TheTurtle Posted February 9, 2017 Report Posted February 9, 2017 My tach and MP steam gauges seem to be fairly inaccurate. My GEMIII seems to be pretty close on the tach but the MP on it is off as well. ATIS and my altimeter show pressure as 30.11. With engine off my steam gauge shows 28ish inches. My GEMII shows 30.0 I bought one of those handheld laser tachs and here are my comparisons. GEM TACH TACH TESTER 992 1070 994 1324 1500 1322 1763 1900 1559 2064 2200 2056 In practice I dont think I care about the MP not being accurate. I fly by MAP numbers only compared to my own plane. eg I climb at 25inches. If that 25inch im seeing is actually 25.5inches it doesnt really matter to me. I decend at 16inches. If what I see as 16inches is actually 15.5 I dont really care. The "number" is the one that works for my plane and I dont see it as an issue of safety. Since my GEMIII tach is fairly accurate I feel safe that I am staying out of the redzone of 2100-2350RPM. However If I was going by the steam gauge I could have been cruising in the red without knowing it. I dont really have a question... Just showing some data for the group. I do sort of wonder how a tach can be inaccurate as its just a spinning cable. My new (to me) tach that came from another mooney seems to have the same inaccuracy as my old one. But at least the new one has a working tach time. I keep missing Insight when trying to call them about the MP, they are east coast i think and have been closed the last couple times I tried calling. If I could get it accurate I would be ok with that. But is it a setting or I need a new sensor or what?
Hank Posted February 9, 2017 Report Posted February 9, 2017 That would be aggravating! You need accurate measurements for both MP a day RPM to set power, otherwise you don't know where the red zone is. At annual last month, we checked my proposal balance (since it was last dynamically balanced in June 2002). I idled at 1000, then stepped up to 1200, 1500, 2000, 2500 and 2700. Found out that my tach was off by 22 RPM. (And balance was 0.01 ips, so we shut down, disconnected and put her away.) MP + RPM is how you set power, according to MAPA's Key Number program. I think for your F it's 50; it is definitely 47 for my C. But it only works if you know what they are, otherwise you are shooting in the dark . . . .
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