As some may know, I recently purchased N231PG sourced from this board, and have flown it about 20 hours since then. I'm a reasonably experienced pilot, am comfortable flying LOP, hard IFR, etc. but this is my first Mooney, first turbo plane, and first with tip tanks. I've PM'ed a lot with @jlunseth and have read most of the "M20K engine settings" threads extensively. Several things about the plane, and the engine, continue to confound me. I'm at the stage where I'm safe, but there are several things that just don't make sense to me that I've assembled into one thread. Thanks in advance for your thoughts/assistance with several threads of questions.
I should say that I'm getting a fuel injector cleaning and fuel flow setup (particularly on the low side) tomorrow, which may clean some of the engine curiosities up. I have a GB engine, gami's, turbo plus intercooler, merlyn wastegate, and JPI engine monitoring/fuel flow with sensors < 12 months old, and the engine baffling, fuel intake and exhaust systems were all replaced 10 months ago. Based on my reading, I try to keep CHT's 380 or less, TIT's below 1600, and EGT's 1550 and below, and MP 36" and below. Within those guidelines, I feel "boxed into corners" LOP and ROP with this engine with very narrow acceptable engine setting windows, as described below.
Takeoff - On takeoff, I shoot for 36", 2700, full rich, cowl flaps open, which gives me about 22 GPH and climb all the way using those settings. Cylinder 2 is my hottest on climb and I find myself lowering the nose to only 1-200 fpm after a few minutes to keep cylinder 2 below 380 CHT. The other 5 cylinders are all around 360 or so. EGT's are all around 1500 and TIT stays about 1560-1570. Eventually, I make it to altitude, but so far I haven't had occasion to go above 13,000.
1. Even at full rich all the way up, I can't seem to keep that one cylinder cool enough to get anywhere significantly high, even though the usual limiting factor seems to be TIT for others. Any guesses?
Cruise (LOP) - After a minute of leveling off/speeding up/cooling off, being one of the cool kids, I then go for the big mixture pull to go LOP. I don't linger about the move in any sense, but I've noticed that my TIT reading will go near/above 1700 during the (rapid) transition. By the time I've pulled back to about as lean as the engine will run smoothly, I'm at something like 33-34", 2500, 1550 TIT 11.5-11.7 GPH, flaps closed. Cylinder temperatures are cool as a cucumber - #3 is the hottest CHT at 350, #2 now is the coldest cylinder at 280, EGT's are in the 1400's.
1. LOP or absolute temperatures? I've read @jlunseth's epics on how you really have little to no idea of what 'peak' is b/c of the mechanism of the Merlyn's. I'm also confused whether I should be paying more attention to leaning off CHT/EGT as GAMI seems to suggest or TIT as the POH does. If I'm looking for, say, 50 LOP TIT, isn't that 1650? If I touched nothing else aside from mixture, I could in theory be 60 degrees LOP CHT, 120 degrees LOP EGT and 130 degrees TIT at 34-36". I'm flying as per settings in the other threads, but can't square the LOP temperatures against maximum power settings.
2. Why is cylinder #2 the hottest on climbout, but the coolest LOP? Vice versa for cylinder #3?
3. The engine is rated to deliver 100% power continuously, yet I've been admonished that 12 GPH LOP (which is 78% power) is in the "red fin/red box" and I shouldn't pull that much power LOP. If the temperatures at that setting are essentially the same as above, why is it any different/more harmful?
4. At the settings above, are the other 5 cylinders that are 280-320 CHT too lean/too cool?
5. On the ROP side, EGT's/CHT's are relatively even across cylinders. On the LOP side, the EGT difference between #2 and #3 blows out to 180 degrees. Why?
6. If I accept that my engine is barely able to run LOP in an acceptable power setting, how do I handle a climb say from 10,000 to 12,000, or a strong downdraft? Go back to full takeoff configuration/ROP?
Descent - I pull back to 20" MP, which zings me back to ROP and a low power setting. I have to richen things a few turns to get to peak TIT for descent, but everything seems to generally cool gradually and be happy.
Cruise (ROP) - "these engines are just too cattywompus/untuned/etc." you say - just fly ROP.
In my last flight, I was stepped down to 6000 and then had to cruise for 25-30 minutes at that elevation. Given that I've already put myself ROP from the descent above, in my mind, I'm basically flying a normally aspirated plane here. At full rich mixture, however, TIT increases pretty quickly at relatively low MP. Anything above, say, 25", results in a TIT getting near 1600 (at 2500 rpm if that matters). CHT's/EGT's are all 340-350/1400's. IIRC, I'm indicating about 12.5 gph.
1. Why does a setting of say, 29" MP result in an unacceptably high TIT, but 36" (takeoff) not? If I was in a normally aspirated plane, the engine would be able to pull 27" or so, so I'm barely asking the turbo to do anything.
2. Is "full rich" rich enough in this context?
3. What's the best way to keep the TIT cool in this situation? I don't have any more red knob to add, and feel like I should be able to get more power out of the engine ROP without making my turbo melt.
4. If I'm having this issue at 6000, would it be worse at higher altitudes with less dense air? If so, how the heck am I supposed to get up to said higher altitudes if LOP barely works and ROP is too hot TIT?
Oxygen System - I had occasion to use the onboard oxygen system last night for the first time - a night flight at 12k. I have two of the Oxysaver cannulas, plugged them in, and rotated the oxygen knob "on", and lo and behold oxygen came out.
1. How does one 'set a flow rate'? The ball in the little meter showed "20,000 elevation", but rotating the knob is almost a binary function - either the ball was at 20,000, or it immediately fell to 0.
2. I consumed about 1/3 of a tank in 2 hours with 2 passengers. Is that normal/acceptable?
1. I'm using the calculator on my 430W's "AUX" page, and at the cruise settings highlighted above, I'm usually somewhere around 170 kt. TAS. I flew back and forth to PHX from SoCal last night, and head/tail winds were forecast to be about 30kt. Going East, GS was about 200 kt., as expected. Coming back West, GS was 120kt., rarely exceeding 130kt. If anything, the storm/winds were dying down. While it's possible the winds were simply stronger than forecast coming back, I've had the same phenomenon seemingly every flight heading West, where TAS - expected wind > GS. This, obviously, could just be psychological, but I don't remember having the same issues in my previous planes.
2. I've flown behind 430's almost since beginning of my flying career, but this one hasn't been updated in quite awhile and the firmware is old (v 2.3?). If I change a field, say, to display the VNAV or cross-track error on the main screen, it doesn't save from one power cycle to another. Is this a firmware issue, a battery backup issue, a configuration issue?
I have a fuel totalizer and use it. Since you never really know how much the line guy put in, error will build over time. Trying to get a visual indication of how much gas is in the tanks is absolutely befuddling. I have tip tanks. The main tanks have those amazingly annoying anti-siphon valves. To make things even more strange, I'm not convinced that my tanks are symmetrically installed and/or the baffles are equal. For example, one main tank will be filled to the anti-siphon valve, yet (what I think) is an equivalent amount of gas in the other wing has the fuel level far below that, with more apparently having sloshed over to the tip tank. The cockpit fuel gauges will burn down to about 25 gallons indicated (on both sides) and remain there for a long time whilst burning off the fuel in the tip tanks, and then descend from there. I know that the answer here is to drain everything and put in a known amount of gas to have some totalizer certainty, but how do other owners do a visual fuel level check? How do you fill the tanks? What is full? What does a full main tank look like? If I (in theory) had empty mains and filled the tip tanks, how long does it take for the gas to drain down to the mains?