Model aircraft
Flying models range from simple toy gliders made of sheets of paper, balsa, card stock or foam polystyrene to powered scale models built up from balsa, bamboo sticks, plastic, (including both molded or sheet polystyrene, and styrofoam), metal, synthetic resin, either alone or with carbon fiber or fiberglass, and skinned with either tissue paper, mylar and other materials.
This allows a greater degree of automation than other manufacturing processes but molds require large production runs to cover the cost of making them.
There is a handful of photo etched metal kits that allow a high level of detail and they are unable to replicate compound curves.
Commercial models are mainly printed by publishers in Germany or Eastern Europe but can be distributed through the internet, some of which are offered this way for free.
In model helicopters, main frames and rotor blades are often made from carbon fiber, along with ribs and spars in fixed-wing aircraft wings.
Microfilm covering is used for the lightest models and is made by spreading few drops of lacquer out over several square feet of water, and lifting a wire loop through it, which creates a thin plastic film.
To increase the hobby's accessibility, some vendors offer Almost Ready to Fly (ARF) models that minimize the skills required, and reduce build time to under 4 hours, versus 10–40 or more for a traditional kit.
For a more mass market approach, foamies, injection-molded from lightweight foam (sometimes reinforced) have made indoor flight more accessible and many require little more than attaching the wing and landing gear.
Another means of attaining height in a glider is exploitation of thermals, which are columns of warm rising air created by differences of temperature on the ground such as between an asphalt parking lot and a lake.
Walkalong gliders are lightweight model airplanes flown in the ridge lift produced by the pilot following in close proximity.
Electric motors and internal combustion engines are the most common propulsion systems, but other types include rocket, small turbine, pulsejet, compressed gas, and tension-loaded (twisted) rubber band devices.
Using it efficiently is one of the challenges of competitive free-flight rubber flying, and variable-pitch propellers, differential wing and tailplane incidence and rudder settings, controlled by timers, can help to manage the torque.
[4][5] Stored compressed gas, typically carbon dioxide (CO2), can power simple models in a manner similar to filling a balloon and then releasing it.
Baronet Sir George Cayley built, and flew, internal and external combustion gunpowder-fueled model aircraft engines in 1807, 1819, and 1850.
These engines are inexpensive, and offer the highest power-to-weight ratio of all glow-engines, but are noisy and require substantial expansion chamber mufflers, which may be tuned.
The power they deliver is more suited to turning larger diameter propellers for lighter weight, higher drag airframes such as with in biplanes.
Owning or operating a turbine-powered aircraft is prohibitively expensive and many national clubs (as with the USA's Academy of Model Aeronautics) require members to be certified to safely use them.
[6] V-1 flying bomb type Pulsejet engines have also been used as they offer more thrust in a smaller package than a traditional glow-engine, but are not widely used due to the extremely high noise levels they produce, and are illegal in some countries.
Electric power now predominated with park-flyer and 3D-flyer models, both of which are small and light, where electric-power offers greater efficiency and reliability, less maintenance and mess, quieter flight and near-instantaneous throttle response compared to internal combustion engines.
The first electric models used brushed DC motors and nickel cadmium (NiCad) rechargeable cells that gave flight times of 5 to 10 minutes, while a comparable glow-engine provided double the flight-time.
Later electric systems used more-efficient brushless DC motors and higher-capacity nickel metal hydride (NiMh) batteries, yielding considerably improved flight times.
No contests were held again until 1927, when the Society of Model Aeronautical Engineers (SMAE) approached Lord Wakefield for a new larger silver trophy for international competition.
The FAI free flight classes include:[9] Also referred to as U-Control in the US, it was pioneered by the late Jim Walker who often, for show, flew three models at a time.
Normally the model is flown in a circle and controlled by a pilot in the center holding a handle connected to two thin steel wires.
There are contest categories for control line models, including Speed, Aerobatics (AKA Stunt), Racing, Navy Carrier, Balloon Bust, Scale, and Combat.
There are variations on the basic events, including divisions by engine size and type, skill categories, and age of model design.
A pilot and a mechanic compete as a team to fly small 370 g (13 oz) 65 cm (26 in) wingspan semi-scale racing models over a tarmac or concrete surface.
For refueling, the pilot operates a fuel shutoff by a quick down elevator movement after the planned number of laps so that the model can approach the mechanic at optimum speed, of around 31 mph (50 km/h).
The mechanics are prepared for crashes and quickly start the second aircraft and transfer the streamer to the reserve model before launching.
Static stability is the resistance to sudden changes in pitch and yaw already described, and is typically provided by the horizontal and vertical tail surfaces respectively, and by a forward center of gravity.
