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Trim Jackscrew Binding


PeytonM

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Every annual ( next one in may) its lube that jack screw.This doesn't mean just take a handful of aeroshell 5 With graphite added and slather on exposed threads.It takes about 10 cycles...one guy in the cockpit ,another gloved up with the shell 5  working it into the screw drive...10 time ,trim full up,trim full down.I believe this methods removes most of dirt contaminated old grease...WD-40 only belongs in my boat

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8 hours ago, Emmet said:

I would love to send it to Lasar, but as I am based in Europe it is more complicated. I do intend to install new bearings and will take a close look at the shims.

Lasar handles world wide mooney parts shipments....

Contact Dan regarding getting parts sent to and from your location....

You won’t be the first...

Best regards,

-a-

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I know - Lasar is where I got the new bearings from. The problems are more customs, high shipping costs ( interestingly it is much more expensive to ship from the US to Europe than vice versa ... ) and long turnaround times.

I might need to go that way when we don‘t succeed - but for the time being I keep my fingers crossed :-)

Anyway, thanks for your help !

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When I rebuild my plane we looked at the jack-screw (it had 1900 hours on it).  The recommendations made to me at the time by knowledgeable mechanics was to replace the jack-screw with new.  This was back in 2010 when the factory was closed and they were taking parts from new airplanes.  Mine was installed and has worked well for 250 hours.  The cost back then was about $1200 for the new jackscrew.  

There is a lot going on back there and I can not begin to guess how much wear between the screw and nut of the jackscrew is acceptable.  You can turn the trim wheel slightly to take out the slop in the system (which includes the wear between the trim wheel and nut in the jackscrew) but it still is not clear how vibrational loads, etc... will effect the system because the wear is still there.  For the cost difference, it just seemed more prudent to start with a new jackscrew.  

There is no explanation in this thread as to how to measure the longitudinal and lateral wear in the jackscrew when it is apart.  

Without this information, it seemed more prudent to count on the factory's knowledge in manufacture and replace this vital assembly with new.

John Breda

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  • 9 months later...

@Sabremech @PeytonM @Vance Harral

Which bolts did you remove to remove the jack screw? Looks like 2 and 4?

Time to do mine while it's down for annual.  

Inked20190120_161540_LI.jpg

Inked20190120_161552_LI.jpg

 

 

Im planning on sticking a 2x4 block under the hinge to keep the tail from slamming down.  Just re reading this thread one more time tonight before going back out to the plane tomorrow.  Got everything lubed up today.  IA coming over tomorrow for the fun stuff.

Edited by TheTurtle
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53 minutes ago, TheTurtle said:

@Sabremech @PeytonM @Vance Harral

Which bolts did you remove to remove the jack screw? Looks like 2 and 4?

Time to do mine while it's down for annual.  

Inked20190120_161540_LI.jpg

Inked20190120_161552_LI.jpg

 

 

Im planning on sticking a 2x4 block under the hinge to keep the tail from slamming down.  Just re reading this thread one more time tonight before going back out to the plane tomorrow.  Got everything lubed up today.  IA coming over tomorrow for the fun stuff.

I removed both 1 and 2, left 3 and 4 in place. I disconnected the trim rod from the bottom of the trim wheel below the floor then pulled it forward to disengage (square slip joint) from the jack screw. Two more bolts that hold the jack screw and remove it by working it forward and out one of the access holes. Not too bad of a job!  

David

Edited by Sabremech
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Lots of good pix and advice on this thread. Also a lot of talk about -- grease. I'm in agreement that the best practice is to follow the manufacturer's directions in the Service Manual unless you absolutely know -- don't think, but know -- of something better.

My M20J Service Manual specifically calls out Aeroshell 7 for the jackscrew and bearings. I'm not sure it's a good idea to use Aeroshell 5 which is a high temperature grease specified for wheel bearings. https://www.shell.com/business-customers/aviation/aeroshell/knowledge-centre/the-aeroshell-book/_jcr_content/par/textimage_1433441235.stream/1445042875796/1d024cf49b16b7091e0368a866e9ca6b0ef6f275ac75de066f2004ed372bbef1/aeroshell-book-5greases.pdf

Grease is basically oil and a thickening agent. Not all greases are compatible with each other. The Service Manual calls out the following greases:

MIL-G-81322 (now MIL-PRF-81322G)  Common greases that meet this spec. are Aeroshell 22 and Mobilgrease 28

MIL-G-3545 (obsolete, superseded by MIL-PRF-81322) -- Aeroshell 5

MIL-G-23827 (now MIL-PRF-23827C Type I and Type II) Type I uses metallic soap thickener -- Aeroshell 33, Mobilgrease 33. Type II uses clay thickener  -- Aeroshell 7. Type I and Type II are NOT compatible with one another. 

MIL-Specs can be found at: http://everyspec.com/

Qualified products meeting MIL-Specs can be found at: https://qpldocs.dla.mil/

Skip

 

 

 

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The trim servo has a lot of torque. What seems to happen is that the mechanism gets stiff for whatever reason, and if you always use electric trim, you don't notice it until the trim motor isn't powerful enough to move it anymore. If it gets to that point, it may be hard to move it manually as well.

There's a lot of trim change in a Mooney over the range of speeds and flap settings. Mooney flaps are more effective at increasing CLmax than on most other GA airplanes and contribute more pitching moment. The Mooney trim system changes the angle of incidence of the stabilizer. This design is favored when the amount of trim range would cause excessive elevator deflection with a trim tab. Common in jets. The M20J stabilizer trims through a range of about 6 degrees. This isn't really enough which is why the trim bungees are needed to bias the elevator along with the stabilizer movement. Even at only 6 degrees, it takes a zillion cranks of the trim wheel to go through the entire range. No wonder everyone likes the electric trim.

 

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59 minutes ago, cliffy said:

And what military airplane has a trim system just like a Mooney?

wait

A U2 Dragon Lady

Do you have a reference for that? I believe that later versions of the U-2 had a variable incidence tailplane, but I don't think the entire empennage rotated as the Mooney. That would have been cumbersome in such a large structure. But, I'm not a U-2 expert.

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1 hour ago, cliffy said:

And what military airplane has a trim system just like a Mooney?

 

wait

A U2 Dragon Lady

 

 

 

Doesn't look that way. picture I saw clearly show conventional trim tabs on the TE of elevators.

The only plane I know that had similar trimming feature was JetStar and recon was tail was designed by Al Mooney.

 

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Check page 78 as to the redesign of the tail similar to the JetStar

Also this "book" gives you everything you ever wanted to know about the U2  - EVERYTHING!!

Long read. I also knew Tony LeVier, the first test pilot (listed in this book). He's long gone now.  

https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20150014963.pdf

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24 minutes ago, cliffy said:

Check page 78 as to the redesign of the tail similar to the JetStar

https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20150014963.pdf

I'll have to look at one next time I see one at a museum. You're probably right. The document you quoted isn't exactly clear in terminology:

"Herb Nystrom led the team that designed the empennage and tail assembly. Following a series of engineering studies, he opted to include an all-moving tailplane similar to the one Kelly Johnson developed for the Lockheed JetStar. This configuration most effectively distributed pitch forces across the entire horizontal stabilizer assembly, widened the airplane’s center-of-gravity limits, and eliminated the need for both ballast and trim tabs"

"Empennage and tail assembly" is redundant. "Tailplane" is another word for horizontal stabilizer. However, the reference to it being similar to the JetStar design would seem to indicate that the entire empennage pivots.

Thanks!

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Cliffy,

That is a great read....

Herb Nystrom led the team that designed the empennage and tail assembly. Following a series of engineering studies, he opted to include an all-moving tailplane similar to the one Kelly Johnson developed for the Lockheed JetStar. This configuration most effectively distributed pitch forces across the entire horizontal stabilizer assembly, widened the airplane’s center-of-gravity limits, and eliminated the need for both ballast and trim tabs.53

 

there seam to be many parallels to Mooneys, Mooney development over time, and  Mooney Transition Training That can be drawn.... enough to make it interesting...

Even the stretched and more powerful U2 was the R version....:)

Best regards,

-a-

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1 hour ago, Sabremech said:

Here’s a photo of the jack screw disassembled. I replaced the bearings in mine plus a good cleaning. Took a bit to get it shimmed correctly when reassembling. 

Nice, David. Can you give more detail about the shimming? How did you get the bearings off the shaft?

Skip

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If you take the shield retainers off the ball bearings, it is easy to remove the balls. There is a notch in the outer race to remove them. Then you can clean the bearings and reassemble them with new grease. I don't see any reason to replace them. You just want to shim the bearings to remove any play, if the bearings can slide back and forth in the housing, it just contributes to tail slop . Don't preload the bearings it will make the trim stiffer.

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4 hours ago, PT20J said:

Nice, David. Can you give more detail about the shimming? How did you get the bearings off the shaft?

Skip

Hi Skip, I replaced the bearings on mine due to roughness. I have 7600 hours on my bird and thought if I’m taking this apart, might as well put new bearings in. I tried to remove them myself but ultimately took it to my machine shop and had the old ones pressed off and new ones pressed on. 

The shiming is just as N201MKTurbo stated with just taking up enough clearance between the housing as to have the bearings roll freely without them moving fore and aft in the housing. 

Thanks,

David

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13 minutes ago, Sabremech said:

Hi Skip, I replaced the bearings on mine due to roughness. I have 7600 hours on my bird and thought if I’m taking this apart, might as well put new bearings in. I tried to remove them myself but ultimately took it to my machine shop and had the old ones pressed off and new ones pressed on. 

The shiming is just as N201MKTurbo stated with just taking up enough clearance between the housing as to have the bearings roll freely without them moving fore and aft in the housing. 

Thanks,

David

Thanks for the info, David. I can feel some roughness when rotating the trim wheel to nose down, but not up. It's not very bad yet, but since I have lubed the front gearbox (which I had out to replace a worn trim wheel shaft bushing), all the u-joints, the King trim servo carrier bearing, and the rear jackscrew, the thrust bearings are all that's left.

Skip

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On ‎1‎/‎22‎/‎2019 at 7:26 PM, cliffy said:

Check page 78 as to the redesign of the tail similar to the JetStar

Also this "book" gives you everything you ever wanted to know about the U2  - EVERYTHING!!

Long read. I also knew Tony LeVier, the first test pilot (listed in this book). He's long gone now.  

https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20150014963.pdf

Thanks for the link, it's a great book. I just went through it quickly but I'll have to read one of these days, it seems it has interesting details about the development of the plane and insight how it was done back in a day of slide rulers, Mylar drawings and such. I know those planes were much simpler then today but they seem to get to the first flight much faster then today regardless of all the tools we have today.

Interesting how they changed the tail as well on the later version. It's a quite a change considering the limited number of the planes they built.

 

Edited by Igor_U
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