Vance Harral

Again, there are multiple Brittain systems, with multiple gyro units. The best advice in this thread is from folks stressing the importance of using the manuals for the specific system one is working with. That said, to answer your specific question, the B-5 system makes use of a Brittain TC-100-EVT turn coordinator. Here's a picture of a TC-100-EVT on Mooneyspace. Note the wiring cable with the multi-pin connector. That's the electrical connection to the B-5 control head. So yes, that particular Brittain Turn Coordinator accepts electrical control signals that control the pneumatic shuttle valve. I don't know if the B-6 system uses the TC-100-EVT or similar. But in general, the nav control unit has to have some way to "tell" the pneumatic servos to turn left/right to track a heading or course. Consequently, there has to be an electro/pneumatic interface somewhere in the system. In at least some Brittain systems - particularly the B-5 - that electro/pneumatic interface is built into the Turn Coordinator itself. It's possible other Brittain autopilot systems have a separate control valve independent of the TC, such that the TC has no electrical connection other than power/ground for gyro drive motor. I'm not intimately familiar with anything other than the B-5 system.

Probably not true. While there are many Brittain variants, my guess is the OP's B-6 system works very similar to our B-5. In the B-5 system, electrical turn left/turn right signals from the autopilot head are sent to the Turn Coordinator, to drive its vacuum shuttle valve left/right to induce turns for lateral navigation. So the Turn Coordinator is not "just to level the wings", but is in fact the electrical/vacuum interface between the navigational functionality in the autopilot head, and the servos which steer the airplane.

Yes. The GI-106A has analog left/right outputs that can be connected to the Brittain, same as any "old school" CDI. We have a Garmin GI-106A CDI hooked to our Brittain B-5 autopilot. Works quite well for tracking GPS, VOR, and LOC courses.

The main thing you're looking for is asymmetric wear patterns on the exhaust valves. It's possible to catch these early, before the valve actually starts to leak enough to cause lower compression readings. You get to see the intake valve too, of course. But my limited understanding (not an A&P) is there's not much to look for on the intake valves other than gross damage. You can also look at the cylinder walls to see if they still have their cross-hatching, and/or if they're beginning to show any signs of abnormal wear. For pictures, see the "What to look for" section of https://blog.aopa.org/aopa/2016/12/20/scope-that-jug/

Simple things first: make sure the (T)ip of the 3-connector TRS plug on the Halo is making good contact with the corresponding terminal of the headset jack in your airplane. Depressing the PTT switch shorts that terminal to ground, and it could be that the exact condition of your jack is such that the Halo plug is making intermittent contact and causing noise or other issues, where other headsets make good contact (or possibly no contact at all - this can still "work" depending on how the PTT is wired to the rest of the com system). Assuming your co-pilot's headset plugs are wired with a PTT switch as well, you can try plugging the halo in over there. If it works there but not on the pilot side, it's very likely that the jack needs to be replaced, or just tweaked a little. There are all kinds of other things that could cause your problem, but this one is easy to check yourself.

There are a number of reasons why a constant speed prop isn't analogous to a manual gearbox transmission in a car, and I try to dissuade people from using that analogy. First, the propeller has a continuous range of pitch, not discrete pitch points. An automatic CVT transmission of the type found in certain Subarus and other modern automobiles is a little more analogous to a constant speed prop; but most drivers barely understand how automatic transmissions work to start with, much less the concept of a continuously variable transmission. Second and more importantly, in a manual gearbox vehicle, the gearshift lever sets the gear ratio directly. A constant speed propeller has no control that directly sets the propeller pitch. Rather, it is constantly and automatically "shifting" the propeller pitch to maintain a selected RPM. A helpful thing to explain to students is that if you were to safety wire the propeller control full forward such that it couldn't be moved at all, you'd still get about 90% of the benefit of the system. In fact, Cirrus SR22 Turbo 5th gen and later aircraft are designed exactly this way: they have constant speed propellers, but there is no propeller control lever, and the selected RPM is effectively hardwired at 2500 RPM. Third, the sweet spots for power and fuel efficiency in cruise on a typical car vs. a typical airplane are so different as to be almost completely unrelated. In almost all cars, you want to be in the highest gear during all cruise operations, downshifting only for unusual conditions like climbing a hill. Airplanes have more complicated and sometimes counter-intuitive RPM relationships. For one thing, selecting the highest "gear" (most coarse pitch) may result in undesirably slow cruise speeds that are not necessarily fuel efficient. Another interesting example from the cruise tables in my POH: 7500', 71% power, 10.4 GPH, and 165 MTAS cruise speed can be achieved at both 23"/2350RPM and 21"/2600RPM. There is no difference in fuel used and (AFAIK) no meaningful difference in operating temperate at these two settings. The reason to select one vs. the other has mostly to do with passenger comfort (noise and vibration), rather than any difference in speed or fuel efficiency. 2360 RPM will usually be less noisy, but may cause greater vibration and therefore passenger fatigue in certain airframes. I've spent hours across years poring over the performance tables of my airplane and thinking about how to best manage the propeller control. And after all that, I've settled on a trivial strategy: prop full forward for takeoffs, climbs, and landings (in case of go-around), full back for engine-out scenarios to minimize drag, and 2500 RPM everywhere else. Again, 90% of the benefit is the governing control system that automatically increases propeller pitch as load decreases, to maintain a constant RPM. Exactly what RPM is selected in cruise is almost an afterthought, and dramatically less important than the operation of the gearshift knob in a manual gearbox automobile. In summary, if you're trying to understand or explain how a constant speed prop works, I actually think the automobile manual transmission analogy hurts more than it helps. That's especially true in the modern era, where many automobile drivers aspiring to be pilots have never driven a manual gearbox automobile in the first place.

Ours didn't rip in half, it just completely departed the airplane altogether (I guess it may have torn before doing so). The only thing holding it on at the time were sheet metal screws through the fairing and into the empennage skin - no nut plate or other backing. It's hard to believe the factory designed it that way, but the parts manual indicates only screws to hold that fairing on. Like you, we had a new fairing fabricated, though we had to do it at a remote airport in order to get back home. Shortly after getting home, we worked with our A&P to drill out the holes in the empennage skin slightly, and install riv-nuts to receive machine screws. Was signed off as a minor mod. I'd definitely recommend that mod to anyone else!

Even if the Bible (Parts Manual) says they are the same, be a little cautious. Mooneys are famously hand-built, and a part from one airplane may not exactly match another, even when they're the same make/model/year/one-serial-number-apart. There are many stories here about less-than-perfect fit of replacement parts for things like baggage doors, windows, etc. I don't know if control surfaces have the same issue, or if those parts are built to much tighter tolerances.

This'll be my last post to this thread unless something else interesting happens. Two weeks of calendar time and 6 hours of flight time on the airplane since the last gasket was installed, with no issues. I think the problems are all licked, but will stay vigilant.

Suction cup bugs work OK for airspeed and altitude marks, but not heading on a DG. The bug needs to move as the DG rotates, so that it keeps marking the same heading.

I realize it feels like a downgrade because it's not glass, but our steam gauge vacuum DG and GI-106A have been serving us very well for the last 8 years. That said, if it were me, I'd spring for a DG with heading bug. I find not having a heading bug on our vacuum DG to be a non-trivial annoyance, and I think you'll miss it vs. the Sandel. Note that for me, this has nothing to do with autopilot functionality, I just like being able to set a manual heading reference for various reasons: when I'm assigned a vector from ATC, to visualize a runway heading or course intercept, etc. I can make do by using the #2 CDI or the heading indicator on our old Brittain autopilot to "remember" a heading, but it's not as good as a heading bug on the DG.

One bump of this thread, since it's the weekend, and I'm hoping a few folks might be out flying and able to snap a quick photo.

Thanks for the data point, cferr59. I don't see any justification in the parts manual for having differently-sized spacers and two washers between the bracket and the nut. But yours is certainly no stranger than mine. I'll hazard a guess that nose gear door brackets get bent in or out a little over time, and some mechanics periodically change bolts and/or add/remove various washers during annual inspections to eliminate slop. Perhaps there is justification for this in AC43-13 as a "standard practice", but I'm not an A&P. I suppose it's even possible this sort of substitution was done at the factory, as various hand-built nose gear doors rolled off the production line - I know there are other places in my parts manual that say things like "spacers as required".

In the midst of the fuel selector debacle described in my other thread, either myself or the adult supervisor in the shop have disconnected and reconnected the port side nose gear door linkage about a half dozen times (this makes it possible to get to the screws on the tunnel panel which must be removed to access the fuel selector, without jacking the aircraft and retracting the gear). In the midst of this, I realized the connecting hardware installed in our airplane is not what's called out in our parts manual. It's been that way for years, is functional, and I'm not particularly concerned about it, but it's a curious mystery. The aircraft is a 1976 M20F, but the parts manual is applicable to C/E/F/G models from 1968-76, and there are no model-specific notes. Wondering if other owners in this age range might comment and/or post pics. First, I quote from that bible: Figure 26, item #23: As I read this, I'd say the connecting hardware should be assembled from fore to aft as: AN23-21A bolt -> forward gear door bracket -> ( some combination/order of 4 Mooney-specific P/N spacers and the rod end) -> aft gear door bracket -> AN960-10 washer, AN365-1032 nut. What we have is decidedly different. I forgot to snap a photo yesterday, but on the starboard side ours is like: AN23-22A bolt (slightly longer than spec) -> forward gear door bracket -> thin washer -> spacer -> rod end -> spacer -> thin washer -> AN960-10 washer, AN365-1032 nut. This assembly does not meet the "rule" that you should be able to see at least one thread of the bolt extending past the nut, even in spite of the longer bolt being installed. I'm not too freaked out about it because it's very close - the end of the bolt is flush with the end of the nut. It's possible if I cranked down the nut I could see a thread, but that would take it way past torque spec and seems like a bad idea. On the port side, the assembly is similar, except instead of an AN23 bolt, there is some sort of 10-32 machine screw installed instead, with a flat screw head. One hopes it's an aircraft-grade machine screw, but who knows? Whatever it's other failings may be, it's long enough that a couple of threads extend past the AN365-1032 nut when appropriately torqued. At first I thought this whole mess might be a ham-fisted attempt to replace misplaced Mooney-specific spacers at some point in the past. If you Google that 550017-005 part number, you'll see some ebay and salvage listings with fairly silly prices (like $20 apiece). But the pictures in this eBay listing look like the spacers we have, so I think there's a good chance we have the correct equipment there. I have no idea when/why the "extra" thin washers were added our assembly, but I can tell you there is a little slop in the assembly without them. That slop could be corrected by bending the gear door bracket slightly, and if we did so, I suspect the correct-size AN23-21A bolt would receive a nut on the tail end with a thread showing. This is my tentative course of action/direction to our mechanic, but I'm not sure we want to go bending on the gear door bracket. God only knows what it would cost to fix if it cracked, and of course I'm gun-shy after the fuel selector incident. As for the machine screw, who knows where it came from? But the head on that machine screw is more svelte than a conventional AN bolt, and you always wonder about clearances inside the gear wells. Maybe I missed a Service Bulletin indicating replacement of the AN bolt with a machine screw? Anyway... all this is a long-winded way of asking other vintage Mooney owners what kind of hardware they have. Comments welcome.

The airplane was test flown today and nothing blew up. So far, so good. Still watching it like a hawk on a daily basis for evidence of leaks, though.