|FEATURE ARTICLE||HOW TO MAKE YOUR OWN LANDING GEAR|
April 2000 R/C Modeler
Vol. 37 No. 4 Pg. 20
Site Sponsor: Hobby Lobby
HOW TO MAKE YOUR OWN LANDING GEAR USING COMPOSITE MATERIALSBy
John R. Lane
This is an article on how to make your own molded landing gear from new, high-tech, high-strength, composite materials. Once constructed and attached to your favorite birds, these babies banish forever those familiar problems of landing gear bends, cracks, and failures. The materials you will use to make your landing gear are carbon fiber, Kevlar, epoxy resin, and glass spheres. First, a few words about the materials used:
There are three common reinforcing materials in use today: (1) fiberglass, (2) carbon fiber, and (3) Kevlar. Notice that all three are used to one extent or other in constructing our beloved models. All have many times the strength of steel and aluminum for the equivalent weight. In other words, these products are really strong and don't weigh much! Both fiberglass and carbon fiber bond readily with CA, epoxy, and polyester, whereas Kevlar only bonds well with the first two. For our landing gear application, Kevlar, carbon fiber, glass spheres, and epoxy will be used.
Fiberglass comes in a variety of forms, such as continuous or chopped strands, woven fabrics, chopped mats, or milled fibers. It comes in three grades: E for electric insulation, S for high strength, and D for things like Radomes. Modelers use the E type product. Fiberglass is mostly silica, or sand, to us non-chemical engineer types. Other elements such as Calcium, Aluminum, and Boron are added in varying degrees. There is a hideously complicated process for making fiberglass (or wonderfully elegant - take your pick), but basically, all this is heated up into a mixture and, under pressure, shoved through a bunch of tiny orifices (holes) in a gadget and out comes something called a filament. The filaments are woven into strands. Then the strands are woven, chopped, or milled depending on the application. Still awake? Okay, let's press on. In addition to its high strength/lightweight characteristics, fiberglass has other interesting properties such as good chemical resistance, doesn't burn, is unaffected by sunlight and bacteria, and is low (relatively) in cost. There are a variety of model aviation applications, such as making structures (i.e., cowls, wheel pants), providing a finishing substrate over wood (to receive paint), wing center section reinforcement, or securing things to one another, such as a firewall to the rest of the fuselage.
II. Carbon Fiber
Carbon fiber has been around since the 1880's and was initially used as a filament in electric light bulbs. In the 1960's it was developed as a stiffening alternative to fiberglass. A cellulose type fiber (polyacrylonitrile, or "PAN") is used as the basis for manufacture of carbon fiber. It is heated to around 1292 degrees Fahrenheit (F) with a yield of 85% carbon, hence the name carbon fiber. It then is further processed at 3000 degreesF with a resultant yield of 99% carbon. The subsequent yield results in a product of minimal stretch with a high tensile load (i.e., you can pull it, but nothing happens) and high strength. Single filaments of carbon are about 70% the weight of fiberglass at about 60% of the strength and is very stiff. Typically, this is the most expensive of the three products. Application uses in model aviation are: acting as a load spreader in the landing gear mount region, used as formers in fiberglass fuselages, or applied on the outside of ducted fan ducts to minimize vibration. Carbon fiber can also be applied under sheeting to stiffen foam wing cores.
Kevlar is a trademarked product of E. I. Dupont de Nemours & Co., and is an organic compound made of carbon, hydrogen, oxygen, and nitrogen. Kevlar 29 was first introduced in the 1970's to replace steel belts in automobile tires. The product is extremely difficult to cut or slash, hence its desirability for the tire application. Kevlar is manufactured in a process similar to fiberglass, with a final product also much like fiberglass (i.e., yarns, fabrics, chopped strands, or milled fibers). Kevlar has a number of very interesting properties: light weight (60% of fiberglass), three times the stiffness of fiberglass, high strength-to-weight ratio, retains its properties in elevated temperatures, is impact and shatter-resistant, damps vibration, and is fatigue-resistant. On the downside, it's more expensive than fiberglass but, as I mentioned, it produces much lighter (40%) structures than fiberglass at equivalent stiffness. The most common non-modeling application that comes to mind are bulletproof vests. Violent applications aside, the uses to which it can be put in model aviation are: molding lightweight, strong structural shapes; wing center section reinforcing; securing firewalls to fuselages; formers in fiberglass fuselages; wrapping pushrod ends; skid surfaces; partial formers inside removable hatches; and any other application where strong, lightweight, vibration damping is required.
Landing Gear Construction
The landing gear constructed in this article is for the Carl Goldberg Models Extra 300. The fabrication time was about one hour. This landing gear will support an airplane of about 12 pounds. Using different mold shapes and lamination layers, the gear's strength can be adjusted up or down to accommodate your plane's style and weight. The materials used in this procedure are Styrofoam, glass spheres, West Systems Pro-Set Epoxy (#125 with #226 hardener), carbon fiber, and Kevlar, the last three of which were obtained from Art's Hobby. See the Credits section for specifics. Styrofoam sheets can be obtained at any hardware or building supply store. They can be glued together to achieve the thickness required for your landing gear. Here's the procedure:
1. Trace the gear profile onto a suitable thickness piece of Styrofoam (as wide as the landing gear needs to be) and use a band saw to separate the male and female portions.
2. Relieve the male mold by about 0.156" (4mm) to allow for the thickness of the gear you are about to mold.
Photo #1: The cut and sanded mold.
4. Line the mold halves with wax paper. Drawing mylar also works well and yields a more shiny and uniform finish on the landing gear outer surfaces. Use a glue stick or an adhesive spray on the liner. If using mylar, make sure the dull surface is towards the mold halves.
5. Cut 3 carbon fiber strips about 22" long and 1" wide.
6. Cut 3 Kevlar strips about 22" long and 1" wide.
7. Cut 9 strips of carbon fiber about 6" long, 1" wide, at 45 degrees to the weave, both on the ends and the long edges.
Photo #2: The materials required for construction.
9. Prepare 3 total ounces of West Systems Pro-Set epoxy and hardener.
Photo #3: The first three carbon fiber strips in the mold.
11. Now paint a 22" piece of carbon fiber and place it in the mold. Paint it again when in place in the mold.
12. Now do 3 more 6" carbon fiber strips like you did in Step 10.
13. Now do another 22" strip as you did in Step 11.
14. Do the final three 6" carbon strips as you did in Step 10.
15. Do the final 22" strip of carbon fiber as you did in Step 11.
16. Now paint the first 3 pieces of the 6" Kevlar with epoxy on one side and apply it to the mold as you did with the carbon fiber in Step 10.
Photo #4: The first Kevlar strip in the mold.
Photo #5: The first three Kevlar strips in the mold.
19. Do another 22" strip as you did in Step 17.
20. Do the final three 6" strips of Kevlar as you did in Step 16.
Photo #6: Now all the strips are in place in the mold.
Photo #7: The mold in compression.
23. After the gear is removed from the mold, sand any imperfections. Saw off the excess overhang portions (at the two ends) of the gear.
Photo #8: Finished gear out of the mold, before sanding.
25. Drill to accommodate axles, wheel pants, and bolt pattern on fuselage. Assemble, go fly, and land with no worries (well, about your gear, anyway)!
Bill Of Materials
For this landing gear (Goldberg Extra 300), the following materials are required:
A) 3-1/2 yards of 1 inch carbon fiber
B) 3-1/2 yards of 1 inch Kevlar
C) West Systems Pro-Set #126 Epoxy and #226 Hardener
D) Glass spheres
E) Stir cups/sticks and brushes
F) Styrofoam sheet
Art's Hobby, P.O. Box 871564, Canton, MI 48187-6564, (734) 455-1927, or via the Internet at:
Art Gajewski, President and Senior Engineer, Art's Hobby.
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