Did You Know?:

The highest ever recorded helicopter landing occurred in 2005 when a pilot named Didier Delsalle landed a helicopter on the summit of Mt. Everest, 29,029 feet from the ground!

Highest Landing Helicopter
(https://verticalmag.com/features/landing-everest-didier-delsalle-recalls-record-flight/)

How do Helicopters Generate Lift?


It may seem obvious that a helicopter can achieve lift from the massive blades spinning on top of it. While that is true, there are a lot of minor details about the rotors that you may not know.

• The shape of the rotors produce the lift by using Bernoulli's Principle which says that since the air flows faster over the top of the blade than the bottom. This causes less air pressure on the top of the blade which generates the lift. (6)

• The cross-section of the blade varies from root to tip. Generally being more angled at the root and more flat at the tip. This helps to balance the loads at each point between the root and tip. (4)

Cross-section of Rotor
              Blade
(http://www.buildahelicopter.com/homebuilt-helicopter-rotor-blades.php)

• Helicopters can have anywhere from 2 to 7 blades, but more blades is not always better. More blades produce more lift, but for smaller helicopters that only need 2 blades, it would be detrimental to add more blades and create an proportional amount of lift compared to the size of the helicopter.

• The more blades that a helicopter has, the faster they have to rotate. On a typical smaller helicopter, they will rotate 400 to 500 times per minute. In a way bigger helicopter like a Chinook, the blades will only rotate at about 225 RPM. (5)

• As the tips of the blades get gain speed as the RPMs go up, they can approach the speed of sound. This is problematic because as the tips get closer to the speed of sound, the airflow over the retreating blade gets smaller and smaller relative to the airflow over the advancing blade. If the airflow over the retreating blade is too low, then it will cause the helicopter to stall. (7)
Rotor Rotating
( http://www.faa.gov/regulations_policies/handbooks_manuals/aviation/helicopter_flying_handbook/)