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got a dent in my nose gear truss. Opinions?


rbridges

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Just now, mike_elliott said:

my bad, i missed it was less than the 1/32" spec of unairworthy.. Fly that sucker...

Zero worries.  I appreciate the discussion.  There are many absolutes in aviation.  This gets into some gray area.  If a truss is compromised the results can be catastrophic.  If a truss needs replaced the cost is minimal compared to the POTENTIAL costs.

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Ahhhh...

Another advantage of having the factory being alive...

We have....

maintenance manuals that got much more detail over the years....

In the event we get some damage that is more unique then what the MMs handle...

We have the factory engineering team that has been consulted on the vagaries of measuring and fixing or replacing parts...

There are a few examples of MSers consulting the factory regarding depth of corrosion on some parts... and methods of repair.

 

Damaged parts are expected to have very little tolerance compared to other machines we may be familiar with...

heavier than air flying machines, designed to have max UL, having taken out all of the extra meat that could have been available to strengthen their impact strength...

There isn’t much surprise that small amounts of damage can easily exceed the design strength of the parts involved.

 

Looking forwards... sort of... the factory improved the design of the nose gear incrementally with stops and pointers and warning labels...

Would using a heavier gauge tube in the compression area improve things? Or move the damage to a new location?

 

Really looking forwards... would Ti tubes or other materials improve the situation..?

 

if the dents have you down... know that the nose gear has given up the ghost instead of breaking something else more expensive further down the line...

 

Hmmm Ti landing gear....  bolt on improvement? :)

PP thoughts regarding a complex aviation maintenance and construction process, not a mechanic or structural engineer.

Best regards,

-a-

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3 hours ago, Mooneymite said:

However, at this point I am questioning the 1/32 "limit".  Where did it come from, is it accurate? 

Ultimate question:  At what depth/severity does the dent become too much?

The limit is quantified in multiple places.   I mentioned previously that the Service Manual for my M20J includes a note, in bold type, in the inspection section, like this:
NOTE

Maximum allowable towing damage on leg assembly is 1/32 inch dent.

I don't know how many other models that that text appears in the SM.

There is also a recent Service Instruction (SIM20-137) from Mooney that affects "ALL M20 SERIES AIRCRAFT" that includes a big red box with "WARNING" that says, "Maximum allowable damage to nose gear leg assembly is 1/32 inch dent.  Contact Mooney Product Support with any damage to:  support@mooney.com"

SIs are not mandatory for Part 91 operators, but it's harder to get around the text in the SM.  

 

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It’s just amazing how many places I go, and try to brief the line guys before they tow... it’s pointless because every time they respond with yes yes! We know how to tow... and then you get this dent they won’t take credit for... of course not! I hate going places that insist on towing my ship. We all know how easy it is to over rotate the nose wheel!

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4 hours ago, Sandman993 said:

It’s just amazing how many places I go, and try to brief the line guys before they tow... it’s pointless because every time they respond with yes yes! We know how to tow... and then you get this dent they won’t take credit for... of course not! I hate going places that insist on towing my ship. We all know how easy it is to over rotate the nose wheel!

Bingo!  That's what aggravated me. 

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I get the frustration. But I think it is useful to look at it from the FBO’s viewpoint. Most FBOs will marshall you to a parking spot by their front door. Their ramp isn’t set up to leave the plane there for a long period, and it’s not reasonable to expect them to  hand tow it 100 yards or more to a parking spot. All tricycle gear planes have towing limits, and the line folks move planes all day long, 7 days a week. The Mooney design is poor in that the turning radius is smaller than most other similar airplanes, and early nose gears had no stops. People have managed to damage them even when hand towing. The problem is somewhat mitigated on later models that have incorporated stops. If you ever have a damaged truss, consider replacing it with the newer model with stops. While an improvement, the newer truss with stops is still not a terrific design. Even the DC-3 (designed in the 1930’s) has a shear pin on the tailwheel. 

I tend to favor the higher end FBOs at larger airports when traveling. I may pay more for gas, but I usually find more experienced line personnel, helpful staff with great negotiated rates at local hotels and nice crew cars. This may not be a perfect answer, but I think it improves my odds of getting away undamaged. The places with the cheapest gas have to make up the difference somewhere and a big cost is labor. Do you really want that minimum wage kid servicing your airplane?

Skip

Edited by PT20J
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On 10/11/2019 at 6:06 PM, markejackson02 said:

Specialized Aero in San Marcos TX repairs them, if I recall mine cost about $800 for repair with a 4 week lead time.

If leaving the plane, I carry my last damaged truss in the baggage compartment and tell the line guys that an A&P / IA did this damage and he knew how to tow too...

I put my hand tow bar and show them how limited the turn radius is

I then show them my new undamaged truss on the nose and video it that part of the session and tell them that the fogoing is why it must be hand towed only and have a sign put on the plane to that effect. Not wanting to pay for a 3rd truss in 3 years. Next one is on the FBO :D

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Just now, Stephen said:

 

If leaving the plane, I carry my last damaged truss in the baggage compartment and tell the line guys that an A&P / IA did this damage and he knew how to tow too...

I put my hand tow bar and show them how narrow the turn radius is

I then show them my new undamaged truss on the nose and video it that part of the session and tell them that the fogoing is why it must be hand towed only and have a sign put on the plane to that effect. Not wanting to pay for a 3rd truss in 3 years. Next one is on the FBO :D

FWIW the Lektro carts wont overstress the nose wheel either. The bucket allows some wheel turning, its not like a tow bar.

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1 hour ago, bluehighwayflyer said:

Really?  I have been playing this game since 1982 and have never heard of that.  Not ever.  Can you further elaborate?

Jim

I seem to recall someone on MS posting that. They may have been using a longer tow bar than standard. If the search worked better, I would look for the post ;) But the real point is that it's a crummy design. 

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On 10/11/2019 at 9:36 AM, mike_elliott said:
Robert, unfortunately, flying it with zero concern will not fix it, nor make it airworthy again. Mooney's engineering dept has determined, be it right or wrong, that 1/32" dent or greater, the part is unairworthy. As much as the internet of engineers here would like it to be ok, it is not ok to fly an unairworthy plane. 
This isnt my opinion, this is Mooney's. Just being the messenger to prevent you from drinking the koolaid of bad advice. Consider getting it fixed, your plane will be sellable, flyable and insurable again.

@mike_elliott just hit on something important. Is your aircraft even covered AT ALL by your insurance carrier if you have knowingly disregarded an issue that makes it unairworthy??? I believe the answer is "no".

Sent from my Pixel 3 XL using Tapatalk
 

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