(VOA) – A California company has developed a drone that looks like a hummingbird. This nano-hummingbird is smaller than drones now used by the United States military. The manufacturer, AeroVironment, develops and tests its drones near Los Angeles. The experimental bird-like aircraft is radio-controlled and has a camera. Matthew Keennon is supervising the project.

"It's being manipulated and controlled to allow the forward and backward flight, the rotation, and also the side to side flight. And all that's happening by just changing the curvature and the shape and different aspects of the wing movement at a very high speed."

The Defense Advanced Research Projects Agency paid for the project. Agency officials wanted a vehicle that could copy something in nature. Matthew Keennon says the challenge was huge and exciting.

"Because every time we made an improvement, got better, we were just so amazed."

AeroViroment has also been testing one of the world's largest drones. The company's Steven Gitlin says this one can fly in Earth's stratosphere.

"And it's designed to fly for up to seven days at a time at about 65,000 feet [19.8 kilometers] altitude and carry a payload that either helps somebody see what they want to see or relays communication from one point to another."

AeroViroment says drones also have civilian uses -- for public safety, security, and search and rescue. And the nano-hummingbird can go places that larger drones cannot.

1. drone /drəʊn/ (n) an aircraft without a pilot, controlled from the ground: máy bay không người lái

• a spy drone: một máy bay do thám
• to use drones to locate major traffickers: dùng máy bay không người lái để truy tìm bọn buôn ma túy.

2. hummingbird /ˈhʌmɪŋbɜːd/ (n) a small brightly coloured bird that lives in warm countries and that can stay in one place in the air by beating its wings very fast, making a continuous low sound (= a humming sound): chim ruồi

• a hummingbird-sized drone: một máy bay không người lái có kích thước bằng con chim ruồi

3. curvature /ˈkɜːvətʃə(r)/ (n) the state of being curved; the amount that something is curved: đường cong, dạng cong

• to have some slight curvature throughout its length: có đường cong nhẹ dọc theo chiều dài
• to change the curvature and the shape: thay đổi đường cong và hình dáng

4. stratosphere /ˈstrætəsfɪr/ (n) the layer of the earth's atmosphere between about 10 and 50 kilometres above the surface of the earth: tầng bình lưu

Lưu ý: Tầng bình lưu hay tầng tĩnh khí là một lớp của bầu khí quyển trên Trái Đất và một số hành tinh. Tầng bình lưu nằm ngay phía trên tầng đối lưu và ở phía dưới của tầng trung lưu. Ranh giới trên cùng của tầng này gọi là ranh giới bình lưu. (www.wikipedia.com)

5. altitude /ˈæltɪtuːd/ (n) the height above sea level: độ cao so với mặt nước biển

• cruising altitude: độ cao hành trình
• high / low altitude airways: trần bay cao / trần bay thấp
• to lose altitude suddenly: giảm độ cao đột ngột
• altitude sickness: say vì độ cao
• We are flying at an altitude of 10,000 meters.
  Chúng ta đang bay ở độ cao 10 km.

6. civilian /səˈvɪliən/ (adj) a person who is not a member of the armed forces or the police: dân sự, thường dân

• to be for civilian use: vì mục đích dân sự
• He left the army and returned to civilian life.
  Ông ấy giải ngũ và trở lại đời thường.