glenn (01/18/83)
Yikes! I just read rabbit!ark's reply to my undersquare/oversquare question, and I can see by his reply that I phrased the question badly, so let me clarify so others don't miss the point... Yes, of course the fact that 25" and 2500 just happen to have similar numerical values (excluding the 00) is coincidence, has no mystical significance, etc etc as rabbit!ark pointed out. It just happens to be convenient to use the "__square" terminology to describe the limits of the engine operation envelope as delineated in the manual - if you like, 0.8 atm/2100RPM is "oversquare", 0.7 atm/2500RPM is "undersquare". Just as an example of what I mean by the terminology, it's possible that some engine/aircraft somewhere has MP/RPM limits of 25"/2600RPM at one end and 21"/3000RPM at the other end. In this case I would consider the former to be "oversquare" and the latter "undersquare", even though the numbers are nowhere near square. The question could probably be better phrased as: "For a given cruise power setting, is there any objective evidence which indicates that it is better (in terms of engine life) to operate towards one end or the other of the MP/RPM envelope?" - Glenn