To produce the aerodynamic forces required for flight, two-winged insects (Diptera) beat their wings back and forth at high wing-beat frequencies. Because the angular accelerations of this oscillating wing system scales quadratic with the wing-beat frequency, acceleration-reaction forces as a result of wing stroke-accelerations are expected to be particularly high for these flying insects. Here, we used computational fluid dynamics (CFD) simulations to systematically study how acceleration-reaction forces and airflow dynamics depend on wing morphology, wing-stroke rate and wing-stroke acceleration. Based on these simulations, we developed an aerodynamic model that captures the stroke-acceleration forces based on the wing-beat kinematics and wing morphology. Furthermore, we explicitly modeled the interaction of the stroke-acceleration with a selection of other known aerodynamic mechanisms. Our analysis shows that particularly for high-frequency flapping flyers such as mosquitoes, the acceleration-reaction forces contribute substantially to aerodynamic lift and drag production.