Mooney landing gear shock disk

[Marc_B]

I know when I had the nose gear discs replaced it made a considerable difference requiring the collar to be flipped from the old position (thick side up) to now being "thick side down."  So you have different settings to get geometry set: collar thick side up, collar thick side down +/- the shim/spacer.  From what I'm told, the material these days is less compressible so that probably accounts for needing more stack "squish" to get it set for proper fore- aft-position.

[Marc_B]

Collar thick side up.  We had to flip this over to get fore aft position aligned.  Thick side down (or add a shim) moves the nose wheel aft.

[jcolgan]

Compression tool and spacer are both in transit headed my way.  The new disc stack was a bit taller than the old ones, but the plane had been sitting up on jacks for over a week by the time the old discs got removed so they had ample time to expand.  Some of my old discs on the nose were from 1981, the mains were from 1969.  I sure hope the new ones are both taller and more pliable.

The spacer is only 0.12 inch thick, but it is much closer to the pivot point so the tire contact point should move aft several multiples of that.  Assuming the drawing is to scale, I think the contact point should be moved aft by  in the neighborhood of 5.2 times the spacer thickness, so maybe 0.624 inch.  
If that close to correct, she might just taxi better that she ever has after this! 

 

 

 

[Fly Boomer]

30 minutes ago, Marc_B said:

Collar thick side up.  We had to flip this over to get fore aft position aligned.  Thick side down (or add a shim) moves the nose wheel aft.

I'm reading the manual excerpt you posted above but, starting with a go-kart I built when I was 10, I have always found that more caster makes a vehicle want to go in a straight line, and less caster makes it want to do anything but.  I don't get why the axle centerline must be moved back (less caster) to prevent bad behavior on the ground.

[Gee Bee Aeroproducts]

Could me made to sample

Mold cost , epdm rubber is best

What does the service manual call for time change ?

 

GB

 

[jcolgan]

51 minutes ago, Fly Boomer said:

I'm reading the manual excerpt you posted above but, starting with a go-kart I built when I was 10, I have always found that more caster makes a vehicle want to go in a straight line, and less caster makes it want to do anything but.  I don't get why the axle centerline must be moved back (less caster) to prevent bad behavior on the ground.

My understanding of things, if your steering pivot point is in front of your ground contact point, friction with the ground will tend to cause the contact point to fall in line behind the pivot point producing a straight rolling tendency.  
If contact point leads pivot point, friction will cause any turn, if uncorrected, to be amplified and be inherently unstable. 
The tire contact with the ground needs to be aft of the nose gear turning point to be stable. 

[Pinecone]

On 3/21/2024 at 4:46 PM, Fly Boomer said:

I'm reading the manual excerpt you posted above but, starting with a go-kart I built when I was 10, I have always found that more caster makes a vehicle want to go in a straight line, and less caster makes it want to do anything but.  I don't get why the axle centerline must be moved back (less caster) to prevent bad behavior on the ground.

Axle moving back increases caster.   Look at shopping cart front wheel.  Axle is well behind the pivot axis.

[MikeOH]

26 minutes ago, Pinecone said:

Axle moving back increases camber.   Look at shopping cart front wheel.  Axle is well behind the pivot axis.

I believe you meant castor, not camber.

[LANCECASPER]

On 3/21/2024 at 3:15 PM, jcolgan said:

 the mains were from 1969

That means you shouldn't have to change them again until 2079 

[Shadrach]

1 hour ago, Pinecone said:

Axle moving back increases camber.   Look at shopping cart front wheel.  Axle is well behind the pivot axis.

If you tried to steer a shopping cart from it's steering pivot point, it would handle horribly.

[Ragsf15e]

Never thought I’d learn so much about the handling qualities of shopping carts on MooneySpace! 

[Shadrach]

6 minutes ago, Ragsf15e said:

Never thought I’d learn so much about the handling qualities of shopping carts on MooneySpace! 

This is a full service forum.  Seriously though, imagine trying to steer a motorcycle with the front end configured like a shopping cart...fork out in front with a trailing link and the axel well behind the pivot. 

[MikeOH]

4 hours ago, Shadrach said:

If you tried to steer a shopping cart from it's steering pivot point, it would handle horribly.

You must live a charmed life...EVERY shopping cart I've ever 'driven' has handled HORRIBLY

[Shadrach]

16 minutes ago, MikeOH said:

You must live a charmed life...EVERY shopping cart I've ever 'driven' has handled HORRIBLY

Much better if you flip them around backwards. They make better tail draggers… 

[jcolgan]

My collar was center drilled, no adjustment possible by flipping the collar.

The service bulletin spacer moved the center of the nose wheel axle aft about 7/8 inch.  She taxis better post install.  Brand new shock biscuits bulging out with the preloaded compression caused by the spacer.

[EricJ]

7 hours ago, Shadrach said:

This is a full service forum.  Seriously though, imagine trying to steer a motorcycle with the front end configured like a shopping cart...fork out in front with a trailing link and the axel well behind the pivot. 

Too much caster just makes it hard to steer, but you have to have some caster or the steering will be unstable and try to deflect uncommanded.    PA-46 have very, very little caster and it can get out of rig fairly easily, which is why a common accident for them is suddenly running off the runway.

Cars have caster, which is why the steering will center if you let go of the steering wheel.  

Mooneys don't have a ton of caster, but enough if the nosewheel caster stays in rig.   When it starts to go out of rig due to bushing wear, etc., the eight-second ride starts to happen when there is insufficient caster.   The diagrams and procedure in the SB are specifically to make sure there's enough caster for the nosewheel to try to self-align rather than be unstable or deflect.

In race cars most folks I knew (myself included) went for maximum caster in front end alignments.    This increases steering effort a bit, but also helps turn-in and speeds up auto-centering which can be crucial in spin or slide recovery, especially if the steering rate is fairly slow.

This is all true for motorcycles as well; the steering will be unstable if there isn't at least a little caster.

 

[Pinecone]

21 hours ago, MikeOH said:

I believe you meant castor, not camber.

DUH.  jet lagged posting.

[Pinecone]

19 hours ago, Shadrach said:

This is a full service forum.  Seriously though, imagine trying to steer a motorcycle with the front end configured like a shopping cart...fork out in front with a trailing link and the axel well behind the pivot. 

Actually if you look at the pivot axis on a motorcycle and extend it to the axle, the axis line IS in front of the axel.

[Pinecone]

11 hours ago, EricJ said:

Too much caster just makes it hard to steer, but you have to have some caster or the steering will be unstable and try to deflect uncommanded.    PA-46 have very, very little caster and it can get out of rig fairly easily, which is why a common accident for them is suddenly running off the runway.

Cars have caster, which is why the steering will center if you let go of the steering wheel.  

Mooneys don't have a ton of caster, but enough if the nosewheel caster stays in rig.   When it starts to go out of rig due to bushing wear, etc., the eight-second ride starts to happen when there is insufficient caster.   The diagrams and procedure in the SB are specifically to make sure there's enough caster for the nosewheel to try to self-align rather than be unstable or deflect.

In race cars most folks I knew (myself included) went for maximum caster in front end alignments.    This increases steering effort a bit, but also helps turn-in and speeds up auto-centering which can be crucial in spin or slide recovery, especially if the steering rate is fairly slow.

This is all true for motorcycles as well; the steering will be unstable if there isn't at least a little caster.

 

EXACTLY.

Also, on race cars the caster causes camber gain on the outside front tire, reducing understeer.

My M3 setup, when I was going a lot track work, made people think something was broken if I parked with the wheels turned.  3.5 degree static camber and a lot of caster will do that.

[Shadrach]

35 minutes ago, Pinecone said:

Actually if you look at the pivot axis on a motorcycle and extend it to the axle, the axis line IS in front of the axel.

Perhaps on some bikes, but I don’t think thats the norm. I have restored a few different motorcycles from various eras (Jap and Brit) and all had triple clamps with the fork mounts offset forward of the steering pivot. The axel mount is typically at the center point of the fork. HD springers have less offset at the triple clamp, but the wheel is offset on a swing arm at the bottom of the fork. Many MX bikes have axel mounts offset forward of the fork, which is already offset forward of the triple clamp.

[Pinecone]

You have to look at the axis of the steering pivot.  And extend that line to past the axle.

It would be just about impossible to ride a bike with negative caster

"Again, the angle this line makes with the vertical is the caster angle. The first purpose of the caster angle is to give stability to the steering wheels, which would otherwise be unmanageable."

"In the context of bicycles and motorcycles, caster is more commonly referred to as "head angle", "rake angle" or "rake and trail", especially in American English. The terms caster or castor angle are still predominantly used in British English."

[PT20J]

It's harder to visualize when the pivot point is at an angle. It's more obvious when the pivot point is vertical as on a shopping cart wheel. The force moving the wheel forward acts at the pivot point and the friction force on the wheel acts in the opposite direction at the ground contact point. When the wheel is moving straight ahead, the two forces are in alignment, but when the wheel is turned, the two forces are not aligned and thus create a restoring torque that turns the wheel back into alignment.

[EricJ]

FWIW, the axle doesn't necessarily have to be behind the steering axis, but the tire contact patch does.    I don't know if that matters conceptually for anybody.    Generally the tire contact patch will be directly below the axle, anyway.

Since the contact patch is lower than the axle, the distance between the steering axis and the contact patch may be larger and easier to see/measure/conceptualize than the distance to the axle.

 

[Shadrach]

 

13 minutes ago, EricJ said:

FWIW, the axle doesn't necessarily have to be behind the steering axis, but the tire contact patch does.    I don't know if that matters conceptually for anybody.    Generally the tire contact patch will be directly below the axle, anyway.

Since the contact patch is lower than the axle, the distance between the steering axis and the contact patch may be larger and easier to see/measure/conceptualize than the distance to the axle.

 

The axel of a bike never is as far as I know.  It either aligns with the fork/fork slider or is ahead of it as pictured.

[Shadrach]

1 hour ago, Pinecone said:

You have to look at the axis of the steering pivot.  And extend that line to past the axle.

It would be just about impossible to ride a bike with negative caster

"Again, the angle this line makes with the vertical is the caster angle. The first purpose of the caster angle is to give stability to the steering wheels, which would otherwise be unmanageable."

"In the context of bicycles and motorcycles, caster is more commonly referred to as "head angle", "rake angle" or "rake and trail", especially in American English. The terms caster or castor angle are still predominantly used in British English."

At no point did any thing I described meet the definition of negative caster with the exception of the shopping cart.