Brooks Townsend wrote: >> So, Mark, are you saying that even with the EIS that you have, you'd go >> down to 9:1?? What if you had a less sophisticated monitering system... >> would you further reduce the c/r??? How much?? <<
Yep, I've done the takeoff-with-detonation thing way too many times already, and that was burning 93 octane auto fuel. From what I can tell, there are places in this country where 91 octane is about as good as you can get, and even then it's likely to have ethanol in it. Theoretically ethanol shouldn't matter because octane rating is simply a measure of the overall resistance of a fuel to detonation, but I've noticed that ethanol narrows the band in which my engine is "happy" in cruise. With normal auto fuel I can fly with the lowest LED of my air fuel ratio meter blinking on and off, and the engine's fine with that lean setting. A little leaner and the power drops off more than the fuel saving, which is why I fly it there. Running 10% ethanol, the engine is only happy with about three LEDs showing before the RPM drop is considerable and noticeable, so I'm burning a good bit more fuel. When I put 100LL in it, I can run way down past the point of any LEDs showing at all, so 100LL saves fuel over 93 octane auto fuel...not a lot, and certainly not enough to offset the cost or the increased lead deposits with leaded fuel, but it's a real observation. Hopefully there will not be the usual theoretical arguments over why this isn't true...it's based on real and repeated observations, and Joe Horton has seen the same thing. To answer your question, I'd feel naked to fly with any less instrumentation than an EIS or equivalent. Knowing the CHT of only one or two cylinders, and not having a bright light flashing between my eyes and a warning tone in my headsets that one particular cylinder has a skyrocketing CHT, I'd have already been down in the trees on several occasions. Yes, the engine runs a little rough and is low on power when detonating, but by the time you've screwed around with carb heat, mixture, fuel supply, alternate ignition, your hands are shaking, and your piston is melted and seized, you are going down. Let's see...a thousand bucks and a couple of extra pounds, or my plane destroyed in the trees....that's a pretty good trade! A lot is said about heavy planes. Mine's heavy, but a lot of that is "safety" features like the EIS, redundancy where it makes sense. I think Steve Bennett recommends CRs down in the lower and mid 8:1 range, and that's probably because he's dealing with some lowest common denominator folks who are on a budget and don't see the need for EGT or CHT indications... Mark Langford ML at N56ML.com website at http://www.N56ML.com --------------------------------------------------------
