Been doing a lot of low level slow flying lately about 3,000 MSL

jasper7821jasper7821
in General Discussion
Question,
I been looking at stuff in the Arizona desert with friends and been flying about 1,000 AGL or 3,000 MSL
I know procedure is when climbing, run full rich until 5,000 MSL then lean out.
While I'm cruising around, should I be full rich, or is it ok to be somewhat lean?
1976 Arrow

Comments

  • JimCJimC
    If slow, go full rich for cooling.
  • flyguydonflyguydon
    I'd lean anytime you are not full power. No sense fouling your plugs and I know my Arrow does not run hot at all at low altitude regardless. If I were flying for example... at 3000 or 3500 on some sort of XC, I would be 50 ROP for the cruise. This nonsense of not leaning below 5000 always baffled me. I get the full power thing, but slow or cruise. BS.
  • JimCJimC
    I repeat, if slow run full rich for cooling. The engine will not cool when leaned for best power when slow even when not producing full power. For example, at 89 mph and a dISA of +40F, it will not cool even when full rich.
  • flyguydonflyguydon
    Wow Jim. I guess I had better get all 4 of my bayonet CHT sensors replaced. They show under 275 on 3 & 4 and at about 300 on 1 & 2 most anytime after a climb and regardless of anything else. I guess I should be worried about my cylinders melting off my crankcase at those ridiculous temps. It is supposed to be 95 out tomorrow. Just for fun I'll go out at 1000 feet and put it into slow flight 50 ROP and take a picture of things for you.
  • JimCJimC
    95 is +35 dISA. Depending a bit upon which model you're flying, at very close to 89 mph and +40 dISA your required outlet opening becomes infinite and your cylinder temperatures will start climbing. I'd appreciate the numbers. If not too much trouble, please check the face temperature rise and face pressure drop as well.
  • 78TARROW78TARROW
    Jasper - If over the southern desert, full rich & max power if someone starts shooting at you. Maneuvering is also recommended. Hits sound like gravel striking the aluminum... :-)
  • Big DogBig Dog
    From the Flight Training Handbook, AC61-21A
    "Some pilots believe that the mixture should never be leaned below 5,000 feet MSL, but this is not necessarily true. Most fuel metering devices are set on the rich side, which means that prudent leaning is permitted-in fact advisable-at almost any altitude when the engine is operated at less than 75% of its rated power. When a 5,000-foot restriction on leaning is recommended by the manufacturer, it usually is applicable during climbs when climb power is being used."
    From the Pilot's Handbook of Aeronautical Knowledge, FAA-H8083-25A
    "Regardless of the actual altitude at which the aircraft is operating, it will perform as though it were operating at an altitude equal to the existing density altitude."
    With respect to JimC, I, the FAA and Piper recommend leaning in the high density altitude of Arizona so long as your temperatures remain in check. I've flow 6 different Arrows of various vintages. Despite student techniques, none have shown a tendency to get hot. They are basically trainers and are designed to take a degree of abuse from the pilot.
  • jasper7821jasper7821
    Thanks guys, I appreciate the input. Next week I'll be in the process of installing a a cheap Westach EGT and CHT for all 4 cylinders so would it be ok to lean if I keep the CHT around 350 and the EGT around 1300

    We're actually flying close to the border checking stuff out.
  • Big DogBig Dog
    Your EGT temps will vary greatly with the exact position of the probe. Half an inch closer or further away from the exhaust valve can make a huge difference. To quote a specific EGT number is relative to each probe, to each cylinder in each cowling. CHT is a much better indicator on what is happening in the combustion chamber and its effects on the cylinder. I would say 350 is safe. Most people consider 400 degrees max, although actual redlines vary from 420-460 degrees.
  • flyguydonflyguydon
    Yupper. The Big Dog hits the nail on the head! And yes, EGT is relative to a handful of things and the only thing that really matters is the relationship to peak EGT. Your actual EGT temps will vary over 100 degrees at peak from say 1000 MSL to 12000 MSL... higher being at the lower altitudes.

    I did not get the chance to play the low and slow heat game today. Maybe next weekend.
  • JimCJimC
    My last post (long) went off into computer never-never land. Disgusting.
  • flyguydonflyguydon
    I agree with you Jim. This new site is not user friendly and very clunky to use. Complicated. It was almost more trouble than it was worth to put my Avatar in there. Must not have been me either, as I see I am the only one that has either figured it out or taken the time to do it. And it will not let you attach pictures... says they are too big, but they aren't.
  • PilotKrisPilotKris
    JimC wrote:
    95 is +35 dISA. Depending a bit upon which model you're flying, at very close to 89 mph and +40 dISA your required outlet opening becomes infinite and your cylinder temperatures will start climbing.
    JimC wrote:
    I repeat, if slow run full rich for cooling. The engine will not cool when leaned for best power when slow even when not producing full power. For example, at 89 mph and a dISA of +40F, it will not cool even when full rich.

    Jim,

    Please explain. It sounds like your saying that at anything over 100F, it will be impossible to cool the engine.

    It seems to me, flying at a speed close to Vy (which is very close to best L/D) would requite the least amount of power per knot of IAS resulting in the greatest engine cooling per BTU consumed and therefore, the lowest CHTs possible.

    In level flight, I don't see how slowing down (unless you're "behind the power curve") is going to make your engine overheat...

    PilotKris
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