Plastic Planes vs Traditional Metal Aircraft.

[Ex FSO GRIFFO]

In a recent conversation re the modern 'Plastic Planes' vs the more traditional metal airframes, it was claimed that the 'Plastics' have no proven method of fixing for stresses caused by e.g.

- hitting a wing on the hangar door,
- or having something heavy dropped onto a wing,
- or, perhaps even a 'heavy landing' where damage may or may not be visible,
(You get the idea...)

whereas in a metal airframe, the damage is usually apparent and 'easily' fixable.

So, Can anyone offer an opinion, of just where do the stresses go if, for example, a wing is run into the hangar door?

Is the damage limited to that section of the wing?
Or is it transmitted through to the wing attachment points on the fuselage, and maybe rip out the wing joining points etc etc.?

The conversation started with 'corrosion issues' and then just morphed into the airframe life and repairs of the 'plastics' vs the 'metals', sort of thing.....

Are the newer compounds etc easily / economically fixed to fly again, or are they a 'throw away' item..??

I did try a search, but it didn't come up with an answer...so,.....

Cheers guys and gals....:ok:

[tail wheel]

There are a few CASA approved composite repairers in Australia who use CAR35 engineers to design and approve repair schemes on a case by case basis.

Most aircraft manufacturers that use composite structures have approved repair schemes available.

[Ultralights]

usually composite airframes are far more tolerant of damge than traditional metal frames, dropping a weight on a composite panel will puncture/crush and delaminate around the impact point, such damage will not cause much residual stresses elswhere as the damage relieves the stress as the fibres and resins are usually broken. wheras metal will stretch, and change its properties permenently not just at the damge point but elsewhere. composite panels have quite a bit of stress resitance to them and the panel will flex/stretch or whatever, but will most likely return to its original state with little or no damage.
a weak point of composits is they dont like water ingress or oil contamination, oil wont effect the undamaged panel, but if it is damaged, it can make repairs very difficult indeed, but water will freeze and expand, expanding the area of damage if it gets into a panel.
the main difficulty at the moment is NDT, to find delaminations or internal damage, but in my experience with composites in the RAAF,NAVY and now Army aiviation sector, is that the damage is hard to find because there is rarely and damage to be found that is not already visible by microcracking of the resin matrix.

[L0u0k0e]

I think when 'plastic' aircraft are all shiny and new, they are definitely better than traditional metal aircraft (lighter, stronger, fatigue & corrosion resistant, more complex shapes) but their main problem is, as Ultralights mentioned, the NDT. It's a lot harder and requires more specialized tools and training to firstly identify the damage and then to repair it. It will be interesting to see how well the composite airframes are doing 10-15 years down the track, after a bit of use and abuse.

[VH-XXX]

Damage to other unseen areas is a very good point around composites. I'm quite sure that over time, mechanics and repairers will get "burnt" over this (as in missing something), but that would have to be an issue with metal aircraft also.

I'm hoping for the day when more LAME's are trained to repair composites so as to bring down the cost of repairs. A mate had a 15cm round hole poked in the side of his carbon fibre aircraft and was charged $6,000 repair it!

[Tankengine]

Go out to any gliding club and you will see composite gliders, some well over 30 years old. Some of these have been rebuilt from wrecks, not much you can't fix with fibre-glass and carbon-fibre!:E
Some LAMEs [with no composite experience] sub contract out [and then sign for] repairs to [unlicenced] glider repairers who do great work!:ok:
[such is our stupid system]:rolleyes:

[Ultralights]

by far the biggest cost with composite repairs is the manpower factor, traditional metal repairs are pretty straight forward, remove fastners, make a doubler/doublers/hand form part, paint it, re-install.
as for composite panels, sand off paint, sand out damaged plies, make a mould in some structural cases. prepare surface (the most important part) with MEK or similar degreaser/solvents, prepair repair plies, lay up repair/ mould new part, then cure the whole lot,(24 hrs in most cases alone) then sand flush/finish, then paint, all this while in full PPE, suitable workspaces, ventilated areas, etc etc. complying with OHandS and toxic hazardous materials

[onetrack]

Despite the arguments in favour of, or against composites... the simple fact that so many Airbuses and other aircraft, containing composites, have been flying for many years... without any definitive figures being produced that composite use has led to an increase in accidents... is probably the best indicator that composites are perfectly satisfactory in practice.

The fact that they are "different" to metals, in their properties, is probably the key to the belief that they are less satisfactory.
It's more difficult to develop a mental picture of what happens in a composite under stress, whereas metal deformation is relatively easily understood (and seen).

The factor that is still a concern, is the flammability of composites. Yes, a metal aircraft burns, for sure... but a composite burns more quickly and more thoroughly.

[Orangputi]

I think a big challenge is the undetected delamination in a pressurised carbon fibre aircraft i.e. the 787. if you run into the side of the fuselage with a belt loader chances are there will no visible damage but an area of significant dleamination in the composite plies. inject this damaged area with water ingress, which will freeze at altitude and you have a time bomb.

Any word on how Boeing are going to handle a situation like this and subsequent in the field repairs (temporary repairs) what about repairs of a permanent nature that would satisfy firstly Boeing, and the FAA and the leasing companies when the aircraft is returned from lease?

any thoughts

[djpil]

chances are there will no visible damage but an area of significant dleamination in I asked that question of 787 design engineers earlier in the year - answer was that it was designed (and apparently substantiated by test) such that if there was no visible damage then sufficient strength remains to take the design loads. Remains to be seen in service I guess.

[Arnold E]

. A mate had a 15cm round hole poked in the side of his carbon fibre aircraft and was charged $6,000 repair it!

CHEAP......

[Ultralights]

dont forget, a delaminating failure doesnt mean the part can no longer carry its full flight load. an area of delimitation is no different to an area on sheetmetal components joined together, the area between the fasteners can be considered as delamination.. dont forget the basic principles behind composites, fibres take tension loads, resin matrix carries the compression load, so a small delamination in a part under tension will not lower its load bearing capacity unless the fibres themselves are broken, Black hawk rotor blades are still serviceable with a surprisingly large size delamination area allowance before requiring repair. so a secion of composite fusealage, would carry a majority of its loads under tension from pressurisation, and shear from flight loads from aerodynamic forces. so a sizeable delam will not reduce its load carrying capabilities significantly, unless of course the resin matrix was cracked and allowed ingress of water.. Quite a few resin systems are designed to be quite flexable when cured. just look at the Karuga variable camber LE slats on the 747! (the white ones) they are 6 ply thick fibreglass panels, nothing more, the shape when deployed is created by the frame behind that bends the panel into its curve when deployed. when retracted, they lie flat. even the classic 747s have them. ahh the joy of a fatigue free component..

[Arnold E]

dont forget, a delaminating failure doesnt mean the part can no longer carry its full flight load.
Hmmm, quite a long bow there me thinks.:cool:

[VH-XXX]

Add the word "nesccesarily" into that sentence Arnold.

[airsupport]

This debate/discussion has been going on for a long time, even here on other parts of PPRuNe (quite heated at times), especially after the sad loss of an American Airlines Airbus A300-600 out of New York.

Personally I don't trust the plastic planes, especially re damage and when water is trapped in them as in the A300.

Give me a good old metal aircraft every time.

[Ejector]

Let me guess, you are a devote brain washed extreme Christian cult member resembling anything against evolution and advances in technology, with "traditional" Metal Aircraft, I think you should be referring to wood and rag as a better comparison in this case..... :ok:

[Frank Arouet]

A traditional aircraft is made of wood and covered with fabric. It has a tailwheel and a control stick. The thrust exceeds drag and lift exceeds gravity. The engine power is optional. Blind flying gadgetry consists of a slip and skid instrument, an altimeter, compass and a functioning timepiece.

A "tin" aeroplane is best described as something resembling a Lockheed Constellation or Beechcraft 18.

Composite aeroplanes are all experimental.

A plastic aeroplane is called an Airfix.

[Ex FSO GRIFFO]

Hi Frank, and Mr E......

I actually own a 'REAL' aeroplane with all of the above 'stuff' that you both mention, but I'm still curious as to the answers to the original question......:)

I'm further informed today, that some insurance companies don't like 'the plastics'......

But then I am encouraged by the gliding fraternity's news via Mr 'Tankengine', and they must have experienced this before....??

and, nah...I'm not looking to buy one...just curious is all..!!

Cheers:ok:

[Clearedtoreenter]

If you want a real bargain buy a Cirrus with damage history in the States. Quite a few to choose from. The market seems to avoid them like the plague for some reason...

[Ejector]

OK, In all fairness th O does bring up some good points and I don't really offer answers !!!!! More playing on words he chose. :ok:

[clunckdriver]

This whole thread got of to a false start, Composites ARE NOT PLASTICS, they are as they say COMPOSITES, just like your chompers in your mouth, {but cheaper to maintain} Untill we sold our companies my wife and I operated over twenty "glass" aircraft and are both trained to repair them. Its true there is a shortage of qualified repair folks but the situation is improving. Dont ever call a composite aircraft plastic around Burt Rutan!

[Ex FSO GRIFFO]

A 'generic' term, if you like Mr 'C',

As distinct from 'wood and wire', or 'tin',.....for those amongst us who wish to know such things, it just refers colloquially to 'all things of composite, carbon fibre, glass', etc etc.:uhoh:

The water ingress - freezing to ice - expanding - problem seems to be acknowledged.

The problems of repairing 'impact' problems are not so well understood - by moi anyway - but then, that's not hard...... ;)

No emotions please - just the facts.....colloquially if you like....:D:D

Cheers:ok:

[airsupport]

As I said before I am not a fan of these composite structures, just something from experience with them.

This is what happened to an Airbus A310 one night at JFK when I was there, NOT the Airbus I was looking after thankfully.

http://i1095.photobucket.com/albums/i474/airsupport/a310fin.jpg

It was grounded for some 7-8 months while people from Airbus fitted a complete new tail, unable to repair.

On that same tour of duty we operated an Airbus A300-600, same type as the American Airlines one that lost its tail, operating obviously also out of JFK and over very similar routes.

Every time we did an A check (or higher) at JFK we spent all night, and I mean all night, among other jobs draining water that had been trapped in the tail.

To this day I still think that it MAY have been part of the reason that the American A300 lost its tail out of JFK, however on a previous post o PPRuNe some years ago most of the Pilots blamed the Pilots.

[Ultralights]

but what caused that damage? composite panels just don't disintegrate bythemselves, even if it was water damage, then thats a maintenance failure, impact damage on composite panels is usually inspected using tap tests to determine any delaminations, and a water tester to check for water contamination of the damage. (well at QF anyway when we still has jobs there)
judging by the pucture, it look like it has been hit by something, and possibly gone undetected for quite some time if that is a result of water/ice damage.. but if its damaged to a point to break the resin and fibres, then there should have also been evidence by a lot of paint damage/scuffing as well.

[airsupport]

Maybe I didn't explain it very well, I thought I did.

The photo is of an Air Jamaica A310 that was damaged by contacting a hangar roof at JFK while under tow.

The trapped water to which I referred was in our A300-600 operating in and out of and serviced at JFK.

[Ultralights]

Hangar damage would have been just as bad with a metal aircraft, but dont forget, if it was a 767/747/ or most other Boeing products, the damage would have been the same, as their construction is similar with the exception that boeing use Metal Spar and attach points. all panels and rudder are still composite.

as for the water trapped, where was the water being drained from? behind the panels? or were holes drilled into the panels themselves to release water?
if its behind the panes, then some uneducated person might have mistakenly plugged the drain holes, or if within the panel, then someone needs to do an inspection of the panel to find its point of entry and repair it.

[airsupport]

True, most aircraft don't like hitting hangar roofs, I was not directly involved in the A310 incident (thank Godness) but was there and wanted some good photos. The ''experts'' that were there at the time all were of the opinion that it would have been a much easier repair had it been a Boeing, or any metal aircraft, as I said Airbus said there was no way to repair it and they eventually replaced the whole fin.

As for our A300-600 I don't know how else to explain it, when the aircraft was in the hangar overnight water drained/leaked/seeped whatever from the tail the whole night, either water that was trapped in there or more likely ice trapped in there melting.

Never thought much of it until the American A300-600 lost its tail out of JFK about 12 months or so later.

[clunckdriver]

FSO, yes I know all about "Generic" terms, the problem is that most airframe drivers are totally clueless when it comes to the difference between a Thermal Plastic and a Composite, one only has to read some of the threads on this web site to work that out, in fact one builder of glass aircraft had to go the legal route to silence one twit in the US who was causing problems with his uninformed writings {Hey he writes in a magazine, so he must be an expert!} So rather than Plastic, lets use another term to avoid confusion and misinformation. {Thats the job of our Government}

[notmyC150v2]

I have been told that the composite aircraft coming on line now will suffer greater levels of damage in a catastrophic accident than the old "tin" aircraft thus making accident investigation somewhat more problematic (i.e. they will disintegrate) .

Any truth to this or just more illinformed nonsense?

[VH-XXX]

C152 - Are you talking about light aircraft as in C172 versus Cirrus etc?

I've seen my fair share of crash outcomes of both and they seem to hold up similarly in terms of crash worthiness and survivability, but in terms of repair it would appear on the face of it that a fibreglass or carbon aircraft can be almost fully rebuilt whereas a tin job would be scrapped much sooner. It would be a hard call to determine the difference in terms of survivability to make any bold claims. I've seen both glass and tin hit powerlines with different results that can't really be compared due to the nature of the crash.

[clunckdriver]

Notmy, its more bloody nonsense, I have spent far too much of my life around smoking holes trying to work out what went wrong, if no fire the composite airframe is in most cases in large chunks, the metal airframe compressed into smaler chunks, the exception being is that if the composite burns there is very little left. {See pictures of Grob corporate aircraft crash} In one composite aircraft crash the cockpit was intact and both ocupants looked OK. the problem was that the" crash cage" was stronger than the internal organs of the human body, in the case of most metal airframe crashes with this kind of deceleration the whole cockpit tends to buckle as a result those inside dont look so good. Sorry to be so graphic but thats the way it is.

[notmyC150v2]

Thanks Clunc that was what I was after. XXX my question was aimed (although poorly worded) at the new Airliners such as 787 et al.

My illinformed source was of the view that they would turn to powder on impact. I have to admit I thought it sounded a reasonable proposition (not knowing how these things work of course).

I didn't think the smaller aircraft like the new Cessna's and LSA's would be travelling fast enough to suffer the same sort of high speed impact.

Clunc your answer does bring one question to mind though. Whenever there is a large aircraft coming into premature contact with the ground at a less than ideal descent profile there is usually flames attached to the result. So I guess that major catastrophies are going to be harder to investigate in future?

[clunckdriver]

Notmy, In the case of larger aircraft the CVR/FDR/Downloaded info should be able to let us know what went wrong, however you have a very valid point when it comes to light aircraft without such equipment, even in the case of metal aircraft I have seen the fire destruction so complete that we really couldnt come to any valid conclusion as to cause. In the case of a composite aircraft intense fire the destruction will render it even more difficult to work out the sequence of events leading up to the impact/fire.By the way, if you happen to have the misfortune to be at such a crash , try not to breath the smoke/fumes, nasty stuff!