June, 2006

Mirage Aircraft hits the road for the summer!
Arizona is a great place to live. Except in the summer! To say it gets "a little hot" in the summer begs the definition of "hot" weather! Maybe the two years of mild weather we experienced at my work near San Jose, California, spoiled us. One thing is for sure, when we came back to Arizona last summer we arrived for the hottest month ever on record. Talk about misery! When each day saw 110 degrees, all the work we were doing around our house had to stop before noon. I never drank so much water and iced tea in my life! Fortunately, as it turns out, we had kept the motorhome we had bought for our California sojourn, which now makes possible a "weather escape" this summer! So when you read this newsletter, we will be out on the open road, headed for South Dakota and Minnesota. Our summer travel opens up possibilities, especially since I am now "retired" from day-to-day working responsibilities and therefore have plenty of time and no schedules to meet. So now we can do some things that before we could only dream about. And one of our priorities while traveling across this great country is to stop and visit with some of our Celerity and Marathon builders. We'll be sure and squeeze in several airplane project visits between our side trips to see the World's Largest Frying Pan, a tour of a candy factory, or while going on to see our friends and relatives. I hope to report to you firsthand on the progress being made by various builders on their airplane projects. The only problem is that you're all pretty well scattered and it may take awhile before I get to where I can see your project or finished airplane. Between visits, we can hit a few fly-ins and air shows. We might even make it to Oshkosh this year! Send me an email if you plan to attend, perhaps we can meet up at the fly-in and chat for awhile. Please note our mailing address, on the masthead above and also in the subscription renewal forms and the merchandise coupon on the last page of this newsletter. My sister-in-law in Rapid City will be sure that the mail gets to us wherever we happen to be. Our email address and my phone number remain unchanged. Check out our newly revived (and revised) Mirage Aircraft Web site! Our Web site, www.mirage-aircraft.com, has been revived and upgraded by Andy Campbell, Celerity Builder in Washington State. Please take a few minutes and look it over, and be sure and recommend it to your friends and fellow EAA members in your local chapter. We are going to once again upload the past issue of Mirage Aircraft News. Also, product information will acquaint new would-be builders with our designs.

New builder takes on Marathon prototype project

As a prerequisite to our extensive travels I have regretfully sold my beloved Mirage Marathon project. Now I can "pay-back" to Karen some of the many hours that I have borrowed over the years to work on aircraft and provide services to our builders. Don O'Rourke of Tucson has taken over this, his first airplane project, and we look forward to his updates in the future. Meanwhile, I'll come around and look at some of your projects!

Using West System™ resins for fiberglassing

In a previous article in this newsletter, I pointed out that there are resins and then there are resins. Just like various grades of glass cloth available. Using the right cloth and resin will give you the correct combination of materials that are lightweight, strong, and easy to work, especially for the new builder. I have always strongly recommended the use of West System™ epoxy based resins for all the fiberglass work to be done on either the Celerity or the Marathon. There are several reasons for this including reputation, availability, cost, workability, etc. Here is a short discussion on glass cloth and fiberglass resins.

Airplane fiberglass systems

The Celerity and Marathon both require a large amount of fiberglassing. You will probably spend more time applying and finishing your fiberglass than either woodworking, building your control systems, or installing your engine and prop. You will need to "get friendly with fiberglassing." To do that you'll have to develop an understanding of what you are working with and acquire a little technique until you reach what I would call a working "comfort level" with the medium. While I have previously written "how-to" articles on fiberglassing for readers of the Mirage Aircraft Builder, these have been somewhat generic as regards the actual materials used in the fiberglassing process. This time I will specifically address the resins and hardeners recommended for the Marathon and Celerity. We recommend that our builders use epoxy resin on their aircraft. And not just any old epoxy resin either, but specifically West System™ resin, which is manufactured by Gougeon Brothers. West System™ epoxies and resins are readily available from Wicks Aircraft Supply or Aircraft Spruce and Specialty Company, our recommended primary suppliers for all that you need to build your airplane. In other words, I don't recommend cutting corners on this! I also have other reasons for preferring West System resins, which I will go into later.

Why epoxy resin?

The most popular resin for constructing homebuilt aircraft is epoxy resin. There are several good reasons for this, including strength, durability, resistance to shrinking, ease of application and ease of repair. Although most of the strength of a fiberglass layup is due to the glass fibers themselves, all you have to do is pick up a limp, stretchy piece of glass cloth to understand that the resin is at least as important as the glass. The strength properties that come about when the glass cloth is treated with an epoxy resin (or "matrix") is what makes fiberglass both usable and useful for sportplane builders. Durability means how well the stuff will hold up under normal use. This includes exposure to sometimes nasty atmospheric elements including raindrops encountered at very high speed, a clumsy person (like me) dropping a tool onto the wing skin, or flexing of the structure under taxi or flight loads. The continued use of epoxy for airplane skin over a quarter of a century provides ample evidence that epoxy resin is up to the task. It is well known in the homebuilt aircraft business that epoxy resins resist shrinkage much better than polyester type resins. One of the main reasons polyester resins are so popular for manufacturing everything from snowmobiles to boats and Corvettes is their low cost. However, the polyester resins are more brittle, and they have been found to shrink as the curing process continues over a long period of time. This stands in sharp contrast to epoxy resin, which reaches its curing endpoint much faster and does not undergo further shrinkage. Ease of application is extremely important for the homebuilder. To me this includes material that is easy on the builder in terms of harmful or objectionable odors. Epoxy resins are more benign in this regard, and the West System epoxies in particular are really quite easy on the olfactory organs. I know-my shop is right off the kitchen, and my wife has a much better "sniffer" than I do! Also, the pot life (reaction time) of the resin mixed with hardener can be tailored to the type of application. Once you have become more proficient, you can use faster West System hardeners, particularly where you will need to come back to do more work on a layup. Until then, the West System slow hardeners give you plenty of time to do a layup, or they can be mixed with fast hardener to give you a medium reaction time. Each of the West System hardener containers has a chart comparing the different hardeners with each other, which puts the information right where the aircraft builder needs it. Ease of repair doesn't rank very high on most builders' list of reasons for choosing a construction material--they don't plan to have any mishaps that will require repairs. Nonetheless, fiberglass aircraft skin made with epoxy resin is easy to repair, compared to aluminum, wood or even fabric skin. In all fairness I should point out that fiberglass layups made with polyester-based resins are also easy to repair.

Types of epoxy resin

Please note, in normal grammatical usage, we use the term "resin" to refer to either the unmixed resin itself (i.e.-no hardener added) or to the mixture of resin and hardener. It should be clear the way the term is used, what is really meant. There are various types of epoxy resin available, and you will want to be sure that the resin you use will do what you want it to do. Since there are various desirable functions (i.e.-rigidity, flexibility, high temperature, low temperature, fast cure time, slow cure, etc.) make sure you get the one that's made for the desired application. For example, the cowling on your airplane is going to see high temperatures from the heat given off by your engine. Therefore, you will want to use a compatible resin for this application, one that won't soften or lose strength in normal usage. Another example might be a control surface such as a flap or aileron. Here you would want a resin that can withstand the stresses of bending. Epoxy resins are also used as adhesives. For example, Hughes™ FPL 16A is an epoxy-type adhesive that's recommended for gluing the wood together when constructing the Celerity and Marathon. However, Larry Burton stated that he constructed an entire wing using West System epoxy resin as the adhesive. If in doubt as to the suitability of a given product for your application, contact the manufacturer of the resin before you do your fiberglass layup.

Types of glass cloth

Glass cloth is the reinforcing fiber that provides the primary strength to the composite structure, when it is combined with the proper matrix. While there are various types of reinforcing fibers, such as Aramid ®, Kevlar ®, etc., we stick to fiberglass, or glass cloth. Glass cloth is manufactured by spinning and weaving together strands of molten silica glass. The thickness of the threads, their spacing, and the types of weaves help determine the weight and suitability of a piece of glass cloth for the purpose you want to use it for. The type of cloth we use is called "E-glass," or "electric glass" because of its high resistivity. The other type, "S-glass" is used where a very high tensile strength fiberglass is needed. Sometimes these types are also used in combination with each other. In addition, fiberglass cloth of either type can also be combined with other expensive fibers like Kevlar ® or carbon fiber. By the way, using Kevlar doesn't make the airplane bulletproof. Kevlar 49 is used for aircraft construction, while Kevlar 129 is the bulletproof material. Also, a Kevlar vest is made much differently than a composite panel that contains Kevlar. The type and orientation of the fiberglass weave is extremely important in aircraft construction. Where tensile strength is desired (i.e.-resistance to pulling), you may in extreme cases want to have nearly all the fibers oriented in that direction, with very few cross-fibers in the weave. Indeed, some aircraft parts such as landing gear legs may be made almost solely with unidirectional cloth. However most aircraft construction is done with bidirectional (or "BID") cloth where roughly the same number of fibers run in each direction. When you take a piece of glass cloth and apply the resin (matrix), you actually weaken the glass cloth somewhat in the process of making it into a usable shape. It actually becomes a lot more brittle. The loss of strength can be calculated. For example, if you have glass cloth with a strength of 275,000 psi but you apply resin to it that by itself is only good for 20,000 psi, you will end up with an average strength of around 147,500 psi. (average of the two strengths) Designers take this into account when they have to decide how many layers of glass cloth and of what strength, are required.

Now go to it!

You don't have to be a professional to do a good job of fiberglassing. All it takes is some basic knowledge, a willingness to learn and a little patience to turn anyone into a good craftsman with composites. Some important things to remember:
  1. Keep your glass cloth clean, and store the resin/hardener according to the manufacturer's recommendations.
  2. Plan the job ahead of time--have all glass cloth pieces cut first.
  3. Protect your skin and eyes.
  4. Mix the ratios of resin to hardener as accurately as possible. Stir for 2 minutes.
  5. Do not mix any more resin/hardener than you can apply in, say 10 minutes.
  6. Try to work rapidly, in a well-vented environment.
  7. Don't be afraid to "push" the resin, to work out air bubbles.
  8. Be sure no area is resin-starved.
  9. Apply peel ply to areas that will receive more resin and cloth in the future.
  10. Sand off the shine before applying a second coat of resin and cloth.
If you have never worked with fiberglass before, we recommend that you purchase our construction video, "Easy Fiberglassing," which is available for $25.00 postpaid from Mirage Aircraft, Inc.. It's approximately two hours long and includes instructions for making a fiberglass fuel tank. Another good fiberglassing video for beginners, "Basic Composite Construction," is about 30 minutes long and is available from the EAA. Visit their Web site (http://www.eaa.org) or call them at (920) 426-4800.

Think you know everything?

(Here's some food for thought! Enjoy! Ed.)
Keep the aeroplane in such an attitude that the air pressure is directly in the pilot's face.
- Horatio C. Barber, 1916 When a flight is proceeding incredibly well, something was forgotten.
- Robert Livingston, "Flying The Aeronca" The only time an aircraft has too much fuel on board is when it is on fire.
- Sir Charles Kingsford Smith, sometime before his death in the 1920's Just remember, if you crash because of weather, your funeral will be held on a sunny day.
- Layton A. Bennett I hope you either take up parachute jumping or stay out of single-motored airplanes at night.
- Charles A. Lindbergh, to Wiley Post, 1931 Never fly the 'A' model of anything.
- Ed Thompson Never fly anything that doesn't have the paint worn off the Rudder Pedals.
- Harry Bill Keep thy airspeed up, lest the earth come from below and smite thee.
- William Kershner Instrument flying is when your mind gets a grip on the fact that there is vision beyond sight.
- U.S. Navy "Approach" magazine, circa W.W.II. The Cub is the safest airplane in the world; it can just barely kill you.
- attributed to Max Stanley, Northrop test pilot If you're faced with a forced landing, fly the thing as far into the crash as possible.
- Bob Hoover It occurred to me that if I did not handle the crash correctly, there would be no survivors.
- Richard Leakey, after engine failure in a single engine aircraft in Africa. If an airplane is still in one piece, don't cheat on it. Ride the bastard down.
- Ernest K. Gann, Never fly in the same cockpit with someone braver than you.
- AD Richard Herman Jr., 'Firebreak' There is no reason to fly through a thunderstorm in peacetime.
- AD Sign over squadron ops desk at Davis-Monthan AFB, AZ, 1972.