The Shell company recently published their Shell Aviation Tech Talk #15 (990 Kb Adobe PDF file) and distributed it to all pilots in Australia and New Zealand. I'm getting a lot of questions from readers there, and from graduates of our seminar.The bulk of the report is an excellent treatise on detonation and pre-ignition, well worth reading.Unfortunately, sprinkled throughout that fine report are a few bits of "common knowledge" that have proven to be not true, or what we call "old wives tales" (OWTs). Most involve mixture settings, with recommendations to run 50F rich of peak (ROP) exhaust gas temperature (EGT). Most readers will nod their heads as they skim past these, and as little as 10 years ago, I would have, too; "Everybody knows that!"But 10 years of looking at hard data from one of the most sophisticated engine test stands in the world, and using the data and information in my own well-instrumented airplane (Bonanza with an IO-550 and Tornado Alley Turbonormalizer) has changed my outlook dramatically.Specifically, a few of the minor points in the report repeat some OWTs about mixtures that have developed in the last 50 years, and which are not supported by the old engineering manuals, or by more recent data from the test facility. We've been working hard for 10 years to dispel these, with some success.I have contacted the author, a very pleasant fellow who seems very interested, and who wrote a long email in support of his position.I repeat for emphasis, it is a fine report -- on detonation and pre-ignition. The author did not have the advantage of "modern data," and fell into the near-universal trap of believing the OWTs. In general, I commend Shell and the author for the bulk of the report.Let me work my way through it, commenting as I go.
This is a companion discussion topic for the original entry at https://www.avweb.com/features/pelicans-perch-83-the-shell-report