Page 50 of the Feb. 2021 issue of the EAA's magazine Sport Aviation reports that

Like any good vintage airplane, the Sea Bird likes to fly coordinated,
and the flying wires will sing out loud if the ball gets off-center.

Why would the wires hum or sing more when the airstream impinges from one side?

All else being equal, a sideslip converts some of the flow's transverse component to an axial component, from the wire's point of view. (Like many airplanes, the Sea Bird's rigging is mostly parallel to the wing.) That should reduce vibration, because axial motion in a wire under tension is hard to provoke: try bowing a violin with the bow nearly parallel to the string.

  • $\begingroup$ Is there really no tag for such wires, by one of their many names (bracing, flying, landing, incidence)? $\endgroup$ Apr 25 at 20:01
  • $\begingroup$ The lines are on the top surface of the wing and may not be under tension on normal flight, so they would only be tight enough to resonate under certain conditions (low/negative lift, sideslip). $\endgroup$
    – Frog
    Apr 25 at 20:19
  • 1
    $\begingroup$ The photos in the print magazine show "landing wires" above the wing, "flying wires" below, and bracing wires at the wingtip pontoons and tail. (But even the detail photos don't reveal any wires' cross section.) $\endgroup$ Apr 25 at 20:25

Here is one reason.

It once was common for suspension wires to be flattened rather than circular in cross-section, to reduce drag. those wires were then aligned with the airflow past the wing and fuselage in cruise. However, any time that airflow was not aligned with the wires, they would present an angle of attack to the slipstream and generate lift, which would pull them out of position, stretch the wires, and twist them to increase the local AoA. Then the wires would shed a vortex, stall (killing the lift), untwist, snap back, and then get pulled out of position again, etc., etc. and the result was the wires would "sing".

You can think of this as a special case of aerodynamic flutter.

  • 2
    $\begingroup$ So the vibration is neither transverse nor axial, but torsional? Neat! $\endgroup$ Apr 25 at 19:59
  • 1
    $\begingroup$ The Sea Bird was 1935. Is there a reference for which years noncircular wires were common? $\endgroup$ Apr 25 at 20:05
  • 3
    $\begingroup$ they were used in the Ryan ST "Sport Trainer" which first flew in 1934. the flat wires are mentioned by James Gilbert in his book The Great Planes. $\endgroup$ Apr 25 at 21:35
  • $\begingroup$ @CamilleGoudeseune The wires would always be non-circular as soon as the first engineer thought of the possibility which was probably right at the beginning. $\endgroup$
    – Nobody
    Apr 26 at 15:30
  • $\begingroup$ @Nobody - I doubt there were any non-circular flying wires in the ww1 era $\endgroup$ Apr 26 at 17:21

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