Introduction
Aeromodelling is the art of designing, building and flying miniaturized aircrafts (powered or non-powered). While Aeromodelling has reached a certain degree of sophistication, one can build a model plane from any material which may include Paper, Balsa, Composites so on and so forth. It is both a hobby and sport; the hobby aspect involves building and assembling model aircraft, and the sport part involves the flying.Aeromodelling activity is consists of two skills basically. One is modeling of Aeromodel and the other one is flying of that model. So lets have a look on both the skills one by one. The later is considered as a sport, hobby while the former is left to designers and aeromodellers. Many times Aeromodelling word is understood as flying of Aeromodel and this is more or less true since most of the persons involved with this activity are involved with flying skill mainly and building skill is left to commercial companies to build and create wealth. Some of the useful pages about Aeromodelling are available here. Go through the side menu items to look for your requirements.....
Types of Aeromodels
Aeromodels can be basically classified into 2 types:- Static and
- Flying
Flying aeromodels are, as suggested by the name, model aircrafts capable of actual flight. While static models lay more emphasis on the external appearance of an aircraft, flying models need considerations of weight, balance and strength as well. Shape considerations tend to focus more on the aerodynamics or flight characteristics of the model than just the external looks such as paint and finish. Different building materials may be used for building flying aeromodels but they should have a good weight-strength ratio. Balsa wood and polystyrene foam meet these criteria and are choice materials for construction. Also, bits of glass fiber cloth, plywood and some plastic moulded parts such as propellers and spinner cones may be incorporated in the design. Just like the static models, it is always a good idea for beginners to go for kits rather than trying to build models from sheets of balsa wood!
They may be classified very basically as:
- Powered or
- Unpowered,
Also, depending on the method by which they are controlled in flight, flying aeromodels may be classified as
- Free flight models (with only built-in controls)
- Control-line models or
- Radio-controlled models
The chuck gliders are launched in the air by the chucking action of the hand and are often flown indoors. Hence they are also known as 'Indoor models' Some chuck gliders are made using sheets / blocks of 'thermocol'. These tend to float in air for longer time and have longer wings and higher lift compared to other models of this class. The critical aspect of such aeromodels is the design of the wing, as this decides the time of flight of the model.
Catapult models are also similar to chuck models, except they are launched from a hand-operated catapult, rather than a chuck of the hand. These models are swift, have a longer range and are suitable outdoors. Catapult models need to be stronger than chuck gliders, hence are made of wood / plastic and not thermocol. They are basically model planes which take-off with the aid of a rubber string hooked to it. The tension in the string pushes the model forward when released. These models are usually made out of balsa. The success of the flight depends on the shape of the wings (aerofoil).
Tow-line models are gliders which are launched using a long line with a ring hook, in the open against the wind direction. The launcher runs against the wind after the helper releases the aircraft. Once in air, the aircraft rapidly gains height until it is at the top most point called the 'zenith'. The model automatically detaches from the tow-line as the ring hook slips and glides back to earth in wide circles. The fin is off-set a couple of degrees while constructing, to aid the glider to descend in circles.
Free flight models are aircrafts fitted with an internal combustion, reciprocating engine (usually small compression ignition engines of capacity around 0.75 cc). They are launched in an open field and gain height as a virtue of pre-set elevators, as long as the engine is running. Calculated amount of fuel is filled in the tank to gain a desired height. When the engine cuts, the free flight model glides back to the earth, freely, just like a glider!
Rubber powered models are simplest class among the powered aeromodels. They also fall in the category of 'Indoor models' and are similar to chuck gliders, but made of balsa wood. They have a propeller which drives power from the unwinding of a twisted rubber band. Special rubber powered motors are also supplied with some kits. They also come under free flight models.
Control-line models are a stepping stone towards the radio-controlled models and are usually fitted with compression ignition engines from 1 - 3.5 cc capacity and are controlled by means of two metal cables, which control the elevators of the aircraft. A fixed rudder position in the design of the aircraft ensures that the aircraft flies in circles around the flyer but pulling away, to keep the control line taut at all times. Depending on the flight characteristics and the ease of maneuvering, the control-line aircrafts may be trainers or aerobatic models or speed models. Trainer models are sturdy and have low speeds and sluggish controls to allow a beginner to gain experience in flying powered aircrafts. The aerobatic models are light weight, overpowered and have sharp controls which allow the flyer to perform in-flight aerobatics with the model. Speed models are racing models, generally used in competitions and are dedicated to very high speeds. Some of the aerobatic and speed models are powered by glow-plug engines for an extra boost of power.
Radio controlled models fly like real aircrafts and are a keen aeromodeller's ultimate dream. They are remotely controlled by means of a radio transmitter. The receiver fitted in the aircraft picks up the transmitted signals and manipulates the flight controls to fly and even perform aerobatics. Generally a 4 channeled radio with 4 servos fitted on the aircraft gives the flyer (pilot) control of the elevators, ailerons, rudder and the throttle. The more the channels on your radio the finer control you can exert on the aeromodel. These models are powered by a single / multi-cylinder glow plug reciprocating engine. There is a huge variety of engines available in several price ranges differing in their engine capacities, types (some are 2-stroke engines while others are 4-stroke), cylinder configurations, throttle controls and accessories. Some advanced models also incorporate jet engines or solid rock motors which use a solid propellant.
Types of RC planes: Powered sailplanes are popular choices for electrically-powered planes since a relatively low amount of power is required to sustain flight. This corresponds to long flight times of 10-20 minutes and more. Some gliders are capable of high speeds and advanced aerobatics, others are designed for seeking and circling in hot air packets called thermals. The smallest sailplanes are about 4-5 feet in wingspan and can fly effectively as pure gliders or with .049 engines or 50-100 watt (035 class) motors. They require the smallest radio equipment due to their small fuselages. Standard-class sailplanes are the next largest at slightly over 9 foot wingspans. Sailplanes larger than this are classified as open class gliders. Relatively few of these planes are powered, but could be modified to accept 200-400 watt (15 to 40) electric motors as desired.
Trainers are used to learn flying rc models. Although the easiest way to learn to fly R/C planes is through sailplanes, many opt for the more traditional Cessna-like trainer approach. Most trainers are gas-powered, but several kits also come in an electric flavor. Most of these planes are designed for 100-250 watt (05-15) motors and have wingspans of 3-5 feet. They generally fly somewhat faster than the typical sailplane, but still slowly enough for the novice to comprehend the situation and respond correctly. Trainers are generally high-wing planes with flat-bottom airfoils and plenty of dihedral for positive stability and high lift at low speeds. Most good trainers, if placed in an unusual or hazardous attitude, will recover on their own if there is sufficient alititude.
Sport and Aerobatic models: After mastering the basics of flight, many modelers seek planes that are less overtly stable than trainers and hence make better aerobatic planes. Such planes range from 3-9 foot wingspans with 100-1500 watt (05-90) motors. Unlike sailplanes and trainers which utilize a flat-bottom airfoil, most sport planes use semi-symmetrical and symmetrical airfoils. This can sacrifice some lifting capability but usually improves handling in gusty wind conditions and during aerobatic maneuvers. The plane tends to be neutrally stable -- they "go where they're pointed"; i.e. they don't self-recover from bad situations as readily as trainers.
Pylon racers: Some pilots choose to design low drag planes that will go as fast as possible. Such planes typically have 3-4 foot wingspans and use 200-400 watt motors, reaching speeds well in excess of 100 mph! Some gas kits can achieve speeds of 200 mph. By comparison, typical sport planes fly at 40-60 mph, sailplanes from 20-60 mph.
Scale models: Exact scale models of all varieties of civilian and military planes are also popular targets for model airplane enthusiasts. Details are easier to implement in larger models, so such planes tend to be above 5 feet in wingspan and have high power requirements (300+ watts). Civilian planes with light wing loadings, such as the classic J-3 Cub, and multiengine models as displayed above, are excellent electric flyers. Ducted fan models: For those who like special challenges, you can model jet aircraft with electrics as well! Electric ducted fan models are a new exiting and challenging part of the hobby.
Ducted fan models powered by an electric motor have only been possible for a couple of years. Contrary to typical prop planes, where a "slow"-turning, high torque motor is desired, in ducted fan models high RPMs are needed on relatively few NiCad. Fortunately, R/C car aficionados use high speed motors for racing purposes often with "only" 6-7 cells. Also, motors used in pylon racers are also frequently suitable for ducted fans.
RC Helicopters: R/C helicopters are an interesting aspect of the hobby. Such models can hover and move exactly like their full-size counterparts -- in addition to non-scale abilities such as inverted flight and stunning aerobatics. Relatively few electric helicopters have entered the market due to the short flight times (you can't exactly glide a helicopter). Helicopters tend to be more complicated and costly to build and maintain, a trait which R/C helicopters also inherit.
IS BALSA THE LIGHTEST WOOD IN THE WORLD? No! Most people are surprised to hear that botanically, balsa wood is only about the third or fourth lightest wood in the world. However, all the woods which are lighter than balsa are terribly weak and unsuitable for any practical use. The very lightest varieties don't really resemble wood at all, as we commonly think of it, but are more like a tree-like vegetable that grows in rings, similar in texture to an onion. It is not until balsa is reached that there is any sign of real strength combined with lightness. In fact, balsa wood is often considered the strongest wood for its weight in the world. Pound for pound it is stronger in some respects than pine, hickory, or even oak.
Balsa is a very 'friendly" wood to work with - so light, so soft, so easily worked into so many things. You don't need heavy duty power saws and sanders like you would if working with a hardwood. If you are just starting out in the model airplane hobby, here are the tools that are recommended that you get: A knife or razor blade will work well for cutting balsa sheets and sticks up to 3/16" thick. Use a razor saw for sizes thicker than 3/16". Always keep replacement blades on hand - blades do wear out and a dull blade can make it impossible to do a good job.
YOU WILL ALSO NEED SANDING BLOCKS:
In addition to the cutting tools, you will need an assortment of different size sanding blocks. These are indispensable tools for model construction. You can buy ready-made sanding blocks or make your own. The most often used general purpose sanding block is made simply by wrapping a full 9" x 11" sheet of sandpaper around a 3/4" x 3" x 11" hardwood or plywood block. Use three screws along one edge to hold the overlapped ends of the sandpaper in place. Use 80 grit garnet sandpaper on the block during general construction. Another handy sanding block to have can be made by gluing 80 grit garnet sandpaper onto a 24" or 36" long piece of aluminum channel stock. Most hardware stores carry a rack of aluminum in various sizes and shapes. This long sanding block is very helpful for shaping leading and trailing edges, and other large pieces, accurately. Last, but not least, glue sandpaper onto different sizes of scrap plywood sticks and round hardwood dowels. These are handy for working in tight places and for careful shaping where a big sanding block is too hard to control.
In selecting balsa sheets for use in your model, it is important to consider the way the grain runs through the sheet as well as the weight of the sheet. The grain direction actually controls the rigidity or flexibility of a balsa sheet more than the density does. For example, if the sheet is cut from the log so that the tree's annular rings run across the thickness of the sheet (A-grain, tangent cut), then the sheet will be fairly flexible edge to edge. In fact, after soaking in water some tangent cut sheets can be completely rolled into a tube shape without splitting. If on the other hand the sheet is cut with the annular rings running through the thickness of the sheet (C-grain, quarter grain), the sheet will be very rigid edge to edge and cannot be bent without splitting. When the grain direction is less clearly defined (B-grain, random cut), the sheet will have intermediate properties between A and C grain. Naturally, B-grain is the most common and is suitable for most jobs. The point to bear in mind is that whenever you come across pure A-grain or C-grain sheets, learn where to use them to take best advantage of their special characteristics. The following chart illustrates the 3 basic grain types for sheet balsa and lists the most appropriate uses for each.
B-GRAIN sheet balsa has some of the qualities of both type A and type C. Grain lines are shorter than type A, and it feels stiffer across the sheet. It is a general purpose sheet and can be used for many jobs. Sometimes called "random cut". DO: Use for flat fuselage sides, trailing edges, wing ribs, formers, planking gradual curves, wing leading edge sheeting. DON'T: Use where type A or type C will do a significantly better job.
C-GRAIN sheet balsa has a beautiful mottled appearance. It is very stiff across the sheet and splits easily. But when used properly, it helps to build the lightest strongest models. Most warp resistant type. Sometimes called "quarter grain". DO: Use for sheet balsa wings and tails, flat fuselage sides, wing ribs, formers, trailing edges. Best type for HL glider wings and tails. DON'T: Use for curved planking, rounded fuselages, round tubes, HL glider fuselage, or wing spars.
Designing RC Model
R/C Model Design Aerodynamics, Flight mechanics and Structures are three important branches of Aerospace engineering which play a crucial role in designing a full scale aircraft. But in designing a model plane, first two branches play important role and the third one is not considered in detail.
Radio controlled model aircraft can be designed using some basic rules of thumb or more appropriately, design paramaters. These basic design parameters can be applied to a trainer or sport model. There are no complex or magic formulas to solve. These paramaters have been proven to work by a multitude of sport models that have been developed using these rules. A modeler who has built a few models and has gained some knowledge of common structures can design a plane that suits his individual needs.
The design begins with selecting the size of engine that will be used. This will become the determining factor for the entire design. The wing area is first selected from the table.
Radio controlled model aircraft can be designed using some basic rules of thumb or more appropriately, design paramaters. These basic design parameters can be applied to a trainer or sport model. There are no complex or magic formulas to solve. These paramaters have been proven to work by a multitude of sport models that have been developed using these rules. A modeler who has built a few models and has gained some knowledge of common structures can design a plane that suits his individual needs.
The design begins with selecting the size of engine that will be used. This will become the determining factor for the entire design. The wing area is first selected from the table.
Engine/Wing Area
| ENGINE | WING AREA |
| .049 | 200 - 250 sq. in. |
| .10 | 250 - 350 sq. in. |
| .15 | 300 - 450 sq. in. |
| .25 | 400 - 500 sq. in. |
| .40 | 500 - 700 sq. in. |
| .60 | 600 - 850 sq. in. |
After selecting the engine size and wing area, the next step is to determine the wingspan and wing chord that will give this wing area and an aspect ratio between 5:1 and 6:1. If .40 size engine is selected, the wing area will be 500 - 700 sq. in. To make things simple, and area of 600 sq. in. and a span of 60" is chosen. This will give a chord of 10" and an aspect ratio of 6:1. The rest of the design will be based on the chord length.
The next step in determining the configuration of the wing is selecting the airfoil according to the purpose of the model.
The next step in determining the configuration of the wing is selecting the airfoil according to the purpose of the model.
Airfoil Type
| AIRFOIL SHAPE | CHARACTERISTIC |
| Flat Bottom | Slow, docile, forgiving, poor inverted flight |
| Semi-Symmetrical | Good lift, penetration, aerobatic, and inverted flight |
| Symmetrical | Best aerobatic and inverted flight |
The fuselage length is now calculated using the 10" chord. The nose will be 10" - 15" and the tail will be 20" - 24". Taking the median dimension of these, the fuselage length will be 44 1/2" (12.5" nose + 10" chord + 22" tail). The engine thrust is usually set for 0 degree to 3 degree down and 0 degree to 3 degree to the right. The landing gear is selected as a matter of preference. A conventional landing gear is set even with the leading edge of the wing. The main gear of a tricycle landing gear is placed 1 1/2" behind the center of gravity. The width of either main gear is 1/4 of the wingspan.
The stabilizer area will be 20% - 22% of the wing area. The area for the 600 sq. in. wing would be 126 sq. in. nominal. The aspect ratio for the stabilizer is 3:1. Using a stabilizer chord of 6 1/2", the length of the stabiler would be 19 1/2" and the area would be 127 sq. in. The elevator is 20%; of the stabilizer area or 25 sq. in.
The fin is 1/3 of the stabilizer area and the rudder is 1/3 - 1/2 of the total fin area. For the current example, the total area of the fin would be 42 sq. in. and the rudder would be 21 sq. in.
The type of structure that is designed will depend on the use for which the model is intended and the personal preference of the builder. The slab sided fuselages are easier to build than the truss work structures but are also heavier and stronger in most cases. Foam wings are easier to build than built up wings but are heavier and more accurate. A little knowledge of structure goes a long way in the design of a model. In many cases, a modeler will design using the structural configuration of another model and simply change the appearance or the size of the model.
These design parameters were originally collected by Romney Bukolt and published in "Marcs Sparks" in about 1975. Since that time, the validity of the parameters has been proven by the many different models which have been designed using this method.
Propellor Selection Chart
2-Stroke Engine
| ENGINE SIZE | PREFERRED SIZE | ALTERNATE SIZE |
| .049 | 6 x 3 | 5 1/4 x 4, 5 1/2 x 4, 6 x 3 1/2, 6 x 4, 7 x 3 |
| .09 | 7 x 4 | 7 x 3, 7 x 4 1/2, 7 x 5 |
| .15 | 8 x 4 | 8 x 5, 8 x 6, 9 x 4 |
| .19 - .25 | 9 x 4 | 8 x 5, 8 x 6, 9 x 5 |
| .29 - 30 | 9 x 6 | 9 1/2 x 6, 10 x 5 |
| .40 | 10 x 6 | 9 x 8, 11 x 5 |
| .45 | 10 x 7 | 10 x 6, 11 x 5, 11 x 6, 12 x 4 |
| .50 | 11 x 6 | 10 x 8, 11 x 7, 12 x 4, 12 x 5 |
| .60 - .61 | 11 x 7 | 11 x 7 1/2, 11 x 7 3/4, 11 x 8, 12 x 6 |
| .70 | 12 x 6 | 11 x 8, 12 x 8, 13 x 6, 14 x 4 |
| .78 - .80 | 13 x 6 | 12 x 8, 14 x 4, 14 x 5 |
| .90 - .91 | 14 x 6 | 13 x 8, 15 x 6, 16 x 5 |
| 1.20 | 16 x 6 | 16 x 10, 18 x 5, 18 x 6 |
| 1.50 | 18 x 6 | 18 x 8, 20 x 6 |
| 1.80 | 18 x 8 | 18 x 10, 20 x 6 |
4-Stroke Engine
| ENGINE SIZE | PREFERRED SIZE | ALTERNATE SIZE |
| .20 - .21 | 9 x 6 | 9 x 5, 10 x 5 |
| .40 | 11 x 6 | 10 x 6, 10 x 7, 11 x 4, 11 x 5, 11 x 7, 11 x 7 1/2, 12 x 4 |
| .45 - .48 | 11 x 6 | 10 x 6, 10 x 7, 11 x 7, 11 x 7 1/2, 12 x 4, 12 x 5, 12 x 6 |
| .60 - .65 | 12 x 6 | 11 x 7 1/2, 11 x 7 3/4, 11 x 8, 12 x 8, 13 x 5, 13 x 6 |
| .70 | 12 x 6 | 11 x 7 1/2, 11 x 7 3/4, 11 x 8, 12 x 8, 13 x 5, 13 x 6 |
| .80 | 13 x 6 | 12 x 8, 13 x 8, 14 x 4, 14 x 6 |
| .90 | 14 x 6 | 12 x 10, 13 x 8, 14 x 8, 15 x 6 |
| 1.08 | 16 x 6 | 15 x 8, 18 x 5 |
| 1.20 | 16 x 6 | 14 x 8, 15 x 6, 15 x 8, 16 x 8, 17 x 6, 18 x 5, 18 x 6 |
| 1.60 | 16 x 6 | 15 x 6, 15 x 8, 16 x 8, 18 x 6, 18 x 8, 20 x 6 |
| 2.40 | 18 x 10 | 18 x 12, 20 x 8, 20 x 10 |
| 2.70 | 20 x 8 | 18 x 10, 20 x 8, 20 x 10 |
| 3.00 | 20 x 10 | 18 x 12, 20 x 10 |
