The VTOL (vertical takeoff and landing) military aircraft is capable of rising vertically under the action of its jet exhaust, which can be “vectored” from θ ≅ 0 for takeoff and hovering to θ = 90° for forward flight. The loaded aircraft has a mass of 8600 kg. At full takeoff power, its turbo-fan engine consumes air at the rate of 90 kg/s and has an air–fuel ratio of 18. Exhaust-gas velocity is 1020 m/s with essentially atmospheric pressure across the exhaust nozzles. Air with a density of 1.206 kg/m³ is sucked into the intake scoops at a pressure of −2 kPa (gage) over the total inlet area of 1.10 m². Determine the angle θ for vertical takeoff and the corresponding vertical acceleration a_y of the aircraft.