+20 year old donuts (1966 M20E)

[Shadrach]

So this is what 53-year-old donuts look like on an aircraft that has spent 95% of its life inside. Squish test was done before the side-by-side photo. I look forward to seeing how the new donuts perform in the sub-freezing temperatures.
 

 

Edited June 23, 2021 by Shadrach

[carusoam]

Wow Ross!

Looks like you may have one donut that is squeezed more than the others…

Replacing that donut might help the whole stack height somewhat…

are you sure that isn’t an upside down ‘99 date code?  

Somebody has done a nice job for decades keeping UV and oil away from the donuts…

Great pic!

Best regards,

-a-

[HRM]

The landings will be noticeably wonderful.

[carusoam]

If the rubber has hardened…. As most rubber tend to continue to do over time…

The new ones will probably have a nice shock absorption quality to them….  Most noticeable while taxiing across cracks in the pavement…. 
Memory from my M20C days…

Best regards,

-a-

[Vance Harral]

Just now, carusoam said:

The new ones will probably have a nice shock absorption quality to them….  Most noticeable while taxiing across cracks in the pavement…. 

I see this assertion a lot here.  But having replaced both main and the nose gear pucks twice over 17 years of ownership, I'll offer a contrary data point: we couldn't tell any difference at all with new pucks vs. old, either during taxi or on landing.  Note that we didn't replace the pucks "just because", we replaced them because they exceeded the prescribed limits in the maintenance manual.  Still, no detectable difference reported by anyone in the partnership before/after, and that's from multiple partners with varying levels of skill and seat-of-the pants sensitivity.

Possible explanations:

• Puck flexibility may be more of a feel factor on heavier, later model Mooneys, vs. our lighter vintage model.  I was actually looking at this just yesterday.  Someone parked a late model long body on the ramp next to the fuel pump, and compared with ours at fuel up, it sits considerably lower on the same gear.  The tail in particular was about 8" closer to the ground, which I can only assume is due to greater compression of the mains.
• We replace pucks as soon as they exceed tolerances, and we've gotten about 10 years of service per set.  But I occasionally see owners here talking about replacing 20-, 30- even 40-year old pucks.  Who knows how far out of tolerance those have gotten?  I'm sure it's possible to let them get in such horrible condition that they're effectively made of stone, in which case there will obviously be a noticeable difference when replaced with new.

Anyway, the point is not to dispute others observations.  Just want to reassure owners - at least of vintage era Mooneys - who follow the maintenance manual recommendations, that they didn't get swindled just because changing out the gear pucks doesn't automatically produce greaser landings and luxurious taxi rides.

[Shadrach]

2 minutes ago, Vance Harral said:

I see this assertion a lot here.  But having replaced both main and the nose gear pucks twice over 17 years of ownership, I'll offer a contrary data point: we couldn't tell any difference at all with new pucks vs. old, either during taxi or on landing.  Note that we didn't replace the pucks "just because", we replaced them because they exceeded the prescribed limits in the maintenance manual.  Still, no detectable difference reported by anyone in the partnership before/after, and that's from multiple partners with varying levels of skill and seat-of-the pants sensitivity.

Possible explanations:

• Puck flexibility may be more of a feel factor on heavier, later model Mooneys, vs. our lighter vintage model.  I was actually looking at this just yesterday.  Someone parked a late model long body on the ramp next to the fuel pump, and compared with ours at fuel up, it sits considerably lower on the same gear.  The tail in particular was about 8" closer to the ground, which I can only assume is due to greater compression of the mains.
• We replace pucks as soon as they exceed tolerances, and we've gotten about 10 years of service per set.  But I occasionally see owners here talking about replacing 20-, 30- even 40-year old pucks.  Who knows how far out of tolerance those have gotten?  I'm sure it's possible to let them get in such horrible condition that they're effectively made of stone, in which case there will obviously be a noticeable difference when replaced with new.

Anyway, the point is not to dispute others observations.  Just want to reassure owners - at least of vintage era Mooneys - who follow the maintenance manual recommendations, that they didn't get swindled just because changing out the gear pucks doesn't automatically produce greaser landings and luxurious taxi rides.

Mine have always measured within limits but I had an occasion to jack one wheel this winter and didn’t need to measure to see that they had failed in the sub freezing temp. 25 mins later they were within limits again. In warm weather they expand immediately. I don’t expect to feel much difference. My pucks are not hardened but the calendar age was bordering on silly so here we are.

[carusoam]

Vance,

Let me clear up my observation a bit…

It comes from my M20C experience… the donuts were probably decades old… but, not original…

They had noticeable weather checking on the surface… (cracks and crevices)  they also had white paint overspray on some of the donuts…

The plane lived outside for its entire life…

The age issue I am discussing is the hardness of the rubber itself…. It gets more hard as the years go by…

This is separate from the compression…. These are pretty independent of each other, sort of…

Rubber can be a live chemistry where cross linking continues on over years…. This is probably why they get harder over the years….
 

There isn’t any solvent that is evaporating out or some kind of softener/molecular lubricant like flexible PVC hose has…

We have two things going on…

rubber is one part liquid like… it continues to flow over decades… our donuts flow downwards under stress, and outwards where nothing is holding them in place…  the perfect cylinders when we buy them… look like toroids (donuts) after we are done with them… 

rubber is another part solid… and gets more solid over decades… additional cross linking over time… it is  very likely that new donuts will be more flexible than NOS parts that sat on a shelf unused for a decade…

 

Briefly we see…

one thing that says time to toss them out… the dimensional change…

Another thing  that says… man these things give a stiff ride… a seat of the pants feel.

The third thing is a visual clue… that really only goes skin deep… the surface cracks haven’t penetrated very much… nobody has seen broken donuts…

Oddly,  if you have decades old donuts that were stored outdoors… I bet your seat of  the pants instrumentation will detect a difference the day you swap in the new donuts… 

Unfortunately, the memory attached to the seat of the pants instruments fades over time…

It is near impossible to tell that it is time to change donuts by taxiing…

I bet it may be more obvious for CFIIs that get to fly in multiple Mooneys… every month…

Briefly, be looking for three different age related affects for rubber donuts… we only measure one…

1) Compression

2) Hardening (Vance gave an interesting time line where hardness doesn’t become a noticeable issue)

3) Environmental affects… cracking and oxidation… or paint overspray dissolving the Outer layer…

PP thoughts only… not a rubber chemist… 

It is an interesting technical discussion… probably a good idea to invite Gert…

Best regards,

-a-

 

[carusoam]

One note regarding comparisons between Long bodies and other Mooneys…

The gear is different, it just looks the same…

The first LB… used the gear from the mid bodies and is stuck at a MGTOW that leaves very UL for practical four seat flights…

The M20M TLS got the new leg design… that has carried through until the next schedule update for LBs… where the MGTOW is rumored/hoped for an increase…

The big deal with the current leg design… the nose up ground attitude of  LBs is a few degrees higher than the previous Mooneys…

Which makes them look like they are squatting on their main gear… from inside the cockpit the long nose really is more noticeable…

Under donut compression… LBs have heavier engines and more fuel in their tanks… they compress faster than lighter Mooneys… they somewhat compress evenly…

I don’t think anyone has measured a change in stance due to compression…. 

The change of stance, if there is one, would be directly to the speed at which the plane wants to rotate… as it changes the AOA while on the runway…

Hmmmmm…. Very interesting…. Wheel barrowing has been observed by some pilots new 2Mooneys….  Is it donut compression related?

PP thoughts only…

Best regards,

-a-

[Gert]

3 hours ago, carusoam said:

Vance,

Let me clear up my observation a bit…

It comes from my M20C experience… the donuts were probably decades old… but, not original…

They had noticeable weather checking on the surface… (cracks and crevices)  they also had white paint overspray on some of the donuts…

The plane lived outside for its entire life…

The age issue I am discussing is the hardness of the rubber itself…. It gets more hard as the years go by…

This is separate from the compression…. These are pretty independent of each other, sort of…

Rubber can be a live chemistry where cross linking continues on over years…. This is probably why they get harder over the years….
 

There isn’t any solvent that is evaporating out or some kind of softener/molecular lubricant like flexible PVC hose has…

We have two things going on…

rubber is one part liquid like… it continues to flow over decades… our donuts flow downwards under stress, and outwards where nothing is holding them in place…  the perfect cylinders when we buy them… look like toroids (donuts) after we are done with them… 

rubber is another part solid… and gets more solid over decades… additional cross linking over time… it is  very likely that new donuts will be more flexible than NOS parts that sat on a shelf unused for a decade…

 

Briefly we see…

one thing that says time to toss them out… the dimensional change…

Another thing  that says… man these things give a stiff ride… a seat of the pants feel.

The third thing is a visual clue… that really only goes skin deep… the surface cracks haven’t penetrated very much… nobody has seen broken donuts…

Oddly,  if you have decades old donuts that were stored outdoors… I bet your seat of  the pants instrumentation will detect a difference the day you swap in the new donuts… 

Unfortunately, the memory attached to the seat of the pants instruments fades over time…

It is near impossible to tell that it is time to change donuts by taxiing…

I bet it may be more obvious for CFIIs that get to fly in multiple Mooneys… every month…

Briefly, be looking for three different age related affects for rubber donuts… we only measure one…

1) Compression

2) Hardening (Vance gave an interesting time line where hardness doesn’t become a noticeable issue)

3) Environmental affects… cracking and oxidation… or paint overspray dissolving the Outer layer…

PP thoughts only… not a rubber chemist… 

It is an interesting technical discussion… probably a good idea to invite Gert…

Best regards,

-a-

 

OK, I'll take a bite! The Lord disks were made by an injection technique where the rubber mixture is injected into the mold in a molten state through multiple ports. This method in itself was problematic with surface cooling of each injected "blob" before they had a chance to mix.

The composition of the rubber has been such that it did not allow ozone protection or UV protection. The latest composition is a mixture of 80% Natural Rubber and 20% Styrene Butadiene Rubber with good resistance to weathering and Ozone cracking. The maximum continuous service temp is 80 Deg C in air with short term service of 110 Deg C possible. The Lord Rubber mix has a much lower service temp. The manufacturing is also done with the material mix inside the mold before it is compressed to form the Disks. The current composition should outlast the Lord type by many years. UV and Ozone exposure tests have successfully concluded this

 

Best Regards

Gert

[Shadrach]

11 hours ago, Gert said:

OK, I'll take a bite! The Lord disks were made by an injection technique where the rubber mixture is injected into the mold in a molten state through multiple ports. This method in itself was problematic with surface cooling of each injected "blob" before they had a chance to mix.

The composition of the rubber has been such that it did not allow ozone protection or UV protection. The latest composition is a mixture of 80% Natural Rubber and 20% Styrene Butadiene Rubber with good resistance to weathering and Ozone cracking. The maximum continuous service temp is 80 Deg C in air with short term service of 110 Deg C possible. The Lord Rubber mix has a much lower service temp. The manufacturing is also done with the material mix inside the mold before it is compressed to form the Disks. The current composition should outlast the Lord type by many years. UV and Ozone exposure tests have successfully concluded this

 

Best Regards

Gert

Gert,

I was strongly considering ordering discs from you. At the end of the day, timing was the major issue.  I had to pay 50% more for what is likely an inferior product but I needed them on a schedule that did not work with manufacturing and shipping from S.A.  Had I known about you sooner and planned the process better, I surely would’ve gone that route.

Edited June 23, 2021 by Shadrach

[Vance Harral]

13 hours ago, carusoam said:

The M20M TLS got the new leg design

Interesting.  What exactly is different?

I got my information about greater compression on long bodies causing the tail-down/nose high attitude from this LASAR article, which specifically says, "You may notice that the long bodies are “dragging” their tail -so to speak- but that’s usually due to the more extreme compression of the main gear shock biscuits, due to their weight."

I was under the impression the greater gross weight allowed on long-body Mooneys is due to more robust brakes and slightly higher stall speeds, rather than a change in the leg design.  But all I really know is the part number and count of shock disks appear to be identical for all Mooneys, other than the very ancient models that used the Firestone disks (of which essentially all have been converted to Lord).  When you order shock disks from LASAR or other sources, there is not one type/count for long bodies and another for older airplanes.  So I'd like to understand how the landing gear leg design is different on long bodies, while still using the same type and count of shock disks.

[Hank]

Just now, Vance Harral said:

Interesting.  What exactly is different?

I got my information about greater compression on long bodies causing the tail-down/nose high attitude from this LASAR article, which specifically says, "You may notice that the long bodies are “dragging” their tail -so to speak- but that’s usually due to the more extreme compression of the main gear shock biscuits, due to their weight."

I was under the impression the greater gross weight allowed on long-body Mooneys is due to more robust brakes and slightly higher stall speeds, rather than a change in the leg design.  But all I really know is the part number and count of shock disks appear to be identical for all Mooneys, other than the very ancient models that used the Firestone disks (of which essentially all have been converted to Lord).  When you order shock disks from LASAR or other sources, there is not one type/count for long bodies and another for older airplanes.  So I'd like to understand how the landing gear leg design is different on long bodies, while still using the same type and count of shock disks.

I've always heard thicker-walled tubing, but same OD.

[Vance Harral]

For reference, here's a comparison photo of long vs. mid-body at rest.  I realize the M20R is 12" longer behind the gear, but that doesn't really account for why the tail is so much lower.  Look at the line of the fuselage bottom behind the wing.  It's essentially parallel to the ground on the long-body, but distinctly rising on the M20F.  Every line on the long body is tilted rearward, relative to the ground: bottom of the fuselage, chord angle of wing and horizontal stab, vertical stab, top of cowl, prop arc, etc.

If the difference in the gear leg design is just the thickness of the tubing, that doesn't change the overall geometry.  The difference in sitting-on-the-ground angle has gotta be the greater weight compressing the shock disks more, right?

 

[Shadrach]

23 minutes ago, Vance Harral said:

For reference, here's a comparison photo of long vs. mid-body at rest.  I realize the M20R is 12" longer behind the gear, but that doesn't really account for why the tail is so much lower.  Look at the line of the fuselage bottom behind the wing.  It's essentially parallel to the ground on the long-body, but distinctly rising on the M20F.  Every line on the long body is tilted rearward, relative to the ground: bottom of the fuselage, chord angle of wing and horizontal stab, vertical stab, top of cowl, prop arc, etc.

If the difference in the gear leg design is just the thickness of the tubing, that doesn't change the overall geometry.  The difference in sitting-on-the-ground angle has gotta be the greater weight compressing the shock disks more, right?

 

One must take into account that the stretch was done at the baggage compartment. The correct way to look at it would be to extend that F model’s fuselage at the cabin door and on the same vector. It would indeed account for some of the tail low stance. It’s tough to say how much is disc compression without measuring the height of each aircraft’s wing at the same station.  Also hard to eyeball the difference in height at the nose because of the different cowl design. The nose gear swing arm appears to be at approximately the same angle.

[Vance Harral]

2 minutes ago, Shadrach said:

The correct way to look at it would be to extend that F model’s fuselage at the cabin door and on the same vector.

This is pretty easy to visualize in the comparison photos, because both aircraft have horizontal striping that follows the fuselage side skin lap joint used as the level reference for the airframe.  On the M20F, that level line is parallel to the strip of white between the red and gold stripes.  On the M20R it's parallel to all the gold striping.

There's no question the M20R "squats" relative to the M20F.  Just look at the ground relative to the striping.

[Hank]

Yes, long bodies are more nose up. I've seen the figure, maybe 5°? 8°? I forget. Always thought it was an intentional design change, it's certainly addressed in Takeoff and Landing procedures. Maybe Don Kaye remembers, he's trained many people in long bodies.

[carusoam]

Vance,

All I know about the differences in leg design is the ability for the LBs to carry the full load that they do… 3368LBs.

Where the first LB, the M20L, are hindered by their legs to handle the additional weight…

People who have added engine upgrades post Porsche have a really challenging UL situation…

And there doesn’t seem to be an easy way to swap in the newer gear design… that would make a lot of people happy…

Even more if there wasn’t that hurricane / chainsaw debacle in Florida…

 

Thanks for the great pics showing ground attitude differences…

First day in an LB… you notice something important during the pre-flight…

You go to set the little airplane on the attitude indicator… and it is really far off from your prior GA experience… 

I tried to look up the ground attitude for the O…. I have no idea where to find that reference…

Its 73 inch prop has 11” of ground clearance if that helps any?

the nose is longer… and the tail is longer….

Let me know if you know where in the POH to find that detail…

Best regards,

-a-

[Shadrach]

Circling back around on the old donut deterioration compared to new.  I did some testing today.  The most significant difference I can see (and it’s a big one) is the amount of compressibility. I think the old discs respond similarity for about the first 25% of compression after that they are stiffer and do not have the ability to increase in circumference (bulge) like the new discs. This is likely why many folks don’t notice much of a difference during taxi and normal landings. Even so, I’d estimate my suspension has an additional inch of travel with the new discs, maybe more.

[brndiar]

44 !!!! Years old Donuts go to retirement.

Despite their senior age, they always served well ....

 

lg,m

 

[carusoam]

Short body Mooneys are so light on their feet!

-a-

[outermarker]

Does anyone have the disc removal tool for the main gear that they would want to sell? Sometime this year I plan to change out the discs.

 

[A64Pilot]

45 minutes ago, outermarker said:

Does anyone have the disc removal tool for the main gear that they would want to sell? Sometime this year I plan to change out the discs.

 

I believe there is a procedure for the mains that essentially uses the aircraft weight to compress them, negating the need for a tool. I’ve not done it myself though.

[Greg Ellis]

52 minutes ago, A64Pilot said:

I believe there is a procedure for the mains that essentially uses the aircraft weight to compress them, negating the need for a tool. I’ve not done it myself though.

This thread goes into some good detail about removing the shock discs using aircraft weight to compress the discs.  It may be helpful.

[N201MKTurbo]

1 hour ago, outermarker said:

Does anyone have the disc removal tool for the main gear that they would want to sell? Sometime this year I plan to change out the discs.

 

I have the main and nose tools in my hangar. You are welcome to come here and use them. I loaned my nose tool out once and didn't see it for 8 years. (yes it finally came home) So I'm not letting them out of my sight any more.

[outermarker]

@ Turbo...I hope you loaned them to someone based at your airport. Thanks for the offer too.