A High Efficiency Low Noise VTOL/ESTOL Concept Using CoFLow Jet Airfoil

This paper proposes a novel air vehicle concept that has the VTOL and ESTOL capability naturally combined together using CoFlow Jet(CFJ) active flow control airfoil. The CFJ-VTOL system is an integrated system with propellers mounted above the CFJ wing suction surface. Different from the conventional VTOL systems that rely solely on the propellers completely facing upward to generate the vertical lift, the propellers of the CFJ-VTOL system faces forward and upward and only generate a part of the total lift. An important function of the propellers is to pull flow to the CFJ airfoil at static condition. The CFJ airfoil then generates very high lift coefficient at extraordinarily high angle of attack(e.g. > 70°) with a much lower power consumption rate than the propellers. In other words, the CFJ-VTOL makes use of the CFJ wing to generate substantial or even the majority of the lift at vertical takeoff and landing, whereas the wings of conventional VTOL aircraft generate no lift at takeoff and landing even though they produce all the lift at cruise. Such an integrated CFJ-VTOL system has the potential to reduce the power loading by 20% or more at the VTOL phase. For the same lift coefficient, the disk loading is significantly reduced with a benefit to decrease the noise. Furthermore, the upper wing mounted propeller is shield by the wing to mitigate downward radiating noise of the propeller. The maximum injection jet Mach number is 0.3 - 0.4, is at fairly low level for jet noise. The CFJ-VTOL system hence is also potentially much quieter than the conventional VTOL. The resultant force of the propeller-CFJ airfoil system at the static condition is controlled by the airfoil orientation angle. By rotating the same propeller-CFJ airfoil system forward, the system can generate both very high lift and thrust for ESTOL, which further reduces the power consumption and noise level compared with the VTOL system. The same system can be potentially used either for VTOL or ESTOL depending on the situation with significantly reduced takeoff/landing power and noise. This paper presents the numerical results evidencing the advantages by 2D CFJ-VTOL airfoil and 3D wing simulations.