Ken Mintz Composite Information pg.3 ==
Page 1 Introduction=================================
Page 2 A Short Description of Fiber Types and Properties=====
Page 4 The Matrix===================.==============
Page 5 Setting Up The Shop===========================
Page 6 Preparing to Layup and More Tools=.==============
Page 7 The Core and Its Preparation.====================
Page 8 Hot Box Pictures and Dimensions.======.==========
163 Home Page====================================
Subject: Composites Corner No. 3 - Advantages and Disadvantages of Composites
This time I will give a brief discussion of the advantages offered by composites along with a listing of the
disadvantages that such materials present.
Since the introduction of the familiar forms of composites during WWII in secondary structures like radomes
and some panels, etc. composites have revealed through the experience of their use problems and new
construction advantages notably in aviation but also across a wide range of other applications such as boats
and recreational equipment. The advantages that made the new materials attractive were:
* High strength-to-weight and stiffness-to-weight ratios as much as 4 to 10 times better than metals. However,
experience has shown the industry as well as home builders that lightweight structures are NOT guaranteed.
Careful engineering and care in application of materials, especially the resins, are required to produce truly
lightweight structures. Burt Rutan said it best when he noted that, " If you take care of the ounces the pounds
will take care of themselves". In the case of resin application more is NOT better but is definately heavier.
* Composite structures can be tailored to meet a variety of loading and environmental requirements. This is
done by means of the proper orientation of the fibers and by the selection of the resins used. In our composite
homebuilts this is best shown in the fiber orientation of the spars where the major fibers are aligned along the
length of the spar to deal mostly with bending loads.
* Composites do not experience fatigue like metals do. This is exemplified in their now common use in
helicopter rotor blades. They can fail by fatigue but will last much much longer than metals can. However,
they do not like fasteners or the holes necessary for them. Abrasion and compression damage occur in
these areas especially if the fasteners are heavily loaded and/or are removed and reinstalled frequently.
* Composites by themselves do not corrode which makes them popular in marine applications. However,
some like carbon based composite fibers cause sever corrosion when placed in contact with metals like
the above mentioned fasteners. The cure for this has been to place a seperation layer of another composite
fiber like good old fiberglass between the metal and the carbon material. Fiberglass does not corrode any
metals that I know of to date. The cause for carbon-on-metal corrosion is basically the same as for dissimila
metals corrosion but seems to work much faster especially in damp environments.
* Perhaps the greatest advantage of composite materials is that complex shapes can be formed as one
component. This often means that fewer fasteners are needed to make a complete device or structure.
Aerodynamically smooth surfaces are comparitively easy to achieve unlike metals. No special tooling such
as the English Wheel are necessary. The smoothly flowing lines of composite aircraft such as Lancairs,
Glassairs and, of course, my own lovely Varieze (once it is repaired) are fine flying examples. Hydrodynamic
surfaces are equally easy to achieve as testified to by the extensive use of composites in racing yacht hulls.
* Composite materials can be formed using a varitey of techniques especially in manufacturing. Us
homebuilders are usually confined to the hand lay-up method though some have used the "chopper gun"
in some applications. This latter method is used most often in making boat hulls where weight is less of a
concern than it is in aircraft fabrication.
Above I have listed advantages of composite construction along with related problems. Next I will list
some specific disadvantages:
* Fabrication with composites is usually very labor intensive. If any of you out there get volunteered to help
lay up a Long EZ wing for example make sure the benefactor of your assistance has plenty of beer, etc
on hand to be consumed AFTER the lay-up process has been completed (though one "beer" canard on an
EZ was found to be surpisingly strong when tested despite the fact that such concerns as fiber orientation
and resin content had been forgotten some time around the second or third six-pack).
* Preparation for painting is also a very labor intensive process. More details on this undertaking later.
The more friends you have for this the faster this onerous job will get done.
* Composite materials can be vary expensive though costs for some like fiberglass and carbon fibers have
come down. I don't think that metals are more expensive but if one has priced a sheet of aircraft aluminium
these days one might wonder. Resins have a shelf life as well so keeping them around forever is not a
good idea if one is going to use them on major structures like wings. Old out-of-date resins can still be used
in many NON-STRUCTURAL applications if they are tested for proper hardening first. More on this subject later.
* Some health and safety concerns have appeared over time. Dermatitis is perhaps the most common
problem. Some extreme cases have necessitated the builder droping his or her project. An effort has been
made in the past to produce nonalergenic resins but I don't think any have been truly successful. Someone
seems to be sensitive to any resin produced so far. Breathing the fumes and especially the dust as from
sanding for painting are to be avoided. More on this later as well.
* Hidden damage can be very difficult to detect. Omitted major structure can also be next to impossible to find.
Paint definately hides a multitude of sins in composite aircraft. A few people have paid with their lives for such
omissions over the last 25 years or so. Much more on this later.
* In industry special training and skills are necessay for both the manufacture and repair of composite structures.
For the homebuilder one mainly needs the hands-on experience and the proper work environment. Tools are
basic. The question is how does one get the initial experience? More on this later also but in short be ready
to make mistakes and do it over.
I hope to get into more specific from now on. All for now..
Phone: (702) 567-1938