An Introduction to RC Flight
The world of Remote Control (RC) flight provides an exciting challenge to people of all ages and experience. Whether you are a beginner pilot, to a highly competitive flier, the world of RC flight provides near endless challenges and equally rewarding experiences
Here is a brief overview, found from wikibooks.org
Most powered model-aircraft, including electric, internal-combustion, and rubber-band powered models, generate thrust by spinning an air screw. The propeller is a type of air screw and is by far the most commonly used device. The blades of the rotating propeller push against the atmosphere, and by Newton’s Third Law, the air’s reactionary force pushes the aircraft.
As in full-size planes, the propeller’s dimensions and placement (along the fuselage or wings) are factored into the design. In general, a large diameter and low-pitch offers greater thrust at low airspeed, while a small diameter and higher-pitch sacrifices thrust for a higher maximum-airspeed. In RC aircraft, the builder can choose from a wide selection of propellers, to tailor the plane’s airborne characteristics. A mismatched propeller will compromise the aircraft’s airworthiness, and if too heavy, inflict undue mechanical wear on the power plant. Scale RC aircraft propellers are usually specified as diameter × pitch, given in inches. For example, a 5×3 propeller has a diameter of 5 inches, and a pitch of 3 inches. The pitch is the distance that the propeller would advance if turned through one revolution in a solid medium. Additional parameters are the number of blades (2 and 3 are the most common).
There are two different methods to transfer rotational-energy from the power plant to the propeller.
- With the direct-drive method, [Comparable performance to Inrunner motors] the propeller is attached directly on the engine’s spinning crankshaft (or motor-rotor.) This arrangement is optimum when the propeller and power plant share overlapping regions of best efficiency (measured in RPM.)
- With the reduction method, [Comparable performance to Outrunner motors] the crankshaft drives a simple transmission, which is usually a simple gearbox containing a pinion and spur gear. The transmission decreases the output RPM by the gear ratio (thereby also increasing output torque by approximately the same ratio). Reduction-drive is common on larger aircraft and aircraft with disproportionately large propellers. On such power plant arrangements, the transmission serves to match the power plant’s and propeller’s optimum operating RPM. Geared propellers were once used very commonly on electric motors, but with the advent of brushed motors are rarely seen.
- In some designs of aircraft, the propeller is replaced by a ducted fan unit. In jet-powered or ducted fan scale aircraft, the engine is a single-piece assembly with no user-changeable parts. The fan blades spin at extremely high speed (>150,000 RPM), limiting most adjustments to the original factory.” This is what the really high Kv [4000+KV] Himaxx motors we carry would be useful for.
So what does this mean in basic, non-plane guy English?
For our purposes here at PCH, we only have a few options for getting the propellers to get their planes in the air. Here is the basic step-by-step process of helping a customer choose a prop.
“Slo-Fly” or “Thin Electric”?
First ask yourself, or the customer what type of plane he or she is flying, and if it is going to be a slower 3D plane that requires more thrust than speed and is often times flying with the nose pointed up, or if it is a slightly faster and typically heavier plane that is more for flying level and no so much doing 3D maneuvers. If it is a slower plane, go with the Slo-Fly prop. If its a faster plane, go with the Thin Electric. Also another rule of thumb is how much stress and load will be put on the prop? If it is a relatively low amount, go with the slow prop, think low and slow, if it is a higher load go with the thicker and stronger Thin Electric Props.
One side note when choosing the props, Slo-Flyer props typically draw more current than the Thin-Electric props, due to their greater surface area, so when looking at the prop range of a motor, reserve the lower end of the range for the Slo-Fly props, and the higher ends of the range for the Thin Electric props.
How big does the prop need to be?
Lets first look at the first of the two numbers on the prop, the diameter. An easy way to think of the diameter of a prop is the bigger the diameter, the more thrust and consequently the more current that will be drawn. There are however limitations to this. If the prop is too big, the plane will be very unstable and be a handful to fly. On the contrary if the prop is too small the plane will not develop enough thrust to maintain flight and either not get off the ground or have very bad stalling characteristics due to its slow speed.
So now that you know the basic difference in the diameter, how do we find which diameter is best for the plane and motor? A very good place to start is by looking at the motor that the prop will be going on. All of the E-Flite, Rimfire and Himaxx motors have a chart that gives a prop range, either in the paperwork for the motor, or on their website. Once you know what the prop range is, as the customer what type of flying he or she will be doing. If it is aerobatics and general cruising, or if they are still new to flying, give them a prop on the higher side of the diameter range. If they are going to be doing just some sport flying, and maybe fast flying a smaller diameter prop will perform better.
Whats the deal with the second number?
The second number on the prop is the pitch or bite of the prop. To be technical, it is how far the prop, in inches, will travel forwards in one revolution through “a hard medium” or something like Jello. How it works is similar to gears in a car. The lower the pitch, the lower the gear. Lower pitched props will have much more thrust and performance at low speeds, which is needed in the case of 3D flying, as well as beginners so they can get out of trouble faster. Higher pitched props, similarly to higher gears in a car, are used for faster flying, were low end power is not needed. You can also think of changing the pitch as changing the pinion gear on an RC car. The smaller the pinion, the more low end acceleration and power, the bigger the pinion the less acceleration, but more high end speed, as well as more amp draw.
What to do with this information?
So now that you know how and which prop sizes do what, how can you use that information to help customers? There are two main areas when this knowledge will come in handy when you might have to get creative on thinking of which props will work, and how they will work. A good rule of thumb is to add up the two numbers of the prop they have, want or was recommended. Lets say the customer needed a new prop has a 9×6 prop but we are out of stock of those. If we add the two numbers we get 15 and can then look for different props whose numbers also add up to 15, such as a 10×5 prop. Although the plane will perform differently, the current draw will stay in the ball park of what it was previously and the customer won’t have any issues with frying his motor and battery.
In the world of RC planes and helicopters, there are numerous options for radio systems that you will have to consider. You can find information about the different type of systems of them here. We highly recommend you invest in a spread spectrum system, such as Spektrum and Futaba’s FASST radios. This system not only is the newest in technology, it is the most reliable, and is not subject to harmful radio interference.
One of the first things you will see and need to take into consideration when you look to by your radio is how many channels. The number of channels your plane needs is determined by how many functions it uses to fly. For example your basic trainers use four channels; throttle, elevator, aileron and rudder. As you start moving into larger and more complex planes, you will need more channels. For example, you need another channel for retractable landing gear, flaps, smoke systems, even brakes. There are limitless possibilities for functions, so you want to make sure your radio can do what you want it to do.
Now that you have an idea of how many channels you will need, and want, you will want to consider how you control the extra channels. Most radios with more than four or five channels are programmable. Programmable radios aren’t as complicated as they sound, and actually make flying your airplane much easier. You can program switches to make landing gear and flaps deploy, as well as having a switch which makes the rates less sensitive, essentially making the plane easier to fly with the flip of a switch. We highly recommend that you invest in a programmable radio, given that the majority of people who get into RC end up upgrading to a programmable radio once they get a hang of how to fly.
When looking at the programmable radios, you will notice one key difference. Airplane vs. Helicopter. There are two simple differences between the two. The airplane radios have a ratcheted throttle stick, and the helicopter radios have a smooth throttle stick. The other difference is the position of the switches. All of the same switches are on the remote, but simply rearranged differently between the airplane and helicopter remotes. And to answer the big question, yes! You will be able to fly an airplane with a helicopter remote, and vice versa. In fact, they both have the exact same software inside of them, which means a helicopter radio has all of the same options an airplane radio has.
After you consider what type, and how many channels you will need you can begin to figure out which one will be best suited to guarantee a successful time in this hobby. Most people new to the hobby are very intimidated by the high prices of some of these systems, but as we will explain, it is nothing to be afraid of. There are radios that will fit anyone’s budget.
On the less expensive end of the spectrum of radios, you have your basic four or five channel remote controls. These remotes are great for your basic park flyers, and gas trainer planes. These remotes in general run anywhere from $50-$100, and will be well suited for flying almost all simple entry level aircraft that do not require many channels. Some examples of these radios are Spektrum’s DX5 and Hitec’s Laser 4.
Moving towards the middle of the range of radios, you will find remotes with six to eight channels in the $150-$350 price range. These are by far the most popular radios on the market. These radios will be able to fly just about any plane. These radios also will last you a long time. The advantage to buying these more expensive radios is you will be hard pressed to outgrow them. Some examples of these radios are Spektrum’s DX6i and DX7, as well as Futaba’s 6EX and 7C.
At the high-end of the spectrum, you have the extremely powerful and more expensive radios. These radios are typically used by seasoned RC veterans, who have very complex aircraft. Although they are pricey, these radios are an extremely good investment, as you will never our grow them, as well as being able to program them to do just about anything. Prices for these radios typically start around $500 and go up into the thousands.
Speed controllers, commonly referred to by beginners as the magic box with wires, are a very important part to electric flight. The role of the speed controller is to control the speed of the motor. They are very easy to set up, although they can seem quite intimidating with all of the different colored wires coming out of it. You plug the batteries into the speed controller, and you also plug the speed controller into the receiver, which will tell the speed controller how fast to turn the motor, or how much power to put out, which it does through the motor wires.
Similarly to the motors, there are two types of speed controllers. You have your simple brushed speed controllers, which just modulate the amount of power from the battery that goes to the motor. These are fairly inexpensive and can only be used with brushed motors.
Brushless speed controllers are much more complicated in how they work, but we will not go into how they work quite yet. Brushless speed controllers can only be used with brushed motors. They can be identified easily as they have three wires that go to the motor, versus the two wires that brushed speed controllers have.
As far as picking which size speed controller you need, i.e. 25 amp, 35 amp etc., you need to take into consideration how much power your motor is going to draw. The motors are typically what determine the size of both the battery and speed controller in the power system of planes. We recommend going 5 to 10 amps over what the motor requires for a speed controller for safety purposes, as well as avoiding having to buy a bigger speed controller than you originally thought. For example if a motor says it draws 18 amps, we would recommend a 25 amp speed controller. This extra buffer ensures that the speed controller will not over heat and shut down, leaving your plane lifeless in the air.