When the US finally decided to evacuate its troops, diplomatic officers, and local allies from Vietnam in 1975, the biggest problem was a lack of helicopter landing zones. The country had left the job so late, it had no choice but to conduct the evacuation with choppers that required large, level clearings — and the US embassy had nothing of the sort, beyond the roof. Heroic efforts were required to finish the job, including having soldiers chop down trees and even push unneeded helicopters into the ocean. But that was 1975 — surely modern technology has come up with something better, by now?

Well, not really. Helicopters offer more control to pilots than ever before, but you’ll still need to be one hell of an ace if you want to put down safely on anything other than a groomed landing strip. That’s a problem if you’re conducting military operations in, say, multiple desert countries, or in ancient, bombed out Mesopotamian cities. These areas are often light on easy landing zones, but strategically require extensive use of helicopters — not a good situation.

Now, DARPA has an idea that could let helicopters land on just about anything — no matter how uneven.

The idea comes back to DARPA’s favorite new word: autonomy. The idea is to give helicopters four independently controlled, autonomous legs with built-in distance sensors. These legs can see the topology of the ground beneath them, and adjust their height accordingly, to keep the helicopter body level. This could let a chopper set down on the side of a slanted roof, the side of a mountain, or just on a highly irregular surface, like a battlefield pock-marked with mortar holes. And since the legs can fold inward as the chopper descends, they can do some shock absorbing to cushion unavoidable hard landings to reduce the risk of damage or injury to passengers.

It could even make helicopters more useful for the Navy, allowing safe landings even during choppy weather with rocking landing decks; it should be able to adjust its orientation while on the ground, potentially swaying with the deck of the ship and keeping the whole from tipping. DARPA’s official statement about the project says it could handle up to a 20 degree grade.

The legs fold up when the helicopter is in flight, like the landing gear on a plane. It’s only been tested with large remote control helicopters, not yet with a full sized version. That full sized version should’t be all that much heavier than regular helicopter landing struts, since they will be hollow, made of metal scaffolding.

This is all part of DARPA‘s Mission Adaptive Rotor (MAR) project — an attempt to bring the unique capabilities of helicopters into the next generation. This landing gear initiative would greatly advance the role of helicopters as the versatile alternative to fixed with aircraft — but it’s not all DARPA’s been working on. Their vision for the VTVL aircraft would include autonomous, modular cargo carriers that could switch between troop transport, cargo carrying, and even combat roles.