RAPID software 1

[Ruag]

Hi,
Does anybody have experience with RAPID?
Ref.

http://airportaircraftsafetyrd.tc.faa.gov/Programs/AgingAircraft/Commuter/rapid/

Does the model take into account fastener bearing? How?

Does the model take into account crack proximity to the next hole? How?

Thanks,
Ruag

 

[CoffinsCorner]

Do you want the manual?

 

[SAITAETGrad]

The FAA regected the RAPID effort as being too "cookbook" in the end and no longer endorse it. If you show up with not much more analysis than your inputs and outputs from RAPID, the FAA probably won't take you seriously. That said, there is a lot of methodology spelled out in the manual.

 

[Sparweb]

I think they still do endorse AFGROW. (Not that I've used it in a long time either)

You can also find a good discussion of doublers, crack propagation, and rivet stresses (including bearing) in Swift's famous paper on damage tolerance in aircraft repairs. If you don't have a copy or never heard of it, I'll dig up an old copy. (public domain article published for FAA and general use).



Steven Fahey, CET

 

[Ruag]

Apparently FAA is still endorsing RAPID providing the download and the user support @:

http://airportaircraftsafetyrd.tc.faa.gov/Programs/AgingAircraft/Commuter/rapid/

Unfortunately I get no reply from the contact person addressed in the web page.

Then:
@ CoffinsCorner: if you think that the manual you have is different from these ones: Analysis Methods Document & User's Manual, then yes please.

@ Sparweb: Are you referring to "Repairs to Damage Tolerant Aircraft" paper by T. Swift? I have it thanks.

Having leafed through the rapid documentation I understood that the fastener bearing and the by-pass stresses are internally calculated by RAPID using the FEM routine.
Ref. RAPID Analysis Methods Document – Appendix A.
By the way bearing stresses for the rivet hole locations are found using the far-field stresses times the nominal first fastener load. Bearing stress ratio is calculated in RAPID for input into the crack growth program.
Since I haven't found any explicit example, can anyone confirm it?

 

[SAITAETGrad]

That I believe is RAPIDC which is the commuter version of the program.

In any case, you are not wrong per say. You CAN find your solution using RAPID/RAPIDC. But, if you just plug in the numbers you are asked for by the software and present the output as your substanatiation, they will be very skeptical about your capability and the quality of the analysis.

Do this: Duplicate your analysis using RAPID, AFGROW, and a spreadsheet. If your results are in a agreement, you are well on your way.

The point is that a complete Fatigue & DT analysis requires expert analysis. The FAA will expect you to prove you have "the goods". This runs contrary to their earlier attempt to make DTE easier and more accessible to non-experts using the RAPID software. They weren't pleased with the quality of analysis they were getting back and therefore canned program development.

As Steven alluded, most people use AFGrow/Nasgro and/or spreadsheets with procedures and loads development from some well known papers.

 

[der8110]

Ruag... Sie sind aus Oberpfaffenhofen?

Thank you for the post, nice to see the link is working again. To answer your questions, the bearing load is determined by an FEM as you noted, then incorporated into the compounded stress intensity factor solution as described in Appendix B of the RAPID Analysis Methods Document or Appendix E of the RAPIDC Analysis Methods Document. Testing shows there is no hole-to-hole phenomenon like edge proximity effects for cracks growing towards a free edge, though one would imagine there should be something observable like that.

The FAA does not "endorse" any computer program, even with all the posturing the individuals are smart enough to avoid such appearances. A bit of history: RAPID was developed in anticipation of the Aging Aircraft Rule which required a large number of repairs to be analyzed for Damage Tolerance in a short period of time. So the model was like SFAR 36 operations - have a technician plug and chug, then have the DT expert review the results and make the recommendations. This is why the passwords and report title pages are set up the way they are. In the end, RAPID didn't provide much advantage over SRM repairs and besides the OEM's started generating usable data anyway. Then, the Small Airplane Directorate provided funding and the Tech Center managed the contract to develop RAPIDC for commuters. Things just ran their course, airlines disposed of their 402's and Merlin/Metros, so the funding stopped (around 2005). Of course you won't get feedback; Dr. Shiao left the FAA this past summer.

RAPIDC (and RAPID) are somewhat limited in the problems they can solve, namely repairs and connector hole doublers in cylindrical pressurized fuselages. Symmetry is another constraint. But the time savings are enormous, and the majority of day-to-day mods can be done. Can't do wings and tails, and flat bulkheads are nigh impossible. AFGROW and NASGRO can do all those and more; of course(!), you are on your own to develop loads, stresses, fastener pattern loads, and model SIF's. If anything, I'd be more worried about the variability and poor assumptions rather than a program (which does all the hard preliminary stuff) being "too canned." But in the end, the output of all these programs require interpretation and implementation (inspection program development).

 

[SAITAETGrad]

der8110, great post. I certainly agree with your last statement with regards to variability and poor assumptions over the issue of canned results. I was just passing along what I had heard directly from the FAA. You could probably say that if you developed your own procedures and developed a Rapid style interface for your more standard problems, the FAA would be very pleased. Likewise, if you duplicated your RAPID results a few times using hand analysis and other software tools. The differentiator seems to be that they want assurance on the capability of the end user...ie they don't want the validity of the model comprimised due to lack of understanding.

 

[Ruag]

@ der8110: Yes, you’re right; OP is my headquarter. How do you know that?

Thanks for your clarification.
The only thing I would add is that EASA accepts RAPID as tool for DT justification; in my case used for antenna installation.

I tried many times to contact Dr. Shiao without success, but fortunately I found two others contacts:
Mr. John Bakuckas and Mr. Felix Abali both working for FAA.

Anyway, they didn't put too much effort in replying me.

 

[der8110]

Herr Ruag - from the Do328 days. Yes, EASA accepts RAPID/RAPIDC, it took about 3 days of convincing.

Dr. Bakuckas was not involved that much with the computer programs. There's no funding so they are going to spend their time on current projects.


Mr. Grad - thanks for passing along what you heard. Rumor control is something we can do for each other. DT methodology is a very specialized field, but in the bigger picture, FAA differences are going to be attracting more attention:

http://www.gao.gov/products/GAO-11-14

 

[Ruag]

Hi,
back to RAPID again
Does anybody know the origin of the Kc=153 ksi sqr(in) tabulated in the material database of 2024-T3?
It should have something to do with the apparent fracture toughness. I can't find it explained in the letterature.
Thanks!