Cotton Propellers

Sun (Auckland), Volume II, Issue 452, 6 September 1928, Page 9

Cotton Propellers

Big Plane’s Equipment

PATENT MATERIAL STANDS HEAT AND STRAIN Most people believe that the propellers of the Southern Cross are made of wood. Some think they are of metal. But the basic material of the three screws which drive the bis plane through the air is cotton fabric. Specially woven and impregnated with phenolic resin this fabric solidifies, under the combined application of heat and heavy pressure, into a substance of great toughness. TONS OF STEAM In the manufacture of propellers the impregnated cotton fabric is cut in templates which, when built up, layer upon layer, assume the exact shape and size of the finished propeller. These lamination of fabric are then accurately measured and adjustments made by removing or adding layers. About 220 laminations make up one propeller. The pile of fabric is next placed in a highly polished bronze mould and heated by steam, a head pressure of several hundred tons being simultaneously applied. The heat and pressure are kept on the mould for several hours until the laminated fabric has become a solidified substance of uniform structure. The propeller in moulding has taken on the high smooth finish that had been given to the surface of the mould in polishing it. USED IN LONG HOPS The propeller is then sawn through the middle of the hub, making two separate blades; the hub end of each is then rough machined to fit a steel balancing arbor and a preliminary check on balance is made. After this check, the hub of the blade is finished to fit the steel hub and a final balance is taken. Each blade is balanced separately against a standard, thereby making them interchangeable. At the time of balancing each blade is checked for angles, track, width, thickness and surface defections. The blade is now a finished product.

These propellers have figured in several of the recent transoceanic flights, among which are the successful ‘ hops” of Lieutenants Maitland and Plegenberger in their large tri-motored army Fokker plane, and Martin Jensen, pilot of the Breese monoplane, Aloha, which finished second in the Bole race from Oakland, California, to Honolulu. Water and moisture have no effect on the propellers and stone bruises will not splinter them. There is no tendency of the propeller to crystallise, and the material is considerably lighter in weight than metal, weighing about one-half as much as aluminium, ancl change of temperature, which is a handicap to wood propellers, has no effect upon it. The propellers of the Southern Cross are not the original propellers used for the trans-Pacifie and trans-Austra-lian flights, but are new ones, duplicates of those used for the original great flights, and were presented to Squadron-Leader Kingsford Smith by the makers. One of the original propellers is being retained by SquadronLeader Kingsford Smith and FlightLieutenant Charles Ulm, one blade each.