Yea, it's like, so hard to write something along this: if (jumpjetting) { rigidbody.AddForceRelative(Transform.up, jumpjetStrength * Time.fixedDeltaTime); jumpjetLeft -= jumpjetRate * Time.fixedDeltaTime; if (jumpjetLeft <= 0) { jumpjetting = false; jumpjetready = false; } } That is the extent of fully physically modeled jumpjet code. Nothing else is required. Full realistic inertia applies and physics engine behaves correctly. If you want extended realism you can account the propellant mass loss to the mass of the rigidbody so the jumpjet will have higher thrust to mass ratio when it's running out. It just shows the extent of incompetence with PGI team.
