AC43.13-1B Table 4-9,4-10 (# req'd rivets) inconsistancies

[RCCDave]

I am teaching aviation maintence at a community college. AC43.13-1B in some ways is a primary reference tool. Tables 4-9 and 4-10 are supposed to let technicians know how many rivets to use for a given material type and thickness. Problem is, both tables list some of the same materials (2024-T3 for example.) How can this be? AC43.13-1A is better, but it shows 2024-T36 on both figures (2.28 & 2.29.)CAM 18 App I Table I & II were computed with different rivet alloy and is of no help (and no longer relevant?) It seems to me when the tables were adopted for 43.13-1A and 1B typos were not caught, and the potential for technicians to have been using incorrect data for the last 35-40 years was established. I am willing to try to calculate the correct alloy that should be included with each table, but as a non-engineer, the results would be suspect at best. I am going to bring this matter up with the local Fisdo, but would like to be able to suggest a solution. Can someone send me in the right direction?

 

[rb1957]

let's see if will taylor has an answer ... i can't see a difference between waht the two tables are describing, and they do have different results in them. personnally, i don't know how you can put 12 5/32 rivets in 1" width of a single lap joint, or even 3 for that matter !

but then i don't like AC43.13 (at least the structures bits).

 

[Sparweb]

I find these tables of limited value, too. Sometimes working on antiquated helicopters I pull it out, because I can't be bothered to do a "real" stress analysis. I ignore Table 4-9 because I usually am not dealing with pure 2024-T3 - most skin is Alclad. The process of cladding aluminum reduces its strength.

Worse than that is the terminology in the fine print: "intermediate frames" isn't very specific either.

This ambiguity between the two tables has not been cleared after several revisions to AC43-13 over the years.

Make sure to emphasize to your students that many aircraft they will work on have specific repair instructions in their Maintenance Manuals; some have Structural Repair Manuals that must be followed instead of AC 43-13.

A secret of mine is that you can often get away with using the SRM for the plane's "big brother" when one doesn't exist for the specific model you're repairing. (Eg. you can try using the Beech 1900 SRM for repairs on a King Air, though you shouldn't expect it to be good for anything more than guidance).

RB: It means you need at least 8 rows at 5/8" pitch. The table is based on the "equivalent strength" model, ignoring many other factors, like the actual loading. This is why we sometimes come across "field repairs" that have been riveted all to hell.


Steven Fahey, CET

 

[rb1957]

yeah, i mislead myself with the word "single" lap ...
and like you say "equivalent strength" has got to be the worst approach to a repair ... to design the fasteners to carry the ultimate strength of the doubler, geez.

somebody (who had the maintenance contract) did a repair for a customer i worked with who asked me (afterwards) to look at it. the worst thing i've seen ... used equivalent strength on the lower surface of a wing ... way, way, way too many rivets. the worst is that they could have gotten the correct stresses from me (via the customer).

to RCCDave, your students should restrict the "equivalent strength" approach to compression surfaces (and then they should be worrying about buckling) and maybe unpressurised fuselages. lower wing skins and pressurised fuselages have design stresses much lower than ftu. if they have to design a repair in the absence of technical data ... don't. AC43-13 is IMHO inconsistent with damage tolerant repairs and frankly i think it should be reworked toremove these design elements; there seems to be lots of usefull stuff about the practicalities of maintaining structures.

 

[WKTaylor]

RCCDave.. and all... FYI/Gee-Whiz...

Following link is to a training film ["cartoon"] developed by Disney studios to teach fundamentals of flush riveting. some VERY indepth aspects are presented... all based on the humble 1/8"D rivet.

http://www.youtube.com/watch?v=5DVPG8go4Jk

Regards, Wil Taylor

 

[sigmatau]

Single lap joint doesn't mean a single row of rivets, it means one lap.