Which AFM? Rev A or Original?

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acecabral
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Joined: Tue Oct 12, 2021 5:55 pm

Which AFM? Rev A or Original?

Post by acecabral »

Hey everyone,

I am looking for help in a topic about which AFM to reference. I own a 195O Cessna 170A with the STC Continental 0300-C model. It has a McCauley 1C172EM7653 prop and my ultimate goal is to make adjustments to my electronics international CGR-30P engine monitor and more specifically my RPM indicator.

At the moment, I have a green range of 2200–2450 rpm, A cautionary range that flashes 2451-2699, and a redline of 2700 RPMs. The AFM supplement Rev A under engine instruments - Tachometer, states a normal operating range of 2200–2450 RPMs The original AFM supplement doesn’t states normal operating range and just the 2700 RPM redline. I

Like most of us, I do not have the original AFM supplement that came with the STC for the engine swap of my current engine.

What I want is the flashing yellow to be removed because I believe it to be distraction when flying at high altitudes. I understand that it’s there for a reason of, but I believe that we should use the full range of our performance envelope.

I mean if Lindbergh didn’t show how to operate at lean of peak in the P39 during WW2, those pilots would of never been in the right spot at the right time.

So, which AFM should I reference to show electronics international that this adjustment is allowed?

Thank you for your time and thoughts
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GAHorn
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Re: Which AFM? Rev A or Original?

Post by GAHorn »

Reading thru ALL the AFMs for all models… I do not see any requirement for a Yellow-Arc at all…. only a green arc and a red line.

The Owners Manuals mention a “cautionary range” between 2450 and 2700 RPM but do not specify it as a “yellow arc”…. and the Owners Manual is not approved anyway. (but it should be mentioned that the “Cruising Performance” charts allows continuous operations all the way up to 2700 RPM….so how can it be considered to be a “cautionary range”>.??) The over-riding document is the AFM which does not require a “yellow arc” ….so it shouldn’t be an issue for no yellow-arc to be identified at all, IMO.
'53 B-model N146YS SN:25713
50th Anniversary of Flight Model. Winner-Best Original 170B, 100th Anniversary of Flight Convention.
An originality nut (mostly) for the right reasons. ;)
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ghostflyer
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Re: Which AFM? Rev A or Original?

Post by ghostflyer »

When I had my continental engine I used to run Bendix mags . I had all sorts of issues with EI tachometer system with the caution lights flashing . Plus I knew the rpm indicated wasn’t correct too. I contacted EI on the matter and they sent me 3 different types [values] resistors to try ,to fit on the P lead in series . They said it was to “tune” the tachometer to the engine .
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