This paper conducts a conceptual aerodynamic design and trade study of a CoFlow Jet(CFJ) VTOL (CFJ-VTOL) air vehicle with high speed cruise Mach number of 0.6. The in house high order accuracy FASIP CFD code is used to conduct the full aircraft 3D simulation and wing design trade studies. The vehicle has a tandem wing tailless configuration with the fuselage designed for 1.5 ton payload or 15 passenger seats. The overall aspect ratio of the tandem wing system is 11.65. The CFJ-VTOL concept has both the propeller and wing generating lift at hovering condition to reduce the required power. At cruise, the CFJ is able to enhance the aerodynamic and productivity efficiency due to increased lift and reduced drag at low energy expenditure. A 2D airfoil study is conducted and selects the NACA6415 based CFJ airfoil to form the 3D unswept and untapered wing. A trade study is conducted to configure the tandem wing system, which positions the large wing in the front and the smaller wing with 50% smaller area aft. Such a tandem wings configuration minimizes the front wing tip vortices and downwash interference to the rear wing. At cruise, a very good aerodynamic efficiency (CL/CD)c of 14.6 is achieved with a lift coefficient of 0.812. At hovering static condition, the CFJ wing is positioned at an angle of attack of 80◦ that keeps the flow attached and generates high lift making use of the flow pulled by the propeller. The CFJ wings generate 19% of the total lift, but consume only 1.5% of the total hovering power. This substantially reduces the disk loading and potentially its associated noise. As a result, the system hovering power is decreased by 21.7%, which reduces the propulsion system weight and benefit the whole mission efficiency. The conceptual aerodynamic design and trade study with high fidelity CFD simulation indicates that the CFJ-VTOL concept is not just feasible to cruise at Mach number 0.6 and higher in transonic regime, it is also possible to increase the mission productivity efficiency substantially (e.g. by 100% or higher) compared to the State of the Art conventional VTOL aircraft.