Mini-IMP Aircraft Company
What is TPG?TPG is an abbreviation for Taylor Paper-Glass. In 1978, Molt watched his associate Jerry Holcomb using TopFlite MonoKote™ as a covering for his sheeted R/C models. Molt noticed that the covering created a structure that was much stronger than traditional methods. With the increasing cost of aircraft plywood and aluminum, Molt found that many potential experimental airplane builders have felt discouraged due to increasing costs, and concern about their ability to perform the manufacturing operations required to build a metal airplane. After contacting various paper manufacturers in the Pacific Northwest, where he lived, Molt hit upon a very common paper product called “Solid Fiber Boxboard” which is readily available and lends itself to the concept. The basic idea of the process is to laminate a very strong material on both sides of the relatively low cost paper “core” material to obtain a strong, rigid, composite SANDWICH structure that is inexpensive and lightweight. The construction technique also eliminates the need for expensive tooling. Only simple wooden formers are required.
The paper is an un-bleached “Kraft” paper which is light tan in color and comes in a wide variety of thickness. The two thickness most appropriate for use in the TPG process are “90 pound Linerboard” which is about 0.025” thick and “Laminated Solid Fiberboard” which is about 0.050” thick.
It was apparent to Molt at that time that GFRP (glass fiber reinforced plastic) i.e. “fiberglass” and polyester resin would serve the purpose at the least cost. Accordingly, after considerable experimentation, Molt and Jerry settled on a tightly woven, plain-weave, glass cloth designated as # 1528 or 7528 which is available from many glass cloth weavers and suppliers.
The resin used was “Koppers Dion 6692T Fire Retardant Resin”. It is a polyester resin. It was chosen for its reasonable physical properties, and cost.
While these are the materials chosen by Molt, the method is applicable to other materials. The use of other cloths and different resins can be considered, but since TPG is very much an experimental material for which specific strength allowables are not available, each piece must be built and tested to at least 2 times the calculated design load. TPG is EXPERIMENTAL !!
Why Use TPG?
In a nutshell, Cost and Workability. The basic materials are quite inexpensive, and is easy to work with and form to the desired shapes. Think of TPG as being a lot like aircraft plywood and you’ll get the idea. The thinner “Linerboard” material can be shaped into simple curved shapes and can be used as a substitute for sheet metal or plywood in areas such as ribs, shear webs, and some larger components. The thicker “Laminated Solid Fiberboard ” can be used for flat pieces such as structural bulkheads, and for gently curved components. It can be curved sharply, by the “scoring” method. It is not practical or possible to make compound curved pieces from a single piece TPG just as it is not practical to do so with plywood. TPG is EXPERIMENTAL !!
How To Do It
Parts are drawn out on the paper core using felt-tip markers and ordinary drafting tools. The paper is then cut to shape along the layout marks with a utility knife and scissors. The paper core is placed in the formers (if any), “sealed” with resin and allowed to cure. The part is then “glassed” on one side or the other with the required number of ply's and orientation of the reinforcing cloth. After cure, the part can be removed from the tooling fixture and the opposite side can receive its structural plays of reinforcing cloth. It is the reinforcing cloth that gives TPG its strength, the paper itself can best be thought of as a stable core material which is essentially self supporting on which to lay up the structural cloth. Pieces of TPG can be joined together by bonding and by the use of mechanical fasteners such as rivets, staples and bolts
It is not practical to cover the entire process here. Jerry Holcomb has written the “instruction manual” for the TPG process which can be purchased from him. Contact him for information at:
1010 N.E. 122nd Avenue
Vancouver, WA. 98664
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