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What are drag and anti drag wires,and how important are they to the performance and strength of the wings of an airplane?

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  • $\begingroup$ stearman.net/index.php/… Helpful link I found though there are no images. $\endgroup$ – ironduke97 Jun 28 '18 at 7:03
  • $\begingroup$ Very helpful article...appreciate!👍 @ironduke97........ $\endgroup$ – David Teahay Jun 28 '18 at 8:56
  • $\begingroup$ So we are supposed to believe that the wings are making thrust, not drag? Something seems wrong with this picture. $\endgroup$ – quiet flyer Nov 5 '18 at 1:35
  • $\begingroup$ It's hard to believe that that would happen in any part of the flight envelope. Is the point that at high angles-of-attack the force generated by the wings acts forward in the aircraft's reference frame, yet still acts aft in relation to the direction of the flight path? $\endgroup$ – quiet flyer Nov 5 '18 at 1:41
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Definition from the Stearman Restorers Association (emphasis added):

Drag wires run from a point inboard and forward in a bay to a point outboard and aft. In this position, the Drag wire is there to RESIST drag forces that would tend to pull the wing tips aft as the airplane travels through the air. Anti-Drag Wires oppose the drag wires running from an inboard aft location to an outboard forward point in its bay. As the name indicates, these anti-drag wires oppose forces in the reverse to the direction of flight.

enter image description hereIn a wing without a structural skin like on a fabric covered aircraft, they provide rigidity in the horizontal plane by creating a wire braced truss system of the spars, longitudinal tubes called compression tubes spaced at intervals between the spars and holding them apart, and the drag anti-drag wires forming an X between each pair of compression tubes.

The drag/anti-drag loads are not that high so fairly small wires can be used. An Aeronca Champ's fabric wing uses about 1/8" steel rods for the job. Some homebuilts just use 1/8 steel control cable. The wires at the root see the most load.

You can also use diagonal tubes that just run from one corner to the other of each bay and take both compression and tension loads. Wires are generally a bit lighter.

For your ultralight, bracing could probably be made from 3/32" cable with thimbles and nicropress fittings at the attachments.

You can see the drag/anti-drag wires in this Goat glider. The plans are open source so there is probably a lot you could copy from this design.

enter image description here

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    $\begingroup$ There are several wires in the photo. You might specify which are drag/anti drag. $\endgroup$ – Pilothead Jun 28 '18 at 5:07
  • $\begingroup$ A better photo will be needed to show the difference too... $\endgroup$ – jwzumwalt Jun 28 '18 at 5:22
  • $\begingroup$ Diagram added with red dots indicating the D/AD wires $\endgroup$ – John K Jun 28 '18 at 14:59
  • $\begingroup$ Mind if I ask....what's the name of the first airplane pic @John K $\endgroup$ – David Teahay Jul 11 '18 at 8:44
  • $\begingroup$ Sorry David I don't know it was just a random image in Google images. $\endgroup$ – John K Jul 11 '18 at 13:56
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Try pulling 1/8 inch steel cable apart. Steel is very good in tension. (wood is outstanding in compression). The purpose of antidrag wires is to maintain tension in the drag wires. They pull against each other, creating more rigidity or stiffness in the structure.

This type of construction, along with thin undercambered biplane configuration, is not as common these days, stressed skinned cantilever monoplane designs are most popular.

However, especially for the aviation history enthusiast who does not need to go particularly fast, loves gentle landings, and flying with half the horsepower, they are worth looking into.

One caveat is not to go too far downwind with them, it will take you a while to get home. Checking wire tension as part of pre-flight will help as well.

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