Feature: How a helicopter plateau flight test is conducted

BEIJING -- With a snow-capped mountain in sight, helicopter designer Li Shengwei paced up and down at Ninglang Lugu Lake Airport with an altitude of 3,292.9 meters, keeping a close eye on an AC332 helicopter undergoing its plateau flight test.

This new type of plateau civil helicopter was conducting its flight test at the plateau airport located in Ninglang Yi autonomous county of the city of Lijiang, Southwest China's Yunnan province.

"AC332 can fly over the snow mountain over there. It can also take off and land at the base camp of Mount Qomolangma to carry out diversified missions," Li said, while pointing to the Jade Dragon Snow Mountain with a main peak reaching 5,596 meters above sea level.

Specially-designed as a new type of helicopter to be used for plateau missions, AC332 is a dual-engine multipurpose civil helicopter newly developed by the Aviation Industry Corporation of China (AVIC).

"Testing a plateau helicopter on a plateau. It is a harsh test for both the helicopter and the flight test team," said the young designer.

"Happily, it performed well in the plateau flight test here. Higher goals are ahead," Li added, while smiling.

FLYING HIGH FOR PLATEAU MISSIONS

Safety is the lifeline of an aircraft, and the flight test seeks to confirm its safe operations under various conditions, including normal scenarios and those characterized by extremes such as heat and cold, heavy rain and snow.

Therefore, it is a critical challenge for each new type of civil aircraft to undergo and pass its flight test phase -- which is also a mandatory process in obtaining an airworthiness certificate.

"China has independently developed this type of new helicopter. We are on a mission to verify its capabilities," said Wu Zhiyao, a flight test technician at the AVIC HAIG Aircraft Design and Research Institute.

AC332 is a helicopter "born for plateau use." It is capable of taking off and landing in the plateau environment at 4,500 meters above sea level and in 8 degrees Celsius. It is also designed to operate at a flight height of 6,000 meters above sea level, with a flight range of 600 km and a payload of 600 kg.

"The operation of a helicopter relies on air power and engines to generate lift through the rapid rotation of its rotors. A plateau area normally features high average altitude, low atmospheric pressure and reduced oxygen content. Such thin air poses challenges for a helicopter in terms of safe and stable operations in plateau conditions," Wu said while bathed in dazzling plateau sunlight.

Notably, the operational limits within which an aircraft can operate safely and efficiently -- with parameters such as altitude, speed, height and stalling speed during flight, is referred to as its flight envelope.

In the case of AC332, its plateau flight test serves to confirm the flight envelope within which this type of helicopter can operate safely in different atmospheric environmental conditions in a real plateau setting.

Based on information obtained via this flight test, the development team will calculate and draft a flight manual for future users in order to sustain safe operation of AC332, according to Wu.

HIGHER GOALS STILL AHEAD

The AC332 helicopter is designed with a flight ceiling of no less than 7,000 meters above sea level. Its aim is to transport both people and freight over mountains, while also being able to perform diversified missions in grasslands, mountains and other environments, according to Li.

Targeting the goal of operating in a plateau environment, a scientific and full plateau flight test is a must for AC332 to verify its performance and capabilities under both normal and extreme conditions in plateau environments.

"Look! It is returning and we must check the skid shoes. If they have been abraded to some extent in touching down on the runway, we must replace them immediately," Li explained as he pointed at the helicopter hovering overhead.

In fact, the skid landing gear, wide rear door, wide rotor blades and multiple other designs were tailored for AC332 in response to market demands from customers across China -- a vast country with diversified requirements for helicopters, especially when needed for use in plateau and mountainous areas.

Compared with helicopters that feature wheeled landing gear, AC332 with its skid landing gear makes contact with a larger ground area, which is especially useful in wild environments such as plateau meadows, wetlands and mountains.

"This means AC332 is endowed with expanded environmental adaptability and safety, highlighting its capabilities and suitability for medical rescue and other emergency rescue missions," Li said.

Given its huge size and complex terrain, China faces tough and intricate challenges stemming from natural disasters, particularly those occurring in plateau and mountainous regions.

The country has been constantly strengthening its capabilities in the field of air emergency rescue. In this process, the great potential of helicopters and other types of aerial equipment is clearly evident, as they can contribute greatly to China's emergency response abilities, thereby improving the people's safety and well-being.

The AC332 helicopter has now successfully completed its plateau flight test. It conducted a total of 38 flight movements, amounting to 27 hours and 38 minutes of flight time.

AC332 verified its performance in categories such as hovering, take-off and landing, near-ground maneuverability, single-engine failure maneuverability, and multiple other flight test requirements.

Embracing a new challenge ahead, the AC332 helicopter and its flight test team will continue their journey by carrying out an extreme-cold flight test in Mohe -- China's northernmost city known for its harsh climate, with an annual average temperature of around minus three degrees Celsius.

"Experience and confidence are boosted by actions. Looking forward, higher goals are ahead," Li said.