About five years ago, a Kickstarter popped up for the air umbrella. It wasn’t long before the project fell apart and the company made at least some refunds. Old news, we know. But [The Action Lab] recently explored the physics behind the air umbrella and why it wouldn’t be very practical. (Video, embedded below.)
Notice we said not very practical, not unworkable. It is possible to shoot rain away from you by using pressurized air. The problem is you need a lot of air pressure. That means you also need a lot of battery. In particular, [The Action Lab] used a leaf blower and even with that velocity, there was only minimal water deflection. In other words, you are still going to get wet.
The video computes an estimate of the terminal velocity of an average raindrop. We looked at the University of Wisconsin’s The Weather Guys site and they came up with a slightly higher number, but not much higher. According to the university, it is about 20 miles per hour, depending on the size of the drop.
According to the video, the air compressor has to move air a bit faster than that terminal velocity. So the question is, do you want to have a 25 mile per hour airflow right over your head? How long can that compressor run on a small battery in the handle?
As you can see, this isn’t a practical thing, but it still managed to generate quite a bit of backing — over $100,000. We wonder if any of the backers were physicists?