4

Stan "Prop" Dzik

Allmaterials used in the construction of airplanes, whether private or commercial, should be of such quality that the ultimate aim, i.e. safety in flight, will be absolutely positive. Obviously the commercial airplane builders have laboratory testing facilities and are staffed with competent technical and design engineers which precludes the possibility of faulty design, construction, materials, etc. The problem regarding suitable materials can be, for the owner-builder, both engrossing and oft-times severe. He should at all costs avoid it being disastrous. Lacking the facilities of the larger companies, the selection and use of any materials may very

often be the result of his judgment. In order to fortify and facilitate this judgment, specifically in regard to ferrous materials, a rev'ew of some salient features regarding aircraft steel, including tub-

ing, may be deemed necessary. In a broad sense the critical areas would involve analysis, quality (both surface and internal), physical properties, i.e. strength, and specifications. Generally speaking, most airframe tubing is manufactured of

4130 or 8630 analysis steel. The permissible chemistry ranges have been firmly established by the American Iron and Steel Institute, abbreviated as A.I.S.I. In addition to the two grades indicated above a third, designated as TS4130, is sometimes used. Both the 8630 and the T34130 analysis were developed to conserve critical alloying elements. The chemistries of these grades are as follows: .4130 .28/.3S .40/.60 .040 max. .040 max. .80/1.10 .15/.25

Carbon Manganese Phosphorus Sulphur Chromium Molybdenum Nickel

TS4130 .28/.S3 .45A65 .040 max. .040 max. .90/1.20 .08/.15

as 4130 will be adequate and satisfactory for the purpose intended.

Whenever a grade E4130 is encountered, it simply means that the steel was manufactured by the electric furnace process. In addition to the above alloy grades some higher carbon alloy grades such as 4135, 8735, etc., as well as a plain carbon C1025 grade, are sometimes employed. I believe, however, that the build-ityourselfer will usually employ either 4130 or 8630 for airframe

structural purposes. Regardless of the method of steel manufacture, i.e. open hearth or electric furnace, melting practices are such that the inherent grain size of the steel should be #5 or finer, with grains as large as #3 permissible. It may be well at this point to explain the major differences between airframe and aircraft mechanical tubing. Both are produced from carefully manufactured steel, of controlled analysis and grain size. Normally airframe tubing does not require electric furnace magnaflux quality steel whereas aircraft mechanical tubing usually «

does. Airframe tubing is produced to close tolerances, fine surface finish, and controlled physical properties. In regard to the surface finish required of airframe tubing the governmental specifications

8630 .2S/.33 .70/.90 .040 max. .040 max. .40/.60 .15/.25 .40/.70

It may be well to mention that some confusion may still exist, as regards a grade quite prevalent some years ago, namely X4130. Previous to the present standard grades listed above, a grade designated as 4130 and a higher alloyed grade known as X4130, were pro-

duced.

For comparison purposes chemistries of these grades are

here listed: