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Today a small airplane is towing an advertising banner, about 20 by 30 feet, in a circular path around my town's university campus. The banner stays tilted about 45 degrees to make it easier to read by those whom the airplane is circling. Winds are 10 knots gusting to 20, if that matters.

How can it maintain that tilt? Surely the tether can't exert a torque on the banner.

Websites of companies such as Van Wagner Aerial Media and Airplane Banners Nationwide say they can do this, but without explanation:

Each advertisement will be tilted, with your choice between zero and 90 degrees, towards your audience.

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Banners have a lead pole to keep the leading edge straight. This pole is weighted at the bottom, which ensures that the top and bottom of the banner remain in the correct place.

By itself, this would ensure the banner remain perfectly vertical. To achieve the proper angle for viewing on the ground, a tab is attached to the top of the lead pole, adjusted to the required angle to push the top of the pole in the desired direction to achieve the right viewing angle.

Here's a quick sketch to try to illustrate the setup, with the banner, pole, weight, trim tab, and harness:

banner on pole, direct from side, with tab at top and weight at bottom

Here, we're looking at about a 45 degree angle from ahead of the banner, with the trim tab adjusted to the left of the banner's direction of flight, causing the top of the banner to tilt to its right:

oblique view, tab offset to left, causing top of banner to tilt to right

In other words, the tab at the top of the pole acts similarly to an airplane's rudder, where deflection to one side results in a force applied in the opposite direction.

More reading here:
Aviation Stack Exchange: How are banners kept upright?
Pilots of America: Banner aerodynamics
Quora: How are flying banners stabilized?

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    $\begingroup$ I had envisioned this earlier before you posted the picture and thought, 'that wouldn't work because then the constant pressure on the tab would keep the banner rotating." But I didn't envision the weight at the bottom. The tab provides enough pressure on the top to tilt the lead pole, but not enough to overcome the weight at the bottom. Thanks for the drawing! $\endgroup$
    – Arluin
    Nov 10 '20 at 16:56

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