Flight, December 1932

A "Shot-Welded" Aircraft
In our issue of October 27, 1932, we published a brief illustrated description of the Budd "Shot-Welding" process. Below is described the BB.1 amphibian flying boat built by the Edward G. Budd Manufacturing Co., of Philadelphia, for the American Aeronautical Corporation, of Port Washington, New York. This machine, which is built throughout of stainless steel, has all its components joined by the shot-welding process, and is coming to this country shortly, when it will be demonstrated by Mr. Rex Stocken.

   FUNDAMENTALLY based upon the Savoia-Marchetti S.31, the American Aeronautical Corporation's BB.1 amphibian illustrated here was altered in certain minor respects in order to facilitate the joining of structural pieces by the Budd "Shot-welding" process. In the main, however, the machine remains true to the original S.31 design in the matter of external lines, and the main interest attaching to it lies in the novel constructional details.
   The Budd "Shot-welding" process, described in FLIGHT of October 27, 1932, consists essentially in electric spot-welding of extremely short duration, and the process has the advantages that, as the duration of heating is so extremely short, the metal surrounding the weld does not become weakened, nor does it lose its rust-resisting properties if stainless steel is the material welded. Moreover, the process is throughout under perfect control, and a permanent record of each weld is automatically registered for later examination and reference. The process is of American origin, but is being introduced in this country by the Pressed Steel Company, of Cowley.
   The BB.1 is a small single-engined amphibian flying boat with open cockpit accommodation for four, including pilot. The machine has a wing span of 34 ft., a length of 25 ft., a wing area of 292.4 sq. ft., a tare weight of 1,749 lb., and a normal loaded weight of 2,650 lb., which may, however, be increased to 3,300 lb. Fitted with a Kinner engine of 170/200 h.p., the machine has a top speed of 118 m.p.h. and a cruising speed of about 100 m.p.h.
   In general outline design the BB.1 is a typical Savoia flying boat, with flat-sided hull and straight-line vee bottom of the single-step type. The engine is housed in a streamline nacelle in the top plane and drives a tractor airscrew. The undercarriage can be raised clear of the water when the machine is used as a flying boat, but is not buried inside the hull or wings. A tail wheel is used instead of a skid, and as it moves with the air rudder it serves as a water rudder for taxying on the water.
   The hull of the BB.1 is built entirely of stainless steel, and consists of an internal skeleton of frames and light longitudinal stringers of U-section, to which the stainless-steel sheet planking is attached by shot-welding. The fact that the hull is of the straight-line type, i.e., with flat sides and a straight-vee as distinct from curved-vee bottom, facilitated manufacture very greatly, as the sides could be welded up "in the flat" on the bench, and later attached to the frames and stringers as complete units. Similarly with the two halves of the vee bottom. These were first welded together as flat sheets on the bench, and afterwards welded to keel and chines. The whole manufacture of the hull must have been very rapid, but whether or not the Budd shot-welding process would be as readily applicable to the construction of a typical British hull with curved lines is, perhaps, open to doubt. Water-tightness is achieved by running solder into the gaps between welds.
   The biplane wings are of perfectly orthodox type, with two main spars, Frise ailerons, and the usual interplane struts and streamline wire bracing.
   Formed as a Warren girder, each spar is composed of top and bottom flanges of U-section, to which the short ties are joined by shot-welding. The material is, like that used in the hull, stainless steel. It is likely that a wing spar built up in the form of a Warren girder is slightly less efficient than the corrugated box spars habitually used by British constructors, at least for a machine as small as the BB.1, but the difference in weight cannot amount to many pounds, and the facility with which such a spar can be manufactured should be worth a slight sacrifice in structure weight.
   The wing ribs are also of stainless steel, and are assembled on the bench by shot-welding, being "slid" into place on the spars afterwards. The leading edge is covered with thin stainless sheet, up to the front spar.
   Wing-tip floats of usual type are used, and are bolted direct to the lower wing spars by four bolts each. Structurally they are of similar construction to the main hull. The internal stringers of the hull, by the way, are U-section stainless strips similar to those used in the wing spars in order to reduce to a minimum the number of different sections used. In this way, and as a result of the rapidity of shot-welding, the higher cost of stainless steel is somewhat offset, in addition to the other advantages regarded purely as a welding process.
   When, shortly, the BB.1 comes to this country, it will be taken on a tour by Mr. Rex Stocken, when doubtless a large number of FLIGHT readers will take the opportunity to examine this very interesting piece of aeronautical engineering.