Thrust-to-weight ratio

The instantaneous thrust-to-weight ratio of a vehicle varies continually during operation due to progressive consumption of fuel or propellant and in some cases a gravity gradient.

For valid comparison of the initial thrust-to-weight ratio of two or more engines or vehicles, thrust must be measured under controlled conditions.

[2] Aircraft with thrust-to-weight ratio greater than 1:1 can pitch straight up and maintain airspeed until performance decreases at higher altitude.

The metric formula is: The thrust-to-weight ratio of a rocket, or rocket-propelled vehicle, is an indicator of its acceleration expressed in multiples of gravitational acceleration g.[5] Rockets and rocket-propelled vehicles operate in a wide range of gravitational environments, including the weightless environment.

For a takeoff from the surface of the earth using thrust and no aerodynamic lift, the thrust-to-weight ratio for the whole vehicle must be greater than one.

[5] Take-off can occur when the vehicle's g-force exceeds local gravity (expressed as a multiple of g0).

Factors with the greatest effect include freestream air temperature, pressure, density, and composition.

Depending on the engine or vehicle under consideration, the actual performance will often be affected by buoyancy and local gravitational field strength.