|
I'm no chemist, but I do know that the wood glues available before the Great War weren't really up to the standard needed to secure an airframe. Fokker was fond of plywood; but his late-war E.V/D.VIII parasol monoplane's wings suffered rapid deterioration partly through delamination due to weathering, in addition to the poor manufacturing standards that were another cause of the type 'coming unglued' when the wings failed. Nowadays, yes, chemical fastening is the way to go for rapid and easy construction, particularly with modern composites. The less holes drilled in a structure to accomodate mechanical fasteners, the less risk of splits and cracks too.
Albatros certainly knew a trick or two about laying veneers, as their D-series scouts' fuselages show, but even these employed a degree of mechanical fastening to the fuselage formers and stringers that defined the shape, as well as gluing. Their earlier method of covering the fuselage frame by using screw-fastened ply provided great strength with minimal internal bracing as well. But it was certainly easier for less-well endowed manufacturers to build braced, mechanically-fastened structures. Such structures were long on the maintenance time needed to adjust them, to 'true them up'; but they were also relatively easily repaired, and research and development was certainly made easier if a part of the airframe could be changed at a time, rather than the whole lot.
Which was stronger? Depends very much on the application and the quality of the materials used, but the crucial design imperative was to obtain strength with light weight. Fabric-covered framed structures certainly provided that. Their down-side was exactly that which you've described: they DID 'get loose' over time, often a very short time if they were serving in harsh climates such as those encountered in the hotter theatres of the War like Palestine, Mesopotamia and East Africa. Hence the development of all-metal airframes.
The tension and how it was measured? It should be borne in mind that bracing cables or wires need only prevent the structure from 'going out of shape', and that each individual cable/wire bears only a small proportion of the total load imposed on the structure. So, provided the bracing is taut and the airframe's component parts are properly 'true', it'll do the job. My ol' motorbike's wheel spokes are fine, they chime nicely with a sweet 'ding' when I tap 'em with a screwdriver to check their tension; the riggers of early airframes used the same test.
I invite your attention to a splendid book, Volume 4 in the 'RAF Museum' series, 'British Military Aircraft of World War One', published in 1976 by Arms and Armour Press, ISBN 0-85368-261-5. It's a collection of the 'the Official Technical and Rigging Notes for RFC and RNAS Fighting and Training Aeroplanes, 1914-1918'; it includes many diagrams and texts showing the riggers how types such as the B.E.2c and Bristol Fighter should be assembled for service - and nowhere in it is there any mention of pull-force, torque-settings or anything else regarding bracing tension. Granted, the notes were meant to aid rigging, not airframe manufacture, and are more concerned with getting the relationship between the fuselage and flying and control surfaces correct, but any halfway-bright rigger would've been able to brace an airframe without needing to measure the precise tension exerted. His main worry, not to apply too MUCH tension, was addressed by the 'weakest link' built into most bracing of the day: the 2BA thread of the turnbuckle stripping if he heaved his spanner too mightily upon it.
To hell with strain-gauges 'n' such-like, I like me aircraft strong but simple - cheers!
(8;¬)}
Simba.
|