planes are actually even bendable and usually sustain very little or no damage in the event of an accident, even after a nose dive. Some companies have developed similar material with different names, such as AeroCell or Elapor. Amateur hobbyists have more recently developed a range of new model designs utilizing corrugated plastic, also sold as Coroplast. These models are collectively called "SPADs" which stands for Simple Plastic Airplane Design. Fans of the SPAD concept tout increased durability, ease of building, and lower priced materials as opposed to balsa models, sometimes (though not always) at the expense of greater weight and crude appearance. Flying models have to be designed according to the same principles as full-sized aircraft, and therefore their construction can be very different from most static models. RC planes often borrow construction techniques from vintage full-sized aircraft (although they rarely use metal structures). Ready-to-Fly (RTF) Ready to fly (RTF) airplanes come pre-assembled and usually only require wing attachment or other basic assembly. Typically, everything that is needed is provided, including the transmitter, receiver and battery. RTF airplanes can be up in the air in just a few minutes and have all but eliminated assembly time (at the expense of the model's configuration options.) Almost Ready-to-Fly (ARF) Almost ready to fly (ARF or ARTF) airplanes require final assembly typically including engine and fuel tank installation (or electric motor, speed controller, and battery), servo and pushrod installation, control surface attachment, landing gear attachment, and sometimes require gluing the left and right wing halves together. The average ARF airplane can be built with less than 10 to 20 hours of labor, versus 50 to 100+ hours (depending on detail and desired results) for a typical wood kit. The fuselage, wing halves, tail surfaces and control surfaces are already constructed. ARF airplanes typically only include the airframe and some accessories such as pushrods, fuel tank, etc. Therefore, the power system (glow engine, gas engine, or electric motor and any required accessories) and radio system (servos, transmitter, receiver, and battery) must be purchased separately. Hobby Companies like Motion RC and Horizon Hobby have also began to sell ARF+ Models or ARF Plus which are models that are between a full ARF and PNP where they will have some electronics like control surface servos and retracts for the landing gear but will not include a power system (ESC and Motor) Bind-N-Fly (BNF) Bind-N-Fly (BNF)