What if a plane flew on Mars?

A plane zooms down the runway. Its wings push air down, and up it goes!

But Mars has hardly any air. Could a plane fly on Mars?

As a plane rushes forward, its tilted wings turn the passing air downward, and the air pushes the wings up. NASA's lift equation shows that this lift depends on how fast the plane goes, how big and how tilted its wings are, and how thick the air is.

On Mars, the air is extremely thin. So what would happen to a small plane flying there at its normal speed? Could it stay up? And if not, what would it take? Fly the same plane through Earth air and Mars air in the model.

NASA Glenn's lift equation, L = C_L · ρ · ½v² · A, makes lift directly proportional to air density. Mars's surface air, by NASA's fact sheet, has a mean pressure of 6.36 mb against Earth's 1014 mb and a density of about 0.016 ± 0.006 kg/m³.

This lab flies a 1,100 kg plane with 16.2 m² of wing at 60 m/s and a 5° wing tilt, first through sea-level air (1.225 kg/m³) and then through the model's Mars air (0.020 kg/m³). The question: what share of its weight can the wing still support, and what speed or wing size would restore flight?

On Earth, the air is thick. The wings push lots of air down.

The air pushes back up hard. The plane flies easily!

In the model, the small plane weighs about 1,100 kilograms and has about 16 square meters of wing. Flying at 60 meters per second through the thick air near Earth's surface, its wings make about one and a half times as much lift as its weight. Plenty to fly.

The model says that at this wing tilt, the plane needs at least about 50 meters per second to stay up.

At sea level (ρ = 1.225 kg/m³), with v = 60 m/s, α = 5° and an aspect ratio of 7.5, the model's lift coefficient is 0.433 and the lift 15.5 kN against a weight of 10.8 kN: 143%. The speed needed at this tilt is 50.1 m/s, and the slowest possible speed, at the model's 15° stall angle, is 28.9 m/s.

The model compares lift with weight only. It has no engine, drag or flaps, so it answers one question: could this wing hold this plane up at this speed?

Now Olly flies into Mars air. It is very, very thin.

The wings push only a tiny bit of air. The lift is much too weak. The plane can't stay up!

Choose the Mars air. Everything else stays the same. Now the wings make only about 2 percent of the lift the plane needs. The model says it would have to fly at about 392 meters per second to stay up, more than three times as fast as this lab's slider can go.

Even at the top speed of 120 meters per second, with the wings tilted to 15 degrees, where this model's wing makes the most lift, lift reaches only about 28 percent. To fly, the plane would need giant wings: at 120 meters per second and 15 degrees, at least about 58 square meters, more than three and a half times the area.

One catch: the model weighs the plane with Earth's gravity. Mars pulls only about 38 percent as hard, so setting the mass to about 420 kilograms stands in for the plane's weight on Mars. Even then, at 60 meters per second the wings make only about 6 percent of the lift needed.

At ρ = 0.020 kg/m³ the lift falls to 0.253 kN, 2.3% of weight, and the speed needed rises to 50.1 × √(1.225/0.020) = 392 m/s. At the slider's 120 m/s and 5° the ratio is 9.4%; at 15°, the peak lift coefficient of 1.30, it is 28.1%.

Within the controls, flight returns only with much more wing: at 120 m/s and 15°, the smallest wing that flies is 57.8 m²; 61 m² gives 106% of weight, and the airliner-scale 150 m² gives 260%. One caution: the model always computes weight with Earth's gravity. On Mars the plane would weigh about 38% as much: 1,100 kg × 3.71/9.81 ≈ 416 kg on Earth's scale (418 kg with NASA's mean of 3.73 m/s²), and the mass slider's 10 kg steps make 420 kg the nearest stand-in. Even then the plane at 60 m/s makes only 6.1% of its Mars weight, and at 120 m/s and 15° it needs about 22 m² of wing.

Wings fly by pushing air down. Thin air means less air to push.

Less push down means less lift up. So a plane on Mars must go super fast or have giant wings.

A wing makes lift by turning air downward, and the air pushes back up. In thin air, every second the wing meets far less air, so it can push much less of it down. The lift drops in step with the air's thickness.

Going faster helps a lot, because lift grows with the square of speed: twice as fast gives four times the lift. Bigger wings help too. But Mars's air in the model is about 60 times thinner, so a plane would need about eight times its normal speed, or wings about 60 times bigger, to make up for it.

Lift scales linearly with ρ and with S, and with v², so at fixed tilt the speed needed scales as 1/√ρ: a factor of √61 ≈ 7.8 between the model's Earth and Mars air. Equivalently, wing area must scale with 1/ρ at fixed speed.

Model limits: a symmetric wing with thin-airfoil lift and a fixed 15° stall, no flaps, no drag or thrust, and Earth's g in the weight. It treats Mars air exactly like Earth air, only thinner. NASA Glenn notes that lift also depends on the air's viscosity and compressibility, effects folded into a lift coefficient that is usually measured by experiment; the model's fixed coefficient leaves them out, so the 392 m/s figure shows the size of the problem rather than a design.

People did fly something on Mars! It was a little helicopter called Ingenuity.

Its blades were big for its size, and they spun super fast. It flew 72 times!

On April 19, 2021, NASA's Ingenuity helicopter made the first powered, controlled flight on another planet. NASA says Mars's air is so thin that Ingenuity had to be very light, about 1.8 kilograms, with rotor blades much larger and spinning much faster than a helicopter that light would need on Earth: about 2,400 turns a minute.

Ingenuity was built to make no more than five test flights. Instead it made 72, over nearly three years, flying 17 kilometers in all and climbing as high as 24 meters. Its last flight was on January 18, 2024.

NASA states that because Mars's atmosphere is 99% less dense than Earth's, Ingenuity had to be light, with rotor blades much larger and spinning much faster than a helicopter of its mass would need on Earth. The 1.8 kg helicopter had two counter-rotating rotors 1.2 m across, spinning at about 2,400 rpm; its specification sheet gives the flight environment as less than 1% of Earth's density.

Designed as a technology demonstration of at most five flights in 30 days, Ingenuity flew 72 times between 19 April 2021 and 18 January 2024: 128.8 minutes aloft, 17.0 km covered, and altitudes up to 24.0 m. NASA's mission page says it was the first aircraft to achieve powered, controlled flight on another planet. In the terms of the lift equation, larger blades add area and faster spinning adds speed, the two levers this lab shows.