Leaning Feedback and Lessons Learned

Martin HMartin H
in General Discussion
Hello All,

Well I just fly in from Philly and boy........ You fill in the blanks. The trip overall went very well.

Here is what I learned:
- Cherokees do NOT like high density altitudes, hot summer days, with full loads. I know - I was SHOCKED! LOL Every airport I departed (and due to the late times I departed) was at 2800 ft or above density altitudes.

- Climb to altitude (I tried to get up to 7500 feet on each leg). The JPI indicated that the CHT for Cylinder #3 was usually at 450-480 during the climbs. Yes, I would lower to 85-90 Knots to keep temp down, but climb was less than 500 - in some cases it was about 200 fpm.

- upon reaching altitude - I leaned via the Tach - keep leaning until highest number - upon drop off, enrichen. Engine did run smoothly, but even at level altitude - the CHT was around 440.

- I talked to my mechanic upon reaching destination - he recommended that I watch the EGTs while leaning.

- on return trip (same approx conditions) - I leaned as previously mentioned - and the EGTs for #3 were 1500 ish. the others were in the mid 1300s.

now - during the leaning process - my fuel burn did lower to 9.8 gph. while during climb and fully rich, it was about 13 gph.

any more feedback?

Martin

Comments

  • ghendrghendr
    Martin,

    CHT's above 450 are not good. The metal loses half of its strength at 400, and yes the red line is 500, but don't go there.

    You might have cooling baffle issues. Have that checked if you have not already done so.

    Sounds like you were at gross weight. Unless you have had your airplane weighed lately, you might have been over gross weight. I was shocked to find that my airplane weighs 80# more than calculated, even though every mod was accounted for in weight and balance data. I think the factory weight was not accurate.

    Good luck!
  • PilotKrisPilotKris
    Check your timing and baffles. Those temps (CHT) are high.

    You're mechanic doesn't know what he's talking about. EGT Temps (absolute) are meaningless. EGT temps relative to peak EGT are important.

    It isn't likely that you can get LOP with your engine (and you wouldn't likely want the corresponding loss of power) so if your CHTs are getting too hot, you only have 3 options.

    1. Reduce power
    2. Increase airspeed
    3. Grossly enrichen mixture

    I think your temperate issues are baffle related (what's oil temp doing during all of this?).

    PilotKris
  • PilotKrisPilotKris
    Nothing "baseless" about it. How do I know? Prima facie evidence.

    If the mechanics recommendation for high CHTs was to "watch EGTs while leaning"... yes, he doesn't know what he's talking about (at least in this case).
  • PilotKrisPilotKris
    PF Wrote:
    > Sorry, Kris - but I think you're reading something
    > that's not there. The mechanic recommended that he
    > lean based on EGT instead of CHT. Sound advice.


    Now who's reading something that isn't there?

    Besides, even if that's what Martin's mechanic meant (you'll have to ask Martin), it's still bad advice. "Watching EGTs" (whatever that means) is not the best way to lean a carburetored, fixed pitch engine.

    PilotKris
  • Jeff SJeff S
    Well, to get past the sniping, Martin here's another thing you should consider when climbing on hot days in a Cherokee. You don't have to get there all at once. Down here in the South, with a fully-loaded Warrior, I'd practice step climbs. Climb 500 or 1000' (depending on conditions) and level off for a few minutes to let some air blow over the engine. Lather, rinse, repeat. Do this until you get to the altitude you want.

    If you're flying IFR just tell them what you're doing.

    There's nothing like a long sustained climb at high horsepower on a hot day to get an engine to temps that will take a LONG time to cool once you get to cruising altitude.
  • PropFanPropFan
    Not to stray too far from the original post, but is it fair to say that engine temp is not really an issue as long as oil temp is OK? For example, Lycoming recommends getting the oil temp up to at least 180 if possible. But, I have yet to reach that temp. even while climbing out on very warm days. Per the POH for my 180C, I use an en route climb speed of 100 mph.
  • PilotKrisPilotKris
    PropFan Wrote:
    > Not to stray too far from the original post, but
    > is it fair to say that engine temp is not really
    > an issue as long as oil temp is OK?

    If you have the stock instrumentation (only Oil Temp) AND mechanically your engine/airframe is in good shape, if you stay within the POH limitations, there should be no problems with CHT as long as Oil Temp is within limits.

    If your oil is really that cool, there is likely a problem with your Vernatherm (oil thermostat) but I'd check the accuracy of the Oil Temp gauge first. Pull it out, ground the case and put it in boiling water. If you're anywhere near sea level, it should be indicating 212F.

    Multiprobe engine monitors offer little benefit operationally for carburetored engines but are excellent diagnostic tools. Martin's CHTs are quite high. So high that I suspect mechanical problems (timing, baffles).

    PilotKris
  • Tim MorrisonTim Morrison
    I climb at 90 kts until I get higher and it just won't climb at that speed much. By then the OAT is lower so cooling is better and I pitch up to 85 or 80. Don't have any problem with CHTs or oil temp.
  • PropFanPropFan
    PK: yes, I think calibrating the Vernatherm sounds like a good idea. I'm still in that new-owner stage where I'm almost reluctant to do anything more complicated than adding fuel and oil. Haven't paid enough A&P bills yet to assuage my reluctance, but I'm getting there quickly. :)
  • PilotKrisPilotKris
    Not just the Vermatherm, calibrate the gauge too
  • Tom WileyTom Wiley
    Martin,

    Check your baffling and timing as suggested. I don't know what you're flying, but I fly a PA28-180 (O-360-A3A), I recently took off at DA 6800, 30lb over gross, climb out was slow at 400ft/min. I always lean for peak power on the ground, then lean of peak once cruise is established. (>6000 ft) My highest CHT was comparable, all others were <400, fuel flows were slightly less than yours, 9.2 and 12.7, but sound comparable. I also have the horner wing tips, which definitely increase the rate of climb. (Best mod on the plane!) I suppose the prop pitch could also be different. E-mail me if you want me to send you the CHT & EGT logs from my analyzer for you to compare.
  • Aviation LawAviation Law
    I owned a Cherokee a long time ago and flew out of Van Nuys where the temps get pretty hot during the summer months. I learned that climbing in 500 foot increments will reduce engine temps and it only adds a few more minutes to reach your desired altitude. Also, I would take the advice of all the other posts and check the air inlets and bafflings. but it is not uncommon to have the slow climg rate and high temps in summer with a close to gross usefull load.
  • houston21481houston21481
    Martin H Wrote:

    > The JPI indicated that the
    > CHT for Cylinder #3 was usually at 450-480 during
    > the climbs.

    Hi Martin - Welcome back, glad you had a great trip. Did you end up flying into Wings?

    I noticed that when reporting your CHTs in climb, you focused on #3. Was that one running particularly hot? For what it's worth, when I first bought my JPI, we discovered that #3 ran quite a bit hotter than the other cylinders. With a closer look, we found that the metal intercylinder baffle between #1 and #3 was a little loose. Taking care of that dropped #3 back into parity with the other cylinders. Take this for what it's worth - I have a different engine than you do and all I can do is speak to my personal experience.
Sign In or Register to comment.