Plane characteristics

Wing location

High wing

The easiest planes to fly are typically ones that have a high wing, or a wing that is on top or above the plane's fuselage. Wing dihedrals (bend or change of angle in wing relative to fuselage) or polyhedrals are also common. Most trainers and park flyers have this configuration.

These planes hold most of their weight under the canopy of the wing structure and tend to react more like a glider. For this reason, they are very stable and easy to fly. If a high wing plane is out of control, stability can often be regained by returning the controls to a neutral position, allowing the plane to naturally fall back into a gliding position. Because of the wing shape, wing position, and drag under the wing due to the fuselage, these planes fly slower than their mid and low wing counterparts, but can usually do some aerobatic maneuvers.

High wings are typical of many vintage private planes. For example, the Piper Cub and the Cessna 170.

Low wing

Low wing planes offer a higher level of flying difficulty because the weight of the plane sits on top of the wing structure, making the balance a bit top heavy. Most wing configurations provide a slight dihedral to provide a bit more balance during flight.

The weight distribution and wing position of a low wing plane provides a good balance of stability and maneuverability. The plane's moment of inertia about the rotation axis is lower because it is closer to the wing, therefore rolls require much less torque and are more rapid than a high wing plane.

Low wings are typical of World War II war planes and many newer passenger planes and commercial jets.

Mid-wing

Mid-wing planes are usually considered the most difficult to fly. The wings are usually located right in the vertical middle of the fuselage, near the bulk mass of the aircraft. Very little leverage is needed to turn and rotate the plane's weight.

Mid-wings are often straight without any dihedral providing an almost symmetrical aerodynamic structure. This allows the plane to be relatively balanced whether rightside-up, upside-down, or any other position. This is great for military jets, sport planes and aerobatic planes, but less advantageous for the learning pilot. Because of this symmetry, the plane doesn't really have any natural or stable flying position, like the high wing planes, and will not automatically return to a stable gliding position.

Number of channels

The number of channels a plane requires is determined by the number of mechanical servos that have been installed. On smaller models, usually one servo per control surface is sufficient.

• Ailerons - controls roll.
• Elevator - controls pitch (up and down).
• Throttle or, if electric, motor speed.
• Rudder - controls yaw (left and right).
• Retracts - controls retractable landing gear.
• Flaps - used to steepen the landing approach angle, let the plane land at a slower touchdown speed, and get the plane off the ground slightly faster during takeoff.
• Auxiliary 2 - controls lights, cameras or other device.

If you are a complete beginner there are planes with three channels which operate on only Throttle, Elevator and Rudder. It is suggested to practice simulation before operating a RC aircraft as it will reduce any damage or disappointment on your very first flight. People who have mastered their simulation flights should move on to 4 channel aircraft for their first flight experience. Four channel aircraft are controlled by throttle, elevator, rudder, and ailerons.

For complex models and larger scale planes, multiple servos may be used on control surfaces. In such cases, more channels may be required to perform various functions such as deploying retractable landing gear, opening cargo doors, dropping bombs, operating remote cameras, lights, etc.

The right and left ailerons move in opposite directions. However, aileron control will often use two channels to enable mixing of other functions on the transmitter. For example when they both move downward they can be used as flaps (flaperons), or when they both move upward, as spoilers (spoilerons). Some aircraft, such as the Concorde do not have an elevator. When that function is mixed with ailerons the surfaces are known as elevons. Each of these mixes are common on radio control planes.

Tiny ready to fly RC indoor or indoor/outdoor toy aircraft often have two speed controllers and no servos, as very small and inexpensive servos are not yet available. There can be one motor for propulsion and one for steering or twin motors with the sum controlling the speed and the difference controlling the turn (yaw).

Turning

A three channel RC plane will typically have an elevator and a throttle control, and either an aileron or rudder control but not both. If the plane has ailerons, turning is accomplished by rolling the plane left or right and applying the correct amount of up-elevator. If the plane has a rudder instead, the wing needs to have a significant amount of dihedral (V-bend in the wing). The rudder will turn the plane so that one wing will turn into the wind, causing it to lift and roll the aircraft. Many trainers and electric park fliers use this technique.

A more complex four channel model is usually turned like a full size aircraft; it is rolled into a turn with ailerons and then a small amount of 'back pressure' is required to maintain height. This is required because the lift vector, which would be pointing vertically upwards in level flight, is now angled inwards so some of the lift is turning the aircraft. A higher overall amount of lift is required so that the vertical component remains sufficient for a level turn.

For the perfectionist, a small amount of rudder can be applied when rolling into or out of a turn, in the direction of the rolling motion to correct adverse yaw.

Many radio controlled aircraft, especially the low end `toy' models, are designed to be flown with no movable control surfaces at all. Instead, the planes typically have two propellers or ducted fans, one on each wing and the plane is controlled only by this. Usually the planes only have two control channels -- throttle and yaw. In general this results in a plane that flies poorly and is very difficult to fly, though some fly better than others. An example of a plane that is flown in this way is the Air Hogs Dominator.

Some model planes are designed this way because it's often cheaper and lighter to control the speed of a motor than it is to actually provide a moving control surface. Full-scale planes are generally not designed without control surfaces like this because 1) it rarely produces good control even under ideal conditions and 2) a loss of engine power would lead to a total loss of flight control and an almost certain crash.

V-tail systems

A V-Tail is a way of combining the control surfaces of the standard "+" configuration of Rudder and Elevator into a V shape. These ruddervators are controlled with two channels and mechanical or electronic mixing. An important part of the V-Tail configuration is the exact angle of the two surfaces relative to each other and the wing, otherwise you will have incorrect ratios of elevator and rudder.

The mixing works as follows: When receiving rudder input, the two servos work together, moving both control surfaces to the left or right, inducing yaw. On elevator input, the servos work opposite, one surface moves to the "left" and the other to the "right" which gives the effect of both moving up and down, causing pitch changes in the aircraft.

V-Tails are very popular in Europe, especially for gliders. In the US, the T-Tail is more common. V-Tails have the advantage of being lighter and creating less drag. They also are less likely to break at landing or take-off due to the tail striking something on the ground like an ant mound or a rock.

Powerplants

Most planes need a powerplant to drive them, the exception being gliders. The most popular types for radio-controlled aircraft are internal combustion engines, electric motors, jet, and rocket engines. More info on all of these can be found at Model aircraft.

Frequencies and sub-channels

Frequency

Frequency determines the line of communication between a receiver and transmitter. The transmitter and receiver must both be on the same frequency so the plane can be controlled.

Reserved frequencies

Many countries reserve specific frequency bands (ranges) for radio control use. Due to the longer range and potentially worse consequences of radio interference, model aircraft have exclusive use of their own frequency allocation in some countries.

USA and Canada reserved frequency bands

• 72 MHz: aircraft only (France also uses US/Canada channels 21 through 35).
• 75 MHz: surface vehicles.
• 50/53 MHz: for all vehicles, with the operator holding a valid amateur radio (FCC in the USA) license.
• 27 MHz: general use, toys.
• 2.400-2.485 GHz: Spread Spectrum band for general use (amateur radio license holders have 2.39-2.45 GHz licensed for their general use in the USA)

US frequency chart available at [1], Canadian frequency chart available at [2]

European reserved frequency bands

• 35 MHz: aircraft only.
• 40 MHz: surface vehicles.
• 27 MHz: general use, toys, citizens band radio.
• 2.4 GHz spread spectrum: surface vehicles.

Singapore reserved frequency bands

• 29 MHz: aircraft only

Australian reserved frequency bands

• 36 MHz: aircraft and water-craft (odd channels for aircraft only)
• 29 MHz: general use
• 27 MHz: light electric aircraft, general use

New Zealand reserved frequency bands

• 35 MHz: aircraft only
• 40 MHz: aircraft only
• 27 MHz: general use
• 29 MHz: general use
• 36 MHz: general use
• 72 MHz: general use

Detailed information, including cautions for transmitting on some of the 'general use' frequencies, can be found on the NZMAA website.

Amateur radio license reserved frequency bands

• 50 and 53 MHz in the USA and Canada
• 433–434 MHz in Germany

Remarkably, there are specific bands in 35 MHz called A and B bands. Some European countries allows only use in A band, whereas others allow use in A and B band.

Channels

Most RC aircraft in the USA utilize a 72 MHz frequency band for communication. The transmitter radio broadcasts using AM or FM using PPM or PCM. Each aircraft needs a way to determine which transmitter to receive communications from, so a specific channel within the frequency band is used for each aircraft (except for 2.4 GHz systems which use spread spectrum modulation, described below).

Most systems use crystals to set the operating channel in the receiver and transmitter. It is important that each aircraft uses a different channel, otherwise interference could result. For example, if a person is flying an aircraft on channel 35, and someone else turns their radio on the same channel, the aircraft's control will be compromised and the result is almost always a crash. For this reason, when flying at RC airfields, there is normally a board where hobbyists can post their channel flag, so everyone knows what channel they are using, avoiding such incidents.

A modern computer radio transmitter and receiver can be equipped with synthesizer technology, using a phase-locked loop (PLL), with the advantage of giving the pilot the opportunity to select any of the available channels with no need of changing a crystal. This is very popular in flying clubs where a lot of pilots have to share a limited number of channels.

Some new controllers use spread spectrum technology. The most popular of these radio systems is made by a company called Spektrum, though other companies are working on their own versions. Spread spectrum allows multiple applications (pilots) to transmit in the same band (2.4 GHz) with little fear of conflicts. Receivers in this band are virtually immune to most sources of electrical interference. Amateur radio licensees in the United States also have general use of an overlapping band in this same area, which exists from 2.39 to 2.45 GHz.

Monitoring of RC Aircraft Performance

RC Power System Monitor

The increased complexity of aircraft power systems has created the need for tools to measure model performance, both during ground testing and in-flight.

As of 2008, the popularity of lithium-polymer (LiPo) based electric power systems increased the need for in-flight monitoring, due to the fragility of LiPo batteries. Several light weight and low cost in-flight monitors and meters designed specifically for RC are available in 2008, such as the one pictured at right.

Military usage

Model aircraft are also used in the military, with its primary task to gather intelligence of areas. Most of these devices use ball-bearing engines, similar to those found on R/C boats.

Besides as a reconnaissance vehicle, there are also concerns that it could be used for bomb attacks. Just as Bruce Simpson (aka Rocket Man)'s home-made cruise missile, it could be rigged with an explosive or biological bomb.