I was riding my bike yesterday and saw a helicopter in the sky, flying at a very quick pace. My seat post has been slippng recently, and while my brain was in reverse-engineering mode, I started to recollect how an airplane’s wing disrupts air to achieve lift ( the curve on top slows down air speed, while the wind rushing underneath creates an upward thrust).
The more I thought about this, the more puzzled I was by how helicopters operate. A plane uses a turbine engine or propellor to create forward motion, while the wings generate lift. While it seems fairly obvious how helicopters achieve altitude, or upwards thrust, things get hazy when considering how they maintain a straight course, and I was downright stumped by how they achieve forward motion.
Here is a crude sketch of a helicopter:
How it goes up is fairly simple. The big rotor on top spins, and pushes air down.
How it stays straight is trickier matter for me to grasp. The tail rotor spins, and somehow keeps the craft straight like a rudder on a boat. If there were a rotor on both sides of the tail, I could easily understand that the props are shaped to push air in the direction opposite (a rotor on the left of the tail pushes air across to the right of the craft, and vice versa). How does only one rotor keep the craft straight? If it spins clockwise, does that push air to the left, and if it spins counterclockwise, does it push air to the right?
Now for the brain-teaser. Once it’s up in the air and isn’t rotating in a stationary circle, how in the name of Cheerios does the craft manage to get going at like 150 miles an hour?
Newton’s third law stipulates that for every action there is an equal and opposite reaction. A jet airliner has turbine engines thrusting directly backwards, thus pushing the craft forward. A car or bicycle relies on the tire’s friction with the ground to drive the vehicle. A boat’s props or sails are oriented to either generate thrust directly aft or capture air and pull the vessel forward. There is no immediately obvious apparatus generating force directly backwards from the helicopter. What?