really got hot enough to clean. Moral: pay attention to run up and takeoff checks, don't get too complacent with routine. Both times I caught the problem, but it was a surprise since I was not expecting trouble as it had been so rare in either plane.

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Bill Greenwood
Spitfire N308WK

Bill, do you mean start the take-off roll on one mag, and then hit the second one to get that last 100 HP at rotation?

Interesting note on spark plugs. A customer of mine reported on some plugs he tested out of the can, brand new. He told me that out of 25, 1 failed the test. I said that was pretty bad. He said that was pretty good, as in most modern aviation plugs 1 out of 12 will not pass a spark plug tester.

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REMEMBER THE SERGEANT PILOTS!

How's your mag timing? (Advanced) Fuel quality? (Low octane) Somewhere in the back of my head I'm thinking that pre-ignition (AKA detonation) can cause cracked plugs. Could be just poor plugs, but could be something else.

Bill do you lean when on the ground?
Of cource CO is a little higher then CT

Phil

As for leaning, I do lean the Bonanza for warm up and taxi, but it is turbocharged so runup, takeoff and climb are at full rich or heads and exhaust valves overheat. It had recent annual at a top shop so assume mags and timng are good, and fuel is 100ll as before. The Spitfire is of course, supercharged and the mixture control is automatic, so no manual leaning, the amount of power being used determines the mixture and as you go past 7 lbs boost or 44 inches(normal takeoff) it gets richer.

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Bill Greenwood
Spitfire N308WK