To PMN.
The savings on weight claimed by CFRP are at best optimistic, at worst lies.
The savings can be made elsewhere too.
The next Gen. of engines is already giving the savings the airlines want and being Green in terms of fuel use and noise, to satisfy the tree huggers.
The new wing designs (747-8 for example) and/or Winglets will give fuel savings too.
There are several fundamental things wrong with primary structures from CFRP.
1). After a few heavy landings, or wing-twangs, it can delaminate from the inside. IMPOSSIBLE to spot by visual inspection. It needs at least a C scan, which means taking the Spar out….yeah, that’s gonna get done. Not.
2) Once it is made (And cooked in the ‘clave), you cannot see the interior construction, you can A, B and C scan it for porosity and flaws and inclusions. You cannot see which way the fibres go except for the two outer layers…….one has to trust the manufacturer to stick Gospel-like to the Ply book and the drawing Compass. One supplier has said to us “We didn’t like the way this particular 45 degree ply was laying, so we swapped it for a series of 90’s” SHREEK! That’s the Chinese for you. They measure quality with a micrometer and think that is it. Of course, all the supply chain need to pass this-n-that quality audits.
At least you can X ray metal and find the grainflow as well as flaws.
3) The temperature melting point of the Resin is 280C maximum. The fibres need the heat of the centre of the Sun, but the resin is as runny as water at 280. Pray for no fire, especially on the lumps, because the Front spar will cop for it, then you’ve got no wing, then a lot of death. Remember that A340? The Carbon bits looked like a Barbers floor in minutes. Resin all gone, fibres in a ball.
3A) Smoke. If you happen to be on the ground and it catches fire, the smoke is creeping death. Very highly toxic.
4) Fasteners. Especially those holding Top Wing Cover on. When lightning taps on the Fastener head, it needs a path to earth (Or fuselage). Copper mesh in the outer Syn Skin layer takes it. However, there is a 0.0001″ gap around a fastener and its hole. Or, a bit under the countersink. This gap contains air, which rapidly expands at a high temperature and will only go one way. Tank.
There are two ways of preventing the expanding gas around a fastener (Miniscule though it is) of entering the fuel tank. As you can imagine, this is a VERY VERY bad thing. A special Sleeved Fastener, tapered too, costing about $3,000 PER HOLE. yes, that’s right.
You can bond all the fasteners together on the inside. Weight and time consuming.
5) Cost. The cost of CFRP in terms of the hours it takes to make and the cost of the Raw Materials. Some Faux CFRP is dirt cheap, but only fit to make a motorbike Mudguard look pretty with a standard Satin harness weave.
6) ICY. Each time you cook an item in the autoclave, the resin and indeed the cloth behaves ever so slightly differently, and you can get a CPT (Cure ply thickness) variation. If it matters, you have to machine the IML (Or the bag face) to the correct thickness.
7) Ingress. We know how to keep water and oil out. But civil a/c get wine, food, urine, sick, poo. All going into the floor beams. Floor is very important structure, as you know from that Aloa 737 which landed Roofless.
8) In Service repairs. Are actually rubbish. It needs a new part but it may take a few flights before that part is ready to be fitted.
9) Wind erosion, yes, it wears in the wind. Leading edges are all clad or made of Ally. A few years into service and erosion will show itself on the high turbulant areas of the wing and H-stabs.
10) “It’s been in the Military as primary structures for years” is the standard stock answer.
Well, this is so.
But, the primary wing spars of a Fighter or light bomber do not have the flexing requirements of an airliner, or even the A400.
The Structure is over-strong to prepare for maximum G tricks and battle damage.
The drivers have a “MUMMY” handle, the platform is only a tool for the job which is disregarded when life is at stake.
I will not be happy until the oldest A400 has got 10,000 hours under its belt, been through 100 lightning storms, had dozens of heavy landings and an engine fire. Then it needs dismantling and every primary part needs a full 100% inspection, destructive testing not NDT. We need to know what really happens in there.
Scared? You really should be.
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