The Physics of Flying Banners

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Have you ever seen a small airplane dragging a banner behind it? Picking up those banners requires some surprisingly demanding piloting skills because the banners tend to throw the aircraft off-balance:

Most of the planes that carry these signs are rather small, and attempting to take off with the sign already in tow would throw off the plane’s center of gravity, preventing it from getting airborne. Carrying the furled up sign in the cockpit or (typically tiny) payload runs the very real risk of getting it tangled up with the aircraft itself, resulting in disaster. In short, the plane can’t take off with the sign already attached. [...]

As seen in this video (but you will have to look closely), the plane flies toward a pair of uprights, dangling a hook about 25 feet behind. The sign is attached to a big loop, which itself lays across a pair of uprights. When the plane flies over the uprights, the hook grabs onto the loop, lifting it — and the sign — skyward. In order to pull off the maneuver, the plane needs to get rather close to the ground — sometimes, no more than 30 or 40 feet above the surface. While the whole process is risky (and there have beenterrible accidents), it really is the only option available.

You can read the rest at Dan Lewis's Now I Know, a daily email service of neat, odd stories.

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