I don't care if you think my statements hold water or not, If you don't care why are you responding and getting so shirty?
As I said before, you can take what I say or leave it, I'll leave it as you have not supported what you say in any way I don't care, but I'm sure not going to educate you. You don't need to educate me in this subject that's for sure, I probably forgot more about polymer chemistry and lay up than you ever knew but you obviously think I'm some sort of dick head. I lead our Polymer R&D team, chair our monthly R&D brainstorming sessions and our team members include one of the worlds leading polymer chemists and composite technologists consulting for Aerospace Companies and Military Establishments both here and in the USA
I will say again for the benefit of the others, the type of resin you use matters for the application, and so does the cloth material. Agreed, but that does not mean VE is unsuitable for the loadings imposed on the Gyro wrap around. There are Epoxies that you wouldn't want to use for this too. Further, not only is the reinforcement type important but also it's weave and direction of lay up. The glass type has significant effect on the properties too and glass formulation/composition is another extremely interesting area. Just as Epoxy only identifies a type of chemical crosslinking reaction 'E' glass or C-glass compositions are wide and varied too, some good some bad dependent upon application. Oh and I don't need educating in this area either as our glass plant R&D is led by me too! We used quadraxially woven 'E'glass for a while on some pipe which was excellent for single layer muli-directional reinforcement and stress distribution, if not a little heavy and expensive. Sadly the uptake globally was insufficient and it's stopped being manufactured
There are certain types of treatment that the cloth fibers must have depending on the resin and the use of the application too.You are refering to organo-functional silanes. There are now hundreds of these and it is sometimes possible to blend them with very interesting results. However, unless you are a big user of reinforcement you will get whatever surface treatment is available which is not very much and whereas Boeing et al may well persuade a glass fibre manufacturer to produce a special I doubt it would be available to RAF. It is of course possible with epoxies and unsaturated ester systems to add the silanes to the resin but great care has to be taken as too little can actually make things worse and too much can be catostrophic
Vinyl ester resin is not a good choice for rotorblades on aircraft. It would work on wind generation blades, because we are talking about a completely different frequency requirement.You mentioned this before, I wasn't sure if you were talking cycles per minute, cracks per mile or something else entirely. Just what is the frequency you refer to and how do you evaluate what is suitable or not in terms of resin, either epoxy or ve? Is it not the total composite including (in this case) the aluminium spar that is relevent?
If your resin is more elastic than your fiberglass cloth, then the resin can stretch farther than the cloth fibers causing them to fail, and once an area becomes weak from the failure of the cloth, cracks in the resin will occur. WHAT?? Better tell our R&D team about this quick and we should withdraw our glass fibre reinforced flexible bellows from the market immediately!!
I doubt anyone has done a proper failure investigation into the cracking of the RAF blades on the upper surface and at the trailing edge, they may well be (and I think they are) different modes of failure. I don't know if the cracking initiates only in the gel-coat on the upper surface (which I suspect) or it is through cracking. I note it occurs on some blades and not on others.
However, if indeed the blades are VE (Wouldn't it be embarassing if they're epoxy? I think just for fun I'll run a sample through our lab and evaluate) I think the story will run more like this - VE polymerises through the monomer, in this case styrene. Without a significant post cure 100% polymerisation never takes place and free monomer remains. The free monomer will over time polymerise or migrate and leave the structure to atmosphere. In the meantime, whilst it remains, it placticises the matrix. Whilst the plasticisation is there, flexural movement/stress is unlikely to cause cracking. As the styrene either leaves or polymerises the matrix becomes more dense and brittle and cracking is then more likely to occur especially in the un-reinforced gel coat. I think that flexiblising the gel coat by the intoduction of some dibutyl phthalate or soya lecathin may well stop the cracking problem.
There are many issues with the use of resins for structural laminates, both epoxy and unsaturated esters. Contolled conditions are essential but whereas those conditions may apertain in some places they don't in all. I give as example another reason why some blades may crack and others not. The speed of cure will determine to a significant degree the length of the polymer chain and with an unsaturated ester system until polymerisation is complete the styrene, which has a high vapour pressure, can dissapear to the atmosphere very quickly, so 45% styrene becomes 32%. Vacuum bagging can initially exaccerbate this until the film is firmly in place as can heating or high temperatures. So if you don't have a strictly controlled atmosphere, winter to summer fabrications can produce structures with different properties. A slow progressive cure (without petrification of course) is generally better than a rapind one. Epoxies also have problems especially as solvents are being removed to aid the environment and wetting out the fibre becomes more difficult. I'm in danger of writing a thesis so I'll stop there.
Building rotorblades for aircraft is completely different, and requires much more experience and knowledge then making wind generator blades. Building a 100ft turbine blade requires knowledge and experience too. More I doubt it's just different. Back when I examined the RAF blades, I told RAF of this problem, and they would not hear of it. You probably gave them the non- scientific reasons you are giving me. I said to them time will tell, and sure enough, it did. There was nothing wrong with the quality of the RAF rotorblades, the problem is in the resin used.Well that depends upon how you view it I guess but your simple (bland) statement that VE is no good for the RAF blades is in my opinion not correct.
Regarding quality. I am very experienced in failue analysis/investigation and I can tell you without doubt that the blades I looked at left something to be desired. I think even the non- technical amongst us would recognise that incomplete foam filling of the space between the skins may result in problems, trailing edge cracking perhaps!
There is no doubt that the right epoxy used in the right way under controlled conditions and with the right reinforcement would produce a better blade, reinforced with carbon fibre even better but is the VE inadequate for this service? In my opinion no. And who is going to want to pay the price for the fancy epoxy blade which is likely more expensive than the all metal construction which also has cycle fatigue issues.
Now to the subject of blade support. I am not sure if the long standing unsupported blade condition contributes to the upper surface cracking or not but gyro blades are of lightweight construction not being driven as with the Heli. The weight of the blade compared with its vertical stiffness is large and under such loads over a prolonged period even the aluminium spar will take a set. It makes sense therefore to support the blades when in storage. Even heli blades say "Push up - dont pull down" because of their weakness in this direction.
