Structural Q's:

[hoggsnortrupert]

I posted same in the Engineering/Tech's forum, no answers, so thought to place same here?

Q: If a A/c ( designed for air transport ) wing has a operational G limitation of eg: +3.5g / -1.2g, What percentage above this does it have to comply to , or what percentage is the norm between the Top of the operational envelope and failure? and just to add to this, EG B 744, how is the G limitation arrived at in the "blending" of margins into both the wing and the fuse?

Q: What FAR, or BCAR,or JAR regulations pertain to the above?

With OLDER A/c, what studies have been done, and what is known about the aging of OLD ALLOYS, IE: the grain structure and crystalization there of?
and is the G limitations of older A/c reviewed by authorities?

I was told by a METALLURGY chemist that such things exist, ( I have never heard of such):suspect:

When flying I hade to do mandatory Human Factors re-currency under JAR, is such mandatory for engineering?

Just and observation: I saw the A-380 landing on the TV awhile ago, at the time I thought the track of the U/c not in proportion with the large lateral arm (IE span).
On the down under forums I read that the machine had issues with the U/c cracking? just an observation, and wonder if anyone else agree's /disagrees.

Info appreciated::ok:

Chr's
H/Snort.

[Genghis the Engineer]

I posted same in the Engineering/Tech's forum, no answers, so thought to place same here?
Q: If a A/c ( designed for air transport ) wing has a operational G limitation of eg: +3.5g / -1.2g, What percentage above this does it have to comply to , or what percentage is the norm between the Top of the operational envelope and failure? and just to add to this, EG B 744, how is the G limitation arrived at in the "blending" of margins into both the wing and the fuse?

The values that you describe are called limit loads - the aircraft is expected to be able to take those loads indefinitely and at any time without any permanent deformation or control restriction. The actual load distribution is determined through a frighteningly complex aeroelastic (aerodynamic + structural) analysis - for Airbus I think that this is done at Filton, near Bristol.

There is a higher load, called the ultimate load (which is not the same as the failure load). The margin between limit and ultimate is called the safety factor. For a modern high-value metal transport aeroplane such as the A380 the SF may be 1.4, although for most other aeroplanes it is 1.5. The slightly smaller value is justified by a very high degree of analysis and testing. For composite structures the SF may increase substantially, and values as high as 2.25 are not uncommon, although it could (with enough justification) be as low as 1.82.

The structure has to be able to take the ultimate load for at-least 3 seconds without catastrophic failure.

The actual failure load, divided by the ultimate load must be at-least 1.0; paranoid airworthiness engineers want it as big as possible, whilst company accountants want it to be as near to 1.0 as possible so as to maximise payload. This value is called the reserve factor = Rf<1.0=no flight testing!



Q: What FAR, or BCAR,or JAR regulations pertain to the above?

Subpart C (particularly paragraphs 301-470 of any of the following standards:

Large aeroplanes: FAR-25, CS.25 or JAR-25
Medium and Small Aeroplanes: FAR-23, CS.23
Non-aerobatic light aeroplanes: CS.VLA or JAR-VLA
Motorgliders: CS.22 or JAR-22
Microlights: BCAR Section S

All of these you can find online: FARs from the FAA's website, CS from EASA, JAR from JAA, and BCAR from CAA.

With OLDER A/c, what studies have been done, and what is known about the aging of OLD ALLOYS, IE: the grain structure and crystalization there of?

There was a lot of interest in this in the 1980s and 1990s. The best starting point if you are researching this would be the proceedings of a 1-day RAeS Conference on 24 April 1990 called "Continued Structural Airworthiness - keeping old aircraft flying". In particular there are two papers in there - one from BA on the ageing of their early 747s, and one from Britannia on the ageing of their then 737 fleet.

and is the G limitations of older A/c reviewed by authorities?

Generally only if there's been a problem, or if the airworthiness status of an aircraft is changing (e.g. from military to civil PtF / experimental).

I was told by a METALLURGY chemist that such things exist, ( I have never heard of such):suspect:

They do, although good old fashioned metal fatigue is usually much more of an problem, or subjects, related to metallic structural modification, such as exfoliation corrosion - this was a big issue for example when some of the old BOAC super VC-10s were returned to service as RAF aircraft, ditto the RAAF F-111 fleet in the 1980s & 1990s.


When flying I hade to do mandatory Human Factors re-currency under JAR, is such mandatory for engineering?

Depends upon who you are. HF training isn't common in engineering, although it happens (I had a boss once who sent me on a course called "how to deal with difficult people with tact and discretion", maybe that's how I ended up a PPrune moderator?). In general continuous training on latest techniques and equipment occurs throughout the engineering profession - ECUK, which is the UK governing organisation for the engineering profession, recommends that we should all do at-least 1 weeks training per year in our specialist fields. But, engineering is much more varied than flying, so it's not prescribed in the same way that's appropriate for most pilots; what's necessary has to be decided locally and is probably different from year to year.



Just and observation: I saw the A-380 landing on the TV awhile ago, at the time I thought the track of the U/c not in proportion with the large lateral arm (IE span).
On the down under forums I read that the machine had issues with the U/c cracking? just an observation, and wonder if anyone else agree's /disagrees.
Info appreciated::ok:
Chr's
H/Snort.

I've no inside knowledge, but I'd be amazed if an aircraft that large and complex, hasn't got issues with cracking going on somewhere. That's what the structural integrity and monitoring programme is all about - identifying and heading those issues off before they ever become life threatening.

But, don't underestimate the tens (probably hundreds or thousands) of thousands of man-hours that will have been spent analysing that structure before it ever flew, plus the structural test rig in Dresden which has to have shown the equivalent of a years airline use before the A380 goes into service, and 2½ service lives before the A380 gets full certification.

G

[hoggsnortrupert]

Genghis::ok:
Matey thanks a big one, very informative, I wish to sus some stuff out, I need to get my facts:
I will PM you in future with some info, and let you tell me, by PM if you think my logic is correct.
Then I will look at posting it.:) :)
Chr's
H/Snort:

[engineer(retard)]

There is a different slant on HF in engineering, inasmuch there is designing for human use, for example cockpits and controls.

There is a Def-Stan for HF aspects either 00-25 or 00-35 (they have not got senility ratings in there yet) and bits appearing in 00-970 (particularly the rotary wing volume). From memory most of it deals with anthropoligical issues 10th to 90th percentile limb lengths but therer are elements of contrast and brilliance for diplays and does provide an eye model.

In terms of process, HF tends to be treated as a branch of basket weaving though.

regards

retard

[Nipper2]

Genghis is right to say that the CAA do not downgrade g limits but the PFA often do. My aircraft was originally designed to operate at a design limit of +6 -3 g. For no real reason the current permit only allows +4 -2 g at the original weights. I understand this is quite common with Permit aircraft.

[Milt]

Structural Qs

Did a double take on that one. 'q' is the aeronautical symbol for "half rho V squared". This has relevance to IAS so that maximum structural q would likely mean max IAS. Exceeding this runs the risk of structual failure resulting from local overpressures.

Genghis
The F-111 structural problems were/are in the high strength D6AC steel heavily loaded elements. Cracking can readily emanate from any 'crack starter' with the crack growing as a result of 'stress corrosion cracking'. Hydrogen ions migrate to the tip of the crack when under load to cause corrosion which then is the growth mechanism for the crack.
This type of cracking is not uncommon in the steel oleos and other steel parts of many undercarriages which obviously are under continual load when not airborne.

[Genghis the Engineer]

Genghis is right to say that the CAA do not downgrade g limits but the PFA often do. My aircraft was originally designed to operate at a design limit of +6 -3 g. For no real reason the current permit only allows +4 -2 g at the original weights. I understand this is quite common with Permit aircraft.

Or at-least no reason that's apparent to you.

It's quite common that the UK regulators (CAA, PFA or BMAA) will decide that the level of proof provided in support of a foreign aeroplane aren't convincing - leading to redesign, different limits or in some cases just no approval at-all.

Opinions differ as to whether this is reasonable, or the UK should be much more willing to accept foreign aeroplanes on the basis of service experience, but I can't see the situation changing in the foreseeable, save possibly for the proposed 115kg category if it happens.

G