Vance Harral

It's been discussed here that slop can be affected by adjusting the shims behind the "baby shoe" bracket, but that's just addressing the symptom, not the real problem. The root cause is wear in the bolt/bushing interfaces, which allow the retract truss and drag link to flex fore and aft. You can check the slop by partially retracting the gear and lifting up on the wheel to remove all tension, then wiggling the linkages. As this video shows, ours had gotten quite bad.

Here's a broader view of the retract mechanism. There are three pivot points in the over-center assembly, each composed of a bolt and nut through a bushing. The red arrow points to the retract truss pivot point, which is supported by the "baby shoe" bracket. Note that the baby shoe bracket has a shim behind it, outlined in orange, which sets the fore/aft spacing of the retract truss. The blue arrow points to the pivot point shared by the retract truss and the drag link. The bolt is held with a castle nut, and this is the nut that hits the main landing gear truss when the mechanism gets sloppy. The green arrow points to the final pivot point, where the drag link connects to the landing gear truss. You can't actually see the bolt and nut in this photo because it's behind the truss, but I promise it's there.

I'm starting a new thread to have a better subject and tags, but this is a continuation of this earlier Mooneyspace thread regarding lack of clearance between the over center link and the main landing gear trusses. First, a review of the problem. As shown in the attached photo, with wear over time, the castle nut for the main over-center link will begin to rub the landing gear truss:

In all the models I'm familiar with, the switch in question is mechanically controlled by the position of the throttle knob. People talk about it being activated at a certain MP setting, but there's nothing that actually measures MP. It would be more accurate to say it activates when the throttle is within about 1" of the stop. You don't need to have the engine installed to activate it.

Welcome to the forums! Assuming your Erie, Colorado location is correct, I'm literally in your back yard - also Erie CO (though our airplane is in Longmont). Would enjoy getting together for lunch if you're inclined. If it helps, our airplane goes in for annual tomorrow up at KLMO, and will be all opened up within a day or two. You're welcome to come take a look while it's apart, though what you see on our 1976 M20F may or may not be relevant to your 1980 M20K. Concur your problem may be bad limit switches. These often clean up with a shot of spray-can contact cleaner. But to really, properly diagnose electrical problems, you're going to want the electrical schematics for your airplane. Ideally you'll find them in your Maintenance Manual (not the Parts Manual). You want them for your particular make/model/serial number, because there have been minor variations in the way the warning systems are wired over the years. This is especially true for the expected behavior of the push-to-test switch. If someone here chimes in with info from another 1980 231, it will be good advice. But advice from any other year or model is arguably a little suspect with respect to your particular airplane (ask me how I know...) Those "resistors" on your sonalerts are almost certainly diodes, not resistors. The part numbers for them will be found in your electrical schematics. We have an EI AV-17 on our airplane as well. It happens to be connected to an EI engine monitor rather than JPI, but the principles of operation are simple. You're correct that it triggers voice alerts when a signal line is pulled to ground. I can explain more about this when/if we get together. Hope that helps, will look forward to meeting up if you're so inclined. PM me for details.

Video is a good idea. It will be mid-next week before I have the opportunity, though - once the airplane is in the shop and on jacks. I'll report back here with progress.

Right, but the landing gear truss that's being contacted isn't aligned with the axis of the bolt you're talking about, at least not in our airplane. It's offset a little, such that the thing that hits the landing gear truss is the edge of the castle nut rather than the end of the bolt. If it were offset just a little further, it wouldn't hit either the nut or the bolt. A little less and it would hit the bolt first. Might vary from airplane to airplane.

It's not a case of the bolt being too long. It frankly doesn't matter how long the bolt is, because it's the nut that hits the landing gear truss, not the bolt threads. My hypothesis (unconfirmed at this time) is that slop at the joint in question is allowing it to flex aft-ward as the over-center locks come into compression. Such an aft-ward "bend" at the joint would move the castle nut closer to the landing gear truss with the gear in the down-and-locked position. New bolts and bushings with tight tolerances should reduce the amount of fore/aft flex at the joint when it comes into compression.

I spoke with Dan at LASAR today about this. He said it shouldn't be necessary to remove the "baby shoe" bracket or do anything with the shim behind it. New bolts and bushings should tighten things up and resolve the issue. But, there are catches. First, Dan said in his experience, part of the issue is slop between the O.D of the bushing, and the hole in the link the bushing goes into. So, they are actually sending us slightly oversize bushings and recommending reaming the link to accept the larger bushing. Furthermore, Dan says on one side of the link (can't remember if it's inboard or outboard side), it may not be possible to get the bolt out without at least partially removing the landing gear truss from the wheel well. So, this seems to confirm my fears the fix is more of a "major" project than a minor one. But what needs to be done must be done... We've ordered parts and will start digging into it next week.

Thanks, Stephen, that's very helpful. I had been looking at the "Gear Retraction System" diagram in my parts manual, rather than the "Main Gear Assembly & Installation" diagram. Both of those diagrams show the triangular truss piece (item #12 in your photo above), but only the latter shows the "baby shoe" and the fasteners that pass through it. In looking closely at the diagram, it appears to me the wear items are the fastener assemblies labeled #10 and #14. The callout for reference -014 is complicated, however, as I mentioned above. It lists 5 different lengths of AN5H bolt with an "as required" note, as well as a "THRU-015" spacer. Looking at your actual photo above as opposed to the diagram, it does appear that there's a spacer of some sort between the #13 and #15 parts. I'm guessing this is the mysterious "THRU-015" spacer, but that sounds like some sort of custom part. I can see how a thicker or greater number of spacer(s) would increase clearance, but would also require longer bolts, and I'm assuming that's why there are different bolt lengths listed. Presumably the clearance was good when the airplane left the factory, though. If so, I'm curious whether a thicker spacer is really the correct solution. Wondering if the problem is simply that the bushings have worn to the point where the whole assembly flexes sideways a bit when the gear moves into the locked position. In that case, new bolts and bushings might fix the problem without changing the spacer or bolt length. Again, I plan to call LASAR tomorrow and see what they have to say about it. Will post info here when I have it.

Thanks for the reply, Stephen. I'm not sure I understand what people mean when they refer to the "baby shoe". Is it the trapezoid-shaped part of the truss, where the bolt and nut of concern run through? i.e. the part outlined in red below? I guess it does look sorta like a baby shoe. If that's what we're talking about, I'm having a difficult time understanding what shims are there, and how they could be "adjusted". Looks to me like a simple bolt/bushing/nut arrangement. I think people sometimes use the word "shim" where I'd just say "washer", and I'm aware there are different thicknesses. Are we just talking about inserting more/different washers? Maybe an oversized bolt? I'm wondering if that's what the parts manual means by these callouts: * ref -014 spacer p/n THRU-015 * ref -014 bolt p/n "as-required" of AN5H<various_sizes> I do want to do something about this at the annual. Ours starts in about a week, would be glad to share experiences with you. For what it's worth, I'm not particularly comforted by the idea there might be more clearance with the weight off the wheels. That would just mean every takeoff and landing generates an additional scraping event. As jetdriven points out, it doesn't take much rubbing to damage the landing gear truss. Anyway, thanks much for the info, and for taking the time to respond. I plan to give LASAR a call Monday morning to discuss further, but would appreciate any additional comments here.

@Stephen, any chance you (or anyone else) could provide a PIREP on the work to fix the clearance issue on these retraction links? Our annual is coming up in February, and I'd like to address our clearance problem. I have a couple of questions about this I'm hoping to research in advance, as opposed to myself and the A&P just diving in uninformed. First, based on looking at my Parts Manual, any/all of the following seem like they could be involved: * ref -010 bolt AN26-17 * ref -010 washer AN960-616 * ref -010 nut AN320-6 * ref -010 cotter AN380-3-3 * ref -010 bushing 914020-017 (Mooney P/N, listed at LASAR for $36.00) * ref -011 bolt AN6-22A * ref -011 washer AN960-616 * ref -011 nut AN365-624 * ref -011 bushing 914020-017 (Mooney P/N listed at LASAR for $36.00) * ref -014 spacer p/n THRU-015 (weird P/N, what is this?) * ref -014 bolt p/n "as-required" of AN5H<various_sizes> (WTF???) * ref -014 bushing p/n 914020-18 (Mooney P/N, can't find in searches) Any comments on what actually needs to be replaced? Most of the above is standard, inexpensive AN hardware, but there are a couple of Mooney-specific part numbers, a "THRU-015 spacer" (is this just a washer?), and an "as required" size of bolt that I don't understand. Second, any comments on the procedure(s) to R&R the hardware? The section in my Maintenance Manual on landing gear discusses R&R of the landing gear themselves, as well as rigging, but I can't find any procedures describing service of the bolts/bushings/washers/nuts associated with the retraction links. I'm hoping it's as simple as running the gear halfway up to relieve tension, then just straightforward wrenching, but hard to say without having done it before. Any tips would be appreciated.

I've had excellent results replacing factory placards after interior work with these guys: http://www.engravers.net/

Another technique for slowing down and staying within the confines of a small practice area is to add drag via steep turns. Cruise to the practice area, reduce power, make clearing turns as necessary, then roll in and put on some "G"s to slow down. The Commercial ACS standard for steep turns is "approximately" 50 degrees of bank, which is 1.5G of load factor assuming level flight. Salty old flight instructors will sometimes ask for commercial steep turns at "59 1/2 degrees" of bank, or about 2Gs. Anything in that range will slow you down pretty well through a 180- or 360-degree turn, and is an excellent demonstration of the drag associated with steep turns. I add the usual safety disclaimers here: clear for traffic before maneuvering, be mindful of the increase in stall speed with load factor, etc. But since the Commercial Certificate requires a greater degree of proficiency in steep turns anyway, it's not an unreasonable technique.

ACS = "Airmen Certification Standards" - the document which governs FAA flight tests. It's an evolution of the old PTS ("Practical Test Standards"). The FAA Commercial Pilot ACS can be found at https://www.faa.gov/training_testing/testing/acs/media/commercial_airplane_acs.pdf. Presumably Transport Canada has some equivalent, it may contain exactly the same language. In any case, you should read whatever document governs your flight test and see if it has anything to say about configuration for slow flight. Yeah, in a 172 the only real choice is where to set the flaps, if any. Way back in the 1990s when I was doing my private pilot training, the instructor that taught me slow flight wanted flaps fully extended (all the way to 40 degrees in some 172 models!), which in turn required enormous amounts of power to maintain level flight. Looking back, I don't think that makes much sense. I demonstrated slow flight in a 172 yesterday to get a CFI checkout at a local flight school, and when I asked the chief pilot where he wanted me to set the flaps for the demonstration, he said he was indifferent about it.

The most experienced instructors I've worked with don't seem to particularly care what configuration is used for slow flight: clean, flaps only, or flaps and gear are all OK. The FAA commercial pilot ACS (do you use this in the Great White North?) doesn't require any particular configuration for the slow flight task, so it really is the pilot's choice... in theory. In practice the examiner may have preferences on the check ride, so it behooves to you to talk to him in advance if possible. That said, the ACS does require the "landing configuration" for power-off stalls and "takeoff configuration" for power-on stalls. Since both of these require gear down, and since slow flight work is often combined with stall work, I typically fly slow flight with the gear down. I also tend to set the flaps to the "takeoff" position, since this reduces the required pitch attitude to maintain level flight at low speed. You can certainly fly slow flight in the clean configuration, but the higher pitch attitude required to do so is less comfortable, and can have a negative impact on cooling.

Airspeed is proportional to power cubed, not squared. A 5% increase in power only gives you about a 1.7% increase in speed, i.e. 153 KTAS becomes 155.6 knots. There may be some good reasons to go with the IO-390, but cruise speed isn't one of them.

I've had really good results from these guys: http://www.engravers.net/

'76 M20F - partially mine, in a partnership '67 TR4-A - belongs to the wife (I married up!)

And a third, namely how it will affect business when/if word of the denial spreads. Aviation insurance is a small industry, not at all like auto, homeowners, and health insurance. I've had multiple brokers tell me claim denials are infrequent at least partly due to industry dynamics. A reputation for weaseling out of claims on technicalities (even when the carrier is legally right) is harder to mitigate in aviation than in the trillion-dollar scale of those other insurance markets.

At least one company (Avemco) used to publish a detailed list of their claim denials every year. It appears they've stopped doing so, but I doubt things have changed much since 2011: https://www.avemco.com/Articles/ART0006-2011.pdf The money quote from that article is, "Of our 460 claims, only 6 (or 1.3%) were denied for all reasons." You can read about the detailed reasons in the article. Most of them are obvious issues almost no one would argue with, such as aircraft being operated by a pilot not named on the policy, or filing an in-flight claim when the policy holder explicitly chose to purchase a no-in-flight-coverage policy. Avemco handles the medical/annual thing by asking if you have one at the time the policy is purchased. Assuming you don't lie about it, they don't deny claims if you later have an incident after your medical/annual expires. Not intending to shill for Avemco here - I used to be a customer but haven't been in years. They're just the only aviation insurance company I know of that has ever published their claim denial statistics. I assume the market is competitive enough that other brokers/underwriters must have similar statistics, but can't say for sure.

How exactly does the initial reporting for "appliances" work with ADlog? Do they give you a big list of possible appliances that might be installed on an M20x, and you check off what you have? Or does the form just say something generic like "list all your appliances, e.g. prop governor, radios, etc."? I freely admit I'm not an ADlog customer, so perhaps my skepticism is out of place. I just find it hard to believe there's much they can do in the way of knowing what appliances are installed on a particular 40+ year old aircraft, at least without sending out a genuinely knowledgeable representative to specifically inspect that aircraft. That inspection is a service I'd willingly pay for. But I already do - to my IA, who gets paid every year at the annual for his professional opinion on AD compliance, regardless of whether I use ADlog or not. He has his own software to assist him in that effort. But in the end, it requires a lot of collaboration between the two of us to get it (mostly) right. I get that ADlog has value outside this issue of appliances we're discussing. But I'd bet a lot of owners of older aircraft using ADlog have a false sense of security about ADlog informing them of "all" ADs that apply to their airplane. As an example, our airplane has Stan Protigal's STC for installation of an H3 halogen landing light. This is not a particularly well-known mod. My guess is it's not on any sort of checklist ADlog might send to a new M20F customer. If someone buys my airplane in the future and signs up with ADlog, how does ADlog know to watch for ADs on that landing light?

We had to do the same thing on our '76 M20F about 10 years back. We chose to just bite the bullet and buy the new rod/joint assembly. Looks like the cost has gone up a couple hundred from when we did it (doesn't it always?)

The first three are straightforward, but I struggle with the last, especially on a 40+ year old airplane. It's tough to identify what's an "appliance" and must be searched for separately. If there's an AD against your fuel pump, will you find it under M20 airframe ADs, or only under Duke/Weldon/etc. as an appliance? What about a landing light? Landing gear motor? Prop governor? Battery? Fuel computer? Radio? It's bad enough these things aren't typically categorized under the M20 airframe, but even worse when the one in your aircraft isn't a factory part, having been installed via a later OEM drawing, an STC, or other method of certification. One of the reasons I don't subscribe to ADlog or a similar service is they seem of limited value. It would be one thing if the vendor came out, did an extensive inspection on your aircraft, and used their skill and knowledge to build a one-off list of "appliances" to track for your aircraft. But my understanding is they put the entire burden on you/your mechanic, to identify and list all appliances specific to your aircraft. If you put in all the effort required to identify every appliance and list them by make/model/serial-no, you can search the FAA site yourself.

To clarify, the "eyeball" indicator has a fixed side and a moving side, both with horizontal white lines as you say. The vacuum lines actuate the moving side, which is essentially an indicator of how much force the system is applying to the elevator. In other words, the vacuum lines are an input to the indicator, driven by an output from the altitude hold unit in your tailcone. The (negative) pressure in the indicator lines is a down-regulated analog of the (negative) pressure in the lines to the elevator boots. The primary purpose of the eyeball indicator is to give the pilot information on what to do with the elevator trim when the system is engaged. If the indicator is consistently indicating an application of up elevator, the pilot should add some up trim, and vice versa. The goal is for the lines to match, most of the time. This indicates the most efficient trim setting, with the autopilot applying little to no elevator force in either direction. But note that when the autopilot is working, the indicator is constantly in motion to small degrees. You only adjust the trim if the average value is consistently above/below the fixed line. In our system (B-5 instead of B-6 but the idea is the same), I find the eyeball indicator to have mixed utility at best. First, I always trim the airplane for level flight prior to engaging altitude hold, so the indicator is mostly neutral most of the time anyway. Momentary changes in the indicator aren't very interesting - again, that's just a confirmation the pitch actuator is actually working. If the indicator is consistently high or low for an extended period of time, that means you've entered a very extended up/down draft, or that one of the boots is starting to leak. A trim adjustment is appropriate in those cases, but those are pretty rare events. More importantly, though, I don't think the indicator is intuitive at all. Imagine for a moment that you look at it, and the movable line is higher than the fixed line. What exactly does that indicate? Should you trim up or trim down to fix it? There's a correct answer, of course, but it's not obvious. My motivation to be really educated about the pitch trim indicator and other operational aspects of the altitude hold is hampered by the performance of our system to date. Our altitude hold "works", but performance is weak. We think this is a combination of two issues in our system. The first is the integrity of the seals for the tubing and valves associated with the altitude reference chamber. Ideally these would be perfect. In practice, they have a nonzero leak rate spec'd in the maintenance manual. What this means is that if your altitude varies from the selected altitude for more than a certain amount of time, the reference chamber establishes a new normal, and holds that new altitude instead of the one you originally selected. To prevent this, the system must be able to apply enough force to the elevator to correct altitude variances fairly quickly. That's our second issue. When we encounter an up/down draft, the system applies appropriate correction, but it's often too "soft". Before the system can return the airplane to the originally selected altitude, the reference chamber leaks enough to establish a new reference. We then have to disengage the pitch control, manually re-established the desired altitude, and re-engage. In smooth air this might happen once every 10-15 minutes, which really isn't too bad. In rough air - when you really want the altitude hold - it happens every couple of minutes. So often that it's arguably like not having altitude hold in the first place. We're hopeful performance can be improved by improving the reference chamber seals and/or increasing the gain on the elevator servos, but we haven't gotten around to addressing it yet.