PT20J

This happens during maintenance when the wrong length screws are used. You might want to check the aileron tube inspection panels also. There is at least one where a long screw will rub on a tube. It doesn’t always make a noise.

True enough. All the aerodynamic forces are a function of dynamic pressure. And a K will be probably have more variability than my J since it operates over a wider range of IAS vs TAS because it can fly higher. Still, if the ball is out of center in the cruise condition, it would seem worth checking the rigging.

The springs and incidence change work in concert to trim out the stick force. But, the range of airspeeds and flap settings over which the trim functions is important also. In the M20J the elevator is trailing edge down when in trim regardless of airspeed. To get the same down force with the elevator in trail, the angle of incidence would need to be increased and the spring center point adjusted. But if this were done without changing the physical angle of mounting of the stabilizer to the empennage, it would affect the trim range.

But apparently the “center point” needed to be changed.

External locks really are the best. The knock against them is that they are easier to overlook. There have been accidents. The DC-3 came with external locks and Douglas was thoughtful enough to put a little locker in the tail to store them. One of my FO duties was to confirm that the locks were removed and stowed and the gear pins were removed and on board. Skip

Another interesting hangar experiment (on Js and earlier models) is to run the trim all the way nose down and observe the elevator position, and then repeat with the trim all the way nose up.

If you set the trim where it is in cruise (quite a bit more nose down than the takeoff position) and hold the elevator in the position it sits in cruise, you’ll note that there is quite a bit of spring tension. That force opposes the hinge moment so that the stick force is neutral without having to increase the incidence of the tail farther. That’s why they are called “trim assist bungees.”

One sender is in the root; the other is at the outboard end of the tank. Either can cause an odor in the cabin. The one at the root is obviously in the cabin. But there is a path along the leading edge of the wing for the gas to go downhill into the cabin. I’d check outboard first because you don’t have to remove interior panels. Look for blue fuel stains. Skip

The lowest drag would be with the elevator aligned with the stabilizer and it seems that the original design does that. When the fuselage was lengthened it threw things off. My J, for instance trims with the elevator slightly trailing edge down. A Mooney engineer once told me that Lopresti calculated that it didn’t make enough difference to bother fixing which would have required an expensive redesign of the empennage to change the incidence of the stabilizer. Lengthening the fuselage again and changing the trim system resulted in the long bodies trimming with the elevator slightly trailing edge UP. The purpose of any trim system is to remove stick force. This can be done by changing the incidence of the horizontal stabilizer, using a trim tab to bias the elevator, or using springs. The tab by itself is powerful enough because it taps into aerodynamic force. Springs alone can be troublesome because springs strong enough for cruise speed are too strong at low speeds and make the controls too heavy for landing. Changing the stabilizer incidence may require too much trim wheel rotation with the gearing necessary to make the trim wheel easy to turn. So, it is not uncommon to use a combination of springs and variable incidence. I believe the Piper Cub does that also. Skip

The ball should be centered in cruise without rudder input. You should check your service manual, but for my J the rudder is supposed to be rigged one deg right. You have to this with the plane on jacks and a bar clamped across the rudder pedals. Here’s a good article on rigging. Shoptalk - rigging.pdf

Mooney's have a fairly slow roll rate as @A64Pilot noted. When designing the Predator, it didn't meet the Air Force requirements for roll rate, so Mooney cut down the flaps and lengthened the ailerons. I was working with Roger Hoh on a flight simulator project at the time and Roger (who is a handling qualities consultant and also developed the control laws for the HeliSAS for Robinson Helicopters) told me that the additional pressure on the push pull tubes caused them to bind so that the stick would stay wherever you put it -- there was no centering at all. Maxwells never flew the Predator with the original wing. Don told me that they replaced the wing with one from a scrapped K. Handling qualities are difficult to quantify because they are subjective. If you fly the same airplane for years, it's qualities become normal to you. Back after WW II the NACA was trying to identify engineering specifications that would guarantee good handling qualities. They decided to take an airplane with qualities that a large number of pilots agreed were good and then measure it's stability and control characteristics. They chose the DC-3 because so many had been built and flown during the war and pilots generally thought it a good handling airplane. What they discovered is that it had some real quirks and was mildly longitudinally unstable in approach configuration under certain CG loadings. Pilots generally liked the P-51. But when the 85 gallon fuselage tank was filled, the CG was behind the neutral point and the airplane was unstable in pitch to the point that instrument flight and aerobatics were prohibited by the flight manual until about half the tank was burned off. But the pilots just learned to deal with it and didn't seem to mind. Skip

I know, this is a Mooney site and we all like to think that every aspect of our airplanes is better than all the others. But airplane design is a series of tradeoffs. The Mooney is optimized for cruise efficiency. This leads to tradeoffs in other areas including the control system. Cable controls, tensioned properly, don't have a lot of stretch or lost motion. But Mooney controls have a lot of rod ends in series which creates lost motion, especially as they inevitably wear, and this increases pilot workload. Cables operate on pulleys with bearings which have little friction. Mooney aileron push pull tubes run through a number of guide blocks which have greater friction (you do keep those well lubed, right?). In flight, especially at higher speeds, the ailerons tend to float up (that's why they should be statically rigged slightly down per the manual) and this puts the tubes in compression which flexes them and increases the friction through the blocks. There is only so much wing span and Mooney wanted a lot of flap to (probably to lower the landing speed) so the ailerons have a pretty short span for their area. This means an increased chord which increases the hinge moment requiring more control wheel force to move them. The lack of control wheel throw (probably to keep the wheel out of the way since the cabin is short in height to keep the drag low) doesn't help. The elevator system suffers from friction at the instrument panel ball joint (most airplanes have this problem, but the Mooney seems worse than most). The gadgets placed in the elevator/trim system seem to reduce airspeed stability. I have flown many hours on long cross countries in a Cherokee (made longer by the fact that the airplane is slow) without an autopilot. I don't like flying my J for long periods without the autopilot -- it's a lot of work to hold altitude precisely. I think one problem people have landing is precise speed control which just seems to require more attention in a Mooney than many other airplanes. It's similar to a DC-3. This may be partially caused by the way the elevators are balanced. Most airplanes have overbalanced control surfaces for flutter avoidance. But the Mooney has underbalanced control surfaces. Who knows why? I asked a couple of aeronautical engineer friends and the best guess was to make the controls more responsive initially to changes in position since the underbalance will initially accelerate the control surface movement in the direction of applied control deflection. And, then there is the aileron-rudder interconnect... I've flown a lot of different airplanes. I like my J, but I'm realistic about the tradeoffs. The Cherokee was more fun to fool around in as was a C-152. The best harmonized controls were on the Beaver. I used to fly the Beaver for hours and never missed not having an autopilot. It was a joy to fly, but a float Beaver cruises at about the same speed as a C-150. Nothing beats my M20J for efficient cross country cruising, and I find the cockpit very comfortable for long trips. But, I'm glad for the autopilot. Skip

You can see the spring cartridges and attach points standing behind the tail and looking into the tail cone where they attach to the elevators. It's easy to see what's going on if you move the elevator up and down while watching the mechanism. I usually shoot some LPS2 into the cartridges and onto the attach points. The service manual calls for MIL-L-7870 (which would now be MIL-PRF-7870), but any light machine oil will do.

As @Ragsf15e said you need a G3X, G5 or GI 275 for the GFC 500. Unlike older autopilots, most of the autopilot software resides in the display. The control head is just a user interface and a AHRS used for self checking. The least expensive route would be two G5s. If you want something that looks more like the Aspen, you could get the 7” G3X, but you would still need a standby G5 or GI 275 per the STC. And as @JimB pointed out, the GFC 500 can only be purchased through a Garmin dealer and they will do the installation. You might find a one-man Garmin dealer that will let you help, but most won’t want that because you will just slow them down.

I asked Bob Kromer why Mooney changed the gadgets in the elevator system between the J and K. It was before his time. He asked around and no one remembers past saying that they expected the the handling characteristics of the K to be similar to the J and were surprised that the stability, handling and stall characteristics were different. The change was to fix that. A pilot senses what is called stick free stability when controlling an airplane. (There is also a stick fixed stability, but we don't fly with the stick held rigidly in place. Instead we allow the control surfaces to float to their trimmed position, so it is the stick free stability that concerns us). The normal sense of this is that to increase airspeed relative to trim speed requires a push and to decrease airspeed requires a pull. As the CG moves aft, the forces become less and at a point called the neutral point, they vanish. If the CG is moved farther aft, the forces reverse requiring a push to slow down and a pull to speed up. Adding a down spring (which is usually designed to have a constant force) allows the pilot to still have normal control feel with airspeed changes with the CG farther aft than without the spring. In a sense, it is making up for aerodynamic forces that have become too light. Also, the down spring can alter the control feel at stall by increasing the down stick force. The spring doesn't really affect the actual stability of the airplane, but it allows the pilot to control it normally in situations that would be problematic without the spring. A bobweight works the same way by pulling forward on the stick. But since it is a mass affected by g force, it has the added ability to adjust the stick force per g which is important in maneuvering flight. Too light a stick force per g can result in the pilot accidentally overstressing the airplane during abrupt maneuvers. Skip

No, Mooneys don't have them because the control forces are not heavy enough to require them.

Sounds defective. Mine zeros out in pitch.

All the models through the M20J had "trim assist bungees" which are elevator centering springs with the center point variable according to the trim setting. The primary effect is to bias the elevator with trim changes so that the angle of incidence of the stabilizer doesn't have to change as much. A secondary effect would be to improve handling qualities. The bungees shouldn't squeak. They are supposed to be lubricated during annual inspection. Starting with the M20K, Mooney changed the system to use a down spring with variable tension according to trim, and a bobweight. This was done apparently to improve handling qualities.

There's an old joke about a guy who was afraid to turn on his lights because the switch said NO.

It also looks like the A/P legend was added. If that means autopilot, it is usually customary to have it on a separate "pull off" type breaker so that it can be quickly disabled if it malfunctions.

You might want to correct the spelling on AUX BUSS BAR. An electrical bus has one 's'. Buss means a kiss.

Is the switch reversible? Could it be installed backwards?

Note that the Concorde recovery procedure is to charge at constant current rather than the normal constant voltage charge.

Sorry to hear that. Given the very rapid CHT rise, it was probably preignition. You can check the spark plugs for damage -- a common cause of preignition is a broken insulator. You might want to use a borescope to check the piston for melting around the edges. But, if it reached 500 F, according to George Braly, the cylinder probably needs to be replaced.

How much harm is done is a function of how old the battery is, how deeply it was discharged, how long it sat discharged and at what temperature. Concorde has a procedure for a deep discharge recovery in its component maintenance manuals available on its website.