PT20J

Sounds like a solid plan. Be sure to share the results. I’m curious myself.

Hmmm. It did wander a bit. So, Hank, what did you decide?: finewires or massives (or maybe BY massives)? Don’t keep us in suspense Skip

We may be trying to get overly precise about something that's just an approximation anyway. When you get past the first decimal point, lots of things have an effect. Look at the Lycoming chart below for an IO360-A and notice that the 65% best economy BSFC varies from about 0.44 at 2700 rpm to 0.40 at 2200 rpm.

The calculation of %power based on fuel flow is based on the observation that BSFC (lb/hr/hp) is relatively constant for all internal combustion engines over the range of ~20 to 50F LOP. You can get very accurate if you know the LOP BSFC for your engine. The factors based on compression ratio are just approximations based on typical BSFC for a range of engines and the fact that lower compression engines are slightly less efficient and therefore have higher BSFC.

I used to win beers with this one, “Bet you I can turn on the radios by pulling a CB.” Even long time Mooney check pilots don’t always know about this. The avionics relay is designed to be fail safe - if it fails or loses power, the avionics bus (not buss, that’s a kiss - look it up) will fail ON. The avionics switch powers the avionics bus relay when it is in the OFF position and de-powers it when ON. Pulling the AUX breaker cuts power to the relay and voila, the radios go on.

Went out to test the autopilot today. Wilder ride than I had planned. Moderate turbulence ( hit my head on the ceiling a couple of times despite having the belts really cinched down, had trouble tuning radios, difficult to read the approach plate - yeah, it was rough). A/P captured KPAE 16R Y ILS localizer and glideslope perfectly. Wind picked up with ATIS advertising 160 at 20 gusting to 32. (Well, at least it’s straight down the runway). Big power changes up and down to maintain 90 kts approach speed. KAP 150 never off more than half a dot localizer or glideslope to DA. It may be old, but it’s a pretty darn good autopilot. Landing surprisingly uneventful. Bonanza following me in called it “sporty.”

The best part of doing these things yourself is that you appreciate when an experienced A&P does it in half the time and realize that some of the cost is paying for experience.

I changed the wing-mounted landing and taxi lights on my J. I used Whelen Prometheus Plus because they are PMA'd and the 135 company I sometimes fly for has had really good experience with them. They would be a snap to install if they went in from the front, but Mooney never seems to do anything the easy way. You get access through an inspection cover under the wing behind the lights. You need an allen wrench to loosen the screws that clamp the lights in place, and there is minimum room to work in there. It gets easier by the third lamp. After installing them, it's a good idea to check the alignment per the maintenance manual. Also, although it's not necessary, it's not a bad idea to remove the clear plastic lenses to check for cracks and stop drill if necessary. I also found that the Whelen bulb rims were a little thinner than the GEs and they had a little play in the mountings, so while the lenses were off, I put a couple of daps of clear RTV over the bulb and frame junctions to prevent any vibration movement while making them still easy to remove if ever necessary. Skip

The APS power formulas and the JPI calculations are approximations, but seem reasonably accurate. Really, the only way to know for certain the power being developed is to have a torquemeter. Many of the large radial engines had one built in (calibrated as BMEP) and Roy LoPresti installed one in the airplane when developing the 201. That's why the M20J AFM power tables are very accurate. If you take Lycoming's published sea level and altitude curves for the IO-360 and create a power table similar to the Mooney table, you'll find that the Mooney requires 1 to 1.5" more MAP to generate the same power. This is the difference between running in a test cell and running on an airframe with it's less perfect induction and exhaust system. Here's the ubiquitous chart from Lycoming (also reproduced in some Continental publications) that gives idealized engine parameters as a function of mixture strength. Note that the BSFC is approximately constant during the "best economy" range from about 10F LOP to 75F LOP. It is higher, and therefore less efficient, anywhere outside this range. The curve most likely isn't quite this flat, and Continental in the second chart below calls the best economy range 25-50F LOP which seems reasonable. Despite what the APS guys say, power is related to fuel flow both ROP and LOP. I do not believe they are trying to be misleading - they are just oversimplifying. If you operate within the "best economy" range, power is easily calculated from fuel flow because BSFC is essentially a constant. If you are ROP it's more complicated. I chose the chart below from Continental to show this. Note that the best economy (LOP) lines are essentially linear, whereas the best power and full rich lines (ROP) curve up slightly. But, they don't curve a lot. So a first order approximation for ROP power as a linear function of fuel flow wouldn't be far off. The problem with coming up with a single formula is the vertical offset between ROP and LOP mixtures - not the linearity. Skip

Interesting problem and good data on the issues you found and the troubleshooting. First, the ALT breaker should not trip unless one of three conditions occur: 1) the alternator or it's wiring shorts; 2) the breaker is bad; 3) someone replaced the alternator with a unit capable of putting out more current than the approved original. Since your alternator works, I would suspect 2 and verify 3. Nancy Narco says (remember her?) that your Com 2 was installed by a hack. I'd look into whatever else this shop did and get it all cleaned up. But it also sounds like the Narco is toast since it didn't work on the bench. The crappy wiring may not have been the issue. The interesting question is why the Com2 breaker didn't pop. It might be defective also. If you had a weak ALT breaker that tripped early, and a Com 2 breaker that didn't pop, and a hard short in the Narco, you might get the symptoms you have. This will be a "peel the onion" sort of troubleshooting exercise (frustrating, but better than intermittents!). You're on the right track and doing the right things so far. Keep at it and you will get it solved. Skip

Get out the IPC and make a list of the parts you'll need to do the conversion. Call Corrine at LASAR and get a price quote. When you get off the floor, I think you'll decide to figure out how to adjust/lubricate/live with your present cowl flaps.

If I understand the theory correctly, the fine wires are supposed to ignite weak mixtures more rapidly because the electrodes project further into the combustion chamber whereas the the massives could have the spark jump the gap at the base of the electrodes up inside the plug. So, it seems that the BY plugs might do the same thing (if the theory is correct) at lower initial cost. The long term cost is probably a wash as the longer life is claimed by some to offset the higher cost. I think @Shadrach had a good point though: if the performance difference were repeatedly measurable, the Champion and Tempest marketing departments would likely be touting it. But, if you tried the fine wires and are convinced there is an improvement, good for you. For others, your mileage may vary. I'm going to try the Tempest BY plugs when the Champion plugs that came with my rebuilt engine wear out (which may only be a couple of hundred hours - we'll see.) Right now, it's running very well on the Champs both LOP and ROP. Skip

Another possibility is that these things are not all related. It will take between 110 and 150% of the breaker rating to trip it, and at those small overloads it will take several seconds to heat up enough to trip. The alternator shouldn’t be able to trip it unless the alternator has a short. Or ... if the breaker is bad. The Stratus problem could just be an old worn out battery and unrelated. Not sure how the Narco would fit in, but it’s old and if funny things were going on with the electrical system, it my have just given up. I would start by figuring out why the ALT breaker is tripping because that should never happen unless there is a major fault. Likely the breaker is bad since the alternator and voltage regulator seem to be working after resetting it. I wouldn’t expect a fault that trips a 70A breaker to be transient. Skip

So if I understand correctly, three things happened: 1 The ALT breaker tripped 2 The Stratus battery is swollen 3 The Narco radio fried. The alternator shouldn’t normally be capable of putting out enough current to trip the ALT breaker. The purpose of the breaker is to isolate a fault in the alternator or its wiring from the battery. A swollen Li-ion battery is indicative of over charging which could be due to over voltage. Newer avionics will withstand a wide range of bus voltages - usually about 8 to 33 VDC. The old Narco is less tolerant of over voltage. Did you notice the bus voltage after you reset the ALT breaker? This might be a voltage regulator/alternator problem. Hard to tell without doing some troubleshooting. Skip

I think some folks get carried away with LOP thinking that if a little is good, a lot must be better. If you go really lean, the fuel flow drops off impressively. But, the power and thus the airspeed drops off even faster. The BSFC actually increases and you use more gas to get where you’re going later.

Curious what “useful limit” you are measuring and if you are rotating even to odd, not just top to bottom and how often. Not doubting your observation, but I’ve just always gotten much longer life. What I would really be interested in is a comparison of fine wire and BY massives - anyone done that? Skip

Autopilots Central charged me $2119.78 for the KC 191 repair. They couldn't initially reproduce the problem, but found a voltage low and suspected the power supply. They replaced a bunch of electrolytic capacitors and a couple of resistors in the power supply as the capacitors are known to leak electrolyte when they get old. I'm sure this improved the long-term reliability of the computer, but it didn't fix the problem. They took it back and ran it on the bench for a month and did see the problem off an on, but could not determine the cause. At that point, they sent it to Mid-Continent and there the problem was found and fixed. Autopilots Central handled all this additional work under warranty so I only paid the initial $2K. If I had another autopilot problem that required taking the airplane to the shop, I would not hesitate to go to Autopilots Central or Executive Autopilots. But, I think Mid-Continent might be the better choice for repair of individual components. M-C is a BendixKing repair station and Autopilots Central and Executive Autopilots go to them when they can't solve a problem or get parts. I talked to Aspen about the ACU and got the impression that failures are not that uncommon. It seems just a coincidence that the ACU failed while I was fiddling with the autopilot. In my case, it is probably a bad 15V internal reference since the problem affected both the CRS and HDG outputs. Good news is that I found a good used ACU for $550 on eBay and Aspen will exchange one for $660 or sell a new one for $880 (list prices, maybe some negotiating room if you do a lot of business with an Aspen dealer) so they aren't expensive as airplane parts go. This is the original ACU, not the ACU2. Skip

It started with the autopilot failing in flight at random intervals. It would annunciate a TRIM failure and kick off. Sometimes, it would also trip the TRIM breaker/switch. Then eventually, it would intermittently fail TEST. I sent the KC 191 computer to Autopilots Central and they eventually sent it to Mid-Continent. The problem turned out to be a cold solder joint on the connector for the internal cable that connects the two circuit boards together. When I got it back, the autopilot worked except HDG and NAV moves were inop. I checked some voltages on the KC 191 tray connector and determined that the outputs from the Aspen ACU were bad. I swapped the ACU for one I bought on eBay and now all is good. Skip

The old style trim stops are plain nuts on the forward trim screw (under the trim wheel) and can jam. The mod replaces them with stepped stop nuts that are jam proof. Until you get this fixed, avoid running the trim all the way to the stops.

A year ago, Mooney's price through LASAR was: 720115-9501 1-1/2" extension kit $258.21 (one kit does both pilot pedals) 720115-9503 3" extension kit $258.21 (one pedal - requires 2 kits for both pilot pedals) Check the equipment list in the AFM; some planes came from the factory with the 1-1/2" kit installed. Skip

Wow, great job. I used Permatex 81158 black silicone adhesive. It adheres well to clean ABS and it’s easy to get the two parts apart again if you ever need to by working a long blade between them to cut through the adhesive. Check that the metal piece that holds the lamp holders is assembled correctly - mine was upside down and backwards - and rivet it to the bottom plastic part with black pop rivets per the IPC. Otherwise, it’s really difficult to replace the bulbs after assembly. Skip

I'm curious - we all know that the Mooney's sit low and the stiff gear makes the plane do a kind of scary hobby horse teetering when taxiing over rough surfaces (paved or not). But how many have actually had prop strikes taxiing off pavement?

Well, I always though Mike Busch's advice to buy the latest model, lowest time airframe you can find/afford to be a good idea. An older model is not a bad idea if you want to leave it pretty much as is, but if you go mod crazy, you will put a lot of money in it that you are unlikely to recoup. On the other hand, Mooney got carried away adding bells and whistles to later versions that didn't really add anything but cost to maintain: two position electric flaps, electric cowl flaps, LED gear and flap indicators, etc.

Too far away for you probably, but as a price point, I had my McCauley resealed by Northwest Propeller Service in Puyallup WA for $1500 + $120 parts last September. Dick Jacob actually recommended against doing an overhaul unless they found something when they had it apart (they didn't). It came back looking and running like new. Skip

I think Brad is suggesting that high heat and high pressure are a bad combination. His numbers are pretty conservative. Your numbers are not very conservative (75%@50ROP). In fact, that power setting is outside the factory recommendations for my airplane. I think your point is that the engine is under no eminent threat at that power setting. Inducing detonation in an NA injected Lycoming is nearly impossible at any setting. Nevertheless, some of them still need cylinder work at mid time. I don’t have any data to suggest that power settings have any bearing on mid time cylinder work, but I’d not begrudge someone setting conservative parameters. The thing is, those parameters keep shifting. 400 used to be the get your attention CHT then it was 380. if 380 is good, why not set the alarm for 370 if 370 is good why not...rinse and repeat enough times and people keep revising there parameters down to the point that they’re ultra conservative and proclaim anything outside their comfort zone as abusive. I am thrilled with the engine monitor tech we have today but it can get extreme. Folks managed to run engines to TBO long before we had decent monitors but you wouldn’t think that possible the way we talk today. I think you hit the nail on the head. Sometimes I feel like the red box is the new shock cooling. My point in choosing 75% at 50F ROP and 360F (which is within Lycoming's allowable operating range, though just barely) is that this is often described as "the worst possible" operating point because the peak pressure will be at its highest there. But is that really bad if it is well within the design constraints of the engine? We don't have the engineering data, so we don't know. We do know that it isn't going to detonate - APS has data for that. And, we can reasonably assume that it isn't going to do any bottom end damage given that bottom end problems (except for camshafts) are rare. So, the question is: what's the extra pressure going to do to cylinders if the CHT doesn't get too high? It doesn't help me understand if someone says it "cooks" them, or you'll "shorten" their life, or it will cause "damage". This just means that the author doesn't really know and is just repeating something they heard or read - like the OWT about lean mixtures frying valves that went on for so long. It would be really interesting if someone could show that the rings blow apart or the valve heads break off from an extra 100 psi of peak pressure, but I haven't seen that. I think these engines have proven to be amazingly strong and reliable. That is not to say that they won't last longer with more conservative operation, but I think obsessing over red boxes (which John Deakin himself has said is more of a concept than exact numbers) misses the point. I do think there is ample evidence that to get maximum service life, the engines should be operated frequently and the CHTs should be kept below 400F. Since I have no way to measure peak pressure, and I wouldn't know the design range for it even if I could, I don't lose sleep over it. Skip