The Secret Service found a "quadcopter" drone on White House grounds. The Post's Carol D. Leonnig explains how the White House is protected from aerial threats. (Jorge Ribas/The Washington Post)

At some point Sunday night, someone flew a small drone onto the grounds of the White House. White House press secretary Josh Earnest told reporters that the drone -- or, to remove the ambiguity of that overly broad term, the small quadcopter -- posed no threat to the building or its inhabitants.

The incident raises the question: Could a small unmanned aerial vehicle (UAV) pose such a threat? To answer that, we need to know the answer to three other questions. How far can a UAV fly? How is it controlled? And: What can it carry?

We spoke with Parker Gyokeres of the aerial photography company Propellerheads to answer those questions.

There are two types of UAVs that are available to the general public: Multicopters, which was the type of device found at the White House, and remote-controlled planes. The technology for the latter has been around for decades, Gyokeres noted, so the threat (such as it is) is nothing new. Remote-controlled planes can fly much farther than multicopters, over the span of ten to fifteen minutes. The duration of a copter UAV is shorter, which is largely a function of battery life. More battery power means a longer flight -- but it also means a heavier, larger device.

In other words, UAVs are more than capable of making it from some distance away from the White House toward the building. And they can do so precisely.

Kevin Vertucio, of Bristol, Pa., practices flying his "quadcopter" while wearing goggles connected to the small camera seen at the bottom center of the craft, in Yardley, Pa., Tuesday, Sept. 10, 2013. (AP Photo/Mel Evans)

"You can send them on autonomous flight routes," Gyokeres explained. "You can open up a map and click-click-click and have it travel your route. You don't need to having coding ability. You just need Google Earth on your computer." Commercial UAV pilots use this to survey land and plan out routes for photography. In theory, it would allow someone from some distance away to direct a UAV -- copter or plane -- to a precise location. "You can buy an APM 2.5 flight controller for sixty bucks," Gyokeres said, "that will put it within three feet, anywhere within 60 miles."

Assuming you're not trying to get into a forest. One of the scourges of UAV flight is trees; planes and helicopters, as you might suspect, are incapable of navigating through branches. "They'll fly into buildings, they'll fly into trees, they'll fly into all kinds of things," Gyokeres said. But there are more advanced flight controllers that allow you to set altitudes at waypoints, meaning that you could drop a device into a particular spot. Without such a planned route, the pilot would need to be fairly close to the target.

To answer the payload question, we can look to the news. Last week, a multicopter crashed in a parking lot in Mexico, spilling its cargo of methamphetamine. At the time, a DEA official explained that using drones to deliver drugs was "a new trend in smuggling." "This method will only allow a small amount of drugs to be flown at a time," the official said, "and, coupled with the ease of detection, does not make this method very profitable to these drug trafficking organizations." Not to mention: It crashed.

The same holds true for using a UAV for some sort of attack. "Unless you're delivering an envelope of something nasty," Gyokeres said, "the biggest risk is of lacerations from the blades." Steve Cohen, who organizes the New York City Drone User Group, explained that a larger payload was possible. "A good comparison would be the cinematography community that uses these," he said. "You can certainly lift 25 pounds and have an aircraft that weighs another 15, so a 40-pound device."

But the size of the device increases "exponentially" with weight, Gyokeres explained. That's unlikely to change over the short-term; the bigger the payload, the more thrust needed to power the copter, the more batteries that are needed. That makes the device bigger, and more easily seen. (More on this in a second.) Gyokeres compared the utility of using a drone to attack the White House to technology available in the Middle Ages: "Literally, a truck with a trebuchet on it would be a more effective delivery platform."

Could a larger drone approach the White House at night, unseen? Maybe. But it would likely require the use of a pre-programmed path -- and it's likely that any such attack could be thwarted. Several years ago, a team at the University of Texas demonstrated the ability to trick a drone into flying an unexpected route by sending it incorrect GPS coordinates. GPS, after all, is based on signals from geosynchronous satellites orbiting the Earth. The signals are easy to overpower closer to the ground. Line-of-sight control -- meaning, some guy standing near the White House and eyeballing the UAV to its target -- could also be interrupted; radio signals or WiFi signals can be interrupted from within the building.

Cohen and Gyokeres, both UAV fans, pointed out that many things could potentially be used as methods of attack. (Both were also frustrated that someone who was probably just trying to take photos of the White House drew negative attention to their hobby.) "I think that there are all kinds of ways -- not that I'm versed in them -- to create disorder or disrupt everyday lives if someone were inclined to do so," Cohen says.

Gyokeres noted another incident in the past. "A dude flew a Cessna into the White House a few years ago," he said. "It didn't hurt it."