421 climb settings

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  • #83775
    jltaylor
    Participant

      Just got my 1975 421B home.
      I am showing 36gph on left and 39gph on right when climbing at 35″ MP and 1950 RPM as per Ram.
      My question is that the Ram instructions say to lean to between 31 and 32 gph fuel flow at this cruise climb setting and 130kts indicated. My instructor says to leave them full rich?
      What is the advice out there?

      #95968
      quote JLTAYLOR:

      Just got my 1975 421B home.
      I am showing 36gph on left and 39gph on right when climbing at 35″ MP and 1950 RPM as per Ram.
      My question is that the Ram instructions say to lean to between 31 and 32 gph fuel flow at this cruise climb setting and 130kts indicated. My instructor says to leave them full rich?
      What is the advice out there?

      What are you CHT’s in the climb? Do you have an engine monitor?

      Short answer is that you’re not going to hurt the engines by running them full rich in the climb, and generally the GTSIO’s run cool. If you lean a bit in the climb you will get a touch more performance from the engines, but will increase temps and reduce detonation margin (but, at the reduced power for climb, you should be fine leaning a bit).

      Robert

      #95969
      quote JLTAYLOR:

      Just got my 1975 421B home.
      I am showing 36gph on left and 39gph on right when climbing at 35″ MP and 1950 RPM as per Ram.
      My question is that the Ram instructions say to lean to between 31 and 32 gph fuel flow at this cruise climb setting and 130kts indicated. My instructor says to leave them full rich?
      What is the advice out there?

      I am not sure I understand your instructor’s comment. Cruise climb mixture in a 421C is to the blue triangle. I actually run a little richer than this, at about 150 degrees ROP. Your absolute EGT’s should be ~ 1200 to 1250 or so in a turbo. Full rich is essential for full power takeoffs – but not needed for cruise climb.

      #95970
      sworley
      Participant

        We do just shy of full rich which ends up being about 190pph 1450 EGT and CHTs still very cool (350 max I think). EGTs and CHTs are the important numbers to watch.

        #95971
        quote EPANNING:

        Cruise climb mixture in a 421C is to the blue triangle.

        For those of us without an analog FF gauge, what is the fuel flow at the blue triangle?

        Robert

        #95972
        sworley
        Participant

          Does the blue triangle apply to RAM engines at 35″ mp? I thought that was for the original engines and 32.5″.

          #95974
          quote RCJOHNSON:

          quote EPANNING:

          Cruise climb mixture in a 421C is to the blue triangle.

          For those of us without an analog FF gauge, what is the fuel flow at the blue triangle?

          Robert

          Full power, full rich red line is 280 lbs of fuel per side. (46 gallons per hr per side)

          The 75% blue triangle is 140 lbs per side ( 23 gph per side)

          If you leave it full rich, and just pull back power you end up at about ~200 lbs per side (33 gph) Which makes sense since this is 75% of 280 lbs/hr.

          For my plane, 150 degrees ROP is about 160 lbs per hr (per engine) so 20 lbs above blue line. This is 27 gph per side. On a long climb to FL230 or so I will enrichen slightly and shallow the climb if CHT’s creep above 380. I will do 120 kts IAS to 10,000, then 140 kts IAS above. this seems a good compromise for me for climb rate, cooling, overall duration.

          375 HP * 75% = 280 HP. Assuming a ROP BSFC of 0.5 lb/hr, that’s 140 lbs per hr so the stock blue triangle is not a bad operating point.

          From the 100% power FF max of 280 lbs per hr that is way rich for normal ops. That’s a BSFC fuel consumption of 0.75! This is really rich, it is there to provide wide detonation margin at full power. You don’t need this margin at 75%.

          Below ~65 percent power you can use any mixture as long as it burns evenly. This is below the detonation threshold (as long as CHT’s are below redline and ideally below 380).

          Regarding the RAM engine, 35 MP and blue triangle. What do they put in their manual for climb fuel? I would use that.

          Eric

          #95975
          sworley
          Participant
            quote EPANNING:

            quote RCJOHNSON:

            quote EPANNING:

            Regarding the RAM engine, 35 MP and blue triangle. What do they put in their manual for climb fuel? I would use that.

            Eric

            IIRC RAM says 30-31 gph with 1450 EGT and 410 CHT as maxs @ 35″ and 1900.

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