How do helicopters fly?

Introduction

For most of the people, when you compare helicopters to airplanes, its an ugly, bulky, little thing trying to hold up in the air. But, for me, they are amazing. Being a helicopter pilot, I certainly had to write on this topic. Recently I wrote about how airplanes fly. .I was amazed with the amount of people who wanted to know about helicopters.

The English word helicopter is adapted from the French word “hélicoptère”. It was coined by Gustave Ponton d’Amécourt in 1861. It originates from the word “helix” which means spiral or convolutions and “pteron” means wing.

My seniors say, “Helicopters in general aren’t designed to fly. Its a bunch of moving parts struggling to help it get up in the air”. And after the last 7-8 years of association with flying, I realise, its true!!. Giving some credit to helicopter pilots, let me tell you, as per statistics. 2% variable percentage of the worlds population are pilots and out of that only 0.3% are helicopter pilots. Anyway, lets get into the technicalities…

Basics of Helicopters

Lets first look into the definition of helicopters as per the FAA. “A helicopter is an aircraft that is lifted and propelled by one or more horizontal rotors. Each rotor consisting of two or more rotor blades”. So, as we all know helicopters have two or more blades on top.(Also called as the main rotor) and blades behind(tail rotor).

The helicopter main rotor is the rotating part of that helps it lift up. The main rotor creates lift, but at the same time creates torque.(Torque is a measure of the force that can cause an object to rotate about an axis.) Now this torque causes the helicopter to rotate, because of which a tail rotor is incorporated. The tail rotor creates an anti-torque which stops the helicopter from turning around. In simple words, the tail rotor applies a force in the opposite direction to which the helicopter wants to rotate. I hope the image above clarifies this concept further.

Aerodynamics

Now just like airplanes, a helicopter is also governed by aerodynamics. There are four forces that helps the helicopter to fly.:

1. Thrust: Its the forward force produced by the power plant(engine)/propeller or rotor. This force helps in forward motion.
2. Drag—A retarding force caused by friction of the air molecules against the body of the helicopter.
3. Weight—the combined load of the aircraft itself, the crew, the fuel, and the cargo or baggage. Its basically the force of gravity, that pulls all the weight downward.
4. Lift—opposes the downward force of weight, is produced by the effect of the air acting on the rotors.

Just like I did in airplanes, I would like to explain how lift is created in helicopters. The rotors in a helicopter are like the wings of an airplane, but in aviation both of them are aerofoils. The definition of aerofoil is, “A body shaped to produce an aerodynamic reaction (lift), for a small resistance (drag) force”. Look at the above image.

When air moves through the rotors, due to the curvature of the rotor and Bernoulli Principle combined, and also with the help of controls from the pilot, the air is made to move slower below the rotor as compared to above. Slower moving air creates more pressure than fast-moving air. Hence, a high pressure is created below the rotors and a low pressure above. This causes it to push the rotors upwards, and the same is called as lift.

Controls

There are three major controls in a helicopter that the pilot must use simultaneously during flight. They are:

1. The collective pitch control: is on the left side of the pilot. In layman terms it helps the helicopter go up and down. It gives vertical control. Its used to change the pitch of the rotor blades. Pitch is basically the angle at which the horizontal centre line of the blade and incoming relative air meet. The pitch affects the amount of lift and the drag created by the rotors.
2. The cyclic control: The cyclic pitch control is usually projected upward from the cockpit floor. It maybe between the pilot’s legs or between the two pilot seats in some models. It gives the pilot lateral control by helping the aircraft move forward, backward, left and right.
3. The anti-torque pedals or tail rotor control. : The antitorque pedals, located on the cabin floor by the pilot’s feet. It controls the pitch and therefore the thrust of the tail rotor blades or other antitorque system.

Conclusion

I hope that through this article I have been able to educate you and also eliminate most of the misconceptions. I have tried to make it as simple as I possibly could in a brief manner. Thank-you for the time you took to read across. Feel free to contact us for further info and also you can mail me on sanjithkc@yahoo.com.

Further check out the FAA helicopter manual for detailed info