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Aviation History
1917
1917 - 0047.PDF
JANUARY II, 1917. THE STEEL CONSTRUCTION OF AEROPLANES.* By GROVER C. LOENING, B.Sc, A.M., C.E., Vice-President of the Sturtevant Aeroplane Co. THB Sturtevant Aeroplane Co. has recently developed a newtype of steel construction for aeroplanes, tests of which have shown that it has many advantages in reliability, lightnessand strength that cannot be obtained in wood. For the fuselages, rudders and tail surface, methods of using steelhave been devised which are remarkably successful. The construction of aeroplanes has usually involved theuse of wooden members fastened by steel fittings, which, due to the greater stresses involved in larger aeroplanes, havegradually become more and more bulky and complicated. A study of the construction of large-sized aeroplanes at thepresent time reveals that the weight and cost of manufacture of these metal fittings has become a much larger item thanwas formerly the case. A departure from the usual wooden construction of aero-planes that has been used in a few instances is the application of steel tubing, not only in the bracing members and struts,but also in the wing spars and in the fuselage construction. A study of this development has shown definitely that steeltubing construction is heavier than the customary wooden construction for the same strength. In addition, it has beenfound that the joints are difficult to make in steel tubing construction, requiring a great deal of welding and brazingj'nto suitable sleeves, with the general result that the joint is Several kinds of metal-working tools, metal- forming;machines, angle and channel benders, cornice breaks and powerful presses, were available for this work at the HydePark plant of B. F. Sturtevant Co. After experimenting with the site and strength of various members and withdifferent types of riveted joints and pin -connected joints, designs were drawn op for the fuselage of the Sturtcvnnttractors, consisting of longerons of steel angles and struts of steel channels, with a few special rolled sections peculiarlywell adapted to the work. The computations for the site of all these members weremade following the best engineering practice, on their bending moments, moments of inertia, reliability of fixing, &c. Afterthe sections had bren established by calculations, exhaustive tests were made on the strength of the various members atthe Massachusetts Institute of Technology. The values of strengths thus determined checked remark-ably closely with the computed strength of the members, giving a most striking illustration of the accuracy withwhich steel members can be designed. The stresses on the fuselage induced by the air loads, tail skid loads and whipof the tail being determined, the fuselage was constructed with suitable safety factors. In the flying tests of the various Sturtevant steel aero- w. m m m m m ft m m K ft ft K ft ft*" ft « m ft ft ft ft ft ft ft ft' ft FI4. 1.— Steel con«truc- tlon in fuselage. 1 1 1 MI1MM heavier and not as reliable as desired because of the in-determinate nature of a welded or brazed joint. It has been clear, however, for some time that steel con-struction was desirable for aeroplanes, not only in making them more mechanical, more durable, fireproof and moreweather resisting, but from the fact that steel, as a structural material, has in all branches of engineering been found morereliable and better adapted to manufacturing in quantity. The problem confronting the Stnrtevant Aeroplane Co.,therefore, was to apply the principles of steel construction that had been developed with such success in structural,shipbuilding, engineering, automobile and machine tool work. It was apparent at the outset that what had been done inapplying steel to the construction of aeroplanes required considerable development and modification in order not toincrease the weight of the machines and to simplify the fitting of members to each other. Entirely on its own initiative, therefore, this companydecided to use in aeroplane construction structural steel sections of angles, channels, I-bcams and the like, withriveted and pinned joints, exactly as is the practice in the most refined civil engineering of structures. The only dataavailable to guide this new development was what had pre- viously been obtained by the author in his experiments withthis type of construction in 1912 and 1913. * From Aviation. planes conducted recently, and in several tests of severelandings that have been made, it has been demonstrated that both this design and construction fulfil in every way thefunctions called for. In addition tu the construction of the fuselages themselvesentirely of steel, the engine beds of these aeroplanes are also made of steel, and have definitely demonstrated a similarreliability and correctness of design. Furthermore, it was decided to construct surface framr.sof structural steel, and as a first step towards this end the flaps of the elevator were made of steel channels and angles.After some preliminary experimenting, a method of con- structing these simply was devised, and upon completion itwas found that these flaps were actually lighter, more rigid and much more serviceable than those ordinarily made ofwood or of steel tubing. This was followed by making the rudder and wing flaps alsoof steel, and lately the Sturtevant Co. has-extended this to the construction of the wing itself entirely of structural steelsections. The steel wing construction has received severe tests and thorough demonstration. An account having thus been given of the general natureof the development of this new type of construction, the various features may be taken up in greater detail. Tosimplify the consideration of this matter as much as possible, two instances in which this construction is used will be taken up. 47 ,^_isJikM
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