WW1 construction method

[mdiam]

I have a question for all you experts out there; I have always been interested in the Sopwith Pup, and the construction method used in the fusalage was the wire braced wooden truss method.

Does anyone know if there was significant stretching of the wire bracing over time, and if so, how often it needed to be adjusted or replaced.

I realize the answer has a lot to do with how the aircraft is used, acro, combat maneuvering versus low stress straight and level flight. But since that construction technique was very common in the WW1 era (not just Sopwith) there should be a lot of history to go by.

I've always wondered how much of a maintenance issue that is/was.

Thank you all in advance for all your help!

Mike D.

[jumpinjan]

I don't have any statistical information on Time Between Failures, but if you look at it from an engineering view point, the fuselage wooden members would all be in compression and wood can take compression loads pretty well. There is also the same bracing in the wings and one can find that same technique in homebuilt aircraft. Another thing to consider is WWI aircraft were not expected to have any longevity. They probably were build simple, quick & light just to get as many out there, and stressing performance while trading durability.
Jan

[visaliaaviation]

Typically, wires don't stretch, but the loop and ferrel ends can slip, causing same net effect. This is not an overt problem (avoiding the given the situations you mention), and was not abandon until the late '20's that threaded tie rods replaced wires in production a/c. Travel Air (the Witchita Fokker) employed wire braced (w/ferreled ends) steel tube fuselage and is rather stout allowing huge engines and unlimited aerobatics.

[Wind In The Wires]

On aircraft with threaded flying wires the issue is with the anchors (typically a nut and washer) pulling through the wood anchor blocks. Which is why you'll occasionally see a pilot "twanging" the wires on his walk around.

As to stretch in the wires, G loads stretch the loaded wires enough that the unloaded wires go slack and vibrate so fast that they become invisible which is what creates the singing sound that you hear when watching a biplane doing aerobatics.

BTW, the "rapping" sound you hear when watching a T6 or a Pitts doing aerobatics is the prop tips going supersonic.