Amazon’s drone delivery program stopped being a joke a while ago, but the company still has to overcome serious challenges to make the technology actually work. One of these is getting drones near enough to large populations so they’re more efficient than regular road delivery. Amazon has an idea for that though: Huge. Drone. Beehives.

In a patent application published yesterday, Amazon described how “multi-level fulfillment centers for unmanned aerial vehicles” could help put drones where they’re needed. The application notes that due to “their large footprint,” current warehouses are located “on the outskirts of cities where space is available.” But multi-story drone centers could be built vertically, rather than horizontally, allowing them to be placed within “downtown districts and/or other densely populated urban areas.” And, of course, making them high-rises would let the drones fly in and out without getting dangerously close to pedestrians at street level.

Amazon’s application includes sketches of a number of differently shaped buildings and interior views, showing how human employees would load-up the drones with packages:

But flying large numbers of drones in cities invites other problems too. Who’s going to want to live near a drone delivery tower if it makes so much noise? And what if drones start falling out the sky, making impromptu, and possibly fatal, deliveries? Amazon is obviously thinking hard about these problems, and in the same round of patent applications as the delivery beehive, suggests a few solutions.

For drone noise, the company is suggesting custom rotor designs that would chop through the air more quietly. These include adding “trailing edge fringes,” “leading edge serrations,” “sound dampening treatments,” and “blade indentations for sound control” to rotors, but all focus on the same principle: breaking up the airflow around propellers to try and alter or reduce the sound they make.

The image below shows how “trailing edge fringes” — the tiny plant-like fronds — might be added to the rotor blade. These might make drones quieter, but let’s face it: they’ll also look terrifying.

And the last significant item on Amazon’s patent application list? Drones with multiple sets of rotors and motors, so that if one set fails, the other can take over. It’s a simple idea, but an essential one.

Of course, all these are just applications. It doesn’t mean Amazon is necessarily going to build these things, or that drone deliveries will ever become widespread. What it does show, is that the company is continuing to think hard about the future of deliveries. And who knows? These things always seem silly, right up until the point they’re real.