MBDiagMan Posted April 1, 2020 Report Share Posted April 1, 2020 My trim wheel is so touchy It’s almost impossible to get it trimmed with any precision at all. Anyone else experience this? Quote Link to comment Share on other sites More sharing options...
carusoam Posted April 1, 2020 Report Share Posted April 1, 2020 Two part challenge... 1) sensitivity... the trim wheel is probably effective at changing the trim with just the slightest of movement... possibly, about an 1/8” or less (?) 2) Dead spot... this is where the trim wheel/system is a bit loose. Each time you over trim you need to undo the tiny bit, but first have to go across the dead zone to get there... 3) Any crappy aged grease/rocks in the system adds to the challenge... 4) The collective wear in the system is what builds up to make the dead spot... Is that what you are seeing? Best regards, -a- Quote Link to comment Share on other sites More sharing options...
Yetti Posted April 1, 2020 Report Share Posted April 1, 2020 Clean the chain. clean and lube all the u joints Quote Link to comment Share on other sites More sharing options...
Jim Peace Posted April 1, 2020 Report Share Posted April 1, 2020 3 hours ago, MBDiagMan said: My trim wheel is so touchy It’s almost impossible to get it trimmed with any precision at all. I was just thinking about this today....I flew a J model and I own a C....I felt a small flat spot or resistance in the J while in cruise....still trimmed out well though My C is fine Quote Link to comment Share on other sites More sharing options...
N201MKTurbo Posted April 1, 2020 Report Share Posted April 1, 2020 Do you trim by hand or do you have electric trim? I've always found Mooneys easy to trim precisely. You do have to account for backlash. If you don't have a trim brake, the wheel will un-trim itself, especially in bumpy air. Is that happening? 1 Quote Link to comment Share on other sites More sharing options...
moontownMooney Posted April 2, 2020 Report Share Posted April 2, 2020 I feel like the trim behavior is nonlinear. It seems to take a large amount of trim wheel movement to go from climbout to approximately level cruise flight, but then highly sensitive around the cruise condition. (In my '68 M20F)Sent from my LM-V405 using Tapatalk Quote Link to comment Share on other sites More sharing options...
Hank Posted April 2, 2020 Report Share Posted April 2, 2020 4 minutes ago, moontownMooney said: I feel like the trim behavior is nonlinear. It seems to take a large amount of trim wheel movement to go from climbout to approximately level cruise flight, but then highly sensitive around the cruise condition. (In my '68 M20F) Sent from my LM-V405 using Tapatalk There should be a large trim change between climb and level. One is at reduced speed, converting power into altitude, with a significant nose-up attitude. When you level off, that's a big yoke movement to go level, which must be trimmed away. Then as speed increases, it takes more nose-down trim to hold altitude instead of climbing at the initial trim speed. Takes a few minutes to stabilize. Quote Link to comment Share on other sites More sharing options...
carusoam Posted April 2, 2020 Report Share Posted April 2, 2020 thinking about this out loud... The travel generated by the trim wheel is somewhat linear... a rotating jack screw moves the tail around a point... So... it’s not extremely linear The jack screw part is linear... the rotating around a point is less linear... The affects of that motion are probably squared with airspeed... Hence... the fast re-trim required during a go-around? Trimming to go faster During the descent, doesn’t use much trim at all compared to trimming for landing.... Trimming for configuration changes uses A ton of trim... PP thoughts only... Best regards, -a- 1 Quote Link to comment Share on other sites More sharing options...
MikeOH Posted April 2, 2020 Report Share Posted April 2, 2020 Dead spot. Overshoot a bit, then a touch back. Works for me. 2 Quote Link to comment Share on other sites More sharing options...
takair Posted April 2, 2020 Report Share Posted April 2, 2020 7 hours ago, MBDiagMan said: My trim wheel is so touchy It’s almost impossible to get it trimmed with any precision at all. Anyone else experience this? Try to lube the yoke shafts where they transition through the panel. At least on the old birds they get jerky and make trimming more difficult. Also helps with flare on landing. When you do a control sweep it should be nice and smooth with no jerking or chatter. 1 Quote Link to comment Share on other sites More sharing options...
cliffy Posted April 2, 2020 Report Share Posted April 2, 2020 Is the air smooth or bumpy? Have you ever had the elevator angles checked? Quote Link to comment Share on other sites More sharing options...
PT20J Posted April 2, 2020 Report Share Posted April 2, 2020 One man’s touchy is another man’s precision. It might be helpful to fly another Mooney for comparison. I’d check that the elevator and trim system are properly lubricated and not worn such that there is freeplay (i.e., a dead zone) around the trim point. Skip Quote Link to comment Share on other sites More sharing options...
M20F-1968 Posted April 2, 2020 Report Share Posted April 2, 2020 Has anyone attempted to open and re-lube the gearbox in the trim assembly? I thought of doing that at one time, but decided I had better learn more before attempting. It seemed that it is meant not to be disassembled. I have a 1968 F, the trim has minimal slop (? <3/8"). Just like machine tools, the lead screws and gears need some slop to operate. This is then worsened as the part wears, thus the need to keep well lubricated, and thus my desire to open the gearbox, find out what is there and re-lube to assembly. John Breda Quote Link to comment Share on other sites More sharing options...
N201MKTurbo Posted April 2, 2020 Report Share Posted April 2, 2020 1 hour ago, M20F-1968 said: Has anyone attempted to open and re-lube the gearbox in the trim assembly? I thought of doing that at one time, but decided I had better learn more before attempting. It seemed that it is meant not to be disassembled. I have a 1968 F, the trim has minimal slop (? <3/8"). Just like machine tools, the lead screws and gears need some slop to operate. This is then worsened as the part wears, thus the need to keep well lubricated, and thus my desire to open the gearbox, find out what is there and re-lube to assembly. John Breda I have done it a few times. It comes apart pretty easily. Take apart the U-joint just behind the gear box and remove the indicator cable. Before doing this, run the trim all the way nose up. Mark the indicator position in the cockpit with some masking tape and measure the gap at the bottom of the tail and write down the measurement. Remove all the tape around the top trim wheel, remove all the screws and take the whole assembly out the top. Remove the pins holding the sprockets on and remove the sprockets. Keep track of all the shim washers. Take everything apart and clean the ancient grease off including the chain. Put back together with new grease. 1 Quote Link to comment Share on other sites More sharing options...
M20F-1968 Posted April 2, 2020 Report Share Posted April 2, 2020 Taking the assembly out is not the problem. It is taking the box apart that encloses the gears. It seems like it was built with the intention of never being taken apart. I'll have to look at it again (I have a spare which I can use to investigate). Is the box put together with roll-pins only? If so, they must be in blind holes. I do not recall exactly without seeing the box again. I had a mechanic who took one apart and could not get it back together. Perhaps I start with that, clean it, grease it and reassemble it. John Breda Quote Link to comment Share on other sites More sharing options...
Bob Weber Posted April 2, 2020 Report Share Posted April 2, 2020 As an aging airframe wears, we find different effects of this wear. Every airframe I flew always settled into a pitch attitude other than neutral if you were to measure it with an inclineometer. The point here is that the trim tab will always deflect to put the aircraft in a balanced pitch attitude to fly level. Over the years/hours of flying in this configuration, wear occurs on the pressure side of the threads of the jack screw creating a considerable disparity of friction between adjusting for nose up trim vs nose down trim in the range of flight neutral, with a wind load on the tab. Being immersed in autoflight for so many years I found myself dissecting even the most subtle of command errors out of "my stuff" and realized this disparity becomes much more important as it progresses. Thankfully, with Mooney's, we use a chain and sprockets to tie into the trim system instead of "V"belt technology, but we do move the entire empennage rather than a little tab.. We still have to balance the friction of the trim system with the clutch setting of the servo. In flight, at cruise speed, hand adjust the trim a bit up, and a bit down. If it feels pretty much the same you are probably fine, if not, look a little closer. The challenges and responsibilities of maintaining an aged aircraft... Quote Link to comment Share on other sites More sharing options...
Jim Peace Posted April 2, 2020 Report Share Posted April 2, 2020 9 hours ago, PT20J said: One man’s touchy is another man’s precision. So true,,,when my friend was flying his J yesterday he said he could not get it trimmed, plane kept climbing....I tried it and got it perfect to hold altitude +/- almost 0 feet. He was moving the wheel a lot I was moving it to the smallest degree possible....it does not take much....just fraction of a fraction of a degree of rotation makes the difference.... 5 Quote Link to comment Share on other sites More sharing options...
Bob Weber Posted April 2, 2020 Report Share Posted April 2, 2020 I've watched some of the finest pilots manage a malfunctioning aircraft, justifying some pretty crazy "approaches" to "manage" a malfunction. It's the little things you should be paying attention to. A 30 or 40 year old aircraft will have "new and improved" problems, we need to focus towards this concept... And react accordingly. Fly Safe and Healthy Bob Weber Autopilot Consulting webairconsulting.com Quote Link to comment Share on other sites More sharing options...
mike20papa Posted April 2, 2020 Report Share Posted April 2, 2020 My old A model trims beautifully...just light pressure on the trim wheel does the trick in cruise. I still say the Mooney, because of it's laminar flow wing, is a trim sensitive AC. Always roll it back to the stop for landing and set appropriate for take off. A beast for flying touch & goes. In my Stearman, you can touch the trim wheel once in the spring - and forget about it. But it has a lifting tail. Quote Link to comment Share on other sites More sharing options...
Mooneymite Posted April 2, 2020 Report Share Posted April 2, 2020 During pre-flight, try moving the tail section up/down. If there's any slop, the trim will be inconsistent. There is a close tolerance bolt that may need to be replaced. 1 Quote Link to comment Share on other sites More sharing options...
N201MKTurbo Posted April 2, 2020 Report Share Posted April 2, 2020 11 minutes ago, Mooneymite said: During pre-flight, try moving the tail section up/down. If there's any slop, the trim will be inconsistent. There is a close tolerance bolt that may need to be replaced. Because the tail is always making down force. The trim screw and all of the linkages are in constant tension. The slop in the tail is an indicator of wear, but should have no effect on flying qualities. A severely worn screw probably has lost 5% of its threads and is in no danger of failing. If the bolts or link failed, the hingey thing at the bottom would restrain the tail in a nose up trim condition. Quote Link to comment Share on other sites More sharing options...
Bob Weber Posted April 2, 2020 Report Share Posted April 2, 2020 1 hour ago, N201MKTurbo said: Because the tail is always making down force. The trim screw and all of the linkages are in constant tension. The slop in the tail is an indicator of wear, but should have no effect on flying qualities. A severely worn screw probably has lost 5% of its threads and is in no danger of failing. If the bolts or link failed, the hingey thing at the bottom would restrain the tail in a nose up trim condition. Alaskan airlines ring a bell? I have lived this and guided multiple people thru dealing with this on several different manufacturers of aircraft. I would love to see your experience and data to back up this claim..... Quote Link to comment Share on other sites More sharing options...
N201MKTurbo Posted April 2, 2020 Report Share Posted April 2, 2020 7 minutes ago, Bob Weber said: Alaskan airlines ring a bell? I have lived this and guided multiple people thru dealing with this on several different manufacturers of aircraft. I would love to see your experience and data to back up this claim..... Does Alaska Airlines fly Mooneys? Quote Link to comment Share on other sites More sharing options...
N201MKTurbo Posted April 2, 2020 Report Share Posted April 2, 2020 8 minutes ago, Bob Weber said: Alaskan airlines ring a bell? I have lived this and guided multiple people thru dealing with this on several different manufacturers of aircraft. I would love to see your experience and data to back up this claim..... What claim? I'm commenting on how a Mooney is designed. Some airliners have flying elevators like a Mooney's elevator, I don't know if they have the same kind of limiting device like the Mooney has. Quote Link to comment Share on other sites More sharing options...
Bob Weber Posted April 2, 2020 Report Share Posted April 2, 2020 Just now, N201MKTurbo said: Does Alaska Airlines fly Mooneys? Nope, but both airframes deal with a jack screw, as well as just about every other airframe out there. Wear happens, those that have learned to recognize and react are who I want to be around. Quote Link to comment Share on other sites More sharing options...
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