|
 The general characteristics and principles of helicopter flight have greatly restricted the maximum cruising speed of a helicopter. In order to achieve a significant increase in speed, the flight characteristics or flight principles of a helicopter have to be substantially altered.
The maximum theoretical speed for a helicopter is 250 MPH. The world speed record for a helicopter was set in the U K in 1986 by a company called Westland. Their Westland Lynx helicopter flew at a recorded speed of 249 mph.
The main limiting factor for a helicopter to reach a speed beyond 250 MPH is a problem referred to as retreating blade stall. This term “retreating blade” stall is a well-known critical factor relating to the dissymmetry of lift of the main rotor blades in forward flight. When a helicopter is in a hover (stationary above ground) the main rotor blades are in a balanced state or symmetrical lift is produced on both sides of the aircraft. However, when the helicopter begins to fly forward, the lift becomes unbalanced, this dissymmetry of lift is the result of an advancing blade that is increasing with air speed and a retreating blade that is decreasing with air speed. The advancing blade is moving in the direction of flight of the helicopter and into the oncoming air, thus increasing in the amount of lift. The retreating blade, which is moving toward the tail, is moving in the same direction of the oncoming air, so the amount of lift decreases.
At a relatively low speed (perhaps 150 MPH on a typical 6 passenger civilian helicopter) the helicopter will approach the retreating blade stall. This retreating blade stall will begin with a buffeting or shaking of the helicopter and if the pilot continues to try to make the helicopter fly faster the result of a complete retreating blade stall will occur. At this time the helicopter will pitch up and then roll into the direction of the retreating blade side.
This is an excellent illustration relating to retreating blade stall:
http://www.dynamicflight.com/aerodynamics/retreating/
Introducing the Challis Heli-Plane
One of the many unique aspects of the Challis Heli-Plane is that there is only one fixed wing that is located on the retreating blade side of the aircraft. The one small fixed wing on the retreating blade side begins to produce lift at high airspeed to coincide when the retreating blade is starting to loose its ability to maintain lift. This design presents an opportunity for an aircraft to have a balanced relationship at high speeds between a rotating blade and one fixed wing.
 
Challis Heli-Plane in Flight
|
Challis Heli-Plane Blue Print Features |
|
CENTER OF LIFT IN CRUISE
The main rotors on a heli-plane in the cruise flight only provide lift, as opposed to the rotors on a helicopter that are providing lift and thrust in cruise. The center of lift of the rotor blades on this heli-plane design will migrate forward with increased speed of the aircraft. In order to have a balanced flight condition, the downward angled horizontal stabilizer or tail wing has to provide lift at the rear of the heli-plane when in forward flight. The lift force that is generated from the tail wing as the speed of the aircraft increases is necessary to off set this condition of forward migrating center of lift. |
|
|
CENTER of LIFT IN THE HOVER
When the heli-plane is in the hover, the flight conditions are exactly the same as a conventional helicopter, the center of lift, and the center of gravity, are in line with the main rotor mast. |
|
|
