Main Gear Donuts

[M20 Ogler]

The donuts in my mains were replaced a few months ago. I noticed the left wing tip has about 2 1/2” more ground clearance than the right. Tire pressure are equal so I measured the donut stacks. The right is compressed about 1/8” more than the left. Is there anything that can be done about this? Maybe split the difference between them?

[carusoam]

9 hours ago, M20 Ogler said:

The donuts in my mains were replaced a few months ago. I noticed the left wing tip has about 2 1/2” more ground clearance than the right. Tire pressure are equal so I measured the donut stacks. The right is compressed about 1/8” more than the left. Is there anything that can be done about this? Maybe split the difference between them?

Check with your mechanic to see what’s up with that…

Do a visual check to see what isn’t right.

That just doesn’t sound right… for identical donuts…

Something got left out of one of the stacks…

PP thoughts only, 

-a-

[M20 Ogler]

I was thinking maybe they just compressed one side more than the other. But yeah you may be right about the stack not being correct, I did not think of that. I’ll have to look at it closely. Also PP thoughts only. 

[RobertGary1]

2 hours ago, M20 Ogler said:

I was thinking maybe they just compressed one side more than the other. But yeah you may be right about the stack not being correct, I did not think of that. I’ll have to look at it closely. Also PP thoughts only. 

The mains are only compressed by the weight of the aircraft. 
Do you have similar fuel in both tanks?

[Guest]

Compare the collar on the top of the gear leg.  The hole in the collar should be centered in the height of the collar, also look for a washer under the collar, these are normally used to adjust the nose.

Clarence

[Shadrach]

There is a collar bolt on each side that must be aligned with an access hole in order to disassemble the gear. It will not be aligned with the airplane off jacks but the bolt should be in the same place relative to the hole on both gear.

 

 

Edited June 27, 2021 by Shadrach

[M20 Ogler]

My previous plane was a Beechcraft Sundowner, it’s donuts get heated to 120 degrees for 24 hours then compressed in a press fixture prior to the gear leg being reinstalled on the airplane. I assume Mooney’s would be a similar ordeal. Is it like that for a Mooney?

Edited June 27, 2021 by M20 Ogler

[Hank]

6 minutes ago, M20 Ogler said:

My previous plane was a Beechcraft Sundowner, it’s donuts get heated to 120 degrees for 24 hours then compressed in a press fixture prior to the gear leg being reinstalled on the airplane. I assume Mooney’s would be a similar ordeal. Is it like that for a Mooney?

No. Remove the donuts from the box, stack them up, and assemble onto the post. Weight of the plane compresses them when everything is back together and the wheels are back in the ground. There's no need to pre-compress them.

[Shadrach]

48 minutes ago, M20 Ogler said:

My previous plane was a Beechcraft Sundowner, it’s donuts get heated to 120 degrees for 24 hours then compressed in a press fixture prior to the gear leg being reinstalled on the airplane. I assume Mooney’s would be a similar ordeal. Is it like that for a Mooney?

That reads like a needlessly complicated procedure. If the donuts are manufactured with a reasonable degree of precision with regard to dimensions and material characteristic there should be no need to preform them. I’m trying to imagine what heating and compressing actually does for them.

[Guest]

This may help as well.

[Shadrach]

18 minutes ago, M20Doc said:

This may help as well.

Each of the collars on my bird are machined on one side. The illustration does not show that. Can you verify how it should be oriented. Neither the IPC nor MM make mention of it. We know how it was oriented when removed but it would be nice to get verification.

[67 m20F chump]

I thought you could only push the bolt in one way?

[Guest]

6 hours ago, Shadrach said:

Each of the collars on my bird are machined on one side. The illustration does not show that. Can you verify how it should be oriented. Neither the IPC nor MM make mention of it. We know how it was oriented when removed but it would be nice to get verification.

Flat side forward of there is a clearance issue.

 

[Shadrach]

Just now, M20Doc said:

Flat side forward of there is a clearance issue.

 

Thanks Clarence. Ours were mounted forward with the machined side down. I assumed in any other orientation it miht interfere with the steel gusset when the gear compresses. 

[M20 Ogler]

14 hours ago, Shadrach said:

That reads like a needlessly complicated procedure. If the donuts are manufactured with a reasonable degree of precision with regard to dimensions and material characteristic there should be no need to preform them. I’m trying to imagine what heating and compressing actually does for them.

I’m guessing it’s needed because Sundowners, Sierras, Musketeers and all the other “Mouses” have trailing link landing gear so the donuts have to withstand more leverage. Therefore you have to preload the donuts enough to take the force of a hard landing. Heating them softens them enough to prevent them from splitting when compressing them. And you don’t want to split them they cost about $1400 per stack. 

[Shadrach]

On 6/28/2021 at 1:18 AM, M20 Ogler said:

I’m guessing it’s needed because Sundowners, Sierras, Musketeers and all the other “Mouses” have trailing link landing gear so the donuts have to withstand more leverage. Therefore you have to preload the donuts enough to take the force of a hard landing. Heating them softens them enough to prevent them from splitting when compressing them. And you don’t want to split them they cost about $1400 per stack. 

Take a closer look at the gear on your M20. It is also a trailing link design and with similar geometry. The most obvious difference being that the Beech uses thinner discs but twice as many.

Edited June 29, 2021 by Shadrach

[carusoam]

I like the idea of heating rubber prior to compressing them…. But…

We compress them a lot when the plane is fully loaded and we stall a foot above the runway…

I don’t remember heating them during winter ops in NJ.

-a-

[RobertGary1]

5 minutes ago, carusoam said:

I like the idea of heating rubber prior to compressing them…. But…

We compress them a lot when the plane is fully loaded and we stall a foot above the runway…

I don’t remember heating them during winter ops in NJ.

-a-

I think the main item of interest for Mooney owners is that the mains are not compressed when the plane is airborne. Maybe it would make sense for the nose that is??? Would it reduce the need for the compression tool?

[Guest]

3 hours ago, RobertGary1 said:

I think the main item of interest for Mooney owners is that the mains are not compressed when the plane is airborne. Maybe it would make sense for the nose that is??? Would it reduce the need for the compression tool?

The discs remain under quite a bit of compression while in flight or while on jacks.  If there was no compression we wouldn’t need the compression tools to install them.

Clarence

[RobertGary1]

5 hours ago, M20Doc said:

The discs remain under quite a bit of compression while in flight or while on jacks.  If there was no compression we wouldn’t need the compression tools to install them.

Clarence

The nose does but the mains seem to hang. I can grab the main donuts and spin them around by hand when on jacks.

[Guest]

6 hours ago, RobertGary1 said:

The nose does but the mains seem to hang. I can grab the main donuts and spin them around by hand when on jacks.

Then they’re likely compressed beyond limits.

Clarence

[RobertGary1]

5 minutes ago, M20Doc said:

Then they’re likely compressed beyond limits.

Clarence

But 0.6” is a lot. I’m at 0.3”.  That’s still pretty free when not under load. 
 

-Robert

Edited June 30, 2021 by RobertGary1

[Guest]

My experience has been that under no load on jacks or in flight, there should be no free play in the shock disc stack.

Clarence

[M20 Ogler]

The collar bolt is centered in the access hole on the left main but it is not centered on the right main. I’m having difficulty seeing if there is also a washer in there. 
 

Edited July 4, 2021 by M20 Ogler

[Guest]

14 minutes ago, M20 Ogler said:

The collar bolt is centered in the access hole on the left main but it is not centered on the right main. I’m having difficulty seeing if there is also a washer in there. 
 

You can like the small metal cover off to expose the top collar and the bolt and nut.  Some top collars have an offset hole allowing more or less compression, these are normally installed on the nose.  The mains should be the same height.

Clarence