# What is the bare minimum of air density you need to fly a helicopter?

How high will a helicopter be able to fly before the propellers have not enough air particles to achieve lift?

What is the minimum air density needed to achieve flight with a helicopter?

Could you give me the air density from $$100\%$$ to $$1\%$$ in meters? Only when there is a significant decrease, otherwise it might be too much work.

Correction :

Let say one is a drone and one is a helicopter. The helicopter weighs between $$500-730 kg$$. The drone weighs between $$1-2 kg$$.

Which air density is needed for each of them to fly?

At what altitude would there be not enough air particles to achieve lift and what would the air density be?

• That depends on the power/weight ratio of your power source. Do you mean a helicopter on earth that can carry a person with a currently available engine, or just a device that lifts at least itself with a rotor? Commented Apr 10, 2021 at 22:20
• Yes, an average helicopter and let's for the sake of it also add a drone. A small drone. I am very curious about it. Commented Apr 10, 2021 at 22:56
• One limit would be when the air density is low enough that if you increase the size of the rotor to produce more lift, the extra weight of the rotor increases faster than the extra lift force produced.. Commented Apr 11, 2021 at 0:37
• This is a little like asking how fast can a car drive. A sports car can typically go faster than a truck. Ingenuity was carefully designed to fly in the low density Martian atmosphere. A normal helicopter couldn't. Commented Apr 11, 2021 at 1:42
• @mmesser314 My bad, I added more specific questions. Commented Apr 11, 2021 at 13:26

The lift generated by a helicopter is linearly proportional to the air density (as it is for planes). To fly we need the lift to be greater than the weight of the aircraft, so as the density reduces there will be a point where the lift generated is less than the weight, so we can't fly.

The minimum air density will depend on the weight and aerodynamic design of a given helicopter.

Perhaps the easiest way to get at this is to consider how high a typical helicopter can fly, and how air density typically varies with altitude.

For the first part, see How High up Can a Helicopter Fly? Lots of information here. Extremes: With years of preparation, a helicopter has landed on the summit of Mt. Everest. The altitude record was set in a harrowing flight to 40820 ft.

TLDR – Helicopters with turbine engines can reach altitudes of 25,000 feet during forward flight. However, helicopters cannot fly as high when hovering. The typical maximum height for a hovering helicopter is about 12,000.

As altitude increases, air pressure drops, which makes air density lower. On the other hand, temperature also drops, which means the density doesn't drop as much as it would if temperature was constant. It varies with weather and latitude.

For typical conditions, here is a chart from Wikipedia's Density of air

Air density at sea level is typically $$1.22$$ kg/m$$^3$$, or about $$1/800^{th}$$ the density of water.

$$12000$$ feet is about $$3600$$ m. The chart shows the density to be $$0.7$$ of sea level, or $$0.85$$ kg/m$$^3$$.

Mt. Everest is $$8850$$ meters high. Air density is about $$0.4$$ of sea level density, or about $$0.5$$ kg/m$$^3$$.

$$40820$$ feet is over $$12000$$ m, off the chart. But it looks like the density would be about $$0.3$$ of sea level, or $$0.4$$ kg/m$$^3$$.

Here is a Density Altitude Calculator, if you want more precise answers. You will need temperature.

Drones: The most extreme case is Ingenuity on Mars. The Martian atmosphere is about $$1$$% as dense as Earth's atmosphere. This is equivalent to Earth's atmosphere at $$100000$$ feet.

The highest a helicopter has flown on Earth is $$40820$$ feet. The highest an airplane has flown is $$85000$$ feet. This is new territory for powered flight.

Veritasium has video all about it.

By contrast, most drones are consumer toys. They are limited by the FAA to $$400$$ feet. There isn't much point to making them capable of altitude.

However, maximum climb altitude of a drone considers the question in detail. Air density is important, but energy stored in the battery is also a limitation.

The best existing drone they considered for altitude is the DJI Phantom 2 Vision. They estimate it could reach $$2300$$ m. With some design changes, it could reach $$2800$$ m. A highly optimized drone could reach $$4700$$ m, or $$15000$$ feet. That is a little higher than Mt. Whitney. Air density there is about $$0.6$$ of sea level, or about $$0.7$$ kg/m$$^3$$.

• That is a very in-depth explanation, thank you very much for your time. Commented Apr 11, 2021 at 18:03