An adaptive, model-informed controller based on active disturbance rejection control (ADRC) is developed for tiltrotor aircraft to provide precise and robust control across helicopter, conversion, and fixed-wing modes. The inner loop controls pitch attitude and applies a thrust-augmented state to achieve closed-loop thrust control and real-time compensation for tilt-induced accelerations. The outer loop manages speed and altitude control through coordinated rotor thrust and wing lift. Extensive simulations across the conversion corridor are conducted under five configurations with different levels of model information, including a baseline with on-axis control effectiveness. Results show that improving the inner-loop control-effectiveness matrix has no significant impact. In contrast, incorporating thrust state augmentation and dynamic tilt acceleration markedly enhances control performance, and a third-order speed-shaping profile matched to the speed loop smoothes pitch-attitude regulation. Based on upper-quartile performance metrics, the proposed controller reduces altitude range by 60.0% to 2.5 m, speed deviation by 63.7% to [Formula: see text], pitch attitude variation by 13.1%, and longitudinal stick-cutoff frequency by 64.3% to [Formula: see text].