How They Fly!
What distinguishes coaxials from other RC Helicopters?
Simply, Coaxial helicopters have two main rotors. Most helicopters (RC and Real) only have one main rotor, while Quadrocopters have 4. Notice in the picture to the side that the helicopter doesn't look like a standard one.
This is a very important distinction to make. Because of this, the helicopter is innately more stable in hovering than a single rotor one. Please don't confuse coaxials with quadrocopters, as these two are drastically different in shape and ease of flying.
So why don't coaxials have a standard tail rotor? This is a common question, but the answer also explains why coaxials are so stable in hovering.
This is a very important distinction to make. Because of this, the helicopter is innately more stable in hovering than a single rotor one. Please don't confuse coaxials with quadrocopters, as these two are drastically different in shape and ease of flying.
So why don't coaxials have a standard tail rotor? This is a common question, but the answer also explains why coaxials are so stable in hovering.
Terms:
First, you need to understand lift and torque. Click here to understand what lift and torque are.
Yup, this is why Coaxial helicopters are stable: the two rotors spin in opposite directions, producing an equal torque in the direction opposite that they spin. In essence, they "balance" each other's torque. Because the two torques of the main rotors is balanced, there is no need for a side-mounted tail rotor.
But how do coaxials turn, then?
But how do coaxials turn, then?
Turning
This makes perfect sense one you realize how it works. To turn, one rotor simply spins faster than the other, creating a higher torque in the opposite direction of its rotation. Some coaxials even decrease the speed of the other rotor to maintain the same total lift. This makes the two torques unequal, and thus the helicopter spins to compensate.
Lets do a quick check to see if we understand this concept. If the top rotor is spinning clockwise, would it slow down or speed up to turn right?
If you guessed slow down, you're correct; the torque from the clockwise top rotor exerts a left-turning force on the helicopter, which is balanced by the right-turning torque of the lower rotor. If the top rotor slows though, then the right-turning torque of the lower rotor becomes greater than the left-turning torque of the top rotor. Thus, the helicopter spins right. Another way that the heli could turn right would be to speed up the lower rotor, or to speed up the lower rotor and slow down the top rotor.
Note that depending on the complexity, or perhaps quality, of your coaxial, turning may or may not induce a change in overall lift. If you do find a change in lift, then it is because the heli is either not changing the speed of both rotors or is doing so ineffectively. If the heli only speeds up or slows down one rotor to turn, then the heli will create more lift or less lift, respectively, when turning.
Lets do a quick check to see if we understand this concept. If the top rotor is spinning clockwise, would it slow down or speed up to turn right?
If you guessed slow down, you're correct; the torque from the clockwise top rotor exerts a left-turning force on the helicopter, which is balanced by the right-turning torque of the lower rotor. If the top rotor slows though, then the right-turning torque of the lower rotor becomes greater than the left-turning torque of the top rotor. Thus, the helicopter spins right. Another way that the heli could turn right would be to speed up the lower rotor, or to speed up the lower rotor and slow down the top rotor.
Note that depending on the complexity, or perhaps quality, of your coaxial, turning may or may not induce a change in overall lift. If you do find a change in lift, then it is because the heli is either not changing the speed of both rotors or is doing so ineffectively. If the heli only speeds up or slows down one rotor to turn, then the heli will create more lift or less lift, respectively, when turning.