Plastic Planes vs Traditional Metal Aircraft.
 

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:

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.

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.

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.

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!

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:

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

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.

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

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.

CHEAP......

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..

Hmmm, quite a long bow there me thinks.:cool:

Add the word "nesccesarily" into that sentence Arnold.

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.

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:

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.

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:

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...

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: