Coaxial rotor concept next step in RC helicopter model development
Since the successful introduction of the first Schlütter RC helicopters, model helicopter technology has evolved a lot. The introduction of collective pitch, tail gyro’s, engine rpm stabilization and modern programmable radio transmitters greatly improved RC helicopter control.
Manufacturing quality and design benefited from mass production. Now a day a modern RC helicopter is for example often equipped with lots of ball bearings, carbon fiber frame elements and glass fiber rotor blades. One can even choose between different helicopter power sources such as the reliable piston combustion engines, efficient brushless electric motors with Li-Poly batteries or finally highly sophisticated turbine jet engines.
Who would have believed some years ago that RC helicopter models now range from a feather light 6,9 gram Pixolito ( http://pixelito.reference.be/ ) to giant models with rotor diameters of over 2 meters ?
Even less common and new helicopter geometries have been realized. We can mention banana like twin rotors like the Hirobo CH47 Chinook and MS-Composit CH-46 Sea Knight, some Flettner like models and finally multi rotor crafts like the Tribelle and Intellicopter for instance.
Today a renewed interest for the coaxial helicopter concept is dawning in the RC world. Inspired by the real size successful russian Kamov helicopters more and more attempts to realize a coaxial model appear. The challenge to benefit from this ultimate aerodynamical concept lies in the realization of the more complex mechanical counter rotative drive of the two rotors and the yaw command of the helicopter while maintaining a light structure with good stability and overall control.
The following list shows a couple of radio controlled coaxial helicrafts. It is interesting to compare their different solutions as to drive, yaw command and stability.
Helicopter model development is clearly not over yet and it’s probably just a question of time before more RC model companies will pick up the new opportunity to extend their product range.
* Concentrix ( GB )
( outdoor model, electric power, drive : 2 motors, yaw trough rpm control of each rotor, stability by piëzo on swashplate servos )
* First radio controlled electric helicopter with coaxial rotors and good flight characteristics ( B )
( outdoor model, electric power, drive : multiple stage gearing, yaw trough differential collective pitch, stability : Bell/Hiller bar on both rotors )
* Helicoax ( B )
( outdoor model, electric power, drive : single stage inner and outer gearing, yaw trough differential collective pitch, stability : Bell/Hiller bar on both rotors )
( download flight film ( 11.5 Mb )
* Coaxial project ( D )
( outdoor model, electric power, drive : conical gearing, yaw trough differential collective pitch, limited stability through high rotor rpm and rotor blade mass ? )
http://www.coaxialhubschrauber.de/index.html
* Wisnicopter ( NL )
( outdoor model, piston engine power, drive : back to back of two complete mechanisms, yaw trough differential collective pitch, stability : Bell/Hiller bar on both rotors )
* Kamov Ka25 ( I )
( outdoor model, piston engine power, drive : conical gearing, yaw trough differential collective pitch, stability : high rotor rpm and rotor blade mass ? )
http://members.fortunecity.com/jokerjade99/alittlepieceofengineering/index.html
* Hirobo Lama ( J )
( indoor only model, electric power, drive : two motors, yaw trough rpm control of each rotor, stability : Bell bar on upper rotor only )
* Proxflyer mosquito ( N )
( indoor only model, electric power, drive : two motors, yaw trough rpm control of each rotor, stability : soft rotor shaft/rotor head link )
* Airscoot ( US ) First commercially available coaxial model
( indoor only model, electric power, drive : straight gearing with reversing stage, yaw trough tilting tail airfoil in rotor downwash, stability : Bell/Hiller bar on lower rotor only )
* Airscooter ( US )
( outdoor model, piston engine powered, drive : ?, yaw trough differential collective pitch, stability : Bell/Hiller bar on upper rotor only )
* Epson ( J )
( indoor only model, electric power, drive : two motors, yaw trough rpm control of each rotor, stability : Bell bar on upper rotor only )
http://www.epson.co.jp/e/newsroom/news_2003_11_18_2.htm
* Kamov KA-52 ( D )
( outdoor model, piston engine powered, drive : conical, yaw trough differential collective pitch, stability : high rotor rpm and rotor blade mass ? )
http://www.cad-modelltechnik-jung.de/seite1.htm
Download 6 Mb film http://www.modelltechnik-jung.de/flugtage/kmov.mpg
* Coaxial prototype ( F )
( outdoor model, piston engine powered, drive : conical, yaw : differential collective pitch, stability : Bell/Hiller bar on both rotors )
* Coaxial prototype ( F )
( outdoor model, piston engine powered, drive : conical, yaw : differantial collective pitch, stability : high rotor mass and speed )
* Coaxial prototype ( Hu )
( outdoor model, piston egine powered, conical drive, yaw : differential collective pitch, stability : high rotor mass and rpm + swashplate gyros )
Download video http://www.ramo.hu/heli/videos/coax2004_1st.wmv
* Nasa Coaxial Prototype ( US )
( outdoor model, electricaly powered, back to back of two complete mechnisms, yaw : differential collective pitch, stability : Bell/Hiller bar on both rotros )
http://rotorcraft.arc.nasa.gov/publications/files/Young_AIAA02.pdf