While on the ground, the engines are capable of producing thrust within the ballpark of their maximum, but thrust decreases rapidly during and after takeoff, to as low as 1/3rd of the maximum thrust output. The issue is not that there's a reduction in thrust but the margin in which it is reduced.
The JSBSim version can barely stay airborne, so this may be part of the problem.
While on the ground, the engines are capable of producing thrust within the ballpark of their maximum, but thrust decreases rapidly during and after takeoff, to as low as 1/3rd of the maximum thrust output. The issue is not that there's a reduction in thrust but the margin in which it is reduced.
The JSBSim version can barely stay airborne, so this may be part of the problem.