PT20J

Tire manufacturers recommend replacing on condition, not age. Tubes are frequently replaced along with tires as they stretch and grow in service and may be difficult to reassemble without pinching. If tubes leak significantly, the tube and valve should be leak checked in a tub of water. Taxiing and takeoff also wear tires. It’s not worth altering landing technique to save wear. A Michlen rep once told me that airline tires wear most an takeoff because the weight is greatest (fuel load).

The cylinders of a radial engine are arranged in a vertical plane and gravity causes oil to flow down to the bottom cylinders after shutdown. It can get past the rings, but mostly it fills up the lower rocker boxes and seeps into the cylinders through the valve guides. The starters on radials have a friction clutch that's supposed to slip before any damage is done, but we never trust it and always pull the props through a couple of engine revolutions before starting if it's been sitting a while. Also, when you observe someone starting a radial, you might notice the prop turning a long time before it starts. That's because we count 12 blades before turning on the mags -- just to be sure. It's unlikely that a horizontally opposed engine would have a hydraulic lock from just sitting around. However, if an engine is preserved using Lycoming's procedure in SL 180B, you will have added 2 oz. of preservative to each cylinder and this could certainly cause a problem if it were not removed. If the engine has been sitting a long time, it might be a good idea to pre-oil it as Lycoming recommends before starting a new, overhauled or rebuilt engine. This can be done by removing the spark plugs and spinning the prop either by hand or with the starter until oil pressure is indicated. This will also ensure that there is no chance of a hydraulic lock. Skip

That's what I've always heard from guys that have torn down a lot of engines.

Lycoming Service Letter L180B covers this. The engines that really rust out are the ones that live in high humidity regions and are operated infrequently over a period of years. I can't see one period of inactivity killing it. Think about automobile disk brake rotors. A few weeks of inactivity in high humidity and you'll definitely notice the rust the first time you apply the brakes. But the corrosion is on the surface and comes right off after a stop or two. You have to let them sit a long time to have them actually pit. And, the rotors didn't start out being coated with oil like the engine parts. Of course, if you had known that the annual would take so long, you would have done something differently. But, that's hindsight and you can't do anything about that. Just get it going as soon as possible and fly it often.

Mooney maintains the IPC by annotating the pdf with comments and notes and there is no revision number, so you can’t determine that yours is current. My copy, which is about 6 months old, has about 34 changes noted since the 2003 issue date. So be sure to confirm latest part numbers with your MSC when ordering.

I think Shapeways is pretty honest stating that the switches are not smooth and need sanding. I found it took quite a bit of sanding, so I can see if you sent them directly to an engraver that there would be issues since I wouldn't expect the engraver to spend the time sanding that I put in. The plastic is pretty hard and getting a reasonably smooth surface probably took me fifteen minutes for one cover -- but I'm picky. Also, the material seems a bit porous. Rather than engraving the legends, I found a font in MS Word that was a reasonably close match and then I printed it out on a clear Avery label sheet on a laser printer. Then I cut out the legends and stuck them on and sprayed the switch cover with several coats of semi-gloss clear Krylon. When I put it on the switch, it didn't seem like the fit was quite perfect, but it works great so far. I've attached the legend file I made. RADIO MASTER.docx

I'm curious how many have actually found water in the tank sumps. Maybe it's because I live on the west coast, but I've sumped thousands of times and I can only recall finding water -- and a small amount at that -- once (in Alaska 30 years ago). Now, I am NOT advocating skipping this preflight ritual -- I still sump tanks. I'm just curious about the prevalence of water. Regarding runnups: I fly for a large, well-respected 135 operator (with a very good safety record) and our FAA-approved procedure calls for the mag check, prop check and carb heat check on the first flight of the day only. Skip

The Mooney wing planform is a forward swept tapered wing. Without some form of washout, the stall would likely be uniform over the span. Stall strips disrupt the boundary layer at high angles of attack causing flow detachment (stall).

Actually the "thick" Cherokee airfoil is also laminar flow: NACA 65-415. The purpose of camber and other design parameters is the efficient generation of lift. A flat plate will generate lift at positive alpha, but it also generates a lot of drag. Remember, you only need to generate enough lift to equal the weight (and the tail down force, +/- any effects from any thrust line angle). The trick is to do it efficiently (minimum drag).

Rectangular planform (Hershey bar) wings naturally stall at the root first -- one of the reasons for choosing that planform for RVs and Cherokees. The Mooney wing has aerodynamic washout to accomplish the same thing: NACA 63-215 @ root, NACA 64-412 @ tip. Due to manufacturing tolerances, the left and right wing generally do not reach stall at exactly the same time and the stall strips are added to adjust for that. Not sure how it is done today, but in the early 90's during each airplane's factory test flights, the stall strips were attached with duct tape and adjusted until the roll at stall met specification and then they were permanently installed. At least that's what Rob McDonnell who was VP of Engineering at the time told me.

Actually, stall is the point where CL begins to decrease with increasing alpha. If CL actually went to zero, the plane would be in free fall.

In my case, I installed new bayonet CHT probes in 1, 2, 4 and a 3/8" gasket probe under the factory probe in #3. We sealed the gaps around the baffles with RTV and put new GeeBee baffle seals on which we took great care to fit tightly. The left side has the air filter and the oil cooler which may take cooling air away from cylinders 2 and 4. That's one reason why I was curious what others see for CHT spreads on M20Js. I figured if this was normal, I'd stop investigating. It seems from this and other threads that CHT distributions vary a lot from airplane to airplane.

Here's what I got from Mooney for the M20J drag polars: Cruise clean: CD = 0.0164 + 0.072CL2 Climb, clean: CD = 0.0224 + 0.0697CL2 Climb, gear down, flaps 15 deg.: CD = 0.942 + 0.073CL2 M20K wing aerodynamic coefficient curves attached (quality isn't great: it's a crappy fax from 1991.) Enjoy, Skip Mooney.pdf

Check plug resistance <5K ohms.

MDA is a hard floor whereas you are expected to descend below DA while transitioning to the missed. I like whatever has the easiest setup and most direct navigation. That said, I've suffered the galloping glideslope at KMRY in a 30 kt gusting crosswind, and I've had the tower switch runways 180 deg and forget to switch the localizer, and I've had to shoot the backcourse at KMFR for real when iced up. All mildly unpleasant experiences that would not pertain to LPV approaches.

That's what I ended up doing -- same as on my Subaru. I could only get a box end ratchet on it.

I may still have some drag polars a Mooney engineer sent me in the early 90's for the M20J when I was trying to determine stability derivatives for a flight simulator. I'll look for it when I get to the office. Mooney didn't have much data on earlier models -- just what was required for certification. But Lopresti did a lot of aerodynamic modelling for the 201 and they took more data. You might want to get a copy of Performance of Light Aircraft by John T. Lowry. He has an interesting (and pretty technical) approach to getting at performance data with a minimum of flight testing. Skip

Interesting, my Radio Master broke in exactly the same way. Wonder if it's something about that particular switch. Anyway, I made a replacement from the Shapeways part and it has worked fine ever since.

After flying around for half an hour to warm up the oil, I can do the actual change in a couple of hours or less, not counting inspecting the filter media. This includes removing the cowing, draining the oil and collecting a sample, R&R oil filter + safety wire, add new oil, pull it out of the hangar and do a leak check, then put it back in the hangar and replace the cowling. Of course, I usually find some other useful things to do in the engine compartment while I have the cowlings off. I have a couple of tricks to make it easier on my M20J. First, I buy a cheap painter's tarp (paper on one side, plastic on the other) and cut it into smaller pieces (about 4' square). I roll the nose wheel over this so it is under the engine. Makes cleanup a breeze. I have two rubber tie down straps with S hooks on the ends. After removing the top cowl, I hook these over the pushrod tubes on one end and catch a camloc socket on the lower cowl with the other end -- one on each side. This way, I can unfasten the lower cowl and it hangs by the straps. Then I support it from underneath with one hand while unhooking it from the straps with the other. Reinstalling is the reverse. Easy for one person. After changing the engine to an A3B6, the oil filter is much closer to the firewall. I'm still trying to figure out a combination of wrench parts that will let me get a torque wrench on it. Anyone found something that works? Skip

In my IPC copy, section 32-40-00 has the following note for the main wheel grease seals: "Use new P/N 154-12000 Grease Seal (2 QTY)." A felt seal is still shown for the nose wheel. I got my IPC from Mooney mid-summer when I purchased the '94 J. I don't know what revision it is: Mooney now just adds comments to the pdf file to indicate changes, so it's really hard to know if you have the latest version. I've attached the Parker-Hannifin (Cleveland) document for the seals. Spruce has them: https://www.aircraftspruce.com/catalog/lgpages/clevmoldedgreaseseal.php?clickkey=5623667 Skip PRM95-Molded-Bearing-Seal-6-inch.pdf

Do the wheels have the old felt seals or the newer molded seals? I had a '78J years ago with felt seals that sat outside, and every year the main wheel bearing races would show corrosion at some point around the circumference. Try changing the seals if you have felt. Skip

Most everyone seems to be focusing on the break in process. I appreciate the comments, though I realize that opinions vary on the best way to break in an engine. I did not intend to imply that I thought there was a problem with the engine. The engine is doing fine -- minor wear metals in the filter after a 10 hour oil change, oil consumption down to about a 0.1 qt/hr. and CHT spreads are only 15-20 deg F. It runs well from 125 ROP to 50 LOP. I just found it interesting that the two hottest cylinders were on the left side and wondered if anyone else had seen anything similar. The spreads (not the absolute values) are pretty consistent regardless of mixture or power settings. Skip

I don't want to get too far afield here as I'm mainly curious about the CHT spreads -- and especially which cylinders are hottest and coolest -- on other IO-360 M20Js. But, just for background: 1) The engine is a factory rebuilt with a 2-year warranty, so I am using the break in procedure recommended by Lycoming. The engine was run in a test cell before delivery, so much of the initial break in was done already. I've just been running at 75% to keep the peak cylinder pressures up. 2) I haven't run a GAMI lean test because the fuel flow transducer has become intermittent. However, the flows must be fairly well matched as the engine will run 60 deg F LOP before it starts to lose a lot of power and get rough. Skip

I recently swapped out an IO-360 A3B6D for a factory rebuilt IO-360-A3B6 on a 1994 M20J. I've accumulated about 12 hours on the new engine. I've been running at 25"/2500 rpm, 50-deg ROP at low altitudes to break in the cylinders. The airplane has a JPI EDM 700 with new CHT probes. The factory probe is on cylinder #3 with an EDM ring probe under it (no spark plug gasket probe), and there is good agreement between the factory gauge and the EDM on #3. The baffles are all in good condition with new tight-fitting GeeBee seals. All 9 EDM probes (4 CHT + 4 EGT + oil temp) read within a degree of each other before engine start. I consistently get the following CHTs (+/- 5 deg): 1-360, 2-380, 3-360, 4-375. EGTs are: 1-1390, 2-1410, 3-1400, 4-1420. This isn't a big spread, but I'm curious if others see similar. It's interesting that the even (left) cylinders are hottest. On the other hand, that side has the engine air intake, the cabin air intake, and the oil cooler, all of which I would think would take cooling air away from the cylinders.

No, actually it all went pretty smoothly. I did a lot of research beforehand and had all the parts ready to go. I owe a lot to those on the forum that went before me as their insights were very helpful. For instance, we would not have thought to reinstall the right magneto grounding link on the ignition switch if it hadn't been mentioned here. My IA owns a M20C and has done engine changes, but never on a M20J. We worked on it together and his experience and my research made a good combination with no real surprises. Even with both of us working on it, it took ten full days to hang the new engine.