R/C Airplane Ground School
1. How it all works
The letters rc stand for radio control. You'll often see rc airplanes referred to as remote control, but technically this is an incorrect term. Radio control is the correct term because the airplane is controlled by radio signals that pass through the air from the transmitter (abbreviated to 'tx') to the receiver (abbreviated to 'rx').
The transmitter is the main box that you hold in your hands, the receiver is located inside the airplane and picks up the signals sent out from the transmitter.
The radio signals are sent to the model in the same way as television and radio broadcasts are sent. Signals are generated whenever you move a stick or flick a switch on the tx, and are emitted via the antenna. All radio signals operate on a frequency, measured in megahertz (MHz*). The transmitter and receiver must be on the same frequency for them to work together, and the gadget that determines the frequency is called a crystal. Both the tx and rx need a matching crystal to function.**
*MHz is slowly giving way to the new GHz (gigahertz) system - 2.4GHz to be exact, or 'spread spectrum' technology.
**Spread spectrum sets don't require a crystal, as the technology is slightly different.
Once the radio signal is picked up by the receiver, via the receiver antenna, it is converted into physical movement by the servos. Servos are connected to the control surfaces of the airplane by servo rods, or connecting rods, so any movement of the servo is passed directly to the control surface that it is connected to.
The transmitter is the main box that you hold in your hands, the receiver is located inside the airplane and picks up the signals sent out from the transmitter.
The radio signals are sent to the model in the same way as television and radio broadcasts are sent. Signals are generated whenever you move a stick or flick a switch on the tx, and are emitted via the antenna. All radio signals operate on a frequency, measured in megahertz (MHz*). The transmitter and receiver must be on the same frequency for them to work together, and the gadget that determines the frequency is called a crystal. Both the tx and rx need a matching crystal to function.**
*MHz is slowly giving way to the new GHz (gigahertz) system - 2.4GHz to be exact, or 'spread spectrum' technology.
**Spread spectrum sets don't require a crystal, as the technology is slightly different.
Once the radio signal is picked up by the receiver, via the receiver antenna, it is converted into physical movement by the servos. Servos are connected to the control surfaces of the airplane by servo rods, or connecting rods, so any movement of the servo is passed directly to the control surface that it is connected to.
2. How an RC airplane moves and turns
All controllable airplanes have control surfaces and different control surfaces do different things.
The primary control surfaces are rudder, elevators and ailerons. The most basic rc airplanes will only have rudder control; the rudder is the moveable section (hinged) of the vertical stabilizer, or fin, at the rear end of the airplane. It controls the directional movement of the airplane, or yaw; when the rudder moves left, the plane turns to the left and when the rudder moves right the plane turns to the right.
The elevators are the moving section (hinged) of the horizontal stabilizer, or tailplane, also at the rear of the airplane. Elevators control the pitch attitude of the airplane - whether the nose of the plane is pointing up, down or level.
When elevators are moved up, the airplane will point upwards and thus begin to climb. If the elevators are moved down, the opposite happens. When the elevators are held level, then the airplane will fly level.
The ailerons are the moving sections (hinged) of each wing and are located on the trailing edge (rear) of each wing towards the outer end, or wing tip. Ailerons always come in pairs, one left and one right, and they move in opposite directions to each other. That's to say that when one moves up, the other moves down and vice versa.
Ailerons control the roll of the airplane; left aileron up / right aileron down causes the plane to roll to the left, right aileron up / left aileron down causes the airplane to roll to the right.
Ailerons used in conjunction with the elevators have the same effect as the rudder ie directional control.
The primary control surfaces are rudder, elevators and ailerons. The most basic rc airplanes will only have rudder control; the rudder is the moveable section (hinged) of the vertical stabilizer, or fin, at the rear end of the airplane. It controls the directional movement of the airplane, or yaw; when the rudder moves left, the plane turns to the left and when the rudder moves right the plane turns to the right.
The elevators are the moving section (hinged) of the horizontal stabilizer, or tailplane, also at the rear of the airplane. Elevators control the pitch attitude of the airplane - whether the nose of the plane is pointing up, down or level.
When elevators are moved up, the airplane will point upwards and thus begin to climb. If the elevators are moved down, the opposite happens. When the elevators are held level, then the airplane will fly level.
The ailerons are the moving sections (hinged) of each wing and are located on the trailing edge (rear) of each wing towards the outer end, or wing tip. Ailerons always come in pairs, one left and one right, and they move in opposite directions to each other. That's to say that when one moves up, the other moves down and vice versa.
Ailerons control the roll of the airplane; left aileron up / right aileron down causes the plane to roll to the left, right aileron up / left aileron down causes the airplane to roll to the right.
Ailerons used in conjunction with the elevators have the same effect as the rudder ie directional control.
3. Number of channels
Every operation that is controllable on an rc airplane is referred to as a 'channel'.
The most basic plane will be just one channel which could be either motor control on/off (electric) or rudder movement. A typical nitro airplane will be 4 channel - you have control over 4 things; the motor, elevator, rudder and ailerons.
A more complex rc airplane will have those 4 controls plus retractable undercarriage and landing flaps, making it a 6 channel model.
For the majority of rc pilots 2,3 or 4 channel models are the most popular.
The most basic plane will be just one channel which could be either motor control on/off (electric) or rudder movement. A typical nitro airplane will be 4 channel - you have control over 4 things; the motor, elevator, rudder and ailerons.
A more complex rc airplane will have those 4 controls plus retractable undercarriage and landing flaps, making it a 6 channel model.
For the majority of rc pilots 2,3 or 4 channel models are the most popular.
4. Different types of power units
With the exception of rc gliders, all rc airplanes need a motor of some kind to generate the thrust that pushes the model through the air.
The main two types of motor are glow plug (often called 'nitro', 'gas' or collectively 'IC' [internal combustion]) and electric. There are many many different choices of both glow plug and electric motor available and the size of the motor depends on the size and weight of the model, as well as the desired performance.
RC airplanes powered by glow plug engines are faster and bigger but they require certain items of field equipment to get them started. Electric motors need only the battery pack and are quieter and cleaner making them a very popular choice, especially with beginner rc pilots.
Traditionally, glow plug airplanes were more common but these days electric ones are rapidly catching up in terms of popularity
The main two types of motor are glow plug (often called 'nitro', 'gas' or collectively 'IC' [internal combustion]) and electric. There are many many different choices of both glow plug and electric motor available and the size of the motor depends on the size and weight of the model, as well as the desired performance.
RC airplanes powered by glow plug engines are faster and bigger but they require certain items of field equipment to get them started. Electric motors need only the battery pack and are quieter and cleaner making them a very popular choice, especially with beginner rc pilots.
Traditionally, glow plug airplanes were more common but these days electric ones are rapidly catching up in terms of popularity
5. Trainer RC airplanes
Learning to fly rc airplanes is best done on a trainer. These are planes that have certain built-in design characteristics to make them nice and stable in the air.
The biggest giveaway is the position of the wing in relation to the fuselage. If the wing sits on top of the fuse, then the chances are that the model is indeed a trainer. High wing airplanes always make the best trainers because they are very stable and forgiving; the weight of the fuselage underneath the wing means that the airplane will always want to naturally level itself out if left to fly on its own (providing that it is correctly trimmed by the pilot).
Another giveaway is the amount of dihedral - the upward angle of the wings when looked at from the front of the airplane. More dihedral means more stability in the air, and easier flying.
When learning to fly rc, always go for a trainer style airplane before any other.
The biggest giveaway is the position of the wing in relation to the fuselage. If the wing sits on top of the fuse, then the chances are that the model is indeed a trainer. High wing airplanes always make the best trainers because they are very stable and forgiving; the weight of the fuselage underneath the wing means that the airplane will always want to naturally level itself out if left to fly on its own (providing that it is correctly trimmed by the pilot).
Another giveaway is the amount of dihedral - the upward angle of the wings when looked at from the front of the airplane. More dihedral means more stability in the air, and easier flying.
When learning to fly rc, always go for a trainer style airplane before any other.
6. Weight and Balance
Getting the weight and balance correct before you fly your plane is so important, especially the balance.
Every airplane, whether model or real, has a Center of Gravity ('CG') that is determined in the plane's design stage. This CG is crucial to the airplane's flight characteristics, and getting the plane correctly balanced around the CG is an absolute must before you fly.
Checking the all-up weight (AUW) of the airplane isn't as crucial as the balance, although it's still very important.
To weigh the plane, pop it on some accurate scales with the motor battery pack. Cross-check this weight with the manufacturer's recommended/stated weight to make sure there is no major difference.
If your plane is seriously overweight to what it should be, you need to do something about it because the wing loading is going to be too high for your airplane to fly correctly.
Realistically, your only options are to use a smaller/lighter battery pack or smaller (but still compatible) servos and receiver, and try and push the weight down that way.
Checking the balance (CG) This is the important one, and it's easy enough to do.
With the motor battery pack in position, as per the instructions, mark the stated Center of Gravity. This CG position should be in the manual, and will read something like "75mm (3inches) back from leading edge", for example.
This means that you measure the stated distance back from the leading edge of each wing and mark the spot with a pen on the wing undersides. You should mark the CG close to the fuselage, rather than further out down the wing. One or two inches out from the fuselage sides is fine.
Once marked, place the tip of each index finger on each spot, and gently lift the plane...
Above, lifing the plane on its CG to check balance
If it hangs level, then the CG is good and you don't need to do anything. If it hangs slightly nose down, this isn't a problem either.
If it hangs very nose down, or at all tail down, then you need to adjust the balance to get it to hang level.
Your first option is to try moving the motor battery pack forwards or backwards, depending on which way your airplane is hanging. This is the best thing to do to adjust the CG, because you're not adding dead weight to the plane in the form of ballest.
If you can't shift the pack because it's too tight a fit in its compartment, then you need to add ballast to either the nose or tail end of the plane. If this is the case, add the weight as far out as you can, because this will have the greatest effect with the least amount.
So, if you need to add weight to the nose because the plane is tail heavy, then look at putting modeling clay inside the spinner, for example. Or, if you can't do that, tape something to the underside of the nose, as far forward as you can.
If you need to add weight to the tail end of the airplane, because it's nose heavy, then try and add it to the very rear of the fuselage, where both sides come together so to speak. If your plane is foam, you could screw an appropriate size screw into the foam, for example.
Whatever weight you add to the nose or tail, make sure it's very secure! Having the weight fly off during a flight will upset the CG, and this is going to adversely effect the plane's flight characteristics.
It's important to understand that a slightly nose heavy plane will still fly fine. A tail heavy plane, however, is bad news; the plane will be at best very difficult to control, and at worst completely uncontrollable. If your airplane seems tail heavy when it's balancing on your fingertips, do something about it!
Roll balancing your RC airplane This is often overlooked and isn't as critical as getting the CG correct, but a plane that has one side heavier than the other will want to roll and turn to the heavier side, making your life a bit harder.
To check your plane's roll balance, simply loop some thread around the propeller shaft, and then some around the rear of the fuselage as close to the tail as you can get it. Lift the plane up and let it hang freely - see if it wants to roll to one side or another. If it does, then you need to add some weight to the wingtip of the lighter (higher) side.
Add only enough weight to make the plane hang level, when viewed from the front. Taping the weights to the wingtip is an easy method, although you might want to take the trouble to set them into the wingtip and cover over them to hide them from view.
For foam wings, pushing a small gauge screw, nail or panel pin into the foam is a great way of adding any necessary weight, and is easily hidden with white paint or marker pen.
Take your time with the balancing of your rc airplane, and you'll be rewarded with easier flying and less trimming.
Every airplane, whether model or real, has a Center of Gravity ('CG') that is determined in the plane's design stage. This CG is crucial to the airplane's flight characteristics, and getting the plane correctly balanced around the CG is an absolute must before you fly.
Checking the all-up weight (AUW) of the airplane isn't as crucial as the balance, although it's still very important.
To weigh the plane, pop it on some accurate scales with the motor battery pack. Cross-check this weight with the manufacturer's recommended/stated weight to make sure there is no major difference.
If your plane is seriously overweight to what it should be, you need to do something about it because the wing loading is going to be too high for your airplane to fly correctly.
Realistically, your only options are to use a smaller/lighter battery pack or smaller (but still compatible) servos and receiver, and try and push the weight down that way.
Checking the balance (CG) This is the important one, and it's easy enough to do.
With the motor battery pack in position, as per the instructions, mark the stated Center of Gravity. This CG position should be in the manual, and will read something like "75mm (3inches) back from leading edge", for example.
This means that you measure the stated distance back from the leading edge of each wing and mark the spot with a pen on the wing undersides. You should mark the CG close to the fuselage, rather than further out down the wing. One or two inches out from the fuselage sides is fine.
Once marked, place the tip of each index finger on each spot, and gently lift the plane...
Above, lifing the plane on its CG to check balance
If it hangs level, then the CG is good and you don't need to do anything. If it hangs slightly nose down, this isn't a problem either.
If it hangs very nose down, or at all tail down, then you need to adjust the balance to get it to hang level.
Your first option is to try moving the motor battery pack forwards or backwards, depending on which way your airplane is hanging. This is the best thing to do to adjust the CG, because you're not adding dead weight to the plane in the form of ballest.
If you can't shift the pack because it's too tight a fit in its compartment, then you need to add ballast to either the nose or tail end of the plane. If this is the case, add the weight as far out as you can, because this will have the greatest effect with the least amount.
So, if you need to add weight to the nose because the plane is tail heavy, then look at putting modeling clay inside the spinner, for example. Or, if you can't do that, tape something to the underside of the nose, as far forward as you can.
If you need to add weight to the tail end of the airplane, because it's nose heavy, then try and add it to the very rear of the fuselage, where both sides come together so to speak. If your plane is foam, you could screw an appropriate size screw into the foam, for example.
Whatever weight you add to the nose or tail, make sure it's very secure! Having the weight fly off during a flight will upset the CG, and this is going to adversely effect the plane's flight characteristics.
It's important to understand that a slightly nose heavy plane will still fly fine. A tail heavy plane, however, is bad news; the plane will be at best very difficult to control, and at worst completely uncontrollable. If your airplane seems tail heavy when it's balancing on your fingertips, do something about it!
Roll balancing your RC airplane This is often overlooked and isn't as critical as getting the CG correct, but a plane that has one side heavier than the other will want to roll and turn to the heavier side, making your life a bit harder.
To check your plane's roll balance, simply loop some thread around the propeller shaft, and then some around the rear of the fuselage as close to the tail as you can get it. Lift the plane up and let it hang freely - see if it wants to roll to one side or another. If it does, then you need to add some weight to the wingtip of the lighter (higher) side.
Add only enough weight to make the plane hang level, when viewed from the front. Taping the weights to the wingtip is an easy method, although you might want to take the trouble to set them into the wingtip and cover over them to hide them from view.
For foam wings, pushing a small gauge screw, nail or panel pin into the foam is a great way of adding any necessary weight, and is easily hidden with white paint or marker pen.
Take your time with the balancing of your rc airplane, and you'll be rewarded with easier flying and less trimming.
7. Pre-flight checks
Exact pre-flight checks might differ from model to model, but there are some basic checks that all rc airplanes need to have done, immediately before flight. That is exactly what a pre-flight check is; the final thing you do before take off, to make sure that everything is in order and working correctly.
Listed below (in no particular order) are the minimum checks that you need to carry out before you take off...
The purpose of the range check is to make sure the radio signal is strong, so that you can fly your plane at a normal distance away from you without it going out of radio range. Perform a range check thus: Switch on the transmitter then the receiver, and with the transmitter antenna fully collapsed (ie down)*, walk backwards away from the model for 30 paces or so. As you walk away from the plane, keep moving the control surface sticks of the tx (not the motor!) and closely watch the respective control surfaces of the airplane. * If you've got a 2.4GHz transmitter, you'll need to use its range check feature as per the instructions - collapsing the antenna isn't an option. The range check feature of a 2.4GHz tx reduces the voltage to emulate a weaker signal. Above: an rc airplane range check should be done at a distance of 30 paces (meters) or so away from the plane If you only get a few paces away and the surfaces start 'twitching' or not responding properly to the stick movements, do not fly. Check the batteries of the radio gear, they may need replacing. Low batteries in the transmitter drastically reduce the radio range. Also check for loose connections to the receiver etc. If the batteries and connections are OK but the control surfaces still don't respond properly, then other people may be using your frequency nearby. Again, do not fly if this is the case. Interference is a big killer of rc airplanes, and you need to be sure that your frequency is clear before you get airborne. Whatever the reason, do not fly your plane if you see that control surface response becomes unreliable before you reach 30 paces or so away from the plane! Identify and rectify the problem before flying. Always always always take a few minutes to perform these checks before you commence your flying session. Get into the habit of doing these pre-flight checks every time; they take just a couple of minutes and will save you the grief of a crashed airplane, if something is amiss. |