there's a hinge in my tail

[TheTurtle]

SO I had heard of the "whole tail" moving on mooneys.  Didnt really click on what was happening.  I have the service manual and even printed out all the trim related pages since Im having downtrim issues.  (cant trim down enough to stay level sometimes or descend ever).

Took the inspection panels off to poke around and see what's happening in there.  Was mildly interesting to see the big hinge there. 

I have searched more than once for a good article or a post here about how it all works with the elevator and trim and yoke and hinge.

From looking at it I think what happens is the trim wheel turns a rod going to the back of the plane.  and actually pushes/pulls against the back half of the hinged part pushing it away from the body and raising it up.  This small amount of change at the hinge also pulls against the bungees and pulls the elevators into the trim setting you are dialing in.  so the trim affects the hinge and the actual elevator.  The yoke doesnt affect the trim (obviously) or hinge but basically overpowers what ever trim setting you are at.  the bungees pull the yoke (and elevator) back to where the trim is set.

Can somebody tell me if this is close to correct?

second question...   Heading downhill and over say 160mph i cant trim anywhere near enough to keep it going downhill.  Im actually pushing really hard with my elbows locked out to hold it in a 25/25 dive at 1000fpm+ and in the yellow on ASI.

On the ground today I did full downtrim and judging by the angle of the elevator there is no way in hell I could be climbing with that much down elevator.  My conclusion is im not getting full downtrim in flight.  I did lift up on the elevator while full downtrimmed and it feels solid to me.  I mean to me it doesnt feel like its floppy and airpressure is whats keeping it from staying nose down by flattening out the elevator in flight. 

I also notice with full downtrim on the ground  the yoke has no more travel forward.  IE I cant push the nose down anymore.  This is not the case when flying. 

I also think my bungees are shot.  I can see grease coming out the ends on the side attached to the yoke pushrods.  How many AMUs are those things going to cost me wonders.

 

[Hank]

I descend at 500 fpm and maintain whatever my cruise Manifold Pressure, RPM and EGT were. (RPM shouldn't change; MP increases as you descend, and as the air gets thicker the mixture gets leaner, so I periodically reduce throttle and enrichen mixture to hold the values.) Push the yoke to establish descent, trim the forces off and it stays there. My speed generally stabilizes around 170 mph indicated, and stays there all the way until I level off to decelerate, unless it gets too bumpy--then I level off and reduce throttle before starting back down a little more gently.

Run the trim full up and full down on the ground. Get out and look at your tail at both extremes. You should have elevator movement left at both extremes, although I think the yoke does move as the trim wheel turns. Remember how trim works:  it just moves the tail to hold the attitude that you established with the yoke. On lesser planes, the "trim tab" moves to create force that will hold the elevator wherever the pilot has put it.

Look at your trim indicator when at the extremes of movement on the ground, then check on your next descent.

I hate to sound stoopid, but how do you descend if the elevator won't move enough????

[TheTurtle]

Just now, Hank said:

I descend at 500 fpm and maintain whatever my cruise Manifold Pressure, RPM and EGT were. (RPM shouldn't change; MP increases as you descend, and as the air gets thicker the mixture gets leaner, so I periodically reduce throttle and enrichen mixture to hold the values.) Push the yoke to establish descent, trim the forces off and it stays there. My speed generally stabilizes around 170 mph indicated, and stays there all the way until I level off to decelerate, unless it gets too bumpy--then I level off and reduce throttle before starting back down a little more gently.

Run the trim full up and full down on the ground. Get out and look at your tail at both extremes. You should have elevator movement left at both extremes, although I think the yoke does move as the trim wheel turns. Remember how trim works:  it just moves the tail to hold the attitude that you established with the yoke. On lesser planes, the "trim tab" moves to create force that will hold the elevator wherever the pilot has put it.

Look at your trim indicator when at the extremes of movement on the ground, then check on your next descent.

I hate to sound stoopid, but how do you descend if the elevator won't move enough????

on the ground I can run the trim wheel to the stops in both directions with ease.  In flight it feels much tighter and will hit "rough" stuck feeling spots.  If I bump the yoke a little I can then get some more trim out of it.

like I was saying on the ground full downtrim left no elevator movment in the yoke.  But for some reason in the air with all the downtrim I can wheel in I still  have to push like hell to keep it going down.  So to answer your question... Im not really sure.  I just today discovered enough about how it works to intelligently fly it next time and see if I can figure out exactly whats happening.

I really need somebody with mooney exp to fly the damn thing.  The flight with the PO didnt really tell me much and hes a one or 2 time owner with only 300ish hours in his own plane.  My instructor has 10000+ hours and will fly whatever looks like a plane and work around any quirks so he's not much help for this mooney specific stuff.

I also feel like the ailerons are fairly tight especailly in left turns.  I have the PC button removed so it shouldnt be doing anything but it still feels to tight.  I dont know if its normal as I only have 172s to compare

[Alan Fox]

With full nose down , the hinge should be almost bottomed out , It is normal for the bungees to have grease coming out of the springs , Diving at 25/25 is the problem ,  try pulling the power back to 20/23 and trimming for a specific airspeed , like 160 to 175 MPH , well into the yellow , you should be planning a 3000 foot descent at least 20 to 25 miles out....  

[TheTurtle]

I normally dont descend like that.  Sometimes ATC wants to slot you between a few jets and asks for max forward speed to the fix.  So when my instructor is in the plane and we are messing around and its smooth out I just push her down and go halfway into the yellow, drop a smidge under the glideslope and pull up to slow to gear speed on glideslope.  Works great when I can see outside, no so much under the hood judging by my flight track.

Even in level flight at 25/25 I run out of downtrim and have to hold the yoke.  23/23 it will finally trim out level.

 

[Hank]

Pull the rear belly panel, that's where the jack screw is. It may need grease, it may need to have old, hard grease removed and new, fresh grease in it's place. Use the Search box, there are several threads about doing this. Try "jack screw" and "tail trim" for starters.

i don't fly 25/2500, that's >75% in my C. Above 6500-7000 or so, I'll cruise with the throttle backed away from WOT just enough to cut off the carb enrichment circuit, and 2500. A recent trip at 9500 I used 20-1/2"/2500, and descended at that setting all the way to pattern at 1300, then I leveled off, slowed down into the white arc, dropped Takeoff flaps and adjusted throttle to enter the pattern at 90 mph and full rich. It took some time for me to adjust to starting my descent ~50 nm out . . .

You should be able to do this, too. Oh, my descent is hands off, trimmed at 500 fpm, and every 1000-2000' I pull the throttle out some and nudge the mixture forward. Yes, I can run slightly LOP but don't try it low without a full engine monitor. But it works when cruising high. Your F should do much better with that.

Edited October 19, 2016 by Hank

[TheTurtle]

Just now, Hank said:

Pull the rear belly panel, that's where the jack screw is. It may need grease, it may need to have old, hard grease removed and new, fresh grease in it's place. Use the Search box, there are several threads about doing this. Try "jack screw" and "tail trim" for starters.

wow there are a lot of screws holding that thing on.  now that you mentioned the belly pan I check the maintenance manual and see I did miss that one.  #17 has the trim screw and the chain and gears but it looks like you need some really small hands and a video camera snake to actually so anything in there.

[N201MKTurbo]

I beleve the hinge is there to add torsional stiffness to the tail. 

It sounds like your trim is out of adjustment. Someone may have taken it apart in the past and put it together wrong. You can get the travel boards and set it per the book, or take apart the trim torque tube and give it a turn or two in the nose down direction. 

[Hank]

Just now, TheTurtle said:

 

wow there are a lot of screws holding that thing on.  now that you mentioned the belly pan I check the maintenance manual and see I did miss that one.  #17 has the trim screw and the chain and gears but it looks like you need some really small hands and a video camera snake to actually so anything in there.

Guess I got lucky--my Mooney has the one piece belly. It's 52 screws, and opens the whole thing from the nose wheel well back to the step, lots of room to work on the jack screw. Would it help if you took off the next belly pan forward? Would that give you more room to work, or to see what's there?

[TheTurtle]

Just now, Hank said:

Guess I got lucky--my Mooney has the one piece belly. It's 52 screws, and opens the whole thing from the nose wheel well back to the step, lots of room to work on the jack screw. Would it help if you took off the next belly pan forward? Would that give you more room to work, or to see what's there?

yea i think so.  I have a small electric drill with the torque set really low so I wont strip anything.  Its not that bad on the creeper   ill take it off tomorrow and see whats in there!

[N201MKTurbo]

The jack screw is in the tail. The little screw on the wheel assembly is for the indicator.

[TheTurtle]

Just now, N201MKTurbo said:

I beleve the hinge is there to add torsional stiffness to the tail. 

It sounds like your trim is out of adjustment. Someone may have taken it apart in the past and put it together wrong. You can get the travel boards and set it per the book, or take apart the trim torque tube and give it a turn or two in the nose down direction. 

Im going to have all the rigging checked at annual in december with travel boards.  Trying to figure out how all these systems work so I can talk about it somewhat intelligently.

[Hank]

Good luck! Use an ice pick to align the screw holes putting it back together, and don't use the electric thing to bottom the screws, use a handheld screwdriver. That will make them much, much, much easier to get out the next time (i.e., annual). I paid the extra 2¢ per screw and ordered Teflon washers from Spruce for everything except the ones with countersunk stainless washers.

[TheTurtle]

Just now, N201MKTurbo said:

The jack screw is in the tail. The little screw on the wheel assembly is for the indicator.

hah.  this site is great.  thanks!  i was wondering  how that little thing did anything with the trim.

[carusoam]

This can help you think through the challenge you may be having...

You don't by chance, still have the ADF wire/antenna running from the tail to the top of the cockpit do you?

My M20C had the ADF wire replaced.  The new wire and spring would limit the distance the tail could move.  Limiting the motion, limits the trim available.   It appeared to work properly.  But realistically, the full range was not available!

There is one other well known limitation of the trim's travel.  Old grease stuck on the jackscrew in the tail.  Pretty obvious limitation, right?   The grease has a tendency to dry out over years.  It turns rock hard. Get the trim jack screw fully cleaned and re-lubed.

While on the ground, make sure the trim is going full forward and full backward.

I would be uncomfortable knowing what is holding up the trim.  If it lets loose during flight I would have been known as a test pilot.

Private Pilot experience collected over a few years...

Best regards,

-a-

Took me too long to post.  You guys already covered this... 

[takair]

I was recently greasing and inspecting the jack screw under the boot.  The boot is in good shape, but brittle, so I'm careful with it.  I've been doing this for 20 years and had only one of the two screws holding the boot to the sheetmetal tabs.  This year I thought I would do it right, so I installed the second screw.  I ran the trim up and down and realized I suddenly couldn't get full down trim. Turns out the second tab was bent.  When I added the second screw, the screw caught the jack screw and bent the tab further in.  When the jack screw rotated. It then  basically wedged the jack so it could not turn further.  Took it all apart and corrected this.  You would think that after this many cleanings and lubes I couldn't get this wrong.  Not saying this is your issue, but figured I would share yet another way the rigging can be thrown off and create a potential hazard.  I know many on the forum lube this themselves, so be sure to check your travel after assembly.

[TheTurtle]

where exactly is this jack screw?  Its not well pictured here:

 

[Guest]

3 minutes ago, TheTurtle said:

where exactly is this jack screw?  Its not well pictured here:

 

In the picture you posted there is an accordion boot above the hinge.  Slide the boot back to expose the trim jack screw.  Clean with a bristle brush and stodard solvent, re grease and work it full range, you will need to grease several times to work it back into the screw.

Clarence

[TheTurtle]

Just now, M20Doc said:

In the picture you posted there is an accordion boot above the hinge.  Slide the boot back to expose the trim jack screw.  Clean with a bristle brush and stood are solvent, re grease and work it full range, you will need to grease several times to work it back into the screw.

Clarence

thanks exactly what I needed to know.  going to aircraft spruce to pickup the 15 different greases needed lol.  Cant find kerosine and graphite on google.

[TheTurtle]

20 minutes ago, M20Doc said:

In the picture you posted there is an accordion boot above the hinge.  Slide the boot back to expose the trim jack screw.  Clean with a bristle brush and stood are solvent, re grease and work it full range, you will need to grease several times to work it back into the screw.

Clarence

the service manual calls for Mil-l-7870 which looks like it crosses to aeroshell #3.  I was expecting a grease for some reason.

[cnoe]

Im going to have all the rigging checked at annual in december with travel boards.  Trying to figure out how all these systems work so I can talk about it somewhat intelligently.

TT, having the rigging checked by a Mooney pro sounds like a good idea but in the meantime you might get an idea if it was improperly rigged by measuring the gap between the empennage and the tail. I can't verify these values apply to your plane but my J trims nicely for a power-on descent as well as climb. See the photos for the measurements (full up and down trim).






Sent from my iPad using Tapatalk

[TheTurtle]

6 hours ago, cnoe said:

 

TT, having the rigging checked by a Mooney pro sounds like a good idea but in the meantime you might get an idea if it was improperly rigged by measuring the gap between the empennage and the tail. I can't verify these values apply to your plane but my J trims nicely for a power-on descent as well as climb. See the photos for the measurements (full up and down trim).






Sent from my iPad using Tapatalk

 

thanks.  Ill measure mine and see what I have.

[Shadrach]

16 hours ago, TheTurtle said:

I normally dont descend like that.  Sometimes ATC wants to slot you between a few jets and asks for max forward speed to the fix.  So when my instructor is in the plane and we are messing around and its smooth out I just push her down and go halfway into the yellow, drop a smidge under the glideslope and pull up to slow to gear speed on glideslope.  Works great when I can see outside, no so much under the hood judging by my flight track.

Even in level flight at 25/25 I run out of downtrim and have to hold the yoke.  23/23 it will finally trim out level.

 

I descend at near red line on a regular basis. I don't fully trim for descent, just enough to make the controls reasonably light. Trimming for 500FPM at max power should be easy.  Is your trim indicator working?  If you're still comfortable flying it, why not mark the trim wheel and count how many turns from take-off trim to full nose down on the ground while stationary, then see how that compares to what you get in the air.  There is certainly something wrong.

[TheTurtle]

Just now, Shadrach said:

I descend at near red line on a regular basis. I don't fully trim for descent, just enough to make the controls reasonably light. Trimming for 500FPM at max power should be easy.  Is your trim indicator working?  If you're still comfortable flying it, why not mark the trim wheel and count how many turns from take-off trim to full nose down on the ground while stationary, then see how that compares to what you get in the air.  There is certainly something wrong.

good idea.  ill try that.  Im fine flying it.  its just more work and feels like an old Massey ferguson tractor from the farm.

[cnoe]

LOL! That's the first time I've ever heard a Mooney being compared to a Massey Ferguson. You've got to FIX that thing!


Sent from my iPad using Tapatalk