An interesting posting. I had been wondering whether my tach was telling the true story so I recently purchased a TruTach Digital Tach from Aircraft Tool & Supply ($89.95). During two separate tests I found the tach to be reading an average of 122 RPM low during cruise (2325 - 2450 RPM) and 53 RPM low during idle (700 - 1200 RPM). The cruise tests included a total of 10 data points. I plan to conduct some more tests to further confirm the results with one at 1700 - 1800 RPM. I was unable to check the tach during runup since I was facing into the sun.
Regards Charles McKinnie F-1A, N3050G, GEU -----Original Message----- From: Daniel Cathey <[EMAIL PROTECTED]> To: Coupers <[EMAIL PROTECTED]> Date: Friday, October 23, 1998 6:54 PM Subject: Tach problems >Hi Gang, > >Received a little mail from the FSDO saying that tests on a bunch of planes >showed that many older tachs are indicating from 100 to 200 rpm low. This >means the pilots with these tachs are running their engines at higher rpms >than needed and these inefficient power setting consume more fuel than the >gain in speed warrants. Seems fuel exhaustion - even though the figures >indicated the fuel on board should have been adequate for the trip - due to >the higher rpms has caused a few accidents. > > Went on to say that the tachs only maintained accuracy for a year or two; >should make all of us with our 50 year old planes ( and most probably tachs >that have never been calibrated since new) feel good. Course in the Coupe >you always have the good old wobbly stick on the tank up front to tell you >when the gas is going down and that you should too. But being real cheap, >I want to know (especially now that I have the 100 hp O-200) when I'm >actually using the correct rpms to develop the 65/75 or 85% power setting >shown in the books. Anyone know of anyone in the Oregon area that has a >calibrated strobe tach that can be used to verify in-plane tach accuracy >without removing it and sending it in for calibration. If so, we could >possibly arrange to use it at one of our fly-ins and verify the tachs on >all attending planes in short order. > >Got the knee joint fixed on the plane and actually test flew it for about >an hour last friday, then came down with a bad case of strep throat when >the good weather showed up and have been inside all week. If I get over >this Strep in time will join all for a good lunch in Albany at 1pm this >Sunday. Bring extra money since Bob will have the new shirts and caps! > >Dan N2735H
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