Fibreglass Aircraft vs Aluminium Maintenance Costs
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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.
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.
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Originally Posted by englishal
However the mean time between failures on the G1000 is over 2000 hrs
I wonder how well the actual MTBF of the other components compares with their design specifications.
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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.
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.
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.
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.
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If anyone's interested in composites durability you should read the thread over at the rotorheads forum here:
http://www.pprune.org/rotorheads/386...xying-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.
http://www.pprune.org/rotorheads/386...xying-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.
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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.
I guess the only REAL way to fly is wood and fabric and a leather flying helmet.
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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.
Even at the turboprop level (King Air, TBM, PC12) the build quality is generally at another level compared to the sub-million-quid GA.
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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
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
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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.
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.
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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.
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.
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However, it seems that - again, within economic parameters - metal is no heavier than composites.
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.
The fact is, that until fibreglass aircraft are 100 years old, none of us really has enough information to pontificate.
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.
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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.
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.
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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.
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.
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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.
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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.
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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.
My glider is 1968 glass, and I can confirm that modern carbon construction is much lighter.
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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.
Actually it is found everywhere, from F1 crash cells which dissipate very high impact speeds, to oxygen cylinders under 150 bar of pressure.
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IO540
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.