PT20J

Well, I usually get all tangled up in the anchor line when I try that, so water brakes are the way to go.

I'm scheduled to have a GTX 345 installed in my J in March by a shop that has done a lot of 345 installs. From posts on MS and other forums, it seems that the most common source of dissatisfaction with GTX 345 installations arises from it not playing with other installed avionics as expected. I'm seeking feedback from those more experienced on my proposed installation as well as any configuration/setup/options gotchas that I should consider. Current avionics that will remain: GNS 430W, KAP-150 autopilot, Aspen 1000 PFD (connected to 430W and providing heading, nav and GPSS to autopilot), KMA 24 audio panel. New avionics: GTX 345 w/o GPS replacing KT-76A. The GTX 345 will connect to the GNS 430W via ARINC 429 for WAAS source and ADS-B In traffic and weather display. The GTX 345 will connect to the Aspen PFD via RS-422 for ADS-B In traffic and weather display. The GTX 345 will connect via Bluetooth to an iPad for AHRS and ADS-B In traffic and weather display. The GTX 345 audio will connect to the KMA 24 for traffic annunciation. The GTX 345 will connect to the current yoke-mounted IDENT button. The airplane originally had a Argus moving map (removed by a previous owner) and there remain two currently unused buttons on the right horn of the pilot's yoke from that installation. Anybody got any ideas of something useful to connect them to? Thanks in advance for the help, Skip

Good point - made me chuckle. All that prop cycling has always mystified me. I think it's a holdover from old military manuals since the hydramatic props sometimes required cycling several times to get reasonable response in cold weather (been there, seen that). I have no idea what's magic about three cycles, but that procedure even made it into my M20J POH! To Clarence's point about skipping run up: I've flown for two Part 135 seaplane operators, and the FAA-approved SOP at both was run up on the first flight of the day only. Airplanes are meant to fly. Engines don't cool so well on the ground, and there's sand and gravel and whatnot in the run up areas to erode your prop. Do we wear our airplanes out ground checking stuff too much? Something to think about. Skip

Orcutt’s shop does superior mag work. Bet they’ll run great.

Thanks for the info, David. I can feel some roughness when rotating the trim wheel to nose down, but not up. It's not very bad yet, but since I have lubed the front gearbox (which I had out to replace a worn trim wheel shaft bushing), all the u-joints, the King trim servo carrier bearing, and the rear jackscrew, the thrust bearings are all that's left. Skip

Nice, David. Can you give more detail about the shimming? How did you get the bearings off the shaft? Skip

I'll have to look at one next time I see one at a museum. You're probably right. The document you quoted isn't exactly clear in terminology: "Herb Nystrom led the team that designed the empennage and tail assembly. Following a series of engineering studies, he opted to include an all-moving tailplane similar to the one Kelly Johnson developed for the Lockheed JetStar. This configuration most effectively distributed pitch forces across the entire horizontal stabilizer assembly, widened the airplane’s center-of-gravity limits, and eliminated the need for both ballast and trim tabs" "Empennage and tail assembly" is redundant. "Tailplane" is another word for horizontal stabilizer. However, the reference to it being similar to the JetStar design would seem to indicate that the entire empennage pivots. Thanks!

I took the course 25 years ago when I owned my first Mooney and the manual was something you only got as part of the course. I think it's still that way. It was a nice reference but didn't include much original work except tables of Power/Attitude/Configurations for various models and flight phases which was interesting but something everyone can best work out for themselves based on how they prefer to fly the airplane. The rest was mostly excerpted from the POHs, Service Manuals, AIM, various ACs, etc. It's likely been improved over the years. I'm not saying that the course or material isn't worthwhile, but if you are well-studied and expecting to learn a lot of new things, you might be disappointed. Still, it was a good review and nice to have the material all in one book.

Do you have a reference for that? I believe that later versions of the U-2 had a variable incidence tailplane, but I don't think the entire empennage rotated as the Mooney. That would have been cumbersome in such a large structure. But, I'm not a U-2 expert.

The trim servo has a lot of torque. What seems to happen is that the mechanism gets stiff for whatever reason, and if you always use electric trim, you don't notice it until the trim motor isn't powerful enough to move it anymore. If it gets to that point, it may be hard to move it manually as well. There's a lot of trim change in a Mooney over the range of speeds and flap settings. Mooney flaps are more effective at increasing CLmax than on most other GA airplanes and contribute more pitching moment. The Mooney trim system changes the angle of incidence of the stabilizer. This design is favored when the amount of trim range would cause excessive elevator deflection with a trim tab. Common in jets. The M20J stabilizer trims through a range of about 6 degrees. This isn't really enough which is why the trim bungees are needed to bias the elevator along with the stabilizer movement. Even at only 6 degrees, it takes a zillion cranks of the trim wheel to go through the entire range. No wonder everyone likes the electric trim.

Was wondering about that 90-deg bank. Hey, thanks for the picture. I've been hoping for a charter there someday so I could see how the lake got it's name. Pretty.

Lots of good pix and advice on this thread. Also a lot of talk about -- grease. I'm in agreement that the best practice is to follow the manufacturer's directions in the Service Manual unless you absolutely know -- don't think, but know -- of something better. My M20J Service Manual specifically calls out Aeroshell 7 for the jackscrew and bearings. I'm not sure it's a good idea to use Aeroshell 5 which is a high temperature grease specified for wheel bearings. https://www.shell.com/business-customers/aviation/aeroshell/knowledge-centre/the-aeroshell-book/_jcr_content/par/textimage_1433441235.stream/1445042875796/1d024cf49b16b7091e0368a866e9ca6b0ef6f275ac75de066f2004ed372bbef1/aeroshell-book-5greases.pdf Grease is basically oil and a thickening agent. Not all greases are compatible with each other. The Service Manual calls out the following greases: MIL-G-81322 (now MIL-PRF-81322G) Common greases that meet this spec. are Aeroshell 22 and Mobilgrease 28 MIL-G-3545 (obsolete, superseded by MIL-PRF-81322) -- Aeroshell 5 MIL-G-23827 (now MIL-PRF-23827C Type I and Type II) Type I uses metallic soap thickener -- Aeroshell 33, Mobilgrease 33. Type II uses clay thickener -- Aeroshell 7. Type I and Type II are NOT compatible with one another. MIL-Specs can be found at: http://everyspec.com/ Qualified products meeting MIL-Specs can be found at: https://qpldocs.dla.mil/ Skip

Lyle Panepinto at Southern Seaplane teaches a really good seaplane safety class that includes emergency egress training in a dunk tank.

Appreciate real data - thanks Byron. Curious if you noted any CHT differences between 20 deg and 25 deg ROP and LOP. Did you wind up leaving it at 25?

The real “genius” of Al Mooney was figuring out how to package four people into the smallest wetted area with a cabin wider than a Bonanza.

A Mooney engineer, who had also worked for Cessna, told me years ago that it took 750 hrs. to knock out a Skyhawk and 2000 to build a M20J. Cessna tooled everything. A lot of the Mooney is “hand crafted.”

I thought the timing change was to lower CHTs. Anyway, Lycoming has been shipping all IO-360 engines (except Bendix dual mag versions) with 20 deg BTDC timing for a long time -- I have a Lycoming Operator's Manual from 1982 that states 20 deg BTDC as standard. Interestingly the current 1E10 TCDS (1-10-18) lists timing as 25 deg with 20 deg footnoted as optional. What that means is that you can change the timing back to 25 deg (with the appropriate changes to the magnetos internal timing, data plate, and a logbook entry). I confirmed this with the Lycoming factory rep. Does it make a big difference? I don't know. But the APS folks don't seem to think so. Here's a graph I got from the APS presentation when I attended a seminar in Ada, OK several years ago.

Thanks, Andy, One more mystery solved. Way back in the early '90s, I was working on a flight simulator project and since I owned a '78 M20J at the time, contacted with Mooney engineering. Rob McDonnell was VP of engineering at the time and we had a deal that if he sent me engineering data I needed, I would send him estimates of stability derivatives. He sent me some stuff but he freely admitted that Mooney had been through so many ownership, management and personnel changes that many reasons why things were done the way they were were lost. I can't imagine that it's gotten better over the intervening years. It's interesting to piece all this stuff together. Skip

I'm curious if your airplane has the aileron-rudder interconnect springs. The usual reason for such an interconnect is to alleviate some adverse yaw. If the aileron change made the yaw worse, the springs might have been added to help with that. If the yaw is due primarily to the wide chord of the ailerons, then I would think the springs would be part of the original design. Skip

I didn't know that. The earliest one I've flown was a '67 M20C. Thanks :-)

That's a good point. I was trying to simplify the explanation by relating to commonly understood wing aerodynamics and that was a mistake. Let's try again with a more correct, though more complex, description: Consider the aileron that is deflected UP. (The effect happens in both directions, but it is easier to visualize with the up aileron). As air flows "up" the deflected aileron, it slows until it reaches the sharp trailing edge where it accelerates "around the corner." This flow pattern creates an adverse pressure gradient along the top surface of the aileron and, at some deflection, flow separation begins to occur. As the flow separates, the force on the aileron, and thus the hinge moment, increases. The effect is not linear and tends to cause the aileron deflection to be limited at some point depending on the mechanics of the control system. The effect increases as TAS2. Beveling the trailing edge reduces the acceleration of the air flowing over the trailing edge by increasing the radius of curvature and thus reduces the adverse pressure gradient which in turn reduces the hinge moment. Skip

It's a neat aerodynamic trick. Just as an object with mass tends to move in a straight line unless acted upon by a force, air tends to flow in a straight line unless acted upon by a pressure gradient. Also, in the absence of an adverse pressure gradient, flowing air tends to follow the contour of an adjacent surface. Consider an aileron with a beveled trailing edge deflected downward. The deflected aileron increases the camber of the wing causing the desired rolling moment and the beveled edge further increases the camber locally at the trailing edge. As the air flows over the bevel it tends to follow the contour. This deflection of the air sets up a pressure gradient which results in lower pressure at the top, trailing edge of the aileron. This exerts a "pull" upward on the aileron reducing the force required to deflect it. The Mooney aileron control system is interesting because it is definitely different than other designs of the period. It is notable for using push-pull tubes instead of the more common cables and pulleys. Is that really better? Some postulate that the push-pull tubes are better because they aren't subject to cable stretch, which is certainly true. However, there are a lot of rod ends in the Mooney and over time they can wear enough to increase the dead zone in the control system. Keep them lubed with Tri-flow. Also, the Mooney aileron controls have a lot of friction which increases break out force. Cables running over ball-bearing pulleys generally have less friction than push-pull tubes running through greased phenolic guides. At cruise speeds the ailerons tend to be pulled up (lower pressure on the top of the wing). This is the reason for rigging them down up to -2 deg. The outboard end of the aileron push-pull tube is connected to a bell crank. So, while the predominate motion of the push-pull tube is back and forth, there is a small component of fore-aft motion caused by the eccentric effect of the bell crank. This increases the friction on the outermost guide block. As the ailerons move upward, the push-pull tubes can flex under compression and put more pressure on the guides. The effect increases with airspeed. Back in the 1990's, Mooney was considering entering the JPATS competition for the next military trainer (Beech won with the T-6A). Roger Hoh was contracted to help work out handling issues and told me that at high speeds (I don't recall what the engine was -- likely a PT-6) the ailerons drifted up enough to bind the push-pull tubes such that you could move the stick (the test plane had been retrofited with a stick) left or right and it would stay where you put it! All that being said, I like the Mooney controls enough that I recently bought another one. I just keep everything well lubed. Skip

Yep, that's about what I would expect. The Mooney's flaps are different than most GA planes -- not much chord but long span. They are more effective at altering CLmax than adding drag and that's why the Mooney's have slightly greater reduction in stall speed than other brands. Here are some numbers for decrease in stall speed flaps down vs. flaps up in CAS from various POHs: Mooney M20J 7 kts Bonanza A36 6 kts C-182T 6 kts C-172S 5 kts PA28-181 4 kts Of course, there's a tradeoff -- the longer span flaps left less room for the ailerons which forced the use of a wide chord, short span aileron that has greater hinge moment -- thus the need for the beveled trailing edge to reduce the stick force. I'm in favor of any SOP that makes sense and can be used consistently, and I see no problem with doing it the way you suggest. Personally, I just don't like changing configuration after I start downhill, but that's just me.

Mooney has used a lot of confusing language for flap speeds in the POH over the years. The TCDS is a better source of regulatory information. It doesn't appear to me that Mooney began specifying airspeed limitations w.r.t. flap deflection in the TCDS until the J model where (for most serial numbers) the limitation is for full flaps only. That said, I've always thought the flap system one of the weaker parts of the Mooney design. Just note how much flex there is in the mechanism in any position except up against the stops. To reduce wear and tear, I'm in the camp that uses the gear to slow down to the top of the white arc, and then I go to 15-deg for the approach. For this reason, I put the gear down and get the flaps set before the FAF or GS intercept and reduce power to go down. But, I do a GUMP check at this point. Skip

Mooney IPC calls them out as dust boots. Originals are double-knit fabric. Don't think they'd keep much CO out.