Concept Development of a Pneumatically Driven, Fixed Root Circulation Controlled Helicopter 2007-01-3828
Circulation control technologies have been applied to fixed wing aircraft for approximately four decades. During those early tests an increase in lift coefficient of nearly four times the unaltered airfoil was achieved. Applying these or similar technologies, particularly inducing the coanda effect through blowing slots to rotorcraft blades, can enhance the performance of the helicopter.
The increase in lift coefficient of the rotor blade provides more options to the designer, including decreasing the rotor diameter, decreasing the rotor speed, increasing the payload capacity, or a combination of all three. By either reducing the diameter and/or the rotor speed the blade tip speed can be reduced, thus allowing a higher forward flight speed. Retreating blade stall can also be reduced by applying circulation control to the leading edge of the rotor blade.
A three phase design process is envisioned for the development of a pneumatically driven, fixed root circulation control helicopter rotor. The first phase would be to develop a high lift rotor blade. This would require the modification of conventional helicopter airfoils to incorporate rounded trailing edges and active blowing slots. The second phase would be to determine the ability to cycle the blowing slot velocity to minimize the asymmetry of lift during maneuvering flight, eliminating the need to physically change the pitch of the blade. The third phase would build on the fixed root circulation control blade by adding a jet of air at the tip of the blade, to provide the power to turn the rotor minimizing the torque transferred to the helicopter fuselage.
In the transfer of fixed wing, active circulation control technologies to rotary wing aircraft several major obstacles need to be addressed and overcome. Some of these are, the supply of air to the active circulation control blowing slots given the limited space within the rotor blades and the transmission of the airflow from the non-rotating fuselage to the rotating plan-form of the rotor.