CO-AXIAL HELICOPTERS
Coaxial helicopter are simply all of the helicopters you see that have two sets of blades, one on top of the other one. You can easily identify them because the do not look like the conventional helicopters we are used to seeing flying around ( police, medic, news helicopters). The word co-axial means two axis or in this case axles. The way they work, is that you have two axles or shafts, one is inside the other one. This is designed so that one axle turns in one direction while the other one turns in the opposite direction. This is very beneficial, because it helps stabilize the helicopter. Co-axial helicopters are extremely stable and anyone can learn how to fly them, which makes them a very good beginner helicopter. They are also relatively cheap and can be really fun to fly.
3-Channel Helis
Personally I think any helicopter that has less than 4-channels is considered a TOY and not RC grade helicopter. These are typically the helicopters you find inside Malls here in the USA. They CAN be lots of fun, but are generally very hard to control and are made to only fly inside. The reason I categorized them as toys is because for one, they are generally very cheaply made and once you brake them you will have to buy another one because you cannot find replacement parts for them. If you are serious about learning how to fly real RC-grade helicopters, than skip the 3-channel toys and go for at least a 4-channel co-axial helicopter.
HOW DO 3-CHANNEL HELIcopters WORK?
HOW DO 3-CHANNEL HELIS WORK
If you study the picture to the left you will find a crude explanation of how 3-channel helicopters work and what are their limitations. Lets begin by defining the word channel. A Channel- means each one fuction from your radio. In other words, most radios have at least four channels (two thumb sticks or little joysticks). This is for helicopters only, the left stick in USA mode 1 normally controls up/down and is known as Throtle-channel-1, and left/right known as rudder-channel-2. The right stick controls roll left/right known as aileron-channel-3, and forward/backwards known as elevator-channel-4. This is a good guideline, however this can vary with each radio. The 3-ch helicopters are vary basic and are limited in what they can do. They come in a range of sizes from palm size micro to about 27" in lenght but their operation is basically the same. They consist of a mainframe that has two main motors. These two main motors drive two gears called the main gears that in turn drive two shafts. One of the shafts is inside the other one. This is designed so that the top blades can turn in one direction, while the bottom blades will turn in the opposite direction. This type of drive system is called a co-axial system. From Physics we know that if we have a turning force usually called a torque, there will be an equal but opposite reaction to that force. Therefore if we only had one set of blades, as soon as you start spinning them, the body of the helicopter will turn in the opposite direction ( you can think of when a helicopter gets shot on the tail and starts spinning while it crashes). That is why the co-axial helicopters have two sets of blades one on the top and one on the bottom. Ther rpm's of the motors is controlled by a small speed controller that is making mini corrections to try to maintain the same rpm's on both motors. So if you buy a really cheap 3-ch heli you will see that it does not stay straight, it will constantly want to drift left or right, that is because they have used a very cheap speed controller. The only functions that you have on a 3ch- heli are up/down, left/right, forward/backwards hence the name 3-ch heli. UP/Down- this function is simply controlled by the increase or decrease in the rpm's of both of the motors at the same rate. So as the blades spin faster there is more lift generated and the heli goes up, when they slow down the heli drops. LEFT/RIGHT- the 3ch-helis will not tilt left and right like a real helicopter, instead you only have YAW. YAW means the helicopter turns right or left in relation to the main axis where the blades are attached. Therefore in order to make it turn left or right, one of the motors will slow down or spin faster creating an increase in torque in either of those directions. Forward/Backward- the 3-ch helis also have a tail motor that is generally smaller than the main motors and is located on the top of the tail of the heli. When you push forward, this motor spins in one direction pushing air down and tilting the helicopter forward. When you push back the motor spins in the opposite direction and it pushes air up, pushing the tail down and tilting the heli backwards. Simple right? Like I said these helis are very basic. Also because they cannot tilt left and right like a real helicopter, guess what happens when you are flying it outside and a gust of wind tilts your heli left or right? Well you can not recover because you can't tilt your heli the other way. If you have been flying helis for a while you will recognize that you CAN recover by spinning the tail around to be able to recover using the forward and backwars command but most beginers will not react in time. These helis are also normally very underpowered and will not perform well outside.
4-CHANNEL CO-AXIALS
COAXIAL SWASH PLATE
4-Channel helicopters are a little better because they have more functionality and feel a little closer to the real thing. The power system on the 4-CH helis is also a coaxial system and is very similar to the 3-channel ones. 4-CH co-axial helicopters do NOT have a motor on the tail like the 3-CH helicopters. A lot of 4-Ch helis like the Comanche below have what appears like a tail rotor, but those are only there for looks and have no functionality at all. The main difference on the 4-ch heli is that it has a tilting swash plate that allows it to tilt left and right. You can see by looking at the picture that the servos tilt the swah-plate left/right and forwar/backwards. When the swash-plate tilts, the secondary links will also tilt the blade grips causing the blades to tilt or pitch. The change in angle of the blades or rotating plate will make the heli tilt in either left/right or forward/backwards direction. These helicopters are lots of fun and you will definetly benefit from flying one because you will learn basic controls. Now all of the coaxial helicopters are very very stable so don't assume, that because you can fly one of these you will be ready for a 6-channel heli, but at least you can practice the basic orientations, how to use your radio and you will begin to get confortable flying the helicopter around. In no time you will be doing figure eights inside your house, taking off from you dinning table and landing on top of the coffee table and even chasing your dog! (in my case it was my dog that chased the heli and I had to keep away from her which was lots of fun!). Like the 3-ch helis, the 4-ch ones are also limited to indoors or very calm outdoors conditions, because of their lack of power and agility.
Esky-Comanche
This was My very first RC(Remote Control)-Helicopter. Personally I think that if anyone is new to the hobby, or is seriously thinking about learning how to fly RC-Helis, than this is a good start. These coaxial helis are very stable out of the box and are fairly cheap. Especially if you don't have any RC experience you want to begin here in order to learn basic remote control skills and a little bit of orientation. I flew the comanche for about 3 months before I mastered it and began to get bored of the limitations of a coaxial helicopter. It was time to go for something bigger, faster and better.