Starting today, eager customers of US pizza restaurant chain Papa Johns living in southern North Carolina will have the opportunity to receive their food from the sky, thanks to a new collaboration with Alphabet’s drone company, Wing.

But Papa Johns’ signature pizzas won’t be on offer. Instead, drone-loving North Carolinians will have to choose between three kinds of sandwiches: Philly cheesesteak, chicken bacon ranch or steak and mushroom varieties.

The transition to drone delivery is part of a broader trend in the US and worldwide. Questions about the long-term economics and regulatory picture around unmanned aerial vehicles persist, but Wing boasts partnerships with Walmart, Panera, and DoorDash and is delivering through the sky to customers in four metro areas: Atlanta, Charlotte, Dallas-Fort Worth, and Houston.

However, until very recently, drone operators have struggled to fly full-size pizzas. The familiar and cheap cheese-sauce-bread combo has been loaded onto self-driving cars and autonomous sidewalk delivery vehicles and has been assembled by robots. It’s a fast and satisfying option, especially for busy families tight on time.

For companies hoping to break into the food delivery space, this is unfortunate: 11 percent of the US population eats a slice on any given day, according to the US Department of Agriculture. In a fast-diversifying restaurant industry, getting them to customers is still big business. But the realities of physics, engineering, and the restaurant business conspire to make pizzas a challenge for drones.