Wing rigging practices- German v British

[Rowan Broadbent]

I am intrigued by the British (and French) practice of using double cables for flying wires. The German manufacturers never seem to have done this.

My assumption is that doubling of flying wires was to cope with the higher positive g stresses in normal flight, most modern combat aircraft seem to be stressed roughly 2.5-3:1 positive v negative g and I assume that the same order of difference was true of WWI machinery.

Did the Germans cope with this stress differential by using thicker rigging cables for flying wires? (in conventionally rigged aircraft v cantilever) and if so, what were the comparable dimensions?

Many thanks in advance.

[Albatros_Ace]

well i dont know about your question but i do know albatros just let its wings rip off

[Dan_San_Abbott]

Rowan:
I believe the british practice was a safety factor, a single flying wire shot away the aircraft would loose the wings. With double wires the chance of getting both wires increases the probability considerably. Further two smaller wires in plane have less drag than a single heavier wire.
Blue skies,
Dan-San

['14-'18aviationcollector]

Originally Posted by Albatros_Ace

well i dont know about your question but i do know albatros just let its wings rip off

I believe that practice was an attempt to sacrifice the wings in order to protect the more important fuselage, which of course contains the pilot who must be protected at all costs! .... (tongue possibly very slightly placed in a sideways position, in the general vicinity of the cheek ....) Maybe it was a very early attempt at designed obscelescence ....

[Flamingo]

Hi Rowan

here are two references to german rigging wires, the only ones I know







Hope this is of help

Joachim

[Rowan Broadbent]

Joachim, many thanks, that is a fascinating insight!

Interestingly, in the Cl IIIa example only the rearmost flying wire (no.2)has a substantially geater diameter, equalled only by the higly-stressed landing gear bracing wires (10 & 11).

What would be useful would be some sort of table which relates diameter to breaking strain - or is it a simple linear relationship? Perhaps one of our resident engineers can assist. Also, does length of wire have an effect on breaking strain - I would say not, from my little experience of fishing tackle!

Of course, I am assuming that the wires are of the same tensile strength material......

I can buy Dan's idea about redundancy in flying wires - but because civilian aircraft also seem to have doubled flying wires, I'm ultimately unconvinced that it was only for reasons of combat-worthiness. The drag factor is interesting, but the drag of a rafwire must be smaller than that for a circular section wire anyway, so I'm not sure this is relevant?

Certainly though, if German practice was as demonstrated by these drawings, then effectively doubling the flying wires for additional g-tolerance was a degree of over-engineering by British and French manufacturers.

[YavorD]

As a rule of thumb maximum load of a wire of given material is proportional to a cross section, diameter squared.
In most cases it is not about breaking load. Maximum design load should be below the point on which irreversible plastic deformation happens. Once plastic deformation begins, wire cross section decreases, tension increases and the moment of destruction is not far away.
Regards,
Yavor

[dglewwe]

"...irreversible plastic deformation..."

...that's engineer-speak for "POINK!"

[Romani]

I am not technically qualified to comment, but I will do so anyway in the hope of contributing something

Originally Posted by Dan_San_Abbott

Rowan:
I believe the british practice was a safety factor, a single flying wire shot away the aircraft would loose the wings. With double wires the chance of getting both wires increases the probability considerably.

I don't think so at all, given the multiple bracing wires, I am sure there's a degree of redundancy built in to keep everything together even if a wire was shot. If the loss of a single wire meant the loss of the airplane, then designers would have all gone for extra redundancy (more wires, regardless of section)

Combat accounts fairly often describe shot down airplanes breaking up in the air, but this usually is after going down in an uncontrolled dive, wich in many cases would break up the airplane even if the airframe was intact. we can only guess if he structural failure was caused by a broken longeron or spar or bracing wire.

I don't think it's a case of overengineering, in plain speak "just add some more strength just in case" I think that the British, by going over to RAF flying wires, wich have an aerodynamic foil section, gained in drag reduction but lost strength in the bargain.

RAF wires are "ribbons" of metal while standard bracing wires were coiled wires. Since is often hard to tell in photos and many museums and replicas and extant flying airplanes use substitute steel tubing due to the cost of replicating the original wires (either RAF or coiled wires)
I made very sure to check several photos of different airplanes and found in Jane's a few technical drawings that confirms it. Here's the best one I found, in page 139 (facsimile reprint)



I believe, based on observation and assorted other knowledge (the evolution of barbed wire is a fascinating subject) , that a ribbon is less resistant to being cut than a coiled wire.

In case of the bullet striking the wire squarely, there's no difference, but given the small diameter of wires I would assume most hits would be grazes. As you can empirically check, any small cut into a ribbon under tension will result in this cut expanding and tearing it apart entirely, while a coil will hold as long as one strand is intact.

So I assume the double flying wires are meant to offer a safety factor to compensate for this vulnerability, among other considerations.

[Romani]

Originally Posted by Rowan Broadbent

I am intrigued by the British (and French) practice of using double cables for flying wires. The German manufacturers never seem to have done this.

While we are at it, when did the French start using double wires? I am only thoroughly familiar with the Nieuport 17 and it has single wires, and I can't recall if the subject has been discussed before

Was there a technology transfer from the British to the French and late war (from 1917 onwards) French airplanes were equipped with double RAF bracing wires?