Indeed. As there is no vertical movement in the motion pit above, it has to use the earth's gravity as the resulting G-force vector.
When for example the aircraft accelerates down the runway, the pit would pitch back to a certain angle, so that the simulated G-force from the acceleration "A" and the earths gravity "G" would combine in the force "F" on the avatar's body. If the acceleration of the aircraft is ~9.8m/s (1g), the pit would pitch back 45 degrees. It's not possible to increase the gravity with a stationary 3-axes motion pit, so no way to get "F" to 1.41g.
If the aircraft with a tricycle gear were to brake with 2g, the pit would pitch forward 63.4 degrees.