This look ok to you?

[Nukemzzz]

When I sent my nose truss for Lasar for overhaul they installed the shim for SB M20-202 saying it would make it track better on the ground. Well we just finished weighing the plane and I checked my nose gear per that SB and my nose axle is 1.5” behind the datum when all the Mooney diagrams, including the W&B show the axle in front of the diagram. 

I think as long as I have prop clearance I’m ok, just wondering what the Mooney wizards thought about this. 
 

[RLCarter]

I seem to remember mine was the same and LASAR explained that more Trail is better. 

[markgrue]

Did you check the doughnuts to see if they are squashed?  The nose in the pictures looks a lot lower then I remember.  I realize the tire is flat but still the gear looks a lot lower.

Mark

[Nukemzzz]

12 minutes ago, markgrue said:

Did you check the doughnuts to see if they are squashed?  The nose in the pictures looks a lot lower then I remember.  I realize the tire is flat but still the gear looks a lot lower.

Mark

Yeah. The donuts are squashed pretty tight even before putting weight on the plane because of the shim. 

[markgrue]

2 minutes ago, Nukemzzz said:

Yeah. The donuts are squashed pretty tight even before putting weight on the plane because of the shim. 

I would carefully check wheel well clearance when the nose gear is retracted.  With that much trail it may hit the top of the wheel well.

 

Mark

[Nukemzzz]

14 minutes ago, RLCarter said:

I seem to remember mine was the same and LASAR explained that more Trail is better. 

Yeah, this is what they told me as well, it’s just interesting that it no longer matches the w&b diagram because the axel is behind the truss pivot now instead of in front. This fundamentally changes the nose gear behavior when tracking and steering. I guess it’s good that it’s always on one side instead of compressing across that axis when landing and loading it. 

[Nukemzzz]

12 minutes ago, markgrue said:

I would carefully check wheel well clearance when the nose gear is retracted.  With that much trail it may hit the top of the wheel well.

 

Mark

That’s good thinking. Everything checks out though. 

[Mooneymite]

I recently replaced my nose truss with the LASAR version; my original truss did not have, or need the spacer.  LASAR sent me one without the spacer and no reference to it in any of the paperwork.  After installation, my nose steering was completely out of whack (the plane wandered all over the place!).  I determined that I needed the spacer.  LASAR initially wanted to charge me for it, but after some "discussion" it arrived free of additional charge.

To make a long story short, the folks that rebuild the nose trusses and install the tabs have no idea what year the core truss came off and whether it needs a spacer, or not.  When I sent my core back, I included documentation that my core did not need the spacer, but LASAR seemed to be uninterested, preferring to act like "one size fits all".  One size does NOT fit all.  These trusses obviously went through some design changes.  My 1974 Mooney truss did not exactly match the dimensions of the replacement "one size fits all' truss.

Perhaps you got the truss that I sent in for a core that needs no spacer?

[PT20J]

Well, the Service Manual says it needs to be shimmed if the axel is more than .06 forward of the plumb line, but it doesn’t list a limit aft. More caster will make it track better. As long as retract tests are good and you have wheel well clearance it’s probably fine. Now I’m going to have to measure mine someday - it steers fine, but I have no idea how far aft it is.

Skip

[Delta]

I am just wondering, but was the plane leveled per the Service Manual?

[takair]

 Are the jacks being used to level the plane or is it just sitting in the background?

[DMM]

Here's D Maxwell's comments on SB M20-202.   "https://web.archive.org/web/20191022103354/http://donmaxwell.com/the-eight-second-ride-sb-m20-202/

"The plumb bob should fall in the center of the axle. If the line falls behind the axle, you need to add the spacer provided in the kit, and be prepared for a pleasant experience on your next landing. If the line falls in front of the axle, you have probably been experiencing some shimmy, and the shock disc need replacement." 

 

[David Lloyd]

On 12/23/2020 at 10:46 AM, Nukemzzz said:

Yeah, this is what they told me as well, it’s just interesting that it no longer matches the w&b diagram because the axel is behind the truss pivot now instead of in front. This fundamentally changes the nose gear behavior when tracking and steering. I guess it’s good that it’s always on one side instead of compressing across that axis when landing and loading it. 

Without looking at the w&b diagram, I think I remember a handwritten note on one axle location is shown in front of the pivot to make the drawing easier to use for measurements (and more confusing at the same time).   Maybe that was in a dream.  I'll look but Christmas is going to interfere.  Axle center on mine is barely behind the pivot, yours looks quite different.

[Nukemzzz]

21 hours ago, Mooneymite said:

I recently replaced my nose truss with the LASAR version; my original truss did not have, or need the spacer.  LASAR sent me one without the spacer and no reference to it in any of the paperwork.  After installation, my nose steering was completely out of whack (the plane wandered all over the place!).  I determined that I needed the spacer.  LASAR initially wanted to charge me for it, but after some "discussion" it arrived free of additional charge.

To make a long story short, the folks that rebuild the nose trusses and install the tabs have no idea what year the core truss came off and whether it needs a spacer, or not.  When I sent my core back, I included documentation that my core did not need the spacer, but LASAR seemed to be uninterested, preferring to act like "one size fits all".  One size does NOT fit all.  These trusses obviously went through some design changes.  My 1974 Mooney truss did not exactly match the dimensions of the replacement "one size fits all' truss.

Perhaps you got the truss that I sent in for a core that needs no spacer?

This is exactly what I’m suspecting. But I also don’t know that it hurts to have more trail. Will find out as soon as the weather clears up!

[Nukemzzz]

1 hour ago, Delta said:

I am just wondering, but was the plane leveled per the Service Manual?

Yes, this is why the tire is flat. lol 

It’s also on blocks on the main. 

[Nukemzzz]

1 hour ago, takair said:

 Are the jacks being used to level the plane or is it just sitting in the background?

Used to get the plane on the scales and that’s all. 

[Nukemzzz]

1 hour ago, DMM said:

Here's D Maxwell's comments on SB M20-202.   "https://web.archive.org/web/20191022103354/http://donmaxwell.com/the-eight-second-ride-sb-m20-202/

"The plumb bob should fall in the center of the axle. If the line falls behind the axle, you need to add the spacer provided in the kit, and be prepared for a pleasant experience on your next landing. If the line falls in front of the axle, you have probably been experiencing some shimmy, and the shock disc need replacement." 

 

Yeah, as the disks wear the axle moves back and up. These are brand new shock disks though so it’s going to move even more back as it ages.  

[Mooneymite]

1 minute ago, Nukemzzz said:

This is exactly what I’m suspecting. But I also don’t know that it hurts to have more trail. Will find out as soon as the weather clears up!

The Mooney spacer is a specific thickness for a reason.  There is no range.  I'm guessing this provides an optimum control-ability.  Anything more, or less deviates from optimum.

 

[Nukemzzz]

Does anyone know the actual differences between these parts by year?  It was really hard to the the lower arm connected to the truss as well. Had to flex the disk stack to the side quite a bit to get the holes lined up and it was in the direction that it will move when the gear compresses more meaning there are hints that things aren’t aligned very well and now I’m worried that Lasar thinks all these parts are interchangeable and they aren’t. 

[Mooneymite]

This thread has pictures of the plumb location before and after spacer installation to give you some rough idea how far the plumb line will move:

 

[takair]

Many years ago....before I knew about the SB washer, I learned that the lock collar is not symmetrical.  I don’t know if this is intentional, but I recall that I was able to change the geometry enough to pass caster check by flipping the collar.  I found this one in my spares pile and sure enough, it is not symmetrical.  I used a scale to try to illustrate, but hard to see.  With callipers it is measurable, maybe 1/32”.  Not much, but it does make a difference in the caster angle.  So, there is a chance you can effect a difference by flipping the collar.....of course...it could also make it go the other way.  Apologies in advance if you go through this and it doesn’t help, but it may be worth 1/4” at the axle if yours is like mine.

[Mooneymite]

1 hour ago, takair said:

Many years ago....before I knew about the SB washer, I learned that the lock collar is not symmetrical.  I don’t know if this is intentional, but I recall that I was able to change the geometry enough to pass caster check by flipping the collar.  I found this one in my spares pile and sure enough, it is not symmetrical.  I used a scale to try to illustrate, but hard to see.  With callipers it is measurable, maybe 1/32”.  Not much, but it does make a difference in the caster angle.  So, there is a chance you can effect a difference by flipping the collar.....of course...it could also make it go the other way.  Apologies in advance if you go through this and it doesn’t help, but it may be worth 1/4” at the axle if yours is like mine.

 

I also found this to be true, but the off-center difference was not enough to make a difference in steering.  I definitely needed the spacer on the replacement truss.  I could not figure out if this was just a manufacturing defect in the collar, or if it was intentional.  I couldn't find anything in the service manual, or parts manual that alluded to the asymmetry.

[PT20J]

I'm still puzzled since the Service Manual doesn't show a max rearward dimension. Here's a thought: The new Mooney website has a forum with a section for Technical and Maintenance Tips which they have promised to monitor. Why not post this there and see what happens?

Skip

[PT20J]

3 hours ago, takair said:

Many years ago....before I knew about the SB washer, I learned that the lock collar is not symmetrical.  I don’t know if this is intentional, but I recall that I was able to change the geometry enough to pass caster check by flipping the collar.  I found this one in my spares pile and sure enough, it is not symmetrical.  I used a scale to try to illustrate, but hard to see.  With callipers it is measurable, maybe 1/32”.  Not much, but it does make a difference in the caster angle.  So, there is a chance you can effect a difference by flipping the collar.....of course...it could also make it go the other way.  Apologies in advance if you go through this and it doesn’t help, but it may be worth 1/4” at the axle if yours is like mine.

The M20J Service Manual has a note about it.  Not sure about earlier manuals.

[Mooneymite]

10 minutes ago, PT20J said:

The M20J Service Manual has a note about it.  Not sure about earlier manuals.

 

Good find!