Aircraft Construction

I've been looking at the different methods used to construct aircraft during the Great War and I have a couple of questions.
The current method of building a wood airframe involves gluing the airframe together. Specifially, in modern construction *wood longerons are glued to cross peices, and reiforced with triangular pieces of plywood that are glued and tacked over the joint. This results in a strong, rigid structure. My research suggest that most wood airframes in WWI were mechanically fastened, using some sort of metal fitting, and adjustable wire cross bracing.
*My questions are, What is the stronger method? Are we gluing things now because its easier and cheaper?Did they use glue then as well? Wouldn't all of those adjustable cross braces need "regular" adjustment? Wouldn't that type of airframe get "loose" over time? What amount of tension would be on those cross braces, and how did they measure the tension? *That's enough for now, thanks.

Barry

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.

Now I'm no A&E, but have been around quite a few aircraft and I m' still blown away by how they are built/repaired. Only as strong as it HAS to be. Next time you can, check a typical cabane strut attachment lug welded to the longerons on a Great Lakes or similar bipe. Four postage stamp sized tangs of 4130 sheet with a 1/4" bolt thru each. that's all there is holding that wing to the fuselage! But I don't believe a Lakes ever suffered a structural failure. Only as strong as it had to be.

I suppose that an otherwise faithfull WWI (SE5, etc)repro could be built using more modern wood techniques (Did n't somebody delete the wire bracing in the wings of a Sopwith Tripe- substituting ply wood webs?)
Charlie

[Dan_San_Abbott]

Barry:
You cannot compare what is done today in the light aircraft market with the construction of WW1 aircraft. First of all the light aircraft would not stand up to the rigours of Northern France and Belgium. In the Flanders region, I was told by a native, that it "rained 380 days a year!" Nor would your plywood gusseted fuselage survive a hundred landings on ill prepared very small airfields. These aircraft were fully aerobatic with no limitations. To directly answer your question, the light aircraft of today would not have passed the physical tests that WW1 aircraft were subjected to in design and developement.
There were two glues commonly used in WW1, casein and animal glue (Hooves), neither of which are half as good as any number of glues and cements we have today. I don't think an S.E.5a made today as you suggested would have stood up to combat operational stress of WW1 flying. The reason that the S.E.5a fuselage had a laced fuselage covering, was so the Ack-Emmas could gain access to the fuselage and retighten and true it up, periodically. I am sure you have a tailwheel on your aircraft with a leaf spring shock absorber? Try using a tail skid which transmits all the energy through bungee chord to the wood airframe of the rear fuselage. How about high pressure tires (80 lbs./sq.in.) to transmit the landing shock through forward fuselage while runnying over a rough airfield. The stress of vibrations of the engine, machine guns, the flying and landing wires @ 180 mph in a dive, an S.E.5a would do 200 mph in a dive. The structural flexing of the entire airframe in high speed manouevers. They were built tough to withstand combat, bad weather and lousy airfields. Every structural joint on the S.E.5a was universal! The engineers were not concerned about flying on warm Sunday afternoons off a smooth concrete runway and 1.5 to 2g turns.
Blue skies,
Dan-San

I agree with Dan-San (wow; what a surprise). The only reason light aircraft today aren't built the way the 14-18 machines were is that the latter were a rhymes-with-witch to repair and maintain. That magnificently strong and resilient structure came at a cost: the hundreds of turnbuckles that actually maintained the aircraft's structure had to be adjusted pretty much every time the machine landed. Very few owners of light aircraft today could afford the army of riggers needed to maintain a machine built in this way. Obtaining manpower was less of a problem in 14-18.

[Dan_San_Abbott]

Michael Skeet:
We now have a common ground of understanding, however, I did not know we did not, but now we do. Great!
May your skies be of the most brilliant blue,
Dan-San