Fibreglass Aircraft vs Aluminium Maintenance Costs

[Magic Fingers]

Hi everyone,

I have read many claims by manufacturers of new GA Fibreglass aircraft how cheap they are to maintain and how maintenance friendly they are. Typical examples like the Cirrus, Grob and Diamond all use no corrosion as a big selling point. I have also read many posts, often in drifting threads, suggesting some seem to be in the hangar for much longer than anticipated and stories of annual inspections that were supposed to take 1 day being extended to weeks. The question of how long they will last compared to metal aircraft that are still flying 50 years later is a long way from being answered but I would like to make some real comparisons to the older metal aircraft we are all familiar with.

I have no bias either way except to say that most of my flying is in Pipers. I would just like to see some honest figures for the hours of maintenance required and see if the claims are backed up by experience. The more responses the better and I promise to collate and post the results back for anyone interested.

[englishal]

Not quite sure that your results will give any useful statistics.

For example, there are many more metal aeroplanes flying, and so you'd have to dig through all of these and find out how many had corrosion problem / replacements and come up with an average.

I can tell you though that our rallye had to be totally rebuilt in 2005 due to corrosion in the wings. Required new wings / spars, and a total bare metal re-spray / anti corrosion which cost about £38,000 in total, and took 6 months or so.

[IO540]

I think the composite part will last for decades - that's true.

The possible issue is that on any powered plane (e.g. a Cirrus or a Diamond) there are many metal parts, and from what I hear and see these are often poorly made, with thin plating and they corrode. A while ago I spoke to a Diamond (DA40/42) service shop and he said they were replacing most of the metal fittings around the engine, on every Annual, because they were rusty.

Currently, nobody knows how the "plastic planes" will keep their values. Probably not well, if current depreciation rates are anything to go by. But that is a slightly separate issue from actual corrosion.

A traditional aluminium-hull plane should be OK for about 15 years before needing significant airframe parts. Obviously hangarage helps. These are the really pricey parts and this is why buying something newer is not such a bad deal - you get a free ride for a bit.

[BackPacker]

Newer planes are not "just" using composites instead of stressed aluminium fuselage/wings. They are also using other new technologies, such as glass cockpits, FADEC and diesel engines. That makes the comparison very complex: There is no single aircraft that comes with the option of an alu fuselage vs. fiberglass for instance, so that you can compare like for like.

As for fiberglass itself: it should last for at least 30 years if properly UV protected, even when kept outdoors. Fiberglass makes more complex shapes possible and has no rivets so it's easier to make optimum aerodynamic shapes. And that leads to better performance on less horsepower.

On the other hand - there seem to be less places capable of doing fiberglass repairs vs. aluminium. This may lead to longer repair times and costlier repairs. The sailplane community has lots of experience though with this so if this is ever an issue I'd look there for expertise.

And, as IO540 said, you cannot make an airplane out of 100% composites. There will always be metal parts, whether that's steel or aluminium. And these parts may have the same corrosion issues as comparable parts in aluminium aircraft.

[SNS3Guppy]

Corrosion is only a small part of the picture. The material with which the airframe is composed isn't really what determines how long the airplane will be around. Let's face it...We've still got wood and fabric airframes out there which have been around for three quarters of a century now. The chief determining factor, among many, is how the airplane is maintained and looked after.

The cost of maintaining one over the other is not a direct comparison. Many metal aircraft use fiberglass parts, and fiberglass comes in many forms; there are man composite derivatives. The use of a particular synthetic part and the stresses that particular part incurs play a crucial role in answering the question. The question can only be answered in generalities, however. The major portion of maintenance that an aircraft requires is typically not structural repair...but routine maintenance. Powerplants still cost the same. Tires and wheels still cost the same. Plexiglass still requires care, and interior materials still require care, cleaning, and attention. Wiring is wiring regardless of whether it's run through a carbon fiber duct or supported along an aluminum spar. Fuel systems still use time limited components that wear out, age, and become brittle and leak.

Many sailplanes spend a great deal of their lives in the sun,and flex constantly in flight...yet soldier on with many years and hours of service. Fabric airplanes do likewise, requiring regular inspection and occasional replacement of fabric. Metal aircraft fatigue and require attention, but can go a great many hours of long service without issue. I've flown aircraft with a hundred thousand hours on the airframe which were still in very active constant service. I've flown metal and composite airframes with less than 25 hours total...which suffered catastrophic failures. The opposite may be true of other airframes.

Burt Rutan used to have a section of fiberglass he'd layed up some 40 years ago or more. It's been continuously in the sun since he laid it up. It was outside his office in Mojave, California. Visitors were invited to jump on it, in it's mount, as they approached the front door. I've stood on it myself. His point was that while many considered fiberglass and composite structures to be perishable in the sun and with time, this is not necessarily so.

Which costs more to maintain? Neither, really. Not enough information is provided. Rather than worrying about which one is glass and which one is metal, look at the cost of replacement parts, and their availability. Loook at the mission each one flies. Look at the care each receives. Look at the storage and frequency of maintenance, the cleanliness, and the way the respective aircraft are flown. Look at their design. Then come to a determination after putting all the factors down and make an apples to apples comparison. Anything else is just spitting in the wind.

[A and C]

The biggest problem with GRP aircraft is damage, not a lot of people know how to repair GRP aircraft and most of the quality repair shops started in the glider business.

The other problem is that shoddy repairs are easy to cover up on GRP aircraft and so it is easy to buy a death trap and not know it!

Only time will tell if the current crop of GRP powerd aircraft will be up to the rough & tumble of the light aircraft business after all they will do more hours than the gliders, be subjected to more vibration and will be maintaned by people who untill now had mostly "metal" aircraft to look after.

[IO540]

Also, the jury is still out on the glass cockpit avionics.

The Garmin 1000 stuff seems to be holding up OK, but there are only a few years to go on.

The weakness with glass cockpits is that the maintenance/installation manuals are not (yet) floating freely on the internet (as the manuals for all the separates are) and only a few dealers can work on it. This has the potential for far more downtime than the old type avionics where you can just pop in an exchange altimeter etc etc. This wouldn't bother a renter but it might bother an owner. I don't want to be flying up to Gloucestershire every time there is an issue.

[SkyHawk-N]

This year I went through FAA NDT & Composite (including inspection and repair) classes and as a result would be much happier purchasing a metal used aircraft over a composite one.

[ProfChrisReed]

If it helps my glider was built in 1968.

It has never had any fatigue-related repairs to the fibreglass structure - all repairs have been due to impact damage of some kind. So far as I and my inspector can see, the fibrelass is as structurally sound as the day it was complete. Normally, the only structural maintenance on a glider is for metal parts (or where metal parts such as hinges have become delaminated from their attachment points because of repeated stressing).

UV damages coatings (paint or gel) but not the underlying structure so far as is known. There is the potential for damage if the coating is chipped allowing moisture in long term, but I think (though am not sure) that the main damage this causes is flaking off the surrounding coating.

For an aircraft which is not stored under cover gel coat is a no-no - a glider which has sat out for a year is a sorry sight. The right paint should be as good as on metal.

Skilled repairers can make repairs invisible - crashed gliders have been rebuilt from little more than shards.

The best comparison might be motorgliders like the Grob 109, some of which must be 30 years old. Many live outside, and seem to bear up well.

[edited to ask SkyHawk what there was on the course that put him off composite?]

[IO540]

This year I went through FAA NDT & Composite (including inspection and repair) classes and as a result would be much happier purchasing a metal used aircraft over a composite one.

I was at Socata's factory a couple of years ago, and they showed a small crack in the composite roof, near one of the door hinges, caused presumably by somebody allowing the door to be grabbed by a strong wind.

The man explained how the repair is done... in multiple layers, and it takes several days, and no doubt costs thousands.

With a metal hull, you just rivet a reinforcing plate in there.

Same issues with installing GPS and VHF aerials. If one has a uniform composite hull thickness of say 4mm, one can't just screw a big rod aerial into it (Vne 189kt). I looked into this once and there was simply no approved procedure. Socata provide two scallopped-out aerial locations and that's your lot.

Metal repairs can also be easily inspected.

[SkyHawk-N]

[edited to ask SkyHawk what there was on the course that put him off composite?]

The NDT part of the course gave us hands-on experience on the following techniques over several weeks;

Eddy currents
Magnetic particle testing
X-ray radiography
Infrared thermography
Liquid penetrant inspection
Ultrasonic testing
Acoustic emission

Not many are useful when inspecting for impact damage and delamination of composite materials, due to the very nature of their structure. Ultrasonic is by far the most reliable but not infalible. The FAA recommend the coin tap test, basically dropping a dime on the material and listen out for a difference in the sound, not too techical but suprisingly accurate. NDT of composites is still in it's infancy and there are other techniques we didn't look at in very close details, such as Laser Shearography but I don't believe these are in wide general use at the moment.

NDT of metal including aluminium is a proven science and many of the above methods come up with reliable results. Even an amateur like myself can detect subsurface cracks and flaws as well as the easier surface faults with reasonable accuracy, although obviously a more experienced NDT techician achieves a much greater accuracy.

Composite damage is cut out and filled with replacement material which may or may not be bonded correctly to the existing structure and then covered over with resin and filler making the repair no longer visible. It's difficult to detect whether the repair was done using the correct temperatures and timings, etc, important for the correct strength to be achieved.

The majority of repairs to aluminium are more easily inspected. Rivets can be counted and measured, and sizes and thicknesses of patches can be measured. As as I said above, metal integrity can be relatively easily tested using widely accessible NDT devices.

In summary, I personally believe that damage is generally easier to detect on aluminium aircraft and repairs generally easier to inspect due to the repair techniques used on aircraft. I imagine that a less professional composite repairer can get away with making very unsatisfactory repairs and still make them look good.

If there are any professional NDT people out there it would be interesting to hear what you think.

[englishal]

I'm sure the professionals can repair them just fine. After all professionals repair boats and F1 cars all the time.

You will probably find that composite is less prone to accident damage than metal. Metal can get a hole punched through it fairly easily, composite either doesn't or breaks obviously.

One of my planes(.....I seem to be collecting them ;)) has a hole in the wing, but no damage to the structural components like the spar. Yes it is *easily* repaired, but I reckon had the aeroplane been a Composite structure like the Diamond DA40, it wouldn't have got a hole in in the first place....They seem far tougher to me, as metal does to fabric.

[SkyHawk-N]

I'd rather have a hole in my aluminium aircraft, which I can see and get repaired easily than have a composite aircraft that has been bashed and has hidden delamination damage which is difficult to detect with sophisticated equipment, and that's if you know where to look for it.

[SNS3Guppy]

Try getting a repair done on a compound curve metal surface, vs. one on fiberglass, then determine which one is easier.

Fiberglass is far more tolerant of a sloppy repair, and in many cases easier to do, and easier to do with a good finish. Glass offers many advantages. It's also got disadvantages.

One of the chief inspection methods on many glass and substrate surfaces still remains the coin tap test.

[SkyHawk-N]

Try getting a repair done on a compound curve metal surface, vs. one on fiberglass, then determine which one is easier.

But how about a repair to carbon fibre which retains the components original strength?

[A and C]

Repair of GRP structure is well understood but the skills are not widespread, take the aircraft to a reputable repair company and you can be assured of a safe repair.

The problems come when un or semi-skilled people work on these aircraft simply becase you can't inspect the repair once it it finnished without NDT kit or taking thie repair apart. It is inspection that is the issue with used GRP aircraft NOT the airworthiness of properly conducted repairs.

[Jim59]

I have a GFRP/CFRP glider (EASA CofA) that is two years old. Based on fatigue tests carried out on wing spar sections it has a maximum life of 12,000 hours. This is subject to passing special inspections at 6,000 9,000, 10,000 and 11,000 hours. After that it is scrap.

Some gliders have somewhat shorter airframe lives of only 3,000 hours so it clearly depends on the design of the particular airframe.

My previous glass glider was moulded in 1972 and in its life has had little maintenance to the 'plastic' parts - but a few repairs to metal fittings. However, this is exceptional because it had a very good gel coat. Later gliders used different gel coats that were prone to cracking after a few years (less than ten in some instances) and have had to be re-finished at significant cost (usually in Poland). So again it all depends. Incidentally the 'good' gel coats were alleged to be carcinogenic hence the change - but they were also more difficult to work so it may have been cost-cutting that used inferior gel coats. Some makers are going back to the earlier gel coats that seem to have indefinite life.

My current glider has a polyester finish on top of the gel coat (a factory only option at extra cost) - so hopefully that will avoid the need for it to be re-finished prematurely.

[ProfChrisReed]

Jim 59 wrote:

Some gliders have somewhat shorter airframe lives of only 3,000 hours so it clearly depends on the design of the particular airframe.

Nothing to do with the airframe design. When GRP was introduced no-one knew how it would stand up to the stresses of flying, so a 3,000 hour life limit was set. As gliders began to reach this limit, inspections indicated that there was no deterioration so limits were raised by the manufacturers, and most are now at 12,000 hours (and I expect them to be raised again once some old gliders reach that number).

Problems have arisen where the manufacturer went out of business before raising the hours limits. This happened with the Centrair Pegase, and I think most European gliding bodies had the power to raise the limit on a national basis, so did so. In the US, however, there is no such body, and of course no manufacturer to approve the raise.

I don't know of any GRP glider model which has been grounded due to running out of hours where there is some authority which has the power to raise the hours limit.

_______________________

SkyHawk's comments show how much familiarity plays a role in our perceptions of structural safety. I have many hours flying GRP gliders, rather less in wood and very few in metal. I feel most comfortable in GRP, because I think I could recognise a potential problem, less so in wood and metal because I know of structural failures in both these caused by hidden, unobservable (to me) defects. For major structural repairs to GRP I have to trust the repairer, but the UK system has meant that all repairs have to be undertaken by competent repairers, and there's no history of failures so I guess I trust the system.

SkyHawk's experience is the opposite, so he feels more comfortable with metal.

Repairs to GRP by gliding inspectors don't seem unduly costly. As an example, a bad ground loop can snap the fuselage just in front of the tail, and I think this kind of repair would normally cost £2 to £3k. GRP is pretty strong, thus minor knocks tend to cause no, or merely cosmetic, damage. If I punched my fuselage hard I'd break a knuckle but cause it no damage!

I'm not saying GRP is better than metal or wood, just that it has a very long track record for making structurally sound aircraft.

[Magic Fingers]

Thank you all for the discussion so far. I know it is not a simple question and didn't mean to get to the really complicated stuff but you have already answered many of my questions. I have found it interesting how the avionics packages have been a major cost on many new aircraft, not just the plastic ones. Glass cockpits are brilliant and when they become more prevalent will hopefully lead to more shops becoming capable of repairing them but I am also a mechanic and agree how it can be easier to swap out the older style instruments for repairs, particulary when flying in some of Australia's outback areas.

Again, speaking as a mechanic, I am used to being able to turn around the scheduled maintenance of smaller Cessna's and Pipers pretty quick, I just haven't touched many plastic aircraft yet and have heard a few nasty stories. The unscheduled side is always unknown whether its plastic or metal but as mentioned in several posts the detection of problems can be very different.

Looking forward to hearing more,

Thanks.:)

[englishal]

Theoretically instrumentation failures in a glass cockpit aeroplane such as the G1000 should be just as easy to fix - you open the box and swap the offending module - done in 2 minutes. The problem as IO mentioned was finding someone who can do this.

However the mean time betwee failures on the G1000 is over 2000 hrs, whereas on normal instrumentation it is running at about 800 hrs, so likely you will have less downtime due to failures (my turn coordination has just packed up :mad:)..

Composite technology must be pretty good these days if they are even building airliners out of them!

[SkyHawk-N]

The main experience I had during my NDT course was mainly on carbon fibre structures, not so much fibreglass. On the examples we tested it was extremely difficult to detect some of the faults/delamination in them, and it was difficult to tell whether an anomaly was a repair or a fault. And we learnt how regaining original strength was much more difficult to judge and achieve for composite structures.

Ultraviolet damage is a major worry for carbon fibre aircraft, and paint coverings are much more critical on them, with paint colours being limited for most. Many modern plastic aircraft have very limited maximum airframe hours, some as low as 1,200 hours or so (I can't remember which ones)!

I witnessed material failure for both metal and composite and was shown how composite failure in many cases is sudden and extreme with very little warning. Most of the time metal failure is more gradual (relatively) and more visual warnings will be displayed.

On a different note, some other differences between 'plastic' and aluminium aircraft involve the electrics. As there is no common ground on plastic aircraft two wire electrical systems are required and I have heard that avionics are more difficult to work on due to increased risk of static due to poor bonding.

Yep, I'm afraid I am an aluminium fan.

[soay]

However the mean time between failures on the G1000 is over 2000 hrs
Except for their magnetometers. Mine lasted about 150 hrs and its replacement cost about £700, part exchange.

I wonder how well the actual MTBF of the other components compares with their design specifications.

[IO540]

I am sure a good craftsman can do good repairs, but just take a look at the UK GA maintenance scene. It is a walking disaster...

Sadly, having been an owner for 7.5 years I ever more firmly believe that a large chunk of "owner satisfaction" (which in turn translates into getting real utility value out of one's plane) derives from being able to manage the maintenance.

The way the manufacturers would like things to be is that you take your plane to the dealer and he "looks after all your needs, SIR". That may be OK with a BMW but very very few GA owners are able to organise such a level of service for themselves.

A good friend is a freelance avionics engineer. He can do most things but can't touch any glass cockpit stuff. There are no manuals, there is no expertise in the field. It's back to the Garmin (or whatever) dealer every time.

I had a pile of avionics issues in the first year or so, but they got sorted under the warranty. But as a result I was not able to fly anywhere beyond an hour or two for the first year.

When I go on my long trips, and meet other pilots/planes who have also come a long way, I am expecting to see hordes of glass cockpit spaceships (Cirruses and Diamonds, mainly). In reality very few of them are seen doing long trips.

So, composites are probably fine but buying a composite plane with the very modern kit inside is just a way of buying yourself a barrel, and bending over it while you pay off the finance :)

Glass cockpits were a great opportunity to deal with the two major long term reliability issues in GA avionics (corrosion and vibration) but in the end neither of these has been addressed. The stuff is not sealed and is not built to a higher standard. I would thus not expect modern cockpits to be any more reliable overall.

The way to get more reliability would be by eliminating known issues. Replacing the vac pump with a miniature brushless alternator, replacing the vac driven AI with an electric one or a solid state AHRS product. But an AHRS driven from a second full-size alternator is not so good because those are standard pickup truck alternators which do fail eventually. One can get in-flight redundancy by having two alternators, two buses and everything switchable to either bus, but that doesn't deal with the fact that one cannot depart if either is duff to start with.

[JW411]

The fact is, that until fibreglass aircraft are 100 years old, none of us really has enough information to pontificate.

In the meantime, whilst our government is worrying about swine flu, I am more bothered about the localised outbreaks in western China and northern Bhutan of the deadly oriental GRP virus which, if uncontrolled, will spread across the world and develop into polystyromites which, as we all know, can munch up and destroy a plastic mainspar in minutes without anyone realising.

[AdamFrisch]

If anyone's interested in composites durability you should read the thread over at the rotorheads forum here:

http://www.pprune.org/rotorheads/386491-aw139-lost-tail-taxying-doh.html

It deals with the total tail boom failure of a virtually new AugustaWestland 139 taxiing on the ground (when the forces on the tailboom are very high on a wheeled heli) at Doha. Especially Blakmax has some very valuable input on the detection and repair of debonding of composites.

But in a nutshell - debonding of sandwich constructions (which are pretty much all of them) is not only virtually impossible to detect before it fails catastrophically, but if detected is also 9 times out of 10 repaired wrong and results in a weaker hull.

It's pretty sobering reading.

[englishal]

Seeing as the Pexperts have spoken, I'll pass this thread on to Burt Rutan, so he can wind up Scaled Composites, I'll cc it to Richard Branson too as I think he has a right to know. I'll ask the FAA to ground "Eve", and I'll also cc it to Airbus so they can stop production of various aeroplanes. Better tell Boeing too, as the Dreamliner will be a DEATH TRAP.

I guess the only REAL way to fly is wood and fabric and a leather flying helmet.

[IO540]

I'd imagine (and hope) that Boeing and Airbus etc have vastly better maintenance and inspection procedures that "us" lot in GA.

Even at the turboprop level (King Air, TBM, PC12) the build quality is generally at another level compared to the sub-million-quid GA.

[SkyHawk-N]

"Composite aircraft may hide dangerous flaws" (http://www.newscientist.com/article/dn12951-composite-aircraft-may-hide-dangerous-flaws.html)

[IFMU]

I like aluminum. I'm restoring a 63 year old C140. It is pretty solid. No primer, just alclad, like most Cessnas. I have a 31 year old aluminum glider, which has spent a lot of its life outside. Inside it is all alodined, primed, and will last forever. Outside the paint is horrible. I'll repaint it someday when my other projects are done. I am scratch building a sheetmetal homebuilt. Metal is such an easy medium to work with.

I like composites. The ASK-21's in our fleet are nice flying, decent performing, and very strong. They live in the hangar which helps their condition quite a bit. We have good local people that can repair them quite well if required. I would prefer not to be in a composite glider if lightning was a factor, as not many (do any?) gliders feature conductive mesh as part of the layup. Composites are used quite extensively on expensive aircraft, Airbus and the new Dreamliner to name a couple. How many new helicopters have metal blades? The industry seems to be shifting away from metal. Rotor blades live a harsh life. Composites can't be all bad.

-- IFMU

[Magic Fingers]

Great point about the rotor blades, hardest life imaginable, although not designed for forty years worth of service either, and a totally different use to an airframe. As a mechanic I guess I will have to get up to speed on composite repairs as there will be many more of these aircraft in the future.

Still, as a pilot and aircraft owner also I like knowing more about the metal aircraft that I fly. Real change is always hard to go through.

[IO540]

Composite is the only economic way to get 3D curves on skins, so it will be the future on economic grounds alone.

However, it seems that - again, within economic parameters - metal is no heavier than composites.

What costs a lot on metal airframes is making all the rivets flush, and any kind of 3D curve; the latter is often done with plastic (vacuum moulded) fillets which are CNC machined around the edges.

I am sure the economic case is very different on airliners, because their skins are made using a massively costly process where you start with an ally sheet about 20mm thick (which must cost a fortune), CNC-mill away some 90% of it to make a ~ 3mm thick skin with reinforcing ribs, and then gently shotblast the outside surface to get the right curve (which must cost a fortune, especially in France where the "work ethic" is quite interesting at times, unions are strong, etc). At least that is the process I saw on a visit to some factory many years ago... In this case, a composite hull section comprising the entire hull diameter, laid up against a mould and baked in an oven, is going to be a lot better because one can do away with the internal structures which are necessary in metal planes to hold everything together.

Helicopter blades are a different thing because they are almost purely in tension, and carbon fibre etc is very good at that. And in operation, the whole thing is pre-stressed.

Composite oxygen cylinders are great. I have a "48 cu ft" one which weighs about 3kg which is probably half of the ally version.

[Fuji Abound]

However, it seems that - again, within economic parameters - metal is no heavier than composites.



In a different market place my Caterham is almost all Carbon Fibre whereas the "standard" production car is ali. There is a significant weight saving on every panel in percentage terms, but of course the saving in actual terms is relatively small because the panels are already light. There is an equally significant increase in cost, I suppose by a factor of around double, albeit in retail terms.

Both Cirrus and Diamond use Carbon albeit to a greater extent in the 42. Pre-preg carbon to a high standard of finish is difficult to achieve but both Cirrus and Diamond show no exposed Carbon (other than the odd cockpit embellishment). Carbon is a far superior product than fibre glass including S glass and although it is more expensive much of the cost seems to arise in the laying up process rather than the cost of the underlying raw materials. I suspect a light aircraft made entirely from carbon (other than the space frame perhaps) would result in a very light and strong aircraft indeed. Of couse we are already seeing it used in this way in some of the new generation of very light jets including the main "tube" being wound on a madrell.

In the same vien many hi-tech racing yachts now have hulls made from carbon and spas have been made from carbon for a very long time. I have capsized many a racing dinghy and on the odd occasion ended up with a bent mast - carbon of course does not bend and therefore "seeing" a carbon mast break is a very different experience as it eventually fails under load with a nasty crack. It will be very important the engineers fully understand the different performance characteristics of the materials and how they weather with time. Untreated carbon exposed to UV for any length of time looks dreadful and will suffer. However in the sailing world you only have to "handle" a spini pole made out of carbon as opposed to ali and you will more than appreciate the differences between the two materials even if the owner who is paying the bills does not.

[Fitter2]

The fact is, that until fibreglass aircraft are 100 years old, none of us really has enough information to pontificate.
Personally I think 52 years is enough. The FS24 Phoenix (the first all-composite sailplane) first flew in November 1957, and is still flying.

Composite sailplanes have been in production since the mid 1960s and many of that era are still in regular use.

Hidden defects in wooden and metal structures are known to have caused serious failures, but engineers qualified to know what to look for can maintain any form of construction to a satisfactory level of safety (satisfactory being good enough for me to trust myself to fly in).

The sailplane repair industry probably has a higher proportion of appropriate engineers, since they have much longer experience in composite structures.

[Gipsy Queen]

This is all very well but this nautical carbon fibre stuff almost exclusively has been used on racing and high performance yachts which generally break or sink long before they have established any record of serviceable longevity.

Years ago, Wassmer claimed that the Young's Modulus of Elasticity of their composite structures increased annually - they were unable graphically to demonstrate this progression or at what point the process might be moderated.

I should be very wary of flying in a product from Avions Tupperware unless it was pretty new and in non-turbulent VMC.

Tin technology is tested and understood. :ok:

[Fuji Abound]

This is all very well but this nautical carbon fibre stuff almost exclusively has been used on racing and high performance yachts which generally break or sink long before they have established any record of serviceable longevity.



That really isnt true.

Carbon rigs have been around (relatively) a long time and most certainly have not just been used in racing machines. In fact in cruising yachts it is as important to keep the rig light not just because it improves performance but having less weight aloft and a much easier rig to handle are significant benefits.

The stress on rigs can be enormous. Moreover the marine enviroment is as harsh as any given the combination of salt water, very high levels of UV and significant changes in temperature.

I dont think it is fair to suggest these materials are not pretty well understand by now but equally as new applications are found (the Dream liner) our understanding of these materials will continue to improve for some while yet.

[IO540]

I suspect a light aircraft made entirely from carbon (other than the space frame perhaps) would result in a very light and strong aircraft indeed.

I gather that a 100% carbon fibre construction would be poor for crashworthiness because the stuff either stays in one piece (and subjects the humans to huge G forces) or totally shatters into sharp spikes. For the cockpit, one would have some kevlar as this produces a more gradual deformation.

[Fuji Abound]

Yes that is partly true. From people I work with crash cells in the Formula 1 world are constructed wholly of carbon fibre these days. Even the Firewall and passenger "cell" in some Mercedes are carbon these days. Cells using this type of construction are around three times as strong as the same cell constructed from steel. Under extreme load the cell will of course eventually shatter rather than deform and for this reason an Aramid such as Kevlar is bonded to the inner walls of the cell. Kevlar is also a very light material but with very different properties to Carbon.

[ProfChrisReed]

I think the first gliders with carbon spars were built well over 20 years ago, and are still flying.

My glider is 1968 glass, and I can confirm that modern carbon construction is much lighter.

[englishal]

I've had carbon windsurf masts for decades....My mates yacht has a carbon mast and boom, and come to think of it my windsurf boom is carbon too. I reckon if you had a carbon wing spar based on the windsurf mast principle it would be exceedingly strong and light.

Actually it is found everywhere, from F1 crash cells which dissipate very high impact speeds, to oxygen cylinders under 150 bar of pressure.

[A and C]

You are correct, all "carbon aircraft" are not in fact all carbon, the cockpit structure has a kevlar content to stop the carbon shattering into razor sharp shards in case of an impact.

[Fitter2]

I think the first gliders with carbon spars were built well over 20 years ago, and are still flying.

My glider is 1968 glass, and I can confirm that modern carbon construction is much lighter.

Make that over 30 years Chris, my 1978 Nimbus 2 had a carbon spar, and yes it was lighter than a glass one - I and my 10 year old son could rig it with no clever rigging aids. It isn't flying now, but only because a later owner had a close encounter with a tree, and the tree won. Other examples from then are still happily flying.

But then they used the mechanical properties to make much thinner wings, so up went the weight again, look at the weight of the inner wing sections of the new Arcus.

Current sailplanes actually use appropriate mixes of Carbon, glass and aramid (Kevlar) material.

[Gipsy Queen]

"I dont think it is fair to suggest these materials are not pretty well understand by now but equally as new applications are found (the Dream liner) our understanding of these materials will continue to improve for some while yet." Sorry, don't know how to do this fancy quote stuff.

Well, Fuji, old fellow, I have to admit to having my tongue just a little close to my cheek but nevertheless I do feel that there is much unproved territory in the composite world which may or may not be connected with the continual delays of the Dreamliner. Ductility, that characteristic so important in airframe materials, seems a consideration alien to this sort of plastic (assuming that it is plastic - if it isn't, things get even worse). Although I have some metalurgical understanding, I am far from expert in the field of the newer composites and readily accept that I might be talking through my hat. I'm just glad I don't have to fly them.

I have logged almost 27,000nm in blue water passagemaking (steel hull/alloy spars) and have yet to meet a carbon boat of suitable specification for this type of cruising.

But what was at the back of my mind in my last post was the very different behaviour exhibited by forged alloy propellor blades and those of composite structure when subjected to, for example, a wheels-up. The former just quietly fold out of the way whilst the latter shatter with shrapnel penetrating the hull to irritate the PAX sitting in the line of fire. There has been talk of fuselage reinforcement in this area but I don't know if this has been effected - I'm very much out of things these days but as I notice this is my 100th post, I'm looking forward to receiving my telegram from Danny . . . . ..:=

[Fuji Abound]

Gipsy Queen

PM sent

[A and C]

There is very little carbon on the Cirrus, the later aircraft have a carbon spar web but no other carbon that I can see.

[Fuji Abound]

A and C

Yes, that is correct. On the 42 the whole of the front of the aircraft is carbon and carbon is used elsewhere in the construction.

I have logged almost 27,000nm in blue water passagemaking (steel hull/alloy spars) and have yet to meet a carbon boat of suitable specification for this type of cruising.

I guess the answer to this is partly why would you use carbon in the hull? Weight, or lack of it, is not a significant advantage for a cruising yacht, and may even be a disadvantage. Construction would be a great deal more costly as would the material particularly in the volume needed for a yacht. On the other hand I know of a few manufacturers using carbon rigs in substantially cruising yachts such as Oyster and Trintella. Inevitably these are towards the top end of the market in terms of cost and clearly the mass producers of this world (Bavaria, Beneteau etc) could not produce price competitive yachts if they used carbon. I see some manufacturers are even using Kevlar in hulls to a greater or lesser extent.

Returning to aircraft clearly Boeing is at the cutting edge of using carbon in large CAT aircraft. I have no doubt they have learnt / are learning new lessons.

In so far as light aircraft are concerned I take your point about flying carbon shrapnel, however the risks are probably no more or less comporable with F1. The key would seem to be to ensure the passenger cell is adequately protected. The plastics used to mould the "glass" is capable of withstanding significant impact as is the passenger cell. While there may be an increased risk of flying carbon shrapnel when a blade impacts the runway carbon once again comes into its own in that the shrapnel is very light compared with the same bits of ali and therefore has much less inertia. It is far less likely to penetrate the passenger cell than metal shrapnel.

Thank you for your PM and replied.

[englishal]

The thing about the 42 is that the nose is similar to a F1 car nose, and should the unthinkable happen and you overshoot the runway and slam it into fence, likely you will walk away with bruised ribs.

I heard and interesting fact about the Twin Star - the Tail boom has the strake added to the bottom purely for looks. The boom itself was so strong that this extra strake isn't needed but because pilots coming from traditional aeroplanes would look at it and think "blimey, doesn't look very stong" they added the extra bit to make it "look" stronger.

[wsmempson]

Quote "I heard and interesting fact about the Twin Star - the Tail boom has the strake added to the bottom purely for looks. The boom itself was so strong that this extra strake isn't needed but because pilots coming from traditional aeroplanes would look at it and think "blimey, doesn't look very stong" they added the extra bit to make it "look" stronger."

I had heard that the strake beneath the tail-boom (or empennage) was for lateral stability reasons.

[BackPacker]

I had heard that the strake beneath the tail-boom (or empennage) was for lateral stability reasons.

I was thinking the same thing. I've never flown the -42, but I have some experience with the -40 and it suffers from a roll/yaw oscillation even with the strake on top and keel below. The remedy is to keep your feet lightly on the rudder pedals at all times, but I wonder what would happen without the strake and keel..

[IO540]

Composite tubular sections are very very strong and stiff. Go to a model shop and buy a piece of 10mm OD carbon fibre tubing, 1mm wall, and try bending it. Quite amazing.

Similarly with composite gas cylinders, which start with a (thin) ally cylinder and wrap fibre around it, directionally optimised where the stress is known to be.

Unfortunately it is hard to get that benefit on more general composite sections with dirty great apertures (doors etc) in them like a whole cockpit, without it getting hugely labour intensive. So I think GA composite cockpits are generally over-engineered using cheap materials (glass fibre).