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Discus Cs grounded in France-long
Thanks Robert for the nice summary. Also one should mention the shrinkage
that will normally follow with the broad areas of bonding paste, which (depending on post-cure handling) may lead to expensive refinish for a relatively new glider... Best Regards, Dave "Robertmudd1u" wrote in message ... There are two commonly used ways to get a spar into a composite glider wing. There are several variations to either method. Method 1. Build up the spar, shear web and cap, separately of the wing. This is done by laying up the web and cap all at once, there are several variations to this step also. Lay up the wing skin and cure it. Bond the spar onto one of the skins. This bond line is easy to control as you can see it going together. The next step is to pick up one of the wing molds and place it on top of the other. The bonding paste between the cap and the skin is squeezed out and controlled by the dams as the wing is closed. When the spar and it adhesive mixture comes in contact with the second skin the bonding is done. This side is much more difficult to inspect. Very careful preparation is needed and foam or composite dams are helpful to control the squeeze out of the bonding paste. Typically there is a good fit of the spar cap to the skin on the first skin. The second spar/skin bond line is much thicker, mostly to insure that everything fits and there is enough room for lost of bonding paste. Method 2. Lay up the wing skins and lay in the rovings for the spar cap at the same time, (several variations of this exist). The shear web is made separately and its top and bottom edges have a broad V flange that will act as a dam to control bonding paste flow. Once the wing and its cap are cured the shear web can be bonded to one skin. This bond is again fairly easy to control. Next, just as in method 1. One of the wing molds is lifted up and placed on top of the other and the bonding paste between the top of the shear web and the cap is squeezed out and controlled by the dams as the wing is closed. Either way involves the bonding of long, relatively wide areas, thus opening both methods to the same potential for bonding problems. From a manufacturing point of view I do not see an advantage of one method over the other. There may be other considerations but both methods can work equally well and both are equally open to problems stemming from lack of correct procedures and quality control. Obviously wings using either method are able to pass the strength requirements of the JARs. There are pros and cons to each method. The method used mostly depends on the chief designer's experience and beliefs, i.e. what University Flying Group did he/she belong to, or what is the current method used in the factory. The problem, I suspect, is not in the method but in the process and quality control existent in the Czech factory. I have seen indications of other quality problems from this factory. I am sure SH will correct the problems and keep a closer watch on them. The Czechs have a proud history of manufacturing and technical development, however a lot of that was beaten out of them by the oppressive Soviet system. You can easily tell which skin, wing or fuselage, had the spar, rib or bulkhead bonded to it first. The bond line will be much thinner and neater looking that the one on the opposite side. The bond line that is formed when mold halves are put together is thicker and may have drips associated with it. Robert Mudd |
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Looking at the inspection issue we are dealing with from a Nuclear Power point
of view provides some interesting points. (Not that you would want full NRC approved type Quality Assurance, gliders would start at about $500,000 and come with a second trailer full of paper!) The owner is directly responsible for the quality of the work of any supplier, sub suplier, etc. This can be done by -Tthe supplier/contractor having a full NRC approved QA program. Still you are responsible for the product and are required to routinely audit the suppliers execution of their program. -Preparing your own QA inspection plan, specifically written for the work being done and placing you own qualified inspectors in the suppliers house. -For some smaller parts or pieces that cannot be reasonably purchased in either of the above, buying them comercially. You then have an Engineer develop what are the critical characterics of the item and an inspection plan to verify they are met when the piece arrives. Also from our NDT (Non-Destructive Testing) experience, I have seen some amazing visual inspection techniques. One is a movie taken of a spent fuel assembly (rad levels over 5,000 R/hr) going down a .177 dia hole over 40 feet underwater,where a fuel pin was removed. Used a video recorder on the surface and a very expensive fiber optics "lens" that went down the hole and could be swiviled like an eyeball. Picture was as clear as a bell. Something like this sure could be used to inspect a wing spar glue line when it was still fresh. Some design work would have to be done to provide a inspection path. Inspection techniques available today leave no excuse for something a simple as the glue up of a spar to go unispected, in real time. Bruce Patton 596S |
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