Shimmy issue

[RotorAndWing]

The A&P typically references "Replaced with owner repaired part"

That's not what I asked you.

How does "replaced with owner repaired part" meet the requirements of 14 CFR Part 43?

 

[Henning]

That's not what I asked you.

That is the advantage of being a non A&P owner, I don't have to. I have to provide a suitable repair. I have not changed any dimension or function from the factory specification, I returned it to those specifications and I have done so using a Mil Spec material used to label. I have fulfilled all my obligations for providing this part to return to service. The A&P then inspects the part and determines it will safely do the job, and returns it to service.

As an A&P I would be limited to trying to find a less worn replacement in the salvage yard, or buying new, but the Owner Produced Part paragraphs give me some extra latitude in repairing my own machine.

Regardless of any of that, the repair is safe in every regards.

 

[RotorAndWing]

That is the advantage of being a non A&P owner, I don't have to. I have to provide a suitable repair. I have not changed any dimension or function from the factory specification, I returned it to those specifications and I have done so using a Mil Spec material used to label. I have fulfilled all my obligations for providing this part to return to service. The A&P then inspects the part and determines it will safely do the job, and returns it to service.

Someone has to sign off this repair, and it has to be signed off IAW Part 43. You are attempting to use double talk and "mumbo jumbo" to justify a repair that does not conform to factory specifications or any acceptable data.

Any licensed A&P in his right mind would not sign this off in fear of jeopardizing his license.

Look at it this way, if you called Cessna, Piper, Beech, etc, asked for a tech rep, described your method of repair do you honestly think they will say "sure, go ahead and do it". ?

As an A&P I would be limited to trying to find a less worn replacement in the salvage yard, or buying new, but the Owner Produced Part paragraphs give me some extra latitude in repairing my own machine.

But there are new ones, and there are companies that repair them.

This in no way conforms to Owner Produced Parts paragraph, that is a stretch.

Regardless of any of that, the repair is safe in every regards.

Think Cessna, Piper, Beech or the FAA would agree with that statement?

 

[Henning]

Why does it not conform to factory specifications? I see measurements matched to factory specifications. I see a MilSpec material used in a listed type repair application meant to do exactly this type of job under this type of service. I have met the obligations under PT 43. I can't imagine anyone from the FAA taking issue with the repair.

 

[RotorAndWing]

Why does it not conform to factory specifications? I see measurements matched to factory specifications.

Please show me using factory specifications for material used that shows Devcon.

Again, please show us data "acceptable to the administrator" in doing this repair and returning to service.

I see a MilSpec material used in a listed type repair application meant to do exactly this type of job under this type of service.

Please show the data. Just because it says "MilSpec" does not mean it's approved or accepted as a material to be used in a repair.

I have met the obligations under PT 43

No you haven't.

. I can't imagine anyone from the FAA taking issue with the repair.

I could see an enforcement taking place and list about 8 to 10 regulations they would use to do it with.

 

[Checkout_my_Six]

Oh....yeah.

 

[philiplane]

Shimmy is lateral acceleration caused primarily by loose parts, shake is vertical vibration caused solely by tire imbalance.

Balance the tire assembly first. Then replace all the worn bolts and bushings.

Your shimmy damper will have very little to do at this point, except do what it was intended to do- stop lateral shake caused by temporary imbalance caused by landing on the nose wheel and deforming the tire for a few revolutions.

 

[Henning]

Please show me using factory specifications for material used that shows Devcon.

Again, please show us data "acceptable to the administrator" in doing this repair and returning to service.



Please show the data. Just because it says "MilSpec" does not mean it's approved or accepted as a material to be used in a repair.



No you haven't.




I could see an enforcement taking place and list about 8 to 10 regulations they would use to do it with.

The Mil Spec provides the usage data that allows for approval. MilSpec is spelled out as "acceptable data" in the FARs, the MilSpec for the material specifies this would be a designed application. It's not difficult.

 

[bnt83]

The only places I've seen liquid shim in an approved repair that's structurally loaded is when filling countersinks in a sheet that will be covered by a doubler with no dimples.

Liquid shims are also used to repair the fange of wing skins that form the mating sealing surface of fuel tank access panels as these frequently corrode and grinding away that damage is basically destroying an o-ring seat. Liquid shim restores that surface to seal the tank. These panels are in the floor of the fuel tanks. A citation 750 has over 140 fuel tank access panels

 

[Henning]

This isn't structurally loaded. If the shim fails, which will only happen in a fire, you will gain back a small bit of slack in your nose gear steering.

 

[RotorAndWing]

The Mil Spec provides the usage data that allows for approval. MilSpec is spelled out as "acceptable data" in the FARs, the MilSpec for the material specifies this would be a designed application. It's not difficult.

Show me where it says you can use Devcon as an acceptable method of repair for this.

You're playing word games, games that mean nothing. You have a very infantile knowledge of regulations as they pertain to aviation maintenance of certified aircraft, let alone working knowledge of 14 CFR Part 43.

Just because something says "MilSpec" does not give it automatic approval to repair anything you damn well please.

 

[Henning]

I just need to provide the application data from the manufacturer along with the MilSpec, and the FAA approves it or not. I bet they approve.

 

[RotorAndWing]

I just need to provide the application data from the manufacturer along with the MilSpec, and the FAA approves it or not. I bet they approve.

And I bet not. Call Cessna/Beech/Piper or any other manufacturer, ask for a tech rep. Tell him how you plan on repairing it and see what they tell you.

And it won't be "Sure, we approve that!"

Better yet, call the FSDO and ask for an AW ASI. Tell him how you plan on repairing one and see if he approves.

I already know the answer to that one.

BTW, A real good friend of mine is an AW ASI in the South Florida FSDO, if you want I'll give you his contact information.

 

[Dan Thomas]

Shimmy is lateral acceleration caused primarily by loose parts, shake is vertical vibration caused solely by tire imbalance.

Balance the tire assembly first. Then replace all the worn bolts and bushings.

Your shimmy damper will have very little to do at this point, except do what it was intended to do- stop lateral shake caused by temporary imbalance caused by landing on the nose wheel and deforming the tire for a few revolutions.

Shimmy's root cause is dynamic imbalance. Period. Loose parts are a result of shimmy, not a cause. Loose wheel bearings will aggravate shimmy but they're not the root cause. Statically balancing the wheel (which is, at most, all most light aircraft wheels get) will not eliminate a dynamic balance. Landing on the nosewheel puts stresses on a whole lot of stuff and does a lot more than loosen linkages and cause shimmy.

A few posts back I posted a link explaining the difference between static and dynamic imbalance. Not many appear to have read it. The front wheels of automobiles suffer exactly the same issues as aircrat nosewheels, and dynamic imbalance there can be felt in the steering wheel. It, too, loosens up steering linkages and suspension parts and ruins tires. Many years ago when I was a kid working in a service station, we used a static tire balancer that got rid of the vertical shake but did nothing for shimmy; one sometimes just got lucky. And in cars, the sheer weight and strength of the front end stuff masked the worst of it anyway. Today, though, nobody will tolerate a shaky ride in their vehicles becasue we've become accustomed to having our wheels dynamically balanced to really tight tolerances so that they run smoothly. But we tolerate nosewheel shimmy because "that's what Cessnas do." Baloney. They don't have to do it, and just tightening up all the linkages and wheel bearings is only masking the real problem: the imbalanced wheel.

This wheel could be statically balanced, but will shimmy mightily.

DYNAMIC IMBALANCE
When a tire has more weight on the inside or outside of its tread, it has a dynamic imbalance. Dynamic imbalance is only noticeable when the tire and wheel is spinning. The tire will have a tendency to shimmy from side to side (left and right) which also results in faster tire wear. When the tire is spinning the heavy spot will tend to seek the centerline of the tire. This is why the tire shimmies from side to side. When the heavy spot is in front, it pushes the wheel to one side. After the tire rotates one half revolution, the heavy spot causes the wheel to try to turn in the opposite direction. However, most tires have imbalances on both sides of the tire, requiring counterbalancing weights to be placed on both sides of the wheel.

From http://www.derekweaver.com/learn/wheel-balancer/

When a pilot lifts the nosewheel when it shimmies, he's engaging the centering cam on the torque links that freeze the nosewheel straight ahead, stopping the shimmy. If he brakes hard, the airplane nosedives and puts lots of weight on the nose tire, squashing it and making its footprint so large that it does not change direction easily, thus restricting the shimmy. Both techniques work but shouldn't be necessary.


Dan

 

[Silvaire]

Good post Dan

#1 - shimmy ain't caused by a worn out dampener so rebuilding or replacing the dampener ain't the fix.

#2 - why would you use silly putty to fix something that can be replaced?

#3 - you can't make "owner produced parts" for anything that is available off the shelf from the manufacturer. Don't matter what it cost.

 

[Witmo]

Good post Dan

#1 - shimmy ain't caused by a worn out dampener so rebuilding or replacing the dampener ain't the fix.

#2 - why would you use silly putty to fix something that can be replaced?

#3 - you can't make "owner produced parts" for anything that is available off the shelf from the manufacturer. Don't matter what it cost.

I don't believe #3 is correct. Reference?

 

[Dan Thomas]

#2 - why would you use silly putty to fix something that can be replaced?

I wouldn't use putties to fix that stuff, let alone most anything else on an airplane. The forces involved are high enough to wallow out the holes in those parts, and they're made of good stuff, far harder and tougher than any putty. And the wallowing leaves a relatively small gap, meaning that any fillers are thin and weak and will get pounded out in short order. It's the same issue as using a thinwalled bushing to take up the slop; the thin wall can't take the pounding. Been there, done that in many machine-shop situations.

Here in Canada we have the Owner-Maintenance registration category. In that case, one could machine oversized/undersized bushings or what ever to fix the slop. If I owned an older, eligible airplane I'd register it that way, and make those parts, as long as there's sufficient material left on the original part to support such work. There often isn't. It is aircraft stuff, after all, and is made pretty light.

Dan

 

[Silvaire]

I don't believe #3 is correct. Reference?

Technically you're right Tim, what I meant was that you're not going to easily get it approved. In the end it boils down to 43.13(b) and convincing a mechanic to accept the part that you've produced, install it and sign the logbook. People read 21.303(b)(2) and think that's all there is to it, that they basically have carte blanche to make whatever part they want but it's actually more involved because although you avoid all of the PMA red tape the part still has to meet the same standards and you've got to prove that.

43.13
(b) Each person maintaining or altering,
or performing preventive maintenance,
shall do that work in such a
manner and use materials of such a
quality, that the condition of the aircraft,
airframe, aircraft engine, propeller,
or appliance worked on will be
at least equal to its original or properly
altered condition (with regard to
aerodynamic function, structural
strength, resistance to vibration and
deterioration, and other qualities affecting
airworthiness).

 

[RotorAndWing]

Technically you're right Tim, what I meant was that you're not going to easily get it approved. In the end it boils down to 43.13(b) and convincing a mechanic to accept the part that you've produced, install it and sign the logbook. People read 21.303(b)(2) and think that's all there is to it, that they basically have carte blanche to make whatever part they want but it's actually more involved because although you avoid all of the PMA red tape the part still has to meet the same standards and you've got to prove that.

All one needs to reference is "MilSpec" and you can get anything approved...