M20J Left Roll Tendency In Cruise

[hangareuro]

Hello! I am relatively new to Mooney ownership and brand new to this forum. Last August I bought a 77 M20J and it has been a wonderful airplane so far, minus a couple squawks, this one being the most irritating. In cruise flight (above ~120kts) the airplane likes to roll to the left quite heavily. I flew it with the previous owner twice before buying and it did not do this. The issue seemed to start after the pre-buy and annual that was done last August. In flight with my hands off the yoke and feet flat on the floor the airplane will roll left at a relatively decent rate, slightly uncoordinated. Here is what I have checked so far: 

Rudder / Aileron interconnect springs: Both springs are still attached and in good condition. When on the ground and moving the yoke to the right I feel spring pressure and when letting go the yoke will spring back past center to the left. When moving the yoke to the left there is no spring pressure and it will stay in whatever position I leave it in left of center. The yoke is level and centered in flight. Are there any other springs in the aileron control system that could be broken or disconnected? I have looked through both the maintenance manual and parts catalogue and cannot find anything of the sort. 

Flap rigging: I figured the right flap, being that it is on the side of the airplane with the door, had maybe been stepped on or damaged at some point and was not retracting fully, thus creating more lift on the right wing while in flight with the flaps up. Using protractors and adjusting the flap up stop bolt I matched the right flap position to the left. The issue remained. 

Parasitic drag: With the airplane on jacks and the gear up, all of the doors seat properly and nothing appears out of position. There are no inspection panels or anything hanging down or unattached on the bottom of the left wing that would cause any excess drag on that side of the airplane. 

Engine mounts: The engine does appear to sag very slightly. Based on the logbooks the engine mounts have been shimmed once about 4 years ago. During the annual the IA determined that the mounts did not need to be replaced just yet, and it does not appear that the engine is out of position where it could negatively affect in flight characteristics. I am considering preemptively replacing the mounts anyway. 

The airplane also has the original Century 2B autopilot (roll only) that works somewhat well. The roll tendency tends to overpower it though. I also am not ruling out that the old servo may be part of the issue. 

My next plan of action is to find a shop that specializes in Mooney's (at least has travel boards) locally. I am in the Seattle area and don't know of any shops that can check rigging on Mooney's locally short of LASAR in eastern Oregon. Any insight would be much appreciated! Most of the time I fly the airplane locally and keep the right wing full of gas and that seems to counteract the roll well enough but I have some long cross countries planned for this summer and will need more than one full tank... I attached a photo of the turn coordinator in flight with hands and feet off the controls taken immediately after letting go of the yoke. The left bank will continue to develop within seconds if not corrected. Any ideas or information from the seasoned Mooney owners would be great!

Thanks!

[PT20J]

Mooneys get screwed up because people try to correct a problem by tweaking this and that and then something else and pretty soon it’s all messed up. The worst is when they start bending the trailing edges of control surfaces which is the procedure to make final SMALL adjustments after everything else is set up according to the service manual. Here is an article that gives some things to check. Greg Lehman at Advanced Aircraft in Troutdale can fix it. I’ve also heard that Reliant Aircraft Services at 7S3 is good, but I have no first hand experience. 
Shoptalk - rigging.pdf

[ArtVandelay]

Check the control surfaces when in level flight. If in level flight and they look ok, and it flies uncoordinated, I would look at the rudder.

Try mounting a GoPro camera on the tail hook to see if anything is amiss, like are the gear doors remaining flush. This can happen if a gear door bracket cracks, won’t be obvious from casual inspection. I had to replace both of mine.

[Zippy_Bird]

I’ll ask an obvious question since I didn’t see it mentioned yet… what is the fuel balance between tanks? My M20E presents a strong turning tendency away from an empty tank.


Sent from my iPhone using Tapatalk

[skykrawler]

201407 Control Rigging (knr-inc.com)

 

[Rick Junkin]

@hangareuro I had a similar issue and isolated it to misrigging of my elevators. The document @PT20J Skip attached covers how to do it precisely. But it's easy to visually check on the ground for gross misalignment, which is how I found it on my airplane. Hold one of the bob weights aligned with the stabilizer and look to see if the bob weight on the other elevator is in the same position relative to the stab. If not, you have a starting point for your chosen A&P.

Cheers,
Junkman

[ArtVandelay]

I’ll ask an obvious question since I didn’t see it mentioned yet… what is the fuel balance between tanks? My M20E presents a strong turning tendency away from an empty tank.


Sent from my iPhone using Tapatalk

My J doesn’t, but I have never gone to empty, maybe 7 gallons, so 25 gallon, 150lb imbalance. When I’m alone I always draw down the left tank first.

[EricJ]

14 hours ago, hangareuro said:

Rudder / Aileron interconnect springs: Both springs are still attached and in good condition. When on the ground and moving the yoke to the right I feel spring pressure and when letting go the yoke will spring back past center to the left. When moving the yoke to the left there is no spring pressure and it will stay in whatever position I leave it in left of center. The yoke is level and centered in flight. Are there any other springs in the aileron control system that could be broken or disconnected? I have looked through both the maintenance manual and parts catalogue and cannot find anything of the sort. 

This doesn't sound right to me.

There are springs (aka bungees) that interconnect the rudder and ailerons.   It is described (a little bit) in 27-60-00 in the SMM and shown in 27-10-00 in the IPC (items 36 are the two interconnect springs).   If one side is broken it might do what you're describing. 

[PT20J]

5 hours ago, EricJ said:

This doesn't sound right to me.

There are springs (aka bungees) that interconnect the rudder and ailerons.   It is described (a little bit) in 27-60-00 in the SMM and shown in 27-10-00 in the IPC (items 36 are the two interconnect springs).   If one side is broken it might do what you're describing. 

Hard to tell without actually being there. The nose wheel only turns around 12 degrees so it doesn’t take much offset (especially if it isn’t rigged correctly) to put bias on the interconnect (to answer @hangareuro’s question, there are no other springs in the aileron controls). You can do a quick and dirty check by using the towbar to position the nose wheel so that the rudder is one deg right. That should result in the ailerons being centered and the nose wheel being approximately centered (there is a lot of slop in the steering system so the only way to really tell is to jack it up and c-clamp a bar across the rudder pedals and see if everything lines up, but doing it on the ground with the towbar should point out any gross issues).

[hangareuro]

On 5/26/2024 at 7:45 AM, Rick Junkin said:

@hangareuro I had a similar issue and isolated it to misrigging of my elevators. The document @PT20J Skip attached covers how to do it precisely. But it's easy to visually check on the ground for gross misalignment, which is how I found it on my airplane. Hold one of the bob weights aligned with the stabilizer and look to see if the bob weight on the other elevator is in the same position relative to the stab. If not, you have a starting point for your chosen A&P.

Cheers,
Junkman

I believe you are on to something here. When holding the bob weight on the left elevator flush with the stab the right side weight is noticeably peeking above the right stab. I am thinking this is definitely a contributing factor. Any idea what causes the miss alignment? 

On 5/26/2024 at 9:29 AM, EricJ said:

This doesn't sound right to me.

There are springs (aka bungees) that interconnect the rudder and ailerons.   It is described (a little bit) in 27-60-00 in the SMM and shown in 27-10-00 in the IPC (items 36 are the two interconnect springs).   If one side is broken it might do what you're describing. 

Pulled the belly pan and inspected the springs. Both appear in good condition and are attached normally (photo attached.) I will try the towbar trick mentioned by @PT20J tonight and measure the length of the two springs. Also going to get under the airplane and have someone move the ailerons back and fourth and see if anything looks amiss that would cause the yoke to only spring back from the right not the left. Going to borrow my hangar neighbors jacks and clamp the rudder pedals to grab as much info / measurements I can. Ultimately I think its time for a Mooney expert to get their hands on it. I will check out Advanced Aircraft in Troutdale as that is only about a 45 minute flight from me. 

On 5/26/2024 at 6:01 AM, Zippy_Bird said:

I’ll ask an obvious question since I didn’t see it mentioned yet… what is the fuel balance between tanks? My M20E presents a strong turning tendency away from an empty tank.


Sent from my iPhone using Tapatalk

I have been leaving the left tank mostly empty (5-8gals) and keeping the right tank above half a tank. This mostly counteracts the left roll tendency and as the right tank burns down the airplane starts to want to bank left more and more, even with a near empty left tank. 

[PT20J]

17 minutes ago, hangareuro said:

I believe you are on to something here. When holding the bob weight on the left elevator flush with the stab the right side weight is noticeably peeking above the right stab. I am thinking this is definitely a contributing factor. Any idea what causes the miss alignment? 

Each elevator is connected to the bellcrank in the tail by a push-pull tube the length of which is adjustable by screwing in or out a rod end (service manual figure 27-5). The elevators are suppose to have equal deflection up or down (22 +/- 2 deg.) So, you could measure the travel on both sides and which ever is closest to equal travel in each direction would be correct (assuming that only one is misadjusted) and you could adjust the other to match it.

[hangareuro]

I spoke to Greg at Advanced Aircraft and he's confident we'll sort it out no problem. Thank you for all of the info and insight! Now on to the oil cooler 

[khedrei]

I just wanted to comment on this because I had a similiar rigging issue that is now solved.  I have yet to update my original post.

I have a K model.  Your speed will definitely affect things.  Without rudder trim, the plane can only be rigged to fly straight in a very small envelope.  If you are going too slow, there may be too much right rudder.  In my case, ailerons were originally adjusted incorrectly.  They rigged them again, adjusted the tail into spec, dropped one flap 1 degree, and then bent the trailing edge of the rudder every so slightly as per the maintenance manual.  It flies dead straight with hands and feet off with about 3/4 fuel, and at 28" and 2500 RPM.  Im told that with different amounts of fuel, and obviously different fuel balances on each side will have an impact on things.  My main concern was to make sure the new Garmin servos weren't working too hard.  They have all been replaced once, and one was replaced twice.

It sounds like you have a good shop who is confident to be able to fix it.  Good luck to you.