PT20J

Hard to tell who actually designed something 50 years ago. The important point is that Eaton currently owns the design except for the Plessey units that no one seems to maintain.

Arrows and Seminoles (maybe other Pipers) have no uplocks; the gear is held up by hydraulic pressure. If the electrical system or the reversible motor in the hydraulic pump fails, then pulling the small lever on the console releases hydraulic pressure and the gear extends by gravity and maybe some mild g loading to lock the nose gear. Likewise, the gear will extend if hydraulic pressure is lost. It’s good unless you are a ferry pilot concerned about a hydraulic leak causing the gear to extend over the ocean which would ruin you trip. Skip

Yes

It was beefier than the Dukes it replaced. https://www.donmaxwell.com/ad-75-23-04-sb-m20-190

I went through this when I bought my airplane because the previous owner had dinged a wingtip on a hangar door and it was repaired by Maxwell with factory parts (wingtip, skin and a rib as I recall) and an appropriate logbook entry but no 337. My IA (been an IA for 40 years) insisted this was a major repair and needed a 337. Don insisted it was just a replacement of damaged parts with factory new parts and did not. He was nice enough to file one just to keep my guy happy since, as he said, "It's only a piece of paper." Later I asked the Director of Maintenance at the 135 operation where I worked summers and he said it was one of those areas that is open to interpretation, but in my case he agreed with Maxwell. In the end I don't think it matters much. Damage is damage and the repair will be recorded in the logbooks whether a 337 is filed or not. Skip

And, next time you post an OPP, be sure to include a dimensioned drawing and a bill of materials.

They aren't very critical. I'd just remove one and take it to a hardware store and get the similar size piano wire and a spring.

Maybe it makes sense to remove it and take it to Maxwell or LASAR or someone else who has done a lot of these and have it disassembled, cleaned, lubricated and inspected. If an inspection showed no incipient cracks in the spring, it's probably good for another 1000 hours.

That's for the Dukes actuators which are a completely different design. They used a worm and wheel gear drive (like the flap actuator) that inherently resists back driving. But the gears are very highly loaded and need the moly to prevent wear. 20:1 gears are the worst; 40:1 gears are better from a wear standpoint. You end up having to mix that up (or LASAR used to sell it premixed) because the spec is for 10% moly and the highest commercial moly grease is generally 5%. The fact that they specified so much molybdenum tells you something about the extent of the problem.

I don't think the analogy to a clock spring is accurate because this is a wrap spring and they are different. It would be interesting to take one of these apart which I've never done. But looking at Eaton's exploded diagrams and description it seems possible to make some educated guesses about how they work. First, the problem they are trying to solve is that the actuator needs a brake. Lead screw actuators that use an acme thread such as the trim jack screw have enough friction to be self locking for the same reason you cannot push on a nut threaded onto a bolt and cause the bolt to turn. But the friction also makes it harder for the motor to turn the screw to move the load. So, for highly loaded actuators, a ball screw is used where the screw threads ride on ball bearings. This type of screw has much lower friction, but now when the load applies tension or compression to the screw it can back drive the actuator. The Mooney landing gear will stay down due to over-center locks. But there are no up locks and the weight of the gear would back drive the actuator if there were no brake. Within the Eaton actuator gear train there is a shaft with an input gear on the motor side and an output gear on the screw side. The two gears are not rigidly connected but each is connected to a hub and the spring wraps around (hence the name wrap spring) the two hubs with the tang at each end attaching it to each hub. This assembly is inserted into a tubular metal shell that does not rotate. When the gear is retracted and the weight of the gear tries to turn the lead screw and thus the output gear/hub, the spring unwinds and rubs against this shell and the friction creates the braking effect. This is generically called a wrap spring brake. When you put the gear down, the input hub starts to turn and this tightens the spring around both hubs causing them to turn together thereby driving the screw. The functioning of the spring is dependent on the tangs fixing each end of the spring to it's associated hub. If the tang on the input side breaks, the input hub might turn, but the spring will not tighten around the hubs to lower the gear. Or, the broken piece might jam the mechanism preventing the gear from coming down. If you search the web for wrap spring clutches and wrap spring brakes you will find a lot of animations for how these work in general. However, I have not found any actuators that have such a simple mechanism with such a high dependence on the spring, and most have a lot more parts. It seems that this design was intended to reduce the parts count to a minimum which has the undesirable effect of making the entire mechanism dependent on the stressed spring tangs. The other problem with the design is that the emergency gear extension system only protects against electrical or motor failures and is rendered inoperative by any mechanical failure that prevents the motor shaft from turning. Skip

How much trouble is it to get refills during trips around the US?

@rbp it might be interesting to look at the AP Pitch Torque plot during your flight and compare it to mine. If the torque isn’t a lot higher that might eliminate control friction.

The small ones are 2700 series Camlocs. I believe the IPC calls out -4s. There should be a number embossed on the head of your remaining existing ones and you can go up or down from that to improve the fit. Length varies according to the thickness of the cowling and these things were hand built. Each stud should have a split washer on the engine side to retain it. 2700 studs and washers can be installed without special tools. The larger studs are 4002 series Camlocs. I believe the IPC calls out -5s. Again, the length is embossed on the heads. These require a tool to insert and remove but there is no retaining washer on the stud. The Aircraft Spruce catalog has a chart for panel thickness for determining length if you are unsure and want to measure the parts. Skip

What happened initially is that I dialed the speed back from ~140 KIAS to ~95 KIAS and the AP overcorrected and then about the time it was beginning to settle down, I increased the power which caused it to overcorrect again.

G3X. The G5 also has data logging but fewer parameters. I'm not sure how the G5 logs correlate with the G3X logs when both are in the same system.

Well, I have listed all the one’s I’ve been able to find. If someone has documentation of others, please share.

WD-40 leaves behind a film. I would not use it on the eyeballs. I might try electronic contact cleaner.

Here's some data from my flight described above. Definitely a smoother ride than @rbp

That's because it was a Plessey actuator and they are no longer manufactured or supported. The "retrofit" is an Eaton actuator.

Do you know if that incident involved a Plessey or an Eaton actuator? I know that Mooney was using both well into the 1990s and the accident reported by @1980Mooney(NTSB Accident Number ERA22LA319) involved a Plessey actuator with only 427 hours since spring replacement. Plessey and Eaton are similar but different designs. Plessey calls the spring a torsion spring and Eaton calls it a no-back spring. Mooney has taken to just referring to both as no-back springs. They may or may not be identical parts -- probably not. The original service instruction M20-52 from 1/15/92 listed 2 failures of springs in Plessey actuators at 1200 and 1500 hours respectively. It included GEC/Plessey service instruction SI-11 requiring replacing the spring every 1000 hours. This appears to be the origin of the 1000 Hour replacement interval. I found two additional SDR reports of failures of Plessey actuators (one a broken spring and the other of undetermined cause, but likely the spring from the description). With the accident cited above, that makes at least 4, maybe 5, Plessey spring failures. Service bulletin M20-266A cites a single failure of an Eaton spring and lists a limited number of aircraft that require removal of the Eaton actuator and it's return to Eaton. This is likely the source of the idea that it was a problem related to a particular lot of springs. Subsequently, Eaton issued service instruction SI102000-901-1 that called for inspection of ALL actuators within 100 hrs and recommended replacement of the spring at 1000 hour intervals. Mooney published this as service bulletin M20-279. Apparently, all these bulletins and instructions were causing confusion so Mooney issued a comprehensive consolidated version as M20-282A. So, after all the dust settles, as of 9/22/2004 (the issue date of M20-282A), Mooney has only noted the failure of ONE Eaton actuator spring, which may have been limited to one lot of actuators, whereas 4 or 5 Plessey actuators are known to have suffered spring failures. So, I would be concerned if I had a Plessey actuator because of the several documented failures, but I'm not so sure that the Eaton's are much of a problem. It would be nice if Mooney would publish the actual number of failures of each type. Skip

An '84J should have the eyeballs. They're made from machined Nylatron which is supposed to be self lubricating. The M20J Service Manual says to use Tri-Flow. The problem with Tri-Flow is that it leaves behind an oil film that attracts dust and eventually gums up the ball and makes it sticky. Nylatron is impervious to most solvents, so you might try flushing them out with solvent if they've become stiff. Afterwards, I would leave them unlubricated or perhaps use a silicone spray. A little silicone spray on the shafts themselves from time to time also reduces friction. The eyeballs are difficult to replace when everything is assembled but not hard to replace when the panel was apart for the G3X retrofit. I had them replaced at that time and was amazed at how much stiffer the old ones were compared to the new ones. Skip

It might not be the airport's fault. The article went on to say that in interviews with travelers, many did not associate "Mineta San Jose International" with the city of San Jose. Apparently (and I have believed this for a long time having accumulated more frequent flier miles than I care to count for business travel) airline passengers are stupid. It's why I bought a Mooney. Skip

I think there is a lot of room for improvement. As I said earlier, it sometimes acts like a student chasing airspeed.

Today was a good day for a test flight in my M20J with very smooth air. The GFC 500 performed much better than I remembered from previous tests during an IAS climb. I did it twice with similar results, recording the second one. The test sequence was as follows (the AP was engaged for the entire sequence) : Start in level flight, ALT mode, 1500 MSL, 142 KIAS Switch vertical mode to IAS Set altitude bug to 3500' Set IAS bug to ~96 KIAS As the climb begins, increase power to WOT (prop was already at max RPM) The autopilot initially had some pitch variation but not more than 2-3 degrees and increasing power seemed to aggravate that. But it settled down pretty quickly and did a nice level off at 3500'. https://www.dropbox.com/s/s3lzac6l0xj6zr4/IMG_4718.MOV?dl=0 Skip

That would only apply to models that had squat switches. Did any M20Ks have squat switches?