Fin Rib Kits

[jrichards]

Hi All,

I am pleased, and relieved, to announce successful fabrication of first article new parts for Service Bulletins 112-56B and 114-12B. As you may know, few aircraft ever got any kit, let alone the final factory kit, because it came along so late in the Rockwell years. Many of the aircraft that got earlier Rockwell renditions of this repair during production have failed again.

The 114B/TC models use a different design for the stub fin rib/doubler, without any service life problems to my knowledge. Our new kit converts the stub fin of any 112/A/B/TC/TCA or 114/A to the proven 114B/TC design.

The stub fin holds the entire empennage, onto your airplane. All pitch and yaw loads are transmitted to the fuselage through this critical section. My personal tolerance for any cracks in this structure is zero. What's yours?

This is our most complex part undertaking to date:

1. SolidWorks design capture and tool design (as usual).
2. Five main parts: (rib, doubler, and three spacer strips).
3. CNC routing of rib, doubler, and strips.
4. 20-ton press (full custom tooling) of rib and doubler flanges.
5. 10-ton press of rib and doubler strengthening beads (custom tooling)
6. Fluting of rib and doubler (custom tooling).
7. Dimpling of "lightening" holes (three custom die sets).
8. All the usual treat, prep, and finish.

I attached our drawing of the flange dies (just one part of the tooling) so you can get a feel for what is entailed in an undertaking like this.

We are doing the first installation now, see pic, to be immediately followed by a second.

Next week, I will post a special offering for all of you who need kits now, or want to put one on the shelf. Your response will help me decide how big a batch we can run and how low we can price.

I am hoping for your enthusiastic support of this endeavor as the development cost and time have not been trivial.

The offering is a step-by-step DER Repair Report, accompanied by a Form 8110-3 airworthiness approval, with the parts fabricated and supplied by Aerodyme as an included subcontract service to the mechanic you choose to do the installation.

We appreciate, and need, your support as always,

Jim and Martine

 

[FS]

Re: Fin Rib Kits

The 114B/TC models use a different design for the stub fin rib/doubler, without any service life problems to my knowledge. Our new kit converts the stub fin of any 112/A/B/TC/TCA or 114/A to the proven 114B/TC design.

Jim,

Could you expand on the differences between the SB114-12B kit and the variant used on the 114B/TC? For those of us that do have the -12B (or corresponding SB112-56B on the 112s) kit installed, what improvement(s) does the 114B/TC rib bring to the table? Have you come across any airplanes with the -12B or -56B kit installed that redeveloped cracks?

Also -- for those that aren't aware -- the SB114-12B and SB112-56B kits introduced the "double rivet line" to the area just below the horizontal stabilizer. There were two earlier SB's released to try and fix the problem with cracking in that rib, neither of which quite did the trick.

Another side comment: When I bought my 114, the owners had the SB114-12B kit sitting in the hangar. The invoice showed it was free of charge from Commander (early '90s), but they never bothered to have their A&P install the kit. Even though the earlier SB had been completed and didn't show any signs of cracking, one of my first major maintenance events included having the -12B modification installed. Just for peace of mind.

 

[DKrueger]

Re: Fin Rib Kits

Jim,

I wrote you earlier with a similar question to Frank. My logs show two factory annuals where the fin rib was addressed, but I have NO second row of rivets. I am not sure what this means. I was planning on having he issue addressed during my annual in November.

Is this an area that requires annual inspection like the elevator spar? While using the original method of inspection for the elevator would this area be inspected for cracks as well?

I think I speak for everyone when I say, NO one wants cracks in a critical area.

 

[gmores]

Re: Fin Rib Kits

Very nice Jim. This should be a great help to all those who never got that final factory kit.

 

[janderson]

Re: Fin Rib Kits

great forward progress for the fleet, Jim!!

Judi

 

[jrichards]

Re: Fin Rib Kits

Hi Frank,

Here's my draft of a fin rib chronology.

Jim

 

[cactusair]

Re: Fin Rib Kits

Great Job Jim! I would be interested in this Kit. I would like to know the cost of the final kit!

 

[FS]

Re: Fin Rib Kits

Here's my draft of a fin rib chronology.

Very interesting. Thanks for putting that together. I should have guessed that the 114B/115 series didn't use the cut-off rib plus doubler, but I never thought to even check on how CAC addressed the problem.

 

[jrichards]

Re: Fin Rib Kits

Hi All,

Since posting the chronology earlier today, Don and I have found more records and made some corrections. I'll post an updated chronology next week.

Meanwhile, can we hear from those of you who have the half-way second row of rivets by a show of hands? I have seen this half-row on several airplanes so we assume it was a procedural repair. The 56A / 12A bulletin (I now have a copy) calls only for the "horseshoe" doubler, and 56B / 12B calls for a full doubler, so we are scratching our heads on the in-between case.

Jim

 

[N4843W]

Re: Fin Rib Kits

Jim,this may have been done here before, but a picture or two of the different rib configurations and what they indicate ... or are at least "supposed" to indicate, would be very helpful. With those, people could print and take them to the plane, or open on the laptop and check. Then they can say yes or no with confidence ... wait a minute ... anyone want to bet that we get some pictures back of rivet configurations that don't match anything?

 

[DKrueger]

Re: Fin Rib Kits

I agree with Scott, my logs show that during a factory annual a kit was installed, but I don't see a second row of rivets on the tail. So now I am even more confused.

Plus, we throw around a lot of words that can add doubt or fear in an owner's mind, but nothing is ever quantified. What is the number of repaired airplanes reinspected that have developed cracks? Is it one or is it twenty? I appreciate the passion and effort made, but it's a kit like any of the others correct? It's available if needed after inspection right?

 

[cactusair]

Re: Fin Rib Kits

Jim I have the "horseshoe" doubler installed or 56A mod.

 

[Pete]

Re: Fin Rib Kits

Jim, thanks for the info and update. Really helps if any of us have a problem/crack.

 

[Frank]

Re: Fin Rib Kits

Jim thanks for the summary and the info. Mine has the double row of rivets - thank goodness.

 

[milojevicp]

Re: Fin Rib Kits

Dear Jim,

You are indeed providing a predictable remedy to the legacy issues associated with our wonderful aircraft. I will order one. I have the horseshoe type installation and want a piece of mind in case a future inspection identifies a crack.

Kindest personal regards,

Pete

 

[atjudge]

Re: Fin Rib Kits

I had the horseshoe and it didn't last. Factory used the last rib they had to fix it three years ago. Now have the double rivit row. I'm of the opinion that if you plan on keeping your Commander for a long time, get this fix. It's your best bet for a permanent fix

 

[DKrueger]

Re: Fin Rib Kits

Does anyone know what the factory kit would have been in 1991? They installed a "kit" according to the log, but I don't see any second row of rivets.

Jim, I would be in for the kit as well. It would be nice when words like "several", "many" or "relieved" are used that numbers be given. I realize you run a business which has served the Commander community well for years, but fear is no way to drive sales. You only create skeptics when broad general statement aren't supported by the facts or at least none are offered.

 

[gmores]

Re: Fin Rib Kits

Daniel - As the COG President for the last 10 years I don't know if I've ever seen fleet numbers on this issue, but I can say that based upon the historical experience and evidence of the old CAC changing the design to address the problem, you will have a high likelihood (I'll venture to say 70%+ over the life of the aircraft) of developing cracks if you don't have that last SB applied (double row of rivets).

I'm pretty sure no fear was intended here. We've talked about this issue quite a bit over the years so this is all pretty factual.

So I'd say Allen's comment is right on. If you haven't had that latter SB done and you plan on keeping your Commander, this would defintely be worth looking into.

 

[DKrueger]

Re: Fin Rib Kits

Glenn,
As I said in the prior post, I plan on buying the kit because I do plan on keeping this wonderful airplane. As a relatively new owner and user of the site I'd have no way of knowing, so I apologize if I offended anyone. I am a safety first owner and make that my top priority. My 114 goes in for its annual the last week of November and this kit will be a priority.

Is anyone aware what the kit included that the factor was installing in 1991 ?

 

[FS]

Re: Fin Rib Kits

Does anyone know what the factory kit would have been in 1991? They installed a "kit" according to the log, but I don't see any second row of rivets.

Well, presumably it would have been either the (A) kit or the (B) kit. It's unlikely they were still doing the original kit (before A). If you're not seeing a full second row of rivets then you don't have the (B) kit. Based on Jim's post, if you have the (A) kit then you should see at least a partial second row (less than half way across the vertical stabilizer).

[OOops. Sorry. I just reread Jim's chronology and he says the (B) kit was released in May 1992. So, in 1991 they could not have been installing that kit. Therefore, if the fin rib kit was installed it would have likely been the (A) kit.]

If you're not seeing any evidence of a second row of rivets then either the factory didn't install this particular kit at all, or you're looking at the wrong rivets.

I can't imagine the factory not explicity stating in the log books that SB114-12B (or SB112-56B) was completed. But ya never know.

The other possibility is that the kit which was installed in '91 was either the forward fin attachment kit (for AD 88-05-06) or the wing spar kit (for AD 90-04-07). Those two, though, would definitely be much more explicitly described in the logs in order to demonstrate AD compliance.