Allowable, Scratches, Nicks & Dents 1

[edbgtr]

I need to specify the allowable damage for a new airframe. These are usually in terms of scratches, nicks and dents in terms of length (or diameter), depth of the damage type.
I'd like some advice on how one goes about setting the parameters for this kind of damage in the Structural Repair Manual.
I look forward to your input.
Thank you in advance.

 

[fwz]

according to FAA you can find manufactuer's maintenance manual,from the referene in check & repair sectin you can settle the problem.

 

[baja]

You can start to collect similar allowable damage from repar manual from other similar aircraft, similar components/ material or locations. To justify wether your allowable damage is safe enough, one can perform the stress and fatigue & damage tolerance analysis and test. If I'm in your position then I would propose a test plan to introduced different type of damages with different size into full scale fatigue test article and wait for the results.I believe this full scale fatigue test must be performed for new airframe, you can take this benefit.

 

[brin]

It would depend on whether your acft will be damage tolerant (probably) or not. Check with your regulatory body and get the exact requirement for your SRM.

 

[glenn11897]

For allowable damage, you would usually be concerned with areas where likely damage would occur. i.e. traffic areas for the maintenance personnel (scratching the panels or frames). In my experience we have two types of analysis, one is for flyby and the other is for allowable damage.

Allowable damage is where when a certain scratch is blended and calculated for the new net cross section stress and can still withhold its strength (including fatigue) up to the required life of the aircraft.

Fly-by would be when no possibility of immediate repair can be done. Therefore a much worst damage compared to allowable damage. But for fly-by, the a/c need not be checked for fatigue life since the a/c cannot be flown again without proper repair. Therefore cannot be used for preexisting (fly-by) damage.

Try FAR 25. It has some requirements for structural repairs.

 

[glenn11897]

sorry, didnt realize this is an outdated question...

 

[Highness]

I'm curious to know. Is this for a new aircraft?

 

[edbgtr]

Hello All
I'm amazed that this topic is still receiving attention after all this time. In 2001 I was working in a foreign country and had to establish some "unique" criteria for that particular, new airframe. These criteria were for inclusion in the SRM. I had to establish such criteria without launching into a huge DT analysis program similar to the one US reference SRM I had. The crux of the issue in most of these SRMs is: just how severe can such "minor" damage be and merely be "dressed out" without reinforcement and/or repair action being taken.
So, Highness, yes it was for a new all-metal aircraft in the military trainer class. I had seen how other high performance aircraft manufacturers had determined their criteria, which seemed like an overkill for the program I was working on.
I was hoping to receive some advice from someone who had done such work on airframes before the problem was "beaten to death" using massive amounts of FE and DT analyis on every region of the airframe. Believe it or not there was life before computerized structural analysis came along, and most companies provided very good guidelines for their airframes.
Regards,
Ed.

 

[Highness]

Hi Ed,

Was just interested as I browsed this interesting site with 'loads' of aircraft structural data. I'm an aircraft structural engineer at thé major european airline. Before I worked with Boeing in Seattle and Fokker in Amsterdam on ..... SRM's as a structural repair engineer. Hence my interest. I've worked on allowable damage and repair sections of Fokker 28/70/100 SRM's and Boeing 737NG SRM's so I'm familiar with specifying (and designing) allowable damage and repair data for new as well as in-service aircraft, working closely together with the manufacturer's engineering departments and representatives of the authorities for approval of these data.
Regards,
Pim aka Highness

Aircraft Structures Engineer

 

[plasgears]

I worked on 1st stg Minuteman missile cases and Pershing cases, and one of my duties was to provide analytical justification to accept dents, blended weld repair, blended gouges, etc. It all goes back to knowing the loads and applying it to the defect at hand, very much like the design process. The customer wanted perfection, but that was sometimes an elusive goal.

 

[airmail]

Hi all!

I am working in calculations of allowable damages in a curved panel (fuselage skin) for SRM. The problem is that I don't know how evaluate the damage/hole in the post-buckling effect. Does anybody have an idea?

Thanks in advance