If you have ever tried to move your hand underwater you will have noticed great resistance. Do the same movement in the air and it hardly costs any effort. For a drone, the exact opposite happens: the less air there is, the worse it flies. And at the top of Everest there is barely a third of the air we breathe at sea level. However, DJI has just demonstrated that its new drones can operate up there, transporting loads, mapping glaciers and even helping to carry out atmospheric research at more than 8,800 meters high.
It is not just a technological record. It is also a demonstration of how far engineering can go when it decides to directly confront the laws of physics. The drones They don’t fly because their propellers “push down”, they do so because they accelerate enormous amounts of air.. Each blade works like a small wing that generates a pressure difference: the greater the amount of air available, the more lift it produces.
But Everest poses a very serious problem. almost At 9,000 meters above sea level, the atmospheric pressure is barely a third of that at sea level. That means that each turn of the propeller finds much less air to grab onto. It’s like trying to row in an almost empty pool: the paddle continues to rotate exactly the same, but there is hardly any water to push.
Lift depends, greatly simplifying, on three factors: the density of the air; the size of the propellers and the speed with which they move. If the density decreases, there are only two obvious options left. The first is to build much larger propellers or (the second) to spin them much faster. Regardless of the choice, a new problem arises: more powerful motors are needed, greater electrical consumption is generated, there are more vibrations and more heat. All this forces us to change the design, the materials and even the weight. Which generates a vicious circle. If we add to that that the batteries work worse because it is very cold… It rained on wet. But there is more.
As if the lack of oxygen wasn’t enough, the air on Everest doesn’t stay still either. Currents rise up the slopes, turbulence appears behind ice seracs, and the wind constantly changes direction. For a human pilot it is already complicated, For a drone it means recalculating the thrust of each of its motors hundreds of times per second to remain stable.
And yet, DJI has done it. For this he used two drones. The first was the new FlyCart 100 with which he transported oxygen bottles, ropes, ladders and climbing equipment between base camp and Camp I. Each flight took about eight minutes. The same route normally requires Sherpas to walk between six and eight hours crossing the dangerous Khumbu icefall, one of the deadliest places in the entire mountain. During the test campaign the drone moved more than 10 tons of material and waste.
The second of the protagonists was the Matrice 4E. While the FlyCart was carrying supplies, this second drone mapped, for the first time, more than three square kilometers of the Khumbu Glacier with an accuracy of 1 centimeter. The objective was not to obtain postcard photographs, rather it was to detect changes in the ice practically in real time. Updating these maps allows you to modify ascent itineraries and plan rescues much faster.And all this in an environment in which flying is as complex as demonstrated by the loads that the drones carried: at sea level, The FlyCart 100 can carry 100 kg, but in the Everest tests its payload was 47 kg. It lost more than half of its carrying capacity simply because there was less air.
But perhaps the most interesting consequence is not in Nepal, or even on our planet: it will be on Mars. The Martian atmosphere is approximately 1% as dense as Earth’s. It is so faint that for years many engineers thought a helicopter could never take off there. Until Ingenuity arrived.
NASA’s small helicopter solved the problem by using huge propellers that rotated about 2,500 revolutions per minute, much faster than a conventional ground helicopter. Everest doesn’t look like Mars. But it does represent an excellent natural laboratory. Each improvement achieved in flying where there is almost no air helps to develop technologies capable of operating on other planets or in extremely hostile regions of the Earth. It seems to me to be one of those figures that condense all the physics of the article into a single piece of information and help the reader understand, at a glance, why this achievement has so much merit. I think it is worth highlighting.