Helicopters are powerful machines that have been in use since 1919. They’ve mostly become an important part of emergency services and armed forces around the world, with some governments even using military helicopters for domestic security purposes!
Helicopters equipped with turbine engines can reach heights of up to 25,000 feet when in forward flight. However, helicopters aren’t able to be as high when only hovering. The average height of hovering helicopters is 12,000 feet.
Then why can’t the helicopter fly as high as an airplane? Like everything else in aviation, the ability to fly high requires speed that always involves a trade-off between aerodynamics, engineering, along with commercial requirements.
How High Can a Helicopter Fly?
Helicopter pilots usually operate at altitudes between 8,500 and 12,000 feet, providing there is ideal environment for flying. The higher the aircraft flies, the thinner the air becomes, forcing the rotor blades to produce less amounts of lift.
Most helicopter pilots believe 10,000 feet is the highest safe altitude for flying. At this height, the rotor blades receive greater resistance and create less lift and forward speed. This makes the aircraft unstable and reduces its maneuverability.
A helicopter achieves forward movement through rotational forces generated by its rotor blades. These rotating blades produce lift by moving air downwards. This creates upwards force that pushes the aircraft forwards.
Thinner air reduces the amount of lift generated by the main rotors, reducing the ability of helicopters to climb and move forward.
At high altitudes, air pressure decreases significantly, resulting in lower atmospheric pressures than experienced at sea level. This means fewer molecules of oxygen per cubic meter of air, which makes breathing harder. To protect against this effect, the FAA recommends wearing supplemental oxygen masks at altitudes above 12,500 ft.
What Happens If a Helicpter Flies Too High?
As the helicopter climbs the air starts to become thinner. As the air becomes thinner the main rotor is less effective. The higher the helicopter is flying, it ascends slower because of the lower energy generated by the main rotor.
The helicopter could be at a point that the air is so thin that the blades are unable to produce enough lift to continue to ascend, this is called max operating range.
When a pilot is approaching the upper limit of the operating range the majority of helicopters experience extreme turbulence. The helicopter starts to shake or rattle.
When the helicopter is over its operating envelope at its maximum it becomes extremely unstable. It’s more likely to tip upwards before rolling towards the left. The blades can also stall and cause the helicopter to lose power.
In addition to this danger though, if a pilot goes too far above sea level then the low temperatures could cause ice to form around the rotor discs which reduces airflow through the engine, leading to reduced performance. If this continues long enough then the entire machine risks becoming unbalanced and falling uncontrollably back down towards Earth.
Can a Helicopter Fly to Top of Mount Everest?
A test helicopter pilot named Didier Delsalle had the idea of a helicopter landing on Mount Everest, which is the highest mountain in the world.
In May of 2005 Delsalle achieved his dream and was the very first pilot in a helicopter to take a plane to the summit of Mount Everest. The summit of the mountain is 29,000 feet in height that is more than the highest operational altitude, which is 23,000 feet of the aircraft which Delsalle flew. The flight took many years of planning, as well as several test flights.
Mountains pose particular problems to helicopters because of the extreme vertical angles involved. These slopes create huge changes in elevation between different points along a surface, meaning that the angle of attack required to stay stable increases dramatically.
However, there are several ways helicopters can cope with extreme vertical angles. Most importantly, the main rotor disc features a pitch system allowing the blade tips to rotate vertically instead of horizontally, thus eliminating the need for horizontal stabilizers like wings.
What is The Highest Altitude a Helicopter Has Ever Flown?
The highest altitude a helicopter has ever flown is 40,820 ft (around 12km). It was performed by French aviator Jean Boulet, piloting an Aérospatiale SA 315 Lama.